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Theocharis Stamatatos

Research Group

Publications






[136] Cyanate groups in higher oxidation state metal cluster chemistry: Mixed-valence (II/III) Mn16 and Mn18 clusters

D. I. Alexandropoulos, E. E. Moushi, C. Papatriantafyllopoulou, C. M. Beavers, S. J. Teat, A. J. Tasiopoulos, G. Christou, Th. C. Stamatatos


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The employment of cyanato (OCN-) group in high oxidation state manganese cluster chemistry, in conjunction with carboxylate ions and the organic chelating/bridging ligand 2-(hydroxymethyl)pyridine (hmpH), is reported. The syntheses, crystal structures, and magnetochemical characterization are described for [Mn16O8(OR)4(OCN)4(O2CMe)12(hmp)6(ROH)2] (R = Me (1), Et (2)) and [Mn18O14(O2CR)18 (hmp)4(hmpH)2(H2O)2] (R = Me (3), Et (4)). The 2:1:1:1 reactions of Mn(O2CMe)2·4H2O, hmpH, NaOCN and NEt3 in solvent MeOH or EtOH afford the isostructural complexes [Mn16O8(OR)4(OCN)4 (O2CMe)12(hmp)6(ROH)2] (R = Me (1), Et (2)). The [Mn164-O)43-O)4(μ-OMe)43-OR)6(μ-OR)6] 10+ core of representative complex 1 comprises a MnII4MnIII4 double-cubane subunit attached on either side to two symmetry-related MnIIMnIII3 defective dicubanes. A similar reaction of Mn(O2CR)2·4H2O, hmpH, NaOCN and NEt3, but in solvent MeCN, led instead to the formation of [Mn18O14(O2CR)18(hmp)4(hmpH)2(H2O)2] (R = Me (3), Et (4)). Compounds 3 and 4 are very similar to each other and can be described as a central [MnIII4 (μ-O)6] rodlike subunit attached on either side to two symmetry-related [Mn7O9] subunits. Variable-temperature, solid-state dc and ac magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions in all compounds, and possible S = 2 or 1 (for 1 and 2) and S = 0 (for 3 and 4) ground state spin values. The combined results demonstrate the ability of cyanato groups to facilitate the formation of new polynuclear MnII/III complexes with structures different than these obtained from the use of the related azides.




[135] 'Ligands-with-Benefits': Naphthalene-substituted Schiff bases yielding new NiII metal clusters with ferromagnetic and emissive properties and undergoing exciting transformations

P. S. Perlepe, L. Cunha-Silva, K. J. Gagnon, S. J. Teat, C. Lampropoulos, A. Escuer, Th. C. Stamatatos


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The initial employment of the fluorescent bridging ligand N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2) in metal cluster chemistry has led to new Ni12 (1) and Ni5 (2) clusters with wheel-like and molecular chain topologies, respectively. The doubly-deprotonated nacb2− ligands were found to adopt four different coordination modes within 1 and 2. The nature of the ligand has also allowed unexpected organic transformations to occur and ferromagnetic and emission behaviors to emerge. The combined work demonstrates the ability of some "ligands-with-benefits" to yield beautiful structures with exciting topologies and interesting physicochemical properties.




[134] Dodecanuclear 3d/4f-metal cluster compounds with a 'Star of David' topology: Single-molecule magnetism and magnetocaloric properties

D. I. Alexandropoulos, L. Cunha-Silva, G. Lorusso, M. Evangelisti, J. Tang, Th. C. Stamatatos


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A family of interwoven molecular inorganic knots, shaped like the 'Star of David', was prepared by the employment of naphthalene- 2,3-diol in 3d/4f-metal cluster chemistry; the isoskeletal dodecanuclear compounds exhibit slow relaxation of the magnetization and magnetocaloric properties, depending on the metal ion.




[133] High nuclearity cerium-manganese clusters and their structural and magnetic properties: CeIV3MnIII7 and CeIV5MnIII11

A. E. Thuijs, A. Marton, Th. C. Stamatatos, K. A. Abboud, G. Christou


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The syntheses, structures, and magnetic properties are reported of two new high nuclearity Ce–Mn oxo carboxylate clusters at high CeIV/MnIII oxidation states and with nuclearities of Ce5Mn11 and Ce3Mn7. The compounds are (NnBu4)2[Ce5Mn11O13(OH)2(O2CPh)24(NO3)2](NO3) (1) and [Ce3Mn7O8(O2CPh)17(H2O)4] (2). 1 was prepared from the oxidation of Mn(O2CPh)2 by (NnBu4)2Ce(NO3)6, whereas 2 was obtained from the comproportionation reaction of Mn(O2CPh)2 and Nn Bu4MnO4 in the presence of Ce(NO3)3. Both compounds possess unprecedented structures, comprising an irregular metal topology of several edge-fused triangular units with overall virtual C2 symmetry. Variable-temperature, solid-state dc and ac magnetization studies on 1 and 2 in the 1.8–300 K range revealed predominantly weak antiferromagnetic exchange interactions within the complexes. For 1, the combined dc and ac data indicate an S = 5 ground state but with low-lying excited states consistent with the high nuclearity. For 2, even lower-lying excited states were observed, precluding clear determination of the ground state but with an estimate of S = 2 or 3, or less. Complexes 1 and 2 are new additions to the Ce–Mn family of clusters and the broader class of 3d/4f molecular systems, and 1 is the highest nuclearity Ce–Mn cluster to date.




[132] New structural topologies in 4f-metal cluster chemistry from vertex-sharing butterfly units: {LnIII7} complexes exhibiting slow magnetization relaxation and ligand-centred emissions

E. C. Mazarakioti, L. Cunha-Silva, V. Bekiari, A. Escuer, Th. C. Stamatatos


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The employment of N-salicylidene-o-aminophenol in 4f-metal cluster chemistry has led to a family of {Ln7} clusters with a new core topology that comprises two {Ln4} butterflies sharing a common metal vertex; the {Dy7} derivative exhibits slow magnetization relaxation whereas all heptanuclear compounds show ligand-centred blue-green emissions.




[131] 'All three-in-one': ferromagnetic, single-molecule magnetism and magnetocaloric properties in a new family of [Cu4Ln] (LnIII = Gd, Tb, Dy) clusters

P. Richardson, D. I. Alexandropoulos, L. Cunha-Silva, G. Lorusso, M. Evangelisti, J. Tang, Th. C. Stamatatos


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A new family of isomorphous [Cu4Ln] clusters (LnIII = Gd, Tb, Dy) with a ‘propeller’-like topology was obtained from the use of naphthalene-2,3-diol in CuII/LnIII chemistry; all complexes are ferromagnetically-coupled and display either magnetocaloric properties or SMM behavior depending on the central Ln ion.




[130] Nonemployed simple carboxylate ions in well-investigated areas of heterometallic carboxylate cluster chemistry: A new family of {CuII4LnIII8} complexes bearing tert-butylacetate bridging ligands”

D. Dermitzaki, C. P. Raptopoulou, V. Psycharis, A. Escuer, S. P. Perlepes, Th. C. Stamatatos


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The first use of tert-butylacetate as bridging ligand in 3d/4f metal cluster chemistry, in conjunction with the versatile chelate ligand pyridine-2,6-dimethanol, has afforded a new family of [Cu4Ln8(OH)6-(NO3)2(O2CCH2But)16(pdm)4] clusters with unprecedented structures and slow magnetization relaxation for the {CuII4DyIII8} member. The molecular structure of representative complex 1 consists of a {CuII4GdIII8} cage-like cluster built from two {CuGd3} cubanes which are linked to each other and to two {CuGd} subunits on opposite sides through two η2225 NO3 ions. The metal ions are additionally bridged by μ3-OH, μ3-OR, and μ-OR groups to give an overall [Cu4Gd85-NO3)23-OH)63-OR)2(μ-OR)8]14+ core. Peripheral ligation about the core is provided by the N,O,O-chelating part of the pdm2− groups and, more impressively, by the oxygen atoms of 16 bridging ButCH2CO2 ligands; the latter are arranged into five classes, adopting a total of six different binding modes with the metal centers. The combined work demonstrates the ligating flexibility of tert-butylacetate ion and its usefulness in the synthesis of new 3d/4f-metal cluster compounds




[129] Doubly thiocyanato(S,N)-bridged dinuclear complexes of mercury(II) from the use of 2-pyridyl oximes as capping ligands

P. Danelli, Z. G. Lada, C. P. Raptopoulou, V. Psycharis, Th. C. Stamatatos, S. P. Perlepes


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The reactions between Hg(SCN)2 and the 2-pyridyl oximes, 2-pyridine aldoxime (paoH), methyl 2-pyridyl ketone oxime (mepaoH), pyridine-2-amidoxime (NH2paoH) and di-2-pyridyl ketone oxime (dpkoxH), have been investigated. The products in Me2CO or Me2CO/MeOH are the dinuclear complexes [Hg2(SCN)4(paoH)2] (1), [Hg2(SCN)4(mepaoH)2] (2), [Hg2(SCN)4(NH2paoH)2] (3) and [Hg2(SCN)4(dpkoxH)2] (4), whose structures have been determined by single-crystal X-ray crystallography. The molecular structures consist of centrosymmetric dinuclear molecules in which the two HgII ions are bridged by two bidentate bridging η11:μ (μ1,3) SCN- groups forming a planar (1, 2) or non-planar (3, 4), 8-membered metallacyclic ring. The HgII centers are each chelated by a N(2-pyridyl), N(oxime)-bidentate ligand and are bound to one terminal S-bonded thiocyanato group. Due to the very long HgII-N (bridging SCN- ) distances in 3, this complex can also be described as pseudodimer. The second 2-pyridyl ring of each dpkoxH ligand in 4 remains uncoordinated. The 2D lattice of 1 and 2 is built through H-bonding and π-π stacking interactions. Hydrogen bonds and S...S interactions generate 3D networks in 3 and 4. The IR spectra of the complexes are discussed in terms of the coordination modes of the ligands involved (SCN- , 2-pyridyl oximes). 1H NMR spectra in d6-DMSO indicate that the complexes decompose in solution.




[128] Synthesis and first use of pyridine-2,6-diylbis(pyrazine-2-ylmethanone) in metal cluster chemistry: A {MnIII3Na2} complex with an ideal trigonal bipyramidal geometry

D. P. Giannopoulos, C. Wilson-Konderka, K. J. Gagnon, S. J. Teat, A. Escuer, C. Metallinos, Th. C. Stamatatos


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The successful organic synthesis of a new dipyrazole/pyridine-dicarbonyl organic molecule, namely pyridine-2,6-diylbis(pyrazine-2-ylmethanone) [(pz)CO(py)CO(pz)], followed by its employment in Mn coordination chemistry has yielded the neutral cluster compound [Mn3Na2O(N3)3(L)3] (1), where L2− is the (pz)C(CH2COCH3)(O)(py)C(CH2COCH3)(O)(pz) dianion. The latter group was formed in situ, presumably by the nucleophilic attack of the carbanion CH2COCH3 to the carbonyl carbon atoms of (pz)CO(py)CO(pz), in the presence of Mnn+ ions under basic conditions and in solvent Me2CO. Complex 1 possesses an almost ideal trigonal bipyramidal topology, with the two NaI ions occupying the apical positions and the three MnIII ions residing in the equatorial trigonal plane. The bridging ligation about the metal ions is provided by a μ3-O2− ion and six μ-OR groups from the L2− ligand, while peripheral ligation is completed by three terminal azido groups and the pyridine N and carbonyl O atoms of L2−. Magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the paramagnetic MnIII centres; the use of an anisotropic, equilateral MnIII3 triangle model allowed us to fit the magnetic data and obtain the best-fit parameters: J = −10.8 cm−1, D = −5.3 cm−1, and g = 1.99. The combined results demonstrate the rich chemical reactivity of carbonyl groups and the ability of poly-ketone ligands to stabilize cluster compounds with unprecedented structural motifs and interesting architectures.




[127] Emissive {MnIII4Ca} clusters with square pyramidal topologies: Syntheses, structural, and spectroscopic and physicochemical characterization

A. A. Alaimo, D. Takahashi, L. Cunha-Silva, G. Christou, Th. C. Stamatatos


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The one-pot reactions between Mn(ClO4)2·6H2O, Ca(ClO4)2·4H2O, and the potentially tetradentate (N,O,O,O) chelating/bridging ligand salicylhydroxime (shiH3), resulting from the in situ metal ion-assisted amide−iminol tautomerism of salicylhydroxamic acid in the presence of various fluorescence carboxylate groups and base NEt3, afford a family of structurally similar {Mn4Ca} clusters with distorted square pyramidal topology. The reported complexes (NHEt3)2[Mn4Ca(L1)4(shi)4] (1), (NHEt3)2[Mn4Ca(L2)4(shi)4] (2), (NHEt3)5[Mn4Ca(L2)4(shi)4 (shiH2)2]-(ClO4) (3), and (NHEt3)2[Mn4Ca(L3)4(shi)4] (4) contain a similar [Mn4Ca(μ-NO)4] 10+ core of four MnIII atoms at the square base and a CaII atom occupying the apical site. Peripheral ligation about the core is provided by four η11:μ carboxylate groups of the anions of 2-naphthoic acid (L1), 9- anthracenecarboxylic acid (L2), and 1-pyrenecarboxylic acid (L3). Solid-state direct current magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the 4 MnIII centers, which were primarily quantified by using a simple 1-J fit model to give S = 0 spin ground states with low-lying excited states close in energy to the ground state. Solution studies in solvent MeCN were carried out on all complexes and confirmed their structural integrity. Cyclic voltammetry studies showed a similar well-defined reversible oxidation and an irreversible reduction for all complexes, thus establishing their redox potency and electrochemical efficiency. Emission studies in solution proved the optical activity of all compounds, with the observed “blue” emission peaks attributed to the π-rich chromophores of the organic fluorescence ligands. The combined results demonstrate the ability of shiH3 and fluorescence carboxylates to yield new heterometallic Mn/Ca clusters with (i) the same Mn/Ca ratio as the oxygen-evolving complex of Photosystem II, (ii) structural stability in solution, and (iii) a pronounced redox and optical activity.




[126] Increased skeletal muscle glucose uptake by rosemary extract through AMPK activation

M. Naimi, Th. Tsakiridis, Th. C. Stamatatos, D. I. Alexandropoulos, E. Tsiani


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Stimulation of the energy sensor AMP-activated kinase (AMPK) has been viewed as a targeted approach to increase glucose uptake by skeletal muscle and control blood glucose homeostasis. Rosemary extract (RE) has been reported to activate AMPK in hepatocytes and reduce blood glucose levels in vivo but its effects on skeletal muscle are not known. In the present study, we examined the effects of RE and the mechanism of regulation of glucose uptake in muscle cells. RE stimulated glucose uptake in L6 myotubes in a dose- and time-dependent manner. Maximum stimulation was seen with 5 μg/mL of RE for 4 h (184% ± 5.07% of control, p <0.001), a response comparable to maximum insulin (207% ± 5.26%, p < 0.001) and metformin (216% ± 8.77%, p < 0.001) stimulation. RE did not affect insulin receptor substrate 1 and Akt phosphorylation but significantly increased AMPK and acetyl-CoA carboxylase phosphorylation. Furthermore, the RE-stimulated glucose uptake was significantly reduced by the AMPK inhibitor compound C, but remained unchanged by the PI3K inhibitor, wortmannin. RE did not affect GLUT4 or GLUT1 glucose transporter translocation in contrast with a significant translocation of both transporters seen with insulin or metformin treatment. Our study is the first to show a direct effect of RE on muscle cell glucose uptake by a mechanism that involves AMPK activation.




[125] Structural aesthetics in molecular nanoscience: A unique Ni26 cluster with a 'rabbit-face' topology and a discrete Ni18 'molecular chain'

A. A. Athanasopoulou, M. Pilkington, C. P. Raptopoulou, A. Escuer, Th. C.Stamatatos


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The use of a previously unexplored Schiff-base ligand in Ni(II) carboxylate chemistry has afforded a Ni26 cluster with a record nuclearity that crystallizes with a unique ‘rabbit-face’-like topology, and a Ni18 compound that adopts an unusual ‘molecular chain’ structure.




[124] Conversion of thebaine to oripavine and other useful intermediates for the semisynthesis of opiate-derived agents: Synthesis of hydromorphone

B. Murphy, I. Snajdr, A. Machara, M. A. A. Endoma-Arias, Th. C. Stamatatos, D. P. Cox, T. Hudlicky


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Thebaine was converted to oripavine in three steps by employing two different modes of protection of the diene moiety; as an iron tricarbonyl complex and as a Diels–Alder adduct with thioformyl cyanide. The two C-ring-protected thebaine derivatives were subjected to 3-O-demethylation by four different protocols, providing oripavine derivatives, which yielded oripavine after deprotection. Oripavine was then converted to hydromorphone by a three-step process of ketalization, hydrogenation, and deprotection, without the isolation of intermediates.




[123] New classes of ferromagnetic materials with exclusively end-on azido bridges: From single-molecule magnets to 2D molecule-based magnets

D. I. Alexandropoulos, L. Cunha-Silva, A. Escuer, Th. C. Stamatatos


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A new, flexible synthetic route, which does not require the co-presence of any organic chelating/bridging ligand but only the “key” precursor Me3SiN3, has been discovered and led to a new class of inorganic materials containing exclusively end-on azido bridges; the reported 3d-metal clusters and coordination polymers exhibit ferromagnetic, single-molecule magnet, and long-range magnetic ordering properties.




[122] Structural and magnetic variations in tetranuclear NiII clusters: The effect of the reaction solvent and ligand substitution on the product identity

P. S. Perlepe, A. A. Athanasopoulou, K. I. Alexopoulou, C. P. Raptopoulou, V. Psycharis, A. Escuer, S. P. Perlepes, Th. C. Stamatatos


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Three structurally and magnetically different tetranuclear NiII complexes have been isolated and magnetically characterized, emphasizing the effect of the reaction solvent and organic ligand substitution on the chemical identity of cluster compounds.




[121] Unexpected metal ion-assisted transformations leading to unexplored bridging ligands in NiII coordination chemistry: The case of PO3F2- group

D. Dermitzaki, C. P. Raptopoulou, V. Psycharis, A. Escuer, S. P. Perlepes, Th. C. Stamatatos


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The initial ‘accidental’, metal ion-assisted hydrolysis of PF6 to PO3F2− has been evolved in a systematic investigation of the bridging affinity of the latter group in NiII/oximate chemistry; mono-, di- and trinuclear complexes have been prepared and confirmed both the rich reactivity of PO3F2− and its potential for further use as bridging ligand in high-nuclearity 3d-metal cluster chemistry.




[120] Discrete and encapsulated molecular grids: Homometallic Mn15 and heterometallic Mn24Ni2 aggregates

M. Charalambous, S. M. Zartilas, E. E. Moushi, C. Papatriantafyllopoulou, M. J. Manos, Th. C. Stamatatos, S. Mukherjee, V. Nastopoulos, G. Christou, A. J. Tasiopoulos


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Two molecular grid-like clusters are reported, one is a discrete [3 x 5] grid and the other a [3 x 4] grid within a Mn12Ni2 loop. Both Mn24Ni2 and Mn15 aggregates display novel and aesthetically pleasing structures with the former one being among the highest nuclearity heterometallic MnxMy clusters (M = any transition metal ion).




[119] A class of phase-transfer catalyst with interionic strain: Insight into the bonding of disubstituted N- vs carbene-stabilized NI-centered cations

R. Mirabdolbaghi, T. Dudding, Th. C. Stamatatos


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The straightforward synthesis of a class of nitrogen-based phase-transfer catalysts (PTCs) having markedly dissociated anions due to interionic donor−donor “ion pair strain” and use for catalyzing benzylation and benzylic fluorination is reported. Provided also is insight into the bonding of disubstituted N- vs so-called divalent carbene-stablized NI-centered cations and the unprecedented finding of a cyclopropenium based C−H···πaryl interaction.




[118] A new family of Ln7 clusters with an ideal D3h metal-centered trigonal prismatic geometry, and SMM and photoluminescence behaviors

E. C. Mazarakioti, K. M. Poole, L. Cunha-Silva, G. Christou, Th. C. Stamatatos


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The first use of the flexible Schiff base ligand N-salicylidene-2- aminocyclohexanol in metal cluster chemistry has afforded a new family of Ln7 clusters with ideal D3h point group symmetry and metal-centered trigonal prismatic topology; solid-state and solution studies revealed SMM and photoluminescence behaviors.




[117] Fluorescent naphthalene diols as bridging ligands in LnIII cluster chemistry: Synthetic, structural, magnetic and photophysical characterization of LnIII8 "Christmas-stars"

D. I. Alexandropoulos, A. Fournet, L. Cunha-Silva, A. M. Mowson, V. Bekiari, G. Christou, Th. C. Stamatatos


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The initial employment of the fluorescent bridging ligand naphthalene-2,3-diol in 4f-metal coordination chemistry has provided access to a new family of LnIII8 clusters with a “Christmas-star” topology, single-molecule magnetism behavior, and ligand-centered emissions.




[116] Rare nuclearities in Ni(II) cluster chemistry: a Ni11 cage from the first use of N-salicylidene-2-amino-5-chlorobenzoic acid in metal cluster chemistry†

A. A. Athanasopoulou, C. P. Raptopoulou, A. Escuer, Th. C. Stamatatos


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The reaction between N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH2), ButCH2CO2H, and Ni(ClO4)2·6H2O leads to a new Ni11 cluster comprising Ni4 squares and Ni3 triangles; the compound is antiferromagnetically- coupled with an S = 1 spin ground state and low-lying excited states populated even at the lowest accessible temperatures.




[115] Slow relaxation in the first penta-aza Dy(III) macrocyclic complex

E. Gavey, Y. Beldjoudi, J. M. Rawson, Th. C. Stamatatos, M. Pilkington


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A new macrocyclic complex DyCl3(LN5)·4H2O (1) has been prepared in which the Dy(III) ion is equatorially bound by an N5-donor macrocycle (LN5). Ac susceptibility data reveal slow relaxation of the magnetisation in zero field below 15 K with a distribution of relaxation rates.




[114] The bridging azido ligand as a central “player” in high-nuclearity 3d-metal cluster chemistry

A. Escuer, J. Esteban, S. P. Perlepes, Th. C. Stamatatos


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The chemistry of the azido-bridged coordination clusters continues to attract the intense interest of synthetic inorganic chemists and scientists working in the interdisciplinary field of Molecular Magnetism. In this review we have focused on describing aspects of synthesis, structures and magnetic properties of azido-bridged 3d- and d/d'-metal clusters with nuclearities equal to or higher than 4. Some of the clusters display slow magnetic relaxation at very low temperatures, mainly due to the ferromagnetic metal· · ·metal exchange interactions propagated through the end-on azido ligand. The chemistry of polynuclear, azido-bridged 3d-metal complexes embedded in lacunary polyoxometalates is also discussed.




[113] Tetranuclear lanthanide(III) complexes with a zigzag topology from the use of pyridine-2,6-dimethanol: Synthetic, structural, spectroscopic, magnetic and photoluminescence studies

D. I. Alexandropoulos, L. Cunha-Silva, L. Pham, V. Bekiari, G. Christou, Th. C. Stamatatos


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Reaction between Ln(NO3)3·xH2O (x = 5 or 6) and the potentially tridentate (N,O,O) chelating/bridging ligand pyridine-2,6-dimethanol (pdmH2), in the presence of base NEt3, affords a family of isostructural tetranuclear [LnIII4(NO3)2(pdmH)6(pdmH2)2](NO3)4 (LnIII = EuIII, GdIII, TbIII, DyIII, HoIII, ErIII, YbIII) complexes with a rare zigzag topology. All complexes contain a [Ln4(μ-OR)6]6+ core with bridging ligation provided by the alkoxido arms of six η112:μ pdmH groups. The LnIII ions are eight coordinate with distorted geometries. Direct current magnetic susceptibility studies revealed predominant weak antiferromagnetic exchange interactions between the metal centers, which were quantified in the case of isotropic GdIII4 to give J = −0.09(1) cm−1 and g = 2.00(1). The observation of out-of-phase (χ″M) ac susceptibility signals suggested that the DyIII4 analogue might be a molecular nanomagnet. Solid-state photoluminescence studies showed that the EuIII4 and TbIII4 compounds exhibit intense, sharp, and narrow emission bands in the red and green visible regions, respectively, which arise from the characteristic 5D07FJ and 5D47FJ transitions. The combined results demonstrate the ability of pdmH2 ligand to yield homometallic 4f clusters with interesting magnetic and optical properties.




[112] Supramolecular chains of high nuclearity {MnIII25} barrel-like single molecule magnets

D. P. Giannopoulos, A. Thuijs, W. Wernsdorfer, M. Pilkington, G. Christou, Th. C. Stamatatos


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The first application of 1-methyl-1H-pyrrole-2-carbaldehyde oxime as a ligand for the coordination of paramagnetic transition metal ions has afforded a new {MnIII25} barrel-like cluster linked via Na+ cations into a 1D polymeric topology that exhibits single-molecule magnetic behaviour.




[111] Emissive molecular nanomagnets: Introducing optical properties in triangular oximato {MnIII3} SMMs from the deliberate replacement of simple carboxylate ligands with their fluorescent analogues

D. I. Alexandropoulos, A. M. Mowson, M. Pilkington, V. Bekiari, G. Christou, Th. C. Stamatatos


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The targeted replacement of acetate groups in the optically inactive [MnIII3O(O2CMe)3(mpko)3](ClO4) single-molecule magnet with their naphthalene, anthracene, and pyrene fluorescent analogues has led to three new emissive SMMs with enhanced photoluminescence properties and potential applications in the field of molecular electronics.




[110] Molecular nanoscale magnetic refrigerants: A ferrimagnetic {CuII15GdIII7} cagelike cluster from the use of pyridine-2,6-dimethanol

D. Dermitzaki, G. Lorusso, C. P. Raptopoulou, V. Psycharis, A. Escuer, M. Evangelisti, S. P. Perlepes, Th. C. Stamatatos


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The employment of pyridine-2,6-dimethanol in 3d/4f metal cluster chemistry has afforded a new {CuII15GdIII7} cagelike molecule with a beautiful structure built by fused triangular subunits; the compound exhibits an overall ferrimagnetic behavior with an appreciable ground-state spin value and shows promise as a low-temperature magnetic refrigerant.




[109] A MnII6MnIII6 single-strand molecular wheel with a reuleaux triangular topology: Synthesis, structure, magnetism and DFT studies

S. Zartilas, C. Papapatriantafyllopoulou, Th. C. Stamatatos, V. Nastopoulos, E. Cremades, E. Ruiz, G. Christou, C. Lampropoulos, A. J. Tasiopoulos


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The use of the anion of 3-methyl-1,3,5-pentanetriol (mpt3−) in manganese carboxylate chemistry has afforded the new MnII/III12 cluster [MnII6MnIII6(mpt)6(CH3CO2)12(py)6]·3CH3CN (1·3CH3CN). Complex 1 was isolated in moderate yield by the reaction of Mn(CH3CO2)2·4H2O and H3mpt in a 2.6:1 molar ratio in a solvent mixture of acetonitrile and pyridine. The structure of 1 consists of alternating [MnII2(CH3CO2)3(py)]+ and [MnIII2(μ-OR)2(CH3CO2)(py)]3+ dimeric units (three of each dimer), linked at each end by two alkoxo and one acetate bridges; the mpt3− ligands adopt the η2224 coordination mode. The overall metal topology of this new Mn12 wheel resembles a guitar plectrum, or a Reuleaux triangle. Complex 1 displays an unprecedented structural topology, being the first example of a MnII6MnIII6 wheel constructed from alternating homovalent dimers and the only known Mn12 loop with the trigonal symmetry of a Reuleaux triangle (all other reported loops were ellipsoids). Variable-temperature, solid-state direct- and alternating-current magnetization studies were carried out on complex 1, revealing the presence of antiferromagnetic exchange interactions between the metal ions in the molecule, which lead to a spin ground-state value S = 0; the exchange coupling parameters J were calculated using density functional theory employing a hybrid B3LYP functional.




[108] Slow magnetization relaxation in a 1-D double-chain coordination polymer composed of {DyIII4} repeating units

D. I. Alexandropoulos, C. Li, C. P. Raptopoulou, V. Psycharis, W. Wernsdorfer, G. Christou, Th. C. Stamatatos


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The “unsuccessful” synthesis of the non-commercially available ‘Dy(O2CPh)3’ precursor from the stoichiometric reaction of Dy(NO3)3·5H2O with 3 equivalents of NaO2CPh in MeCN/H2O has led instead to the “successful” isolation and structural characterization of the 1-D coordination polymer [Dy4(O2CPh)12(H2O)8]n·2n(PhCO2H)·n(MeCN) (1·2n(PhCO2H)·n(MeCN)) in excellent yields (~90%). The one-dimensional double-chain structure of 1 was resulted from the linkage of two parallel chains by syn,anti-η11:μ PhCO2- groups. The lattice structure of 1 is further extended to a 2-D network through hydrogen bonding and π-π stacking interactions. The observation of out-of-phase (χ"M) ac susceptibility signals suggested that 1 might be a molecular nanomagnet, and this was confirmed by single-crystal magnetization vs. dc field sweeps that exhibited hysteresis, the diagnostic property of a magnet.




[107] Approaches to molecular magnetic materials from the use of cyanate groups in higher oxidation state metal cluster chemistry: Mn14 and Mn16

D. I. Alexandropoulos, C. Papatriantafyllopoulou, C. Li, L. Cunha-Silva, M. J. Manos, A. J. Tasiopoulos, W. Wernsdorfer, G. Christou, Th. C. Stamatatos


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The initial employment of cyanato groups in higher oxidation state manganese cluster chemistry, in conjunction with the gem-diolate form of di-2-pyridylketone or 2,6-diacetylpyridine dioxime chelate ligands, has afforded structurally interesting MnII/III14 and MnII/III/IV16 clusters, respectively. In both complexes, the end-on bridging cyanato groups show an obvious preference in binding through their O atom, a significantly different ligation than that for the homoatomic-type N3 ligand. The Mn14 compound shows entirely visible out-of-phase signals below 5 K and large hysteresis loops below 2 K.




[106] Slow magnetization relaxation in unprecedented MnIII4DyIII3 and MnIII4DyIII5 clusters from the use of N-salicylidene-o-aminophenol

D. I. Alexandropoulos, T. N. Nguyen, L. Cunha-Silva, Th. F. Zafiropoulos, A. Escuer, G. Christou, Th. C. Stamatatos


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The first use of N-salicylidene-o-aminophenol in 3d/4f chemistry has led to MnIII4DyIII5 and MnIII4DyIII3 clusters with unprecedented metal topologies and stoichiometries; both compounds exhibit out-of-phase signals indicative of the slow magnetization relaxation of a single-molecule magnet.




[105] 2-Pyrrolyloximes in high-nuclearity transition-metal cluster chemistry: Fe10 and Fe12

E. S. Koumousi, A. Routzomani, T. N. Nguyen, D. P. Giannopoulos, C. P. Raptopoulou, V. Psycharis, G. Christou, Th. C. Stamatatos


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The employment of 2-pyrrolyloximes in high-nuclearity transition-metal cluster chemistry has provided access to unprecedented decanuclear and dodecanuclear FeIII cagelike clusters bearing the anion of pyrrole-2-carboxaldehyde oxime (praoH2), the simplest member of this new family of ligands; the identity of the products depends on the nature of the counteranion present in the starting materials.




[104] Rare nuclearities, new structural motifs, and slow magnetization relaxation phenomena in manganese cluster chemistry: A Mn15Na2 cage from the use of triethanolamine/pivalate/azide "blend"

D. I. Alexandropoulos, E. C. Mazarakioti, S. J. Teat, Th. C. Stamatatos


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The combination of azide, carboxylate (pivalate and in situ generated formate) and triethanolamine ligands in higher oxidation state Mn cluster chemistry has afforded a new pentadecanuclear, mixedvalence( II,III) compound with a large S and a negative D value. The unprecedented [MnII2MnIII13] cluster exhibits frequency-dependent out-of-phase (χ"M) signals, characteristics of the superparamagnetic-like slow relaxation of an SMM.




[103] Employment of pyridyl oximes and dioximes in zinc(II) chemistry: Synthesis, structural and spectroscopic characterization, and biological evaluation

K. F. Konidaris, M. Giouli, C. P. Raptopoulou, V. Psycharis, I. I. Verginadis, A. Vasiliadis, A. S. Afendra, S. Karkabounas, E. Manessi-Zoupa, Th. C. Stamatatos


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The employment of pyridine-2-amidoxime (ampaoH), 2,6-diacetylpyridine dioxime (dapdoH2) and pyridine- 2,6-diamidoxime (dampdoh4) in zinc(II) chemistry is reported. The syntheses, crystal structures, spectroscopic and physicochemical characterization, and biological evaluation are described of [Zn(O2- CMe)2(ampaoH)2] (1), [Zn(O2CPh)2(ampaoH)2] (2), [Zn(dapdoH2)2](NO3)2 (3) and [Zn(dampdoH2)2](NO3)2 (4). The reactions between Zn(NO3)2·4H2O and two equivalents of either dapdoH2 or dampdoH2 in MeOH led to the mononuclear, cationic complexes 3 or 4, respectively. The ZnII center in 3 and 4 is coordinated by two N,N' ,N"-tridentate chelating (η3) dapdoH2 or dampdoH2 ligands, and it thus possesses a distorted octahedral coordination geometry. Strong intermolecular hydrogen bonding interactions provide appreciable thermodynamic stability and interesting supramolecular chemistry for compounds 1–4. The characterization of all four complexes with 1H and 13C NMR, and positive ion electrospray mass spectroscopies confirmed their integrity in DMSO solutions. The biological evaluation of complex 3 showed the highest cytotoxic activity against LMS and MCF-7 cells, among the other three complexes (1, 2 and 4). Flow cytometry analysis revealed that all four complexes cause apoptosis to LMS cells, at a dose-dependent manner. The combined work demonstrates the ability of pyridyl monoxime and pyridyl dioxime chelates not only to lead to polynuclear 3d-metal complexes with impressive structural motifs and interesting magnetic and optical properties, but also to yield new, mononuclear transition metal complexes with biological implications.




[102] Hexanuclear zinc(II) carboxylate complexes from the use of pyridine-2,6-dimethanol: Synthetic, structural and photoluminescence studies

E. Katsoulakou, D. Dermitzaki, K. F. Konidaris, E. E. Moushi, C. P. Raptopoulou, V. Psycharis, A. J. Tasiopoulos, V. Bekiari, E. Manessi-Zoupa, S. P. Perlepes, Th. C. Stamatatos


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The employment of pyridine-2,6-dimethanol (pdmH2) in zinc(II) carboxylate chemistry is reported. The syntheses, crystal structures, and spectroscopic characterization are described for the structurally similar cluster compounds [Zn6(OH)2(O2CR)8(pdmH)2] (R = Ph (1); But (2)), obtained in very good yields by the reactions between Zn(O2CR)2·2H2O (R = Ph, But) and pdmH2 in a 3:1 molar ratio in MeOH or MeCN solvent media, respectively. The [Zn63-OH)23-OR)2]8+ core of both clusters can be conveniently described as four edge-sharing triangles (RO- = pdmH-). The three crystallographically unique metal ions in both 1 and 2 are found in three different coordination environments (4-, 5- and 6-coordinate), within the same molecule, a very rare case in hexanuclear Zn(II) cluster chemistry. The benzoate-analogue ZnII6 (1) displays photoluminescence with a maximum at 404 nm, upon maximum excitation at 337 nm, whereas the pivalate-analogue ZnII6 (2) shows a non-emissive character; the origin of the photoluminescence is discussed.




[101] Bis(aqua)bis(η5-cyclopentadienyl)vanadium(IV) bis(trifluoromethanesulfonate) tetrahydrofuran solvate: Synthesis and characterization

Th. C. Stamatatos, S. P. Perlepes, C. P. Raptopoulou, A. Terzis, N. Klouras


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The reactivity pattern of [V(Cp)2Cl2] towards the weakly coordinating CF3SO3- anion in the absence of chelating or bridging organic ligands has been investigated, where Cp- is the η5-C5H5- ligand. The synthesis, single-crystal X-ray structure and physical/spectroscopic characterization are reported for the product [V(Cp)2(H2O)2](CF3SO3)2·THF (1·THF). The coordination about the VIV atom, formed by the two H2O molecules and the centroids of the cyclopentadienyl rings, is distorted tetrahedral. The [V(Cp)2 (H2O)2]2+ cation is connected to the triflate anions via hydrogen bonds. Magnetic susceptibility, EPR and IR data are discussed in terms of the nature of bonding and the structure of the complex.




[100] Solvent-dependent access to two different NiII4 core topologies from the first use of pyridine-2,6-dimethanol in nickel(II) cluster chemistry

K. I. Alexopoulou, C. P. Raptopoulou, V. Psycharis, A. Terzis, V. Tangoulis, Th. C. Stamatatos, S. P. Perlepes


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The use of pyridine-2,6-dimethanol, pdmH2, in reactions with nickel(II) acetate has led to two Ni4 clusters, depending on the solvent. [Ni4(O2CMe)4(pdmH)4]· MeCN (1·MeCN) can be obtained from MeCN and [Ni4(O2CMe)6(pdmH)2(EtOH)2]· 1.2EtOH (2 · 1.2EtOH) from EtOH. Each cluster can be converted into the other in the appropriate solvent. The tetranuclear cluster molecule 1 possesses a distorted cubane {Ni43-OR)4}4+ core (RO- = pdmH-) with the NiII atoms and the alkoxide-type oxygen atoms from the η31 : μ3 pdmH- ligands occupying alternate vertices of the cube; four η11 : μ MeCO2- groups cap four faces of the cube. The four NiII atoms in molecule 2 are located at four vertices of a defective dicubane and are bridged by six oxygen atoms, two μ3 from the η31 : η1 : μ3 pdmH- ligands and four from four monoatomically bridging MeCO2- groups; peripheral ligation is provided by two η1 : η1 : μ MeCO2- groups and two terminal EtOH ligands. IR data are discussed in terms of the coordination modes of the ligands. Variable-temperature direct-current magnetic susceptibility data of 1 and 2 were modelled with two and three J values respectively, indicating diamagnetic ground states (S=0). The sign and the magnitude of the J values are discussed in terms of structural features of the complexes.




[99] First palladium(II) and platinum(II) complexes from employment of 2,6-diacetylpyridine dioxime: Synthesis, structural and spectroscopic characterization, and biological evaluation

E. S. Koumousi, M. Zampakou, C. P. Raptopoulou, V. Psycharis, C. M. Beavers, S. J. Teat, G. Psomas, Th. C. Stamatatos


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Employment of the monoanion of 2,6-diacetylpyridine dioxime (dapdoH2) as a tridentate chelate in palladium(II) and platinum(II) chemistry is reported. The syntheses, crystal structures, spectroscopic and physicochemical characterization, and biological evaluation are described of [PdCl(dapdoH)] (1) and [PtCl(dapdoH)] (2). Reaction of PdCl2 with 2 equivs of dapdoH2 in MeOH under reflux gave 1, whereas the same reaction with PtCl2 in place of PdCl2 gave 2 in comparable yields (70− 80%). The divalent metal center in both compounds is coordinated by a terminal chloro group and a N,N′,N″-tridentate chelating (η3) dapdoH ligand. Thus, each metal ion is four coordinate with a distorted square planar geometry. Characterization of both complexes with 1H and 13C NMR and UV−vis and electrospray ionization mass spectroscopies confirmed their integrity in DMSO solutions. Interaction of the complexes with human and bovine serum albumin has been studied with fluorescence spectroscopy, revealing their affinity for these proteins with relatively high values of binding constants. UV study of the interaction of the complexes with calf-thymus DNA (CT DNA) has shown that they can bind to CT DNA, and the corresponding DNA binding constants have been evaluated. Cyclic voltammograms of the complexes in the presence of CT DNA solution have shown that the interaction of the complexes with CT DNA is mainly through intercalation, which has been also shown by DNA solution viscosity measurements. Competitive studies with ethidium bromide (EB) have revealed the ability of the complexes to displace the DNA-bound EB, suggesting competition with EB. The combined work demonstrates the ability of pyridyl−dioxime chelates not only to lead to polynuclear 3d-metal complexes with impressive structural motifs and interesting magnetic properties but also to yield new, mononuclear 4d- and 5d-metal complexes with biological implications.




[98] "Squaring the clusters": A MnIII4NiII4 molecular square from nickel(II)-induced structural transformation of a MnII/III/IV12 cage

D. I. Alexandropoulos, M. J. Manos, C. Papatriantafyllopoulou, S. Mukherjee, A. J. Tasiopoulos, S. P. Perlepes, G. Christou, Th. C. Stamatatos


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A MnIII4NiII4 molecular square exhibiting slow magnetization relaxation has been prepared from the reaction of a MnII4MnIII6MnIV2 cluster and a simple NiII source.




[97] Single-Strand Molecular Wheels and Coordination Polymers in Copper(II) Benzoate Chemistry by the Employment of α-Benzoin Oxime and Azides: Synthesis, Structures, and Magnetic Characterization

Th. C. Stamatatos, G. Vlahopoulou, C. P. Raptopoulou, V. Psycharis, A. Escuer, G. Christou, S. P. Perlepes


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The use of α-benzoin oxime (bzoxH2) in copper(II) benzoate chemistry, in the absence or presence of ancillary azido ligands, is reported. The reaction of Cu(O2CPh)2·2H2O with one equivalent of bzoxH2 in N,N-dimethylformamide (DMF) affords the decanuclear complex [Cu10(bzox)10(DMF)4] (1) in good yield. Dissolution of 1 in CH2Cl2 leads to the subsequent isolation of the solvent-free complex [Cu10(bzox)10] (2) in moderate yields. Complexes 1 and 2 are isostructural and possess a loop or single-strand molecular wheel topology. The bzox2– dianions behave as η1123 ligands, which give rise to an overall [Cu10(μ-ONR)10(μ-OR')10] core. Both 1 and 2 stack to form nanotubular columns with beautiful supramolecular architectures. The reaction of Cu(O2CPh)2· 2H2O with bzoxH2 and NaN3 in a 1:1:1 molar ratio in MeOH gives the bzoxH2-free complex [Cu(N3)(O2CPh)(MeOH)]n (3), which is a 1D chain. The CuII atoms in 3 are linked by a single, end-on N3- group, a syn,syn-η11:μ PhCO2– ion, and an oxygen atom from the bridging MeOH ligand. The 1D chains are hydrogen bonded into 2D sheets through Nazide···H(OMeOH) interactions. Variable-temperature, solid-state direct-current magnetic studies were carried out on 1– 3. The data for 1 and 2 indicate very strong antiferromagnetic exchange interactions and a S = 0 ground state, which is expected for even-membered loop arrays of CuII atoms. In contrast, 3 exhibits ferromagnetic exchange interactions; the data were fitted to the appropriate equation derived from the Hamiltonian H = –JΣ(Si·Si+1), which includes a zJ' interchain interaction term. The best-fit parameters were J = +49.6(4) cm–1, g = 2.067(3), and zJ' = 2.3(1) K. The combined results demonstrate the ligating flexibility of both the bzoxH2 and azido groups and their usefulness in the synthesis of polynuclear CuII clusters and coordination polymers.




[96] Synthetic model of the asymmetric [Mn3CaO4] cubane core of the oxygen-evolving complex of photosystem II

S. Mukherjee, J. A. Stull, J. Yano, Th. C. Stamatatos, K. Pringouri, T. A. Stich, K. A. Abboud, R. D. Britt, V. K. Yachandra, G. Christou


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The laboratory synthesis of the oxygen-evolving complex (OEC) of photosystem II has been the objective of synthetic chemists since the early 1970s. However, the absence of structural information on the OEC has hampered these efforts. Crystallographic reports on photosystem II that have been appearing at ever-improving resolution over the past ten years have finally provided invaluable structural information on the OEC and show that it comprises a [Mn3CaO4] distorted cubane, to which is attached a fourth, external Mn atom, and the whole unit attached to polypeptides primarily by aspartate and glutamate carboxylate groups. Such a heterometallic Mn/Ca cubane with an additional metal attached to it has been unknown in the literature. This paper reports the laboratory synthesis of such an asymmetric cubane-containing compound with a bound external metal atom, [MnIV3Ca2O4(O2CBut)8(ButCO2H) 4(1)] . All peripheral ligands are carboxylate or carboxylic acid groups. Variable-temperature magnetic susceptibility data have established 1 to possess an S = 9/2 ground state. EPR spectroscopy confirms this, and the Davies electron nuclear double resonance data reveal similar hyperfine couplings to those of other MnIV species, including the OEC S2 state. Comparison of the X-ray absorption data with those for the OEC reveal 1 to possess structural parameters that make it a close structural model of the asymmetric- cubane OEC unit. This geometric and electronic structural correspondence opens up a new front in the multidisciplinary study of the properties and function of this important biological unit.




[95] The first member of a second generation family of ligands derived from metal-ion assisted reactivity of di-2,6-(2-pyridylcarbonyl)pyridine: Synthesis and characterization of a MnII/III4 rhombus

Th. C. Stamatatos, R. Adam, C. P. Raptopoulou, V. Psycharis, R. Ballesteros, B. Abarca, S. P. Perlepes, A. K. Boudalis


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Nucleophilic attack by the carbanion CH2COCH3 at the carbonyl carbon atoms of 2,6-di-(2-pyridylcarbonyl) pyridine, pyCOpyCOpy, in the presence of Mnn+ ions under basic conditions has yielded the cationic cluster [Mn4(OH)2(L)2(H2O)2](ClO4)4 (1), where L2− is the (py)C(CH2COCH3)(O)(py)C(CH2COCH3)(O)(py) dianion. The cluster cation possesses a planar {MnII2MnIII23-OH)2(μ-OR)4}4+ rhombus core, resulting from two μ3-OHions and two η12111213 bridging L2− groups from the in situ formed ligand. Complex 1 is antiferromagnetically coupled with an unusual S=2 ground state resulting from spin frustration effects within the triangular Mn3 subunits of the cluster.




[94] A new family of nonanuclear lanthanide clusters displaying magnetic and optical properties

D. I. Alexandropoulos, S. Mukherjee, C. Papatriantafyllopoulou, C. P. Raptopoulou, V. Psycharis, V. Bekiari, G. Christou, Th. C. Stamatatos


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The initial employment of 2- (hydroxymethyl)pyridine in 4f-metal chemistry has afforded a new family of LnIII9 clusters with a sandglass-like topology and dual physical properties; the DyIII member shows single molecule magnetism behavior, while the EuIII-analogue exhibits intense red photoluminescence.




[93] Towards models of the oxygen-evolving complex (OEC) of photosystem II: A Mn4Ca cluster of relevance to low oxidation states of the OEC

E. S. Koumousi, S. Mukherjee, C. M. Beavers, S. J. Teat, G. Christou, Th. C. Stamatatos


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Synthetic access has been achieved into high oxidation state Mn/Ca chemistry with the 4 : 1 Mn : Ca stoichiometry of the oxygen-evolving complex (OEC) of plants and cyanobacteria; the anion of (Et3NH)2[MnIII 4Ca(O2CPh)4(shi)4] has a square pyramidal metal topology and an S = 0 ground state.




[92] Initial employment of pyridine-2-amidoxime in zinc(II) chemistry: synthetic, structural and spectroscopic studies of mononuclear and dinuclear complexes

K. F. Konidaris, V. Bekiari, E. Katsoulakou, C. P. Raptopoulou, V. Psycharis, S. P. Perlepes, Th. C. Stamatatos, E. Manessi-Zoupa


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The employment of pyridine-2-amidoxime (ampaoH), 2,6-diacetylpyridine dioxime (dapdoH2) and pyridine- 2,6-diamidoxime (dampdoH2) in zinc(II) chemistry is reported. The syntheses, crystal structures, spectroscopic and physicochemical characterization, and biological evaluation are described of [Zn(O2 CMe)2(ampaoH)2] (1), [Zn(O2CPh)2(ampaoH)2] (2), [Zn(dapdoH2)2](NO3)2 (3) and [Zn(dampdoH2)2](NO3)2 (4). The reactions between Zn(NO3)2·4H2O and two equivalents of either dapdoH2 or dampdoH2 in MeOH led to the mononuclear, cationic complexes 3 or 4, respectively. The ZnII center in 3 and 4 is coordinated by two N,N' ,N"-tridentate chelating (η3) dapdoH2 or dampdoH2 ligands, and it thus possesses a distorted octahedral coordination geometry. Strong intermolecular hydrogen bonding interactions provide appreciable thermodynamic stability and interesting supramolecular chemistry for compounds 1–4. The characterization of all four complexes with 1H and 13C NMR, and positive ion electrospray mass spectroscopies confirmed their integrity in DMSO solutions. The biological evaluation of complex 3 showed the highest cytotoxic activity against LMS and MCF-7 cells, among the other three complexes (1, 2 and 4). Flow cytometry analysis revealed that all four complexes cause apoptosis to LMS cells, at a dose-dependent manner. The combined work demonstrates the ability of pyridyl monoxime and pyridyl dioxime chelates not only to lead to polynuclear 3d-metal complexes with impressive structural motifs and interesting magnetic and optical properties, but also to yield new, mononuclear transition metal complexes with biological implications.




[91] Unexpected formation, X-ray structure, and characterization of the triangular [Ti3Ο(OMe)65-C5H5)3](I3) complex from hydrolysis and methanolysis of [Ti(η5-C5H5)2I2]

Th. C. Stamatatos, S. P. Perlepes, M. J. Manos, A. J. Tasiopoulos, N. Klouras


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A convenient route has been developed for the formation of [Ti3IV O(OMe)65-C5H5)3](I3) (2) involving methanolysis (and possibly hydrolysis) of species derived from titanocene diiodide, [TiIV5-C5H5)2I2] (1), under aerobic conditions. Single-crystal X-ray crystallography reveals that the cation of 2 consists of three TiIV’s in a triangular arrangement bridged by a central μ3-oxide; the latter lies 0.686A˚ out of the Ti3 plane. Each edge of the triangle is bridged by oxygen of η1 :μ-MeO-. Terminal ligation is provided by three methoxide and three cyclopentadienyl groups. All TiIV centers are five-coordinate in an extremely distorted geometry. IR and electronic data are discussed in terms of the known structure and coordination modes of O2-, MeO-, and η5-C5H5-. A proposal for the mechanism of the unexpected formation of the triiodide (I3-) counteranion that is present in the crystal structure of 2 is also provided.




[90] Synthetic entry into mixed bismuth-manganese cluster chemistry at high oxidation states: BiIII2MnIV6 and BiIIIMnIII10­ complexes

Th. C. Stamatatos, K. Oliver, K. A. Abboud, G. Christou


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The first high nuclearity, mixed-metal BiIII/MnIV and BiIII/MnIII complexes are reported. The former complexes are [Bi2MnIV6O9(O2CEt)9(HO2CEt)(NO3)3] (1) and [Bi2MnIV6O9(O2CPh)9(HO2CPh)(NO3)3] (2) and were obtained from the comproportionation reaction between Mn(O2CR)2 and MnO4- in a 10:3 ratio in the presence of Bi(NO3)3 (3 equiv) in either a H2O/EtCO2H(1) or MeCN/PhCO2H(2) solvent medium. The same reaction that gives 2, but with Bi(O2CMe)3 and MeNO2 in place of Bi(NO3)3 and MeCN, gave the lower oxidation state product [BiMnIII10O8(O2CPh)17(HO2CPh)(H2O)] (3). Complexes 1 and 2 are near-isostructural and possess an unusual and high symmetry core topology consisting of a MnIV6 wheel with two central BiIII atoms capping the wheel on each side. In contrast, the [BiMnIII10O8]17+ core of 3 is low symmetry, comprising a [BiMn33-O)2]8+ butterfly unit, four [BiMn34-O)]10+ tetrahedra, and two [BiMn23-O)]7+ triangles all fused together by sharing common Mn and Bi vertices. Variable-temperature, solid state dc and ac magnetization data on 1-3 in the 1.8-300 K range revealed that 1 and 2 possess an S = 0 ground state spin, whereas 3 possesses an S = 2 ground state. The work offers the possibility of access to molecular analogs of the multifunctional Bi/Mn/O solids that are of such great interest in materials science.




[89] The first non-acetato members of the bis(anion)octacarboxylatotetrakis{di-2-pyridyl-methanediolate(-2)}enneametal(II) family of complexes: Synthesis, X-ray structures and magnetism of [M9(N3)2(O2CCMe3)8{(py)2CO2}4] (M = Co, Ni)

Th. C. Stamatatos, C. P. Raptopoulou, S. P. Perlepes, A. K. Boudalis


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The combined use of di-2-pyridyl ketone [(py)2CO] and azides (N3-) in nickel(II) and cobalt(II) pivalate chemistry has afforded complexes [Ni9(N3)2(O2CCMe3)8{(py)2CO2}4] (1) and [Co9(N3)2(O2CCMe3)8{(- py)2CO2}4] (2), where (py)2CO2 2- is the gem-diolate(-2) form of (py)2CO. The complexes are isostructural and crystallize in the monoclinic P21/c space group. Their molecular structures consist of nine metal(II) ions, eight of which are arranged as two parallel squares flanking the ninth. DC magnetic susceptometry on powdered samples of 1 (1-p) reveal an overall antiferromagnetic behavior, leading to an S = 0 ground state. AC susceptometry reveals out-of-phase signals between 10 and 27 K, and ZFC and FC experiments show a divergence of the two curves below ~27 K. Magnetization-decay and field-sweep experiments verify the relaxation behavior of the sample. Samples of the complex arising from carefully washed single crystals (1-cr) reveal a similar DC behavior, without however the appearance of cusps in the xΜT versus T curves, and no relaxation. The relaxation behavior has been assigned to NiO impurities. The results illustrate the extreme care that should be taken when examining the magnetic properties of apparently analytically pure materials obtained under heating. Complex 2 exhibits an overall antiferromagnetic behavior, without observation of any relaxation phenomena.




[88] Hyperpolarized NMR in single-file nanotubes

C. R. Bowers, C.- Y. Cheng, Th. C. Stamatatos, G. Christou


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Continuous-flow hyperpolarized xenon-129 NMR is used to characterize gas exchange and diffusion in two types of polycrystalline solids with one-dimensional channels. Expressions for the hyperpolarized NMR selectivesaturation recovery signal are derived for normal and single-file diffusion.




[87] Reactions of the metallocene dichlorides [M(Cp)2Cl2] (M=Zr, Hf) and [Ti(MeCp)2Cl2] with the pyridine-2,6-dicarboxylate(-2) ligand: Synthesis, spectroscopic characterization and X-ray structures of the products

Th. C. Stamatatos, S. P. Perlepes, C. P. Raptopoulou, V. Psycharis, N. Klouras


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The reactivity pattern of the 16-electron species [M(Cp)2Cl2] (M = Zr, Hf; Cp- = η5-C5H5-) and [Ti(MeCp)2Cl2] (MeCp- = η5-C5H4CH3- ) towards the dipicolinate(-2) (dipic2-) ligand under mild (ambient temperature) and convenient (aerobic reactions, aqueous media) conditions have been investigated. The syntheses, molecular structures and spectroscopic (IR, 1H NMR) characterization are reported for the 18-electron products [Zr(Cp)2(dipic)] (1), [Hf(Cp)2(dipic)] (2) and [Ti(MeCp)2(dipic)] (3). The dipic2- ion behaves as N,O,O'-chelating ligand in the three complexes, while the centroids of the Cp- (1, 2) and MeCp- (3) rings formally occupy the fourth and fifth coordination sites about the central metal. The two identical/very similar bite angles of only ~70o make the dipic2- ligand particularly suited to form stable metallocene derivatives with 5-coordinate geometry. IR and 1H NMR data are discussed in terms of the known structures and the tridentate chelating mode of the dipic2- ligand.




[86] Combining azide, carboxylate and 2-pyridyloximate ligands in transition metal chemistry: Ferromagnetic NiII5 clusters with a bowtie skeleton

C. Papatriantafyllopoulou, Th. C. Stamatatos, W. Wernsdorfer, S. J. Teat, A. J. Tasiopoulos, A. Escuer, S. P. Perlepes


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The combined use of the anion of phenyl(2-pyridyl)ketone oxime (ppko-) and azides (N3-) in nickel(II) carboxylate chemistry has afforded two new NiII5 clusters, [Ni5(O2CR')2(N3)4(ppko)4(MeOH)4] [R' = H (1), Me (2)]. The structurally unprecedented {Ni5(μ-N3)23-N3)2}6+ cores of the two clusters are almost identical and contain the five NiII atoms in a bowtie topology. Two N3- ions are end-on doubly bridging and the other two ions end-on triply bridging. The end-on μ3-N3- groups link the central NiII atoms with the two peripheral metal ions on either side of the molecule, while the Ni···Ni bases of the triangles are each bridged by one end-on μ-N3- group. Variable-temperature, solid-state direct- (dc) and alternating-current (ac) magnetic susceptibility, and magnetization studies at 2.0 K were carried out on both complexes. The data indicate an overall ferromagnetic behavior and an S = 5 ground state for both compounds. The ac susceptibility studies on 1 reveal nonzero, frequency-dependent out-of-phase (χM") signals at temperatures below ~3.5 K; complex 2 reveals no χM" signals. However, single-crystal magnetization versus dc field scans at variable temperatures and variable sweep rates down to 0.04 K on 1 reveal no noticeable hysteresis loops, except very minor ones at 0.04 K assignable to weak intermolecular interactions propagated by nonclassical hydrogen bonds.




[85] Nickel/lanthanide single-molecule magnets: {Ni3Ln} ‘stars’ with a ligand derived from the metal-promoted reduction of di-2-pyridyl ketone under solvothermal conditions

C. G. Efthymiou, Th. C. Stamatatos, C. Papatriantafyllopoulou, A. J. Tasiopoulos, W. Wernsdorfer, S. P. Perlepes, G. Christou


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Unusual {NiII3LnIII(μ-OR)6}3+ complexes with a “star” topology have been prepared with ligands derived from the metal-promoted reduction of di-2-pyridyl ketone under solvothermal conditions; the DyIII member shows weak single-molecule-magnet behavior.




[84] A high nuclearity 3d/4f metal oxime cluster: An unusual Ni8Dy8 ‘core-shell’ complex from the use of 2-pyridinealdoxime

C. Papatriantafyllopoulou, Th. C. Stamatatos, C. G. Efthymiou, L. Cunha-Silva, F. A. Almeida Paz, S. P. Perlepes, G. Christou


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The initial employment of 2-pyridinealdoxime in 3d/4f chemistry has led to a NiII8DyIII8 cluster with an unprecedented metal topology; the compound has an unusual structure, is the highest-nuclearity metal oxime cluster to date, and exhibits slow magnetization relaxation.




[83] High-nuclearity, mixed-valence Mn17, Mn18 and {Mn62}n complexes from the use of triethanolamine

Th. C. Stamatatos, D. Foguet-Albiol, W. Wernsdorfer, K. A. Abboud, G. Christou


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The use of both azide and triethanolamine, with or without the presence of carboxylate groups, has provided new Mn17, Mn18 and {Mn62}n complexes with aesthetically-pleasing cage, layered, and linked-chain-type structures; two are also new single-molecule magnets.




[82] Use of the 2-pyridinealdoxime/N,N′-donor ligand combination in cobalt(III) chemistry: Synthesis and crystal structure determination of mononuclear Co(III) complexes

K. F. Konidaris, A. Terzis, C. P. Raptopoulou, S. P. Perlepes, E. Manessi-Zoupa, Th. C. Stamatatos


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The use of 2-pyridinealdoxime (paoH) / N,N′-donor ligand (L-L) “blend” in cobalt chemistry has afforded two cationic mononuclear cobalt(III) complexes of the general type [Co(pao)2(L-L)]+, where L-L= 1,10-phenanthroline (phen) and 2,2′-bipyridine (bpy). The CoCl2/paoH/L-L (1:2:1) reaction system in MeOH gives complexes [CoIII(pao)2(phen)]Cl·2H2O (1·2H2O) and [CoIII(pao)2(bpy)]Cl·1.5MeOH (2·1.5MeOH). The structures of the complexes were determined by single-crystal X-ray crystallography. The CoIII ions are six-coordinate, surrounded by three bidentate chelating ligands, i.e., two pao- and one phen or bpy. The deprotonated oxygen atom of the pao- ligand remains uncoordinated and participates in hydrogen bonding with the solvate molecules. IR data of the complexes are discussed in terms of the nature of bonding and the known structures.




[81] Pressure dependence of the magnetization in Mn7 single-molecule magnets

D. M. Pajerowski, Th. C. Stamatatos, S. Mukherjee, E. S. Knowles, M. Bencomo, M. W. Meisel, G. Christou


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Single-molecule magnet (SMM) clusters of Mn7 can have ground states of S=11 or S=16, depending upon the local symmetry of the clusters. The possibility of inducing a switching of the spin ground state configuration as a function of pressure was investigated by measuring the temperature dependence of the magnetic susceptibility, χΜ(3K ≤ T ≤ 40K), using a home-made resonant coil magnetometer operated near 6 MHz and equipped with a pressure cell capable of producing P≤2GPa. The results indicate the ground states of both materials are robust in the temperature–pressure–frequency parameter space that was probed.




[80] A family of 3-D coordination polymers composed of mixed-valence Mn6 octahedra within Na4 tetrahedra

Th. C. Stamatatos, K. A. Abboud, G. Christou


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The combined use of 1,1,1-tris(hydroxymethyl)ethane (thmeH3) and azides in Mn carboxylate chemistry has yielded a new family of decanuclear [Mn6Na4O(N3)(O2CR)5(thme)4(H2O)4] (R = Me (1); Et (2)) complexes consisting of mixed-valence Mn2IIMn4III units with a very rare [Mn66-O)]14+ octahedral core contained within a tetrahedron of four NaI atoms. The [Mn6Na4] units of 1 and 2 are connected via the Na atoms to neighboring units, giving 3-D supramolecular assemblies with large channel cavities. Variable-temperature, solid-state dc and ac magnetization studies carried out in the 1.8–300 K range reveal that the Mn6 units of 1 and 2 are antiferromagnetically coupled to give S = 0 ground states for both complexes.




[79] In search for titanocene complexes with improved cytotoxic activity: Synthesis, x-ray structure and spectroscopic study of bis(η5-cyclopentadienyl)difluorotitanium(IV)

E. Koleros, Th. C. Stamatatos, V. Psycharis, C. P. Raptopoulou, S. P. Perlepes, N. Klouras


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The 1:2 reaction of [Ti(η5-C5H5)2Cl2] and AgF in CHCl3/H2O yielded the fluoro analog [Ti(η5-C5H5)2F2] (1) in almost quantitative yield (C5H5 is the cyclopentadienyl group). The coordination about the TiIV atom formed by two fluoro ligands and the centroids of the cyclopentadienyl rings is distorted tetrahedral. The compound crystallizes in the orthorhombic space group C2cm. The lattice constants are a = 5.9055(4), b = 10.3021(5), c = 14.2619(9) Å, and α = β = γ = 90°. The complex has been characterized by elemental analyses and spectroscopic (IR, 1H NMR) data. A structural comparison of the four members of the [Ti(η5-C5H5)2X2] family of complexes (X = F, Cl, Br, I) is attempted.




[78] The highest nuclearity manganese/oximate complex: An unusual MnII/III15 cluster with an S = 6 ground state

D. I. Alexandropoulos, C. Papatriantafyllopoulou, O. Roubeau, S. J. Teat, S. P. Perlepes, G. Christou, Th. C. Stamatatos


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The synthesis, structure, and magnetochemical characterization of the largest manganese oxime cluster are reported. The Mn15/ 2-pyridinealdoxime compound is mixed-valence (II/III) and possesses an irregular structural motif with a novel Mn/O core. The oximato-bridged cluster exhibits an S = 6 ground state and a negative magnetoanisotropy.




[77] α-Benzoin oxime in higher oxidation state 3d metal cluster chemistry: Structural and magnetic study of a new MnIII9 complex

E. S. Koumousi, M. J. Manos, C. Lampropoulos, A. J. Tasiopoulos, W. Wernsdorfer, G. Christou, Th. C. Stamatatos


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The initial employment of R-benzoin oxime (bzoxH2) in higher oxidation state 3d metal cluster chemistry has provided access to a new enneanuclear MnIII complex with an unprecedented metalcore topology consisting of two triangular [Mn332-)(μ-ΟΝ)3]4+ fragments connected by a linear [Mn3(μ-ΟΝ)6]3+ unit. The MnIII9 cluster is antiferromagnetically coupled and has an S = 3 spin ground state.




[76] Molecular wheels as nanoporous materials: Differing modes of gas diffusion through Ga10 and Ga18 wheels of different diameters probed by hyperpolarized 129Xe NMR spectroscopy

C.- Y. Cheng, Th. C. Stamatatos, G. Christou, C. R. Bowers


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The study of crystals of molecular wheels as nanoporous materials is reported. Hyperpolarized 129Xe NMR spectroscopy has been used to characterize the mode of molecular diffusion and Xe interactions within the supramolecular nanochannels formed upon crystallization of the molecular wheels [Ga10(OMe)20(O2CMe)10] and [Ga18(pd)12(pdH)12(O2CMe)6(NO3)6](NO3)6. In agreement with expectations based on the collision diameter of the Xe atom relative to the differing internal diameters of the two types of gallium wheels, single-file diffusion occurs in the Ga10 channels, whereas in the Ga18 system the data are consistent with normal, Fickian diffusion. Information about the electronic environment inside the channels was probed by the Xe chemical shift. The interaction of the gas with the channel walls is found to be substantially stronger than the interaction in organic nanotubes and zeolites. The results establish the ability of crystals of molecular wheel compounds to function as a new class of porous nanotubular materials, and ones of a known and variable diameter, for studying the channel diameter dependence of molecular exchange and unidirectional diffusion on the micrometer length scale.




[75] New mixed-valence MnII/III6 complexes bearing oximato and azido ligands: Synthesis, and structural and magnetic characterization

C. Lampropoulos, Th. C. Stamatatos, M. J. Manos, A. J. Tasiopoulos, K. A. Abboud, G. Christou


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The combined use of the anion of methyl 2-pyridyl ketone oxime (mpko) and azides (N3) in non-carboxylate Mn chemistry has afforded two new Mn6 clusters, [Mn6O3(N3)3(mpko)6(H2O)3](ClO4)2 (1) and [Mn6O3(N3)5(mpko)6(H2O)] (2), which are mixed-valence (MnII, 5MnIII). The 1:1:1:1 reaction of Mn(ClO4)2·6H2O, mpkoH, NaN3 and NEt3 in MeOH gave the cationic complex 1, while a similar reaction using additional NaO2CMe led instead to the neutral complex 2. The structurally unprecedented cores of the two cages are very similar, and contain the six Mn ions in a topology comprising three vertex-sharing oxide-centered triangles bridged by two end-on azides. Variable-temperature, solid state dc and ac magnetization studies were carried out for 1 and 2 in the 1.8–300 K range. The data reveal S = 5/2 ground states for both complexes, and fitting of magnetization vs. field (H) and temperature (T) data by matrix diagonalization for 1 gave S = 5/2, D = –1.4(3) cm–1, and g = 1.99(1), where D is the axial zero-field splitting (ZFS) parameter. The combined results demonstrate the versatility of 2-pyridyl ketone oxime anions in the presence of suitable ancillary ligands, such as azides, for the synthesis of new Mn clusters, without requiring the co-presence of carboxylate ligands.




[74] An alcoholysis route to a Cu16 cluster, and the influence of the alcohol

T.- F. Liu, Th. C. Stamatatos, K. A. Abboud, G. Christou


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A systematic investigation of the alcoholysis of copper(II) pivalate (piv-) solutions has led to a series of Cu2, Cu6, and Cu16 products, depending on the alcohol used as solvent. When PrnOH or BunOH was employed, the products were the clusters [Cu16O4(OH)4(OR)8(piv)12(ROH)] (R = Prn, Bun) that are almost isostructural. The Cu16 clusters are antiferromagnetically-coupled with an S = 0 spin ground state.




[73] Strong antiferromagnetic coupling in doubly N,O oximato-bridged dinuclear copper(II) complexes

E. S. Koumousi, C. P. Raptopoulou, S. P. Perlepes, A. Escuer, Th. C. Stamatatos


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The use of di-2-pyridyl ketone oxime, (py)pkoH, and phenyl 2-pyridyl ketone oxime, ppkoH, in copper(II) hexafluoroacetylacetonate chemistry is reported. The reaction of CuCl2·2H2O with one and two equivalents of ppkoH and Na(hfac), respectively, in CH2Cl2 affords the dinuclear complex [Cu2(hfac)2(ppko)2] (1) in excellent yield. The replacement of ppkoH by (py)pkoH gives the isostructural compound [Cu2(hfac) 2{(py)pko}2] (2) in good yield. The CuII atoms in both 1 and 2 are doubly bridged by the oximate groups of two η1112 ppko- and (py)pko- ligands, respectively. The bridging Cu–(R–NO)–Cu' units are not planar, with the torsion angles being 23.2o (1) and 20.3o (2). A bidentate chelating hfac- ligand completes five-coordination at each square pyramidal metal ion. The hfac--free reaction system CuCl2·2H2O/(py)pkoH/NEt3 (1:2:1) gives instead the mononuclear complex [CuCl{(py)pko}{(py)pkoH}] (3) in very good yield. The CuII atom is coordinated by two N,N'-bidentate (py)pko-/(py)pkoH chelates and a monodentate chloride anion resulting in a distorted square pyramidal geometry around the metal center. Variable-temperature, solid-state dc magnetic studies were carried out on the representative dinuclear complex 1 in the 2.0–300 K range. The data indicate a very strong antiferromagnetic exchange interaction and a resulting S = 0 ground state, which is well isolated from the S = 1 excited state. The J value of -720 cm-1 was derived from the fitting of the experimental data using the Hamiltonian H = -J(S1 · S2).




[72] Spin Maximization: Switching of the Usual S = 11 State of MnII4MnIII3 Disklike Complexes to the Maximum S = 16

Th. C. Stamatatos, Katye M. Poole, Dolos Foguet-Albiol, Khalil A. Abboud, Ted A. O’Brien, G. Christou


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The S = 11 ground states of the Mn7 family of mixed-valence complexes with a metal-centered hexagonal topology have been found by density functional theory calculations to arise by spin frustration involving small differences in the magnitudes of the two weakest interactions controlling the alignment of the central spin. Targeted structural perturbation has allowed a complex with the central spin flipped to be discovered, which thus possesses the maximum S = 16 ground state.




[71] Crystal lattice desolvation effects on the magnetic quantum tunneling of single-molecule magnets

G. Redler, C. Lampropoulos, S. Datta, C. Koo, Th. C. Stamatatos, N. E. Chakov, G. Christou, S. Hil


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High-frequency electron paramagnetic resonance (HFEPR) and alternating current (ac) susceptibility measurements are reported for a new high-symmetry Mn12 complex, [Mn12O12(O2CCH3)16(CH3OH)4]·CH3OH. The results are compared to those of other high-symmetry spin S=10 Mn12 single-molecule magnets (SMMs), including the original acetate, [Mn12O12(O2CCHO3)16(H2O)4]·2CH3CO2H·4H2O, and the Mn12O12(O2CCH2Br)16(H2O4]·4CH2Cl2 and [Mn12O12(O2CCH2But)16(CH3OH4]·CH3OH complexes. These comparisons reveal important insights into the factors that influence the values of the effective barrier to magnetization reversal, Ueff, deduced on the basis of ac susceptibility measurements. In particular, we find that variations in Ueff can be correlated with the degree of disorder in a crystal which can be controlled by desolvating (drying) samples. This highlights the importance of careful sample handling when making measurements on SMM crystals containing volatile lattice solvents. The HFEPR data additionally provide spectroscopic evidence suggesting that the relatively weak disorder induced by desolvation influences the quantum tunneling interactions and that it is under-barrier tunneling that is responsible for a consistent reduction in Ueff that is found upon drying samples. Meanwhile, the axial anisotropy deduced from HFEPR is found to be virtually identical for all four Mn12 complexes, with no measurable reduction upon desolvation.




[70] Adventures in the coordination chemistry of di-2-pyridyl ketone and related ligands: From high-spin molecules and single-molecule magnets to coordination polymers, and from structural aesthetics to an exciting new reactivity chemistry of coordinated ligands

Th. C. Stamatatos, C. G. Efthymiou, C. C. Stoumpos, S. P. Perlepes


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The coordination chemistry of di-2-pyridyl ketone and related ligands is reviewed. An outline of the variety of such ligands is presented. References are given to methods for the synthesis of ligands that are not available on the market. The activation of the carbonyl group(s) of some of the ligands towards further reactions seems to be an emergent area of synthetic inorganic chemistry. The coordination chemistry of each ligand with metals is briefly described. Emphasis is placed on structural features and physical properties (mainly magnetic) of the resulting metal clusters and coordination polymers. The structural diversity of the complexes stems from the ability of the deprotonated diol- or hemiketal-type ligands to adopt a variety of bridging coordination modes depending on the number of carbonyl groups, the nature of the extra donor groups in the molecule and on the reaction conditions. Employment of a second organic or inorganic ligand in this chemistry gives an extraordinary structural flexibility in the resulting mixed-ligand systems. The initial use of 1,1'-carbonyldiimidazole and 1,1'-oxalyldiimidazole in copper(II) chemistry, which leads to unprecedented coordination polymers containing alcoholysis and/or hydrolysis "fragments" of the ligands, is also illustrated.




[69] A tetranuclear complex from the employment of pyridine-2,6-dimethanol in copper(II) nitrate chemistry: Synthetic, structural and magnetic studies

G. C. Vlahopoulou, D. I. Alexandropoulos, C. P. Raptopoulou, S. P. Perlepes, A. Escuer, Th. C. Stamatatos


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The use of pyridine-2,6-dimethanol (pdmH2) in copper(II) nitrate chemistry is reported. The reaction of Cu(NO3)2·3H2O with one equivalent of pdmH2 in MeCN affords the known mononuclear complex [Cu(pdmH2)2](NO3)2 (1) in high-yield. The reaction of 1 and NaOMe in an 1:1 ratio, as well as the reaction between Cu(NO3)2·3H2O, pdmH2 and NaOMe in an 1:1:1 ratio, in MeOH gives the tetranuclear complex [Cu4(NO3)2(pdmH)4(H2O)(MeOH)](NO3)2 (2) in moderate yields. The cation of 2 possesses a slightly distorted tetrahedral Cu4 topology with a [Cu4(m2-OR)4]4+ core. The pdmH- ions behave as η1122 ligands. Strong intramolecular hydrogen bonds and π–π stacking interactions provide thermodynamic stability on compound 2. Variable-temperature, solid-state dc magnetic studies were carried out on complex 2 in the 2.0–300 K range. The data indicate predominant antiferromagnetic exchange interactions and a resulting S = 0 ground state, which is expected for a solely, μ2-alkoxide-bridged system with obtuse Cu–O–Cu bond angles that magnetically behaves as a Cu4 ring. A simplified 1 - J model was found to be adequate to describe the variable-temperature dc susceptibility data. The data were fitted to the appropriate equation derived from the Hamiltonian H = -J1(S1·S2 + S2·S4 + S3·S4 + S1·S3), giving the parameters J1 = 99.5 cm-1 and g = 2.11(4). The combined work demonstrates the ligating flexibility of the pdmH2 chelate and its usefulness in the synthesis of oligo- and polynuclear CuIIx clusters with interesting structural and magnetic properties, without requiring the co-presence of carboxylate ligands.




[68] A new family of octanuclear Mn complexes with a rod-like topology

E. E. Moushi, Th. C. Stamatatos, V. Nastopoulos, G. Christou, A. J. Tasiopoulos


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Three new octanuclear compounds were prepared from reactions of [Mn(O2CR)2]·2H2O (R = Et or Ph) with the diols 1,3-propanediol (pdH2) or 2-methyl-1,3-propanediol (mpdH2) in the presence of NaN3. All three compounds [Mn8(N3)4(O2CR)6(L)4(py)6] (L = pd2-, R = Et 1; L = mpd2-, R = Et 2; L = pd2-, R = Ph 3) (py = pyridine) possess a novel near-planar, rod-like topology. Dc and ac magnetic susceptibility studies in the 2–300 K range for complexes 1 and 2 revealed the presence of dominant antiferromagnetic exchange interactions, leading to diamagnetic ground spin states.




[67] 1-D coordination polymers consisting of a high-spin Mn17 octahedral unit

E. E. Moushi, Th. C. Stamatatos, V. Nastopoulos, G. Christou, A. J. Tasiopoulos


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The reaction of [Mn(O2CMe)2]·4H2O with pdH2 (1,3-propanediol) or mpdH2 (2-methyl-1,3-propanediol) in the presence of NaN3 in MeCN/py (py = pyridine) results in the formation of two new one-dimensional coordination polymers composed of a [MnIII6 MnII114-O)83-N3)4]25+ octahedral unit. The peripheral ligation is completed by pd2- (or mpd2-), acetate, pyridine and μ-1,3-N3- ligands. The latter bridges each Mn17 unit to its neighboring one, resulting in the formation of the two 1-D coordination polymers. Variable-temperature dc magnetic susceptibility studies indicate the existence of predominantly ferromagnetic interactions and a resulting giant ground state spin within the Mn17 units and intermolecular antiferromagnetic exchange interactions between the neighboring Mn17 units that result in diamagnetic ground spin states for both polymeric compounds.




[66] A convenient MnIII starting material for the synthesis of homo- and heterometallic manganese carboxylate clusters: Mn9 and Mn10-xFex complexes

C. Lampropoulos, Th. C. Stamatatos, K. A. Abboud, G. Christou


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The use of a convenient source of MnIII ions, namely the [Mn(OR)(O2CR')2]n (R = H, Me, and R' = Me, But) family of 1-D coordination polymers, afforded two new enneanuclear and decanuclear molecular clusters, homometallic [Mn9O7(O2CBut)13(MeCN)2] (3) and heterometallic [Mn10-xFex(OMe)20(O2CMe)10] (x < 10) (4), respectively. Compound 3 was synthesized by a solvent-induced structural transformation, whereas complex 4 resulted from the reaction of [Mn(OH)(O2CMe)2]n with an FeIII source. The core of 3 comprises two [Mn4O2]8+ butterfly units and a [Mn3O]7+ triangular unit fused together by sharing one Mn atom. Magnetic susceptibility measurements of 3 revealed dominant antiferromagnetic interactions within the molecule, and a ground state of S = 1 with many low-lying excited states. Complex 4 is a mixed FeIII/MnIII single-strand molecular wheel, which forms 3D nanotubular stacks arranged in a zig–zag fashion. The described work suggests that the [Mn(OR)(O2CR')2]n compounds represent excellent starting materials for MnIII carboxylate cluster chemistry.




[65] Old ligands with new coordination chemistry: A Mn17Na cluster bearing triethanolamine and azide groups and exhibiting slow magnetization relaxation

Th. C. Stamatatos, K. A. Abboud, G. Christou


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The combination of azide, carboxylate and triethanolamine ligands in higher oxidation state Mn cluster chemistry has yielded a new heptadecanuclear, mixed-valence (II, III, IV) compound with fairly large S and D values, and frequency-dependent out-of-phase (χ"M) signals, characteristics of the superparamagnetic-like slow relaxation of an SMM.




[64] High-spin molecules: A mixed-valence Mn6 octahedron with an S = 11 ground state

Th. C. Stamatatos, K. V. Pringouri, K. A. Abboud, G. Christou


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The employment of 1,1,1-tris(hydroxymethyl)ethane ligand in higher oxidation state Mn cluster chemistry has yielded a new hexanuclear, mixed-valence (II,III,IV) compound with a rare [Mn66-O)]18+ octahedral core. The Mn6 molecule is completely ferromagnetically coupled and possesses an S = 11 ground state, the maximum for a MnII, 2MnIII, 3MnIV species.




[63] New copper(II) clusters and coordination polymers from the amalgamation of azide/benzoate/di-2-pyridyl ketone ligands

Th. C. Stamatatos, J. C. Vlahopoulou, V. Tangoulis, C. P. Raptopoulou, A. Terzis, G. S. Papaefstathiou, S. P. Perlepes


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The employment of the di-2-pyridyl ketone [(py)2CO]/PhCO2-N3- ligand combination in copper(II) chemistry has provided access to the hexanuclear cluster [Cu6(O2CPh)4(N3)2{(py)2CO2}2{(py)2C(OH)O}2] (1), and the coordination polymers [Cu4(O2CPh)2(N3)4{(py)2C(OMe)O}2]n (2) and [Cu2(O2CPh)(N3)2{(py)2 C(OMe)O}]n (3). The structural type (cluster versus polymer) depends on the reaction solvent. Complex 1 has a [CuII63-OR")2(μ-OR")4]6+ core based on a central defective cubane unit and two additional CuII atoms across the missing edges. Complex 2 consists of zig-zag chains and complex 3 consists of extended 2D networks that adopt the herringbone architecture which is not based on T-shaped nodes. Cluster 1 is antiferromagnetically coupled with an S = 0 ground state.




[62] A family of mononuclear CoIII/2-pyridyloximate complexes and their conversion to trinuclear, mixed-valence linear CoII/III3 clusters

Th. C. Stamatatos, E. Katsoulakou, A. Terzis, C. P. Raptopoulou, R. E. P. Winpenny, S. P. Perlepes


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The use of the 2-pyridyl oxime ligands (LH) 2-pyridinealdoxime, methyl 2-pyridyl ketone oxime and phenyl 2-pyridyl ketone oxime in Co chemistry has been investigated and led to two families of compounds. The first family includes the mononuclear octahedral, low-spin complexes [CoIII(L)3], while the second family consists of the trinuclear, mixed-valent linear clusters [CoIII2CoII(L)6]X2 (X = ClO4-, PF6-). The latter are prepared by the reactions of the former with an appropriate CoII source. The structural, physical and spectroscopic properties of the complexes are described.




[61] A Mn17 octahedron with a giant ground-state spin: Occurrence in discrete form and as multidimensional coordination polymers

E. E. Moushi, Th. C. Stamatatos, W. Wernsdorfer, V. Nastopoulos, G. Christou, A. J. Tasiopoulos


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A [MnIII11MnII6( μ4-O)8( μ3-L)4]25+ (L = N3- or OCN-) octahedral unit is reported, occurring within 1D (1) and 2D (2) coordination polymers, as well as the corresponding 0D discrete cluster 3. It possesses a giant ground-state spin value, determined in the case of 3 to be S = 37, the second largest to be reported to date. In addition, compound 3 displays single-molecule magnet (SMM) behavior, and is thus the largest-spin SMM.




[60] Azide groups in high oxidation state Mn carboxylate chemistry: A new Mn11 complex and its conversion to a Mn25 azide complex with Me3SiN3

Th. C. Stamatatos, A. Vinslava, K. A. Abboud, G. Christou


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A new high oxidation state MnIII/IV11 carboxylate complex has been prepared and then converted to a MnII/III25 azide/carboxylate cluster with Me3SiN3; the Mn25 product is the initial example of a higher oxidation state Mn azide complex not stabilized by any chelate ligands.




[59] Initial employment of α-benzoin oxime as a route to high-nuclearity metal clusters: Decanuclear CuII complexes with a wheel topology

G. C. Vlahopoulou, Th. C. Stamatatos, V. Psycharis, S. P. Perlepes, G. Christou


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The initial employment of α-benzoin oxime (bzoxH2) inmetal cluster chemistry has provided access to a new family of decanuclear CuII complexes with a loop or single-strand wheel topology; the CuII10 clusters are antiferromagneticallycoupled with an S = 0 spin ground state, as expected for even-membered loop arrays of CuII atoms.




[58] Quantum phase interference and Néel vector tunneling in antiferromagnetic molecular wheels

O. Waldmann, Th. C. Stamatatos, G. Christou, H. U. Güdel, I. Sheikin, H. Mutka,


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The antiferromagnetic molecular wheel Fe18 of 18 exchange-coupled FeIII ions has been studied by magnetic torque, magnetization, and inelastic neutron scattering. The combined data show that the lowtemperature magnetism of Fe18 is very accurately described by the Néel-vector tunneling (NVT) scenario, as unfolded by semiclassical theory. In addition, the magnetic torque as a function of applied field exhibits oscillations that reflect the oscillations in the NVT splitting with field due to quantum phase interference.




[57] Interpretation of the magnetic properties of a compound consisting of cocrystallized CuII3 and CuII4 clusters through the targeted synthesis and study of its discrete CuII4 component

Th. C. Stamatatos, G. C. Vlahopoulou, C. P. Raptopoulou, A. Terzis, A. Escuer, S. P. Perlepes


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The use of the binary "blend" of MeCO2-/pdmH2 ligands (pdmH2 = pyridine-2,6-dimethanol) in copper(II) chemistry has provided access to a compound consisting of discrete linear CuII3 and cubane CuII4 clusters. The complicated magnetic behavior of the CuII3 + CuII4 complex was clarified and interpreted through the designed synthesis of the individual CuII4 component; a unique 1D (CuII5)n compound containing a CuII3 subunit, which is structurally similar to the trinuclear cluster in the CuII3 + CuII4 compound, was also isolated and structurally characterized.




[56] Initial use of 1,1′-oxalyldiimidazole for inorganic synthesis: Decomposition of the ligand as a means to the preparation of an imidazole- and oxalate(-2)-containing, 1D copper(II) complex

Th. C. Stamatatos, S. P. Perlepes, C. P. Raptopoulou, V. Psycharis, C. S. Patrickios, A. J. Tasiopoulos, A. K. Boudalis


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The use of 1,1'-oxalyldiimidazole, (im)COCO(im), for the synthesis of coordination complexes is explored for the first time. The [Cu2(O2CMe)4(H2O)2]/(im)COCO(im) reaction system in 96% EtOH yields the new, 1D coordination polymer [Cu(ox)(Him)2]n (1), where Him is the neutral imidazole and ox2- is the oxalate(-2) ligand. A mechanism for the hydrolytic decomposition of the ligand is proposed. Complex 1 comprises neutral, zigzag chains with the η1111:μ (2.1111 using Harris notation) ox2- ligand bridging two neighboring CuII centers; two cis Him groups complete a Jahn–Teller distorted octahedral geometry at the metal. The dc, variable-temperature magnetic susceptibility data for the complex reveal antiferromagnetic CuII···CuII exchange interactions.




[55] Alcoholysis/hydrolysis of 1,1'-carbonyldiimidazole as a means of preparing unprecedented, imidazole-containing one-dimensional coordination polymers of copper(II)

Th. C. Stamatatos, S. P. Perlepes, C. P. Raptopoulou, A. Terzis, C. S. Patrickios, A. J. Tasiopoulos, A. K. Boudalis


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The use of 1,1'-carbonyldiimidazole, (im)2CO, for the synthesis of imidazolate (im-) and/or imidazole (Him)-containing copper(II) coordination polymers is described. The [Cu2(O2CMe)4(H2O)2]/(im)2CO reaction system in EtOH yields the new polymeric species [Cu(O2CMe)(im)(Him)(EtOH)]n (1) and the known compound [Cu(im)2]n (2), depending on the reaction conditions. A mechanism for the alcoholysis/hydrolysis of (im)2CO is proposed. Complex 1 comprises neutral, zigzag chains with the η11:μ im- ligand bridging two neighbouring CuII atoms. Each square pyramidal metal centre is coordinated to two imidazolate nitrogen atoms, the pyridine-type nitrogen atom of the terminal imidazole ligand, one acetate oxygen atom and the ethanol oxygen atom. The dc magnetic susceptibility data for 1 have been analysed according to the Bonner-Fisher model for an equally spaced S = 1/2 chain, revealing moderate antiferromagnetic CuII···CuII exchange interactions (J = -33.5 cm-1. The reaction system Cu(NO3)2·3H2O/(im)2CO in EtOH leading to the preparation of known trans-[Cu(NO3)2(Him)4] (3) is also described. With terephthalate(-2) (tp2-), instead of MeCO2-, in MeOH/H2O the product is the new, 1D linear coordination polymer [Cu(tp)(Him)2(H2O)]n·2nH2O (4·2nH2O). Adjacent square pyramidal CuII atoms are singly bridged by the bis-monodentate tp2- ligand, while two monodentate Him groups and one H2O molecule complete five-coordination at each metal centre. The chains of 1 and 4·2nH2O form interesting, hydrogen-bonded 3D networks. The combined work demonstrates the usefulness of (im)2CO in the preparation of interesting CuII coordination polymers which can not be obtained by the use of Him.




[54] A metamagnetic 2D copper(II)-azide complex with 1D ferromagnetism and a hysteretic spin-flop transition

G. Lazari, Th. C. Stamatatos, C. P. Raptopoulou, V. Psycharis, M. Pissas, S. P. Perlepes, A. K. Boudalis


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Compound [Cu3(N3)6(DMF)2]n (1) was initially obtained in a serendipitous way during efforts to prepare a CuII/N3-/Mebta coordination polymer (Mebta = 1-methylbenzotriazole). With the identity of 1 established by single-crystal crystallography, a rational preparative route to this complex was designed and carried out by reacting Cu(ClO4)·6H2O with two equivalents of NaN3 in DMF. Complex 1 is a 2D coordination polymer possessing μ1,1,1 and μ1,1,3 azido ligands. Its structure consists of {Cu3(N3)6(DMF2)} repeating units, which form chains that run parallel to the a axis; their bridging is achieved through end-on azides. The chains form sheets parallel to the ab plane through end-to-end azides. The magnetic properties of 1 have been studied in detail. The complex contains 1D ferromagnetic chains, based on a CuII3 repeating unit, which can be viewed as having an S = 3/2 ground state. The ferromagnetic chains undergo antiferromagnetic coupling, which is weak enough to be overcome by moderate magnetic fields at 2 K leading to a metamagnetic spin-flop transition at 2.7 T. The transition is first-order, leading to hysteresis of the order of 0.2 T.




[53] Azide groups in higher oxidation state manganese cluster chemistry: From structural aesthetics to single-molecule magnets

Th. C. Stamatatos, G. Christou


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This Forum Article overviews the recent amalgamation of two long-established areas, manganese/oxo coordination cluster chemistry involving the higher MnII/MnIV oxidation states and transition-metal azide (N3-) chemistry. The combination of azide and alkoxide- or carboxylate-containing ligands in Mn chemistry has led to a variety of new polynuclear clusters, high-spin molecules, and single-molecule magnets, with metal nuclearities ranging from Mn4 to Mn32 and with ground-state spin values as large as S = 83/2. The organic bridging/chelating ligands are discussed separately as follows: (i) pyridyl alkoxides [the anions of 2-(hydroxymethyl)pyridine (hmpH), 2,6-pyridinedimethanol (pdmH2), and the gem-diol form of di-2-pyridyl ketone (dpkdH2)]; (ii) non-pyridyl alkoxides [the anions of 1,1,1- tris(hydroxymethyl)ethane (thmeH3), triethanolamine (teaH3), and N-methyldiethanolamine (mdaH2)]; (iii) other alcohols [the anions of 2,6-dihydroxymethyl-4-methylphenol (LH3) and Schiff bases]; (iv) pyridyl monoximes/dioximes [the anions of methyl-2-pyridyl ketone oxime (mpkoH), phenyl-2-pyridyl ketone oxime (ppkoH), and 2,6-diacetylpyridine dioxime (dapdoH2)]; (v) non-pyridyl oximes [the anions of salicylaldoxime (saoH2) and its derivatives R-saoH2]. The large structural diversity of the resulting complexes stems from the combined ability of the azide and organic ligands to adopt a variety of ligation and bridging modes. The combined work demonstrates the synthetic novelty that arises when azide is used in conjunction with alcohol-based chelates, the aesthetic beauty of the resulting molecules, and the often fascinating magnetic properties that these compounds possess. This continues to emphasize the extensive and remarkable ability of Mn chemistry to satisfy a variety of different tastes.




[52] A nontwisted, ferromagnetically coupled MnIII3O triangular complex from the use of 2,6-bis(hydroxymethyl)-p-cresol

C. Lampropoulos, K. A. Abboud, Th. C. Stamatatos, G. Christou


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The reaction between Mn(O2CMe)2 · 4H2O and hmcH3 [hmcH3 = 2,6-bis(hydroxymethyl)-p-cresol] in CH2Cl2 in the presence of NEt3 affords the MnIII 3 complex [NEt3(CH2Cl)]2[Mn3O(hmcH)3(hmcH2)3] (1). The anion of 1 contains a [MnIII33-O)]7+ triangular core, with the central O2- ion lying above the Mn3 plane. The complex is ferromagnetically coupled with a resulting S = 6 ground state.




[51] Employment of methyl 2-pyridyl ketone oxime in manganese non-carboxylate chemistry: MnII2MnIV and MnII2MnIII6 complexes

C. C. Stoumpos, Th. C. Stamatatos, H. Sartzi, O. Roubeau, A. J. Tasiopoulos, V. Nastopoulos, S. J. Teat, G. Christou, S. P. Perlepes


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The employment of the anion of methyl 2-pyridyl ketone oxime (mpko-) as a tridentate chelating/ bridging ligand in manganese chemistry is described. The inorganic anion (Br-, ClO4-) used in the reaction affects the identity of the product. The reaction of MnBr2 and one equivalent of mpkoH in the presence of a base affords [Mn3(OMe)2(mpko)4Br2] (3), which is mixed-valence (2MnII, MnIV). The central MnIV atom in each of the two, crystallographically independent, centrosymmetric molecules is coordinated by four oximate oxygen atoms belonging to the η111:μ mpko- ligands, and two η1:μ MeO- groups, while six coordination at each terminal MnII atom is completed by four nitrogen atoms belonging to the 'chelating' part of two mpko- ligands, and one Br- ion. The MnII atoms have trigonal prismatic coordination geometry. The reaction of Mn(ClO4)2·6H2O, mpkoH and OH- (1:2:1) in MeOH gives [Mn8O4(OMe)(mpko)9(mpkoH)](ClO4)4 (4), which is also mixed-valence (2MnII, 6MnIII) and possesses the novel [Mn83-O)4(μ-OMe)(μ-OR")2]11+ core. The latter possesses a U-shaped sequence of four fused {MnIIMnIII23-O)}6+ triangular units, with a MnIII-MnIII edge being shared between the central triangles. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on complexes 3 and 4. The dc susceptibility data for 3 in the 5.0–300 K range have been fit to a model with two J values, revealing weak ferromagnetic MnII···MnIV (J = +3.4 cm-1) and MnII···MnII (J' = +0.3 cm-1) exchange interactions. Fitting of the magnetization vs. H/T data by matrix diagonalization and including only axial anisotropy (ZFS, D) gave ground state spin (S) and D values of S = 13/2, D = +0.17 cm-1 for 3 and S = 3, D = -0.09 cm-1 for 4. The combined work demonstrates the usefulness of mpko- in the preparation of interesting Mn clusters, without requiring the co-presence of carboxylate ligands.




[50] {Mn6}n single-chain magnet bearing azides and di-2-pyridylketone-derived ligands

Th. C. Stamatatos, K. A. Abboud, W. Wernsdorfer, G. Christou


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The synthesis, structure, and magnetochemical characterization of a new manganese single-chain magnet are reported. The compound is a chain of repeating Mn6 units bridged by end-on azide groups and exhibits magnetization hysteresis loops.




[49] Initial use of dioximate ligands in 3d/4f cluster chemistry: Synthesis, structure, and magnetic studies of an unusual [GdIII2MnIVO]8+ complex

C. Lampropoulos, Th. C. Stamatatos, K. A. Abboud, G. Christou


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An unusual [MnIVGdIII23-O2-)]8+ triangular complex has been prepared from the initial use of 2,6-diacetylpyridine dioxime (dapdoH2) in 3d/4f cluster chemistry. The complex has an S = 13/2 ground state, with exchange parameters J = +0.49 cm-1 and J′ = -0.12 cm-1 [H = -2J(Sˆ i ·Sˆ j) convention] for the GdIII···MnIV and GdIII···GdIII interactions, respectively. The origin of this ground state has been rationalized by consideration of the spin frustration occurring within the complex as a function of the relative magnitude of the competing interactions.




[48] Enhancing the quantum properties of manganese-lanthanide single-molecule magnets: Observation of quantum tunneling steps in the hysteresis loops of a {Mn12Gd} cluster

Th. C. Stamatatos, S. J. Teat, W. Wernsdorfer, G. Christou


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[47] A mononuclear MnIII/‘bis-tris’ complex and its conversion to a mixed-valence MnII/III5 cluster

Th. C. Stamatatos, K. A. Abboud, G. Christou


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The use of the anion of 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol (‘bis-tris’ or LH5) as a chelate in Mn cluster chemistry is reported, and two products [Mn(N3)(LH3)] (1) and [Mn5(LH2)3(LH5)- (MeOH)2.5]Cl4 (2) are described. The reaction of Mn(ClO4)2·6H2O and NaN3 with LH5 and NEt3 in a 1 : 1 : 1 : 2 molar ratio in DMF gave complex 1. The reaction of 1, NEt3 and MnCl2·4H2O in a 2 : 2 : 1 ratio in MeOH gave the pentanulear complex 2. Complex 1 contains a distorted-octahedral MnIII atom exhibiting a Jahn–Teller axial elongation. Complex 2 has a mixed-valence MnII2MnIII3 trigonal bipyramidal Mn5 topology, with the apical positions of the [Mn5(μ-OR)7]6+ core occupied by the MnII atoms. Variable-temperature, solid-state dc and ac magnetization studies are reported for 1 and 2 in the 1.8–300 K range. The data for 1 are as expected for a high-spin d4 MnIII complex with S = 2; at low temperature, the effects of zero-field splitting (ZFS) and intermolecular antiferromagnetic interactions via OH···O hydrogen bonds become evident. Fitting of magnetization vs. field (H) and temperature (T) data by matrix diagonalization gave S = 2, D = -3.25 cm-1 and |E| = 0.32 cm-1, with g fixed at 2.00, where D and E are the axial and rhombic ZFS parameters, respectively. The analogous fit for 2 gave S = 3 and D = -0.68 cm-1. The combined results demonstrate the usefulness of ‘bis-tris’ as a new poly-alkoxide chelate for the synthesis of new Mn complexes.




[46] The largest single-strand molecular wheel: Ga20 from a targeted, diolate-induced size modification of the Ga10 "gallic wheel"

Th. C. Stamatatos, S. Mukherjee, K. A. Abboud, G. Christou


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A Ga20 single-strand wheel has been prepared by a targeted, propane-1,3-diolate-induced size modification of the known Ga10 ‘gallic wheel’; the Ga20 reverts back to Ga10 on treatment with an excess of MeOH.




[45] Control of the inhomogeneity degree by magnetic dilution in crystals of antiferromagnetic molecular rings

J. J. Henderson, C. M. Ramsey, E. del Barco, Th. C. Stamatatos, G. Christou


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Employing the electron spin in solid-state qubits is considered a promising method for quantum information processing. In this context, we present a microwave spectroscopic study on magnetically dilute crystals of Fe18 antiferromagnetic molecular rings. Doping with Ga3+, at concentrations ranging from 0.5% down to 0.005%, results in magnetic Fe17Ga (S=5/2) molecules dispersed throughout the lattice, with 2–8 nm average intermolecular separation. The results reveal a significant decrease in the degree of inhomogeneity of the system, hinting at a controlled reduction in decoherence mechanisms inherent to an ensemble of anisotropic molecular magnets while maintaining the crystalline order.




[44] Unusual structural types in nickel cluster chemistry from the use of pyridyl oximes: Ni5, Ni12Na2, and Ni14 clusters

Th. C. Stamatatos, A. Escuer, K. A. Abboud, C. P. Raptopoulou, S. P. Perlepes, G. Christou


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[43] Influence of the Dzyaloshinskii-Moriya exchange interaction on quantum phase interference of spins

W. Wernsdorfer, Th. C. Stamatatos, G. Christou


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Magnetization measurements of a Mn12mda wheel single-molecule magnet with a spin ground state of S = 7 show resonant tunneling and quantum phase interference, which are established by studying the tunnel rates as a function of a transverse field applied along the hard magnetization axis. A Dzyaloshinskii-Moriya (DM) exchange interaction allows the tunneling between different spin multiplets. It is shown that the quantum phase interference of these transitions is strongly dependent on the direction of the DM vector.




[42] A new MnII4MnIII4 cluster from the use of methyl 2-pyridyl ketone oxime in manganese carboxylate chemistry: Synthetic, structural and magnetic studies

C. C. Stoumpos, Th. C. Stamatatos, V. Psycharis, C. P. Raptopoulou, G. Christou, S. P. Perlepes


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[41] High nuclearity single-molecule magnets: A mixed-valence Mn26 cluster containing the di-2-pyridylketone diolate dianion

Th. C. Stamatatos, V. Nastopoulos, A. J. Tasiopoulos, E. E. Moushi, W. Wernsdorfer, G. Christou, S. P. Perlepes


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[40] High-yield syntheses and reactivity studies of Fe10 “ferric wheels”: Structural, magnetic, and computational characterization of a star-shaped Fe8 complex

Th. C. Stamatatos, A. G. Christou, S. Mukherjee, K. M. Poole, C. Lampropoulos, K. A. Abboud, T. A. O’Brien, G. Christou


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[39] Preparation and characterization of new Mn6 and Mn8 clusters obtained from the in situ formation of an unprecedented octadentate ligand

Th. C. Stamatatos, K. A. Abboud, G. Christou


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[38] Di-2-pyridyl ketone/benzoate/azide combination as a source of copper(II) clusters and coordination polymers: Dependence of the product identity on the solvent

Th. C. Stamatatos, V. Tangoulis, C. P. Raptopoulou, A. Terzis, G. S. Papaefstathiou, S. P. Perlepes


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The reactions of di-2-pyridyl ketone with Cu(O2CPh)2 in the presence of NaN3 and LiOH have led to an antiferromagnetically coupled (S = 0) CuII6 cluster with a novel core and to (CuII8)n and (CuII2)n coordination polymers (the former 1D and the latter 2D) with interesting structures. The cluster or polymer formation depends on the reaction solvent.




[37] Spin maximization: Switching of the usual S = 11 state of MnII4MnIII3 disklike complexes to the maximum S = 16

Th. C. Stamatatos, K. M. Poole, D. Foguet-Albiol, K. A. Abboud, T. A. O’Brien, G. Christou


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The S = 11 ground states of the Mn7 family of mixed-valence complexes with a metal-centered hexagonal topology have been found by density functional theory calculations to arise by spin frustration involving small differences in the magnitudes of the two weakest interactions controlling the alignment of the central spin. Targeted structural perturbation has allowed a complex with the central spin flipped to be discovered, which thus possesses the maximum S = 16 ground state.




[36] Covalently linked dimers of clusters: Loop- and dumbbell-shaped Mn24 and Mn26 single-molecule magnets

Th. C. Stamatatos, K. A. Abboud, W. Wernsdorfer, G. Christou


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[35] High-spin Mn4 and Mn10 molecules: Large spin changes with structure in mixed-valence MnII4MnIII6 clusters with azide and alkoxide-based ligands

Th. C. Stamatatos, K. M. Poole, K. A. Abboud, W. Wernsdorfer, T. A. O’Brien, G. Christou


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[34] New Fe4, Fe6, and Fe8 clusters of iron(III) from the use of 2-pyridyl alcohols: Structural, magnetic, and computational characterization

T. Taguchi, Th. C. Stamatatos, K. A. Abboud, C. M. Jones, K. M. Poole, T. A. O’Brien, G. Christou


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[33] Employment of 2,6-diacetylpyridine dioxime as a new route to high nuclearity metal clusters: Mn6 and Mn8 complexes

Th. C. Stamatatos, B. S. Luisi, B. Moulton, G. Christou


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[32] On the origin of ferromagnetism in oximato-based [Mn3O]7+ triangles

J. Cano, T. Cauchy, E. Ruiz, C. J. Milios, C. C. Stoumpos, Th. C. Stamatatos, S. P. Perlepes, G. Christou, E. K. Brechin


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DFT calculations reveal the unusual ferromagnetic exchange observed in an oxo-centered MnIII triangle may originate from a combination of the 'non-planarity' of the bridging oxime ligands and the non-parallel alignment of the Jahn–Teller axes.




[31] Mixed valency in polynuclear MnII/MnIII, MnIII/MnIV, and MnII/MnIII/MnIV clusters: A foundation for high-spin molecules and single-molecule magnets

Th. C. Stamatatos, G. Christou


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Mixed-valent Mn/O dinuclear and polynuclear molecular compounds containing MnIII are almost without exception trapped valence. Large differences between the strengths of the exchange interactions within MnIIMnIII, MnIIIMnIII and MnIIIMnIV pairs lead to situations where MnIIIMnIVinteractions, the strongest of the three mentioned and antiferromagnetic in nature, dominate the intramolecular spin alignments in trinuclear and higher nuclearity mixed-valent complexes and often result in molecules that have large, and sometimes abnormally large, values of molecular spin (S). When coupled to a large molecular magnetoanisotropy of the easy-axis-type (negative zero-field splitting parameter, D), also primarily resulting from individual Jahn–Teller distorted MnIII centres, such molecules will function as single-molecule magnets (molecular nanomagnets). Dissection of the structures and exchange interactions within a variety of mixed-valent Mnx cluster molecules with metal nuclearities of Mn4, Mn12 and Mn25 allows a ready rationalization of the observed S, D and overall magnetic properties in terms of competing antiferromagnetic exchange interactions within triangular subunits, resulting spin alignments and relative orientation of MnIII JT axes. Such an understanding has provided a stepping stone to the identification of a ‘magnetically soft’ Mn25 cluster whose groundstate spin S value can be significantly altered by relatively minor structural perturbations. Such ‘spin tweaking’ has allowed this cluster to be obtained in three different forms with three different groundstate S values.




[30] Synthesis and characterization of a Mn22 single-molecule magnet and a [Mn22]n single-chain magnet

J. T. Brockman, Th. C. Stamatatos, W. Wernsdorfer, K. A. Abboud, G. Christou


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The reactions of [Mn12O12(O2CEt)16(H2O)4] with phenylphosphinic acid (PhHPO2H) in MeCN and MeCN/CH2Cl2 have led to isolation of [Mn22O12(O2CEt)22(O3PPh)8(H2O)8] (2) and [Mn22O12(O2CEt)20(O3PPh)8(O2PPhH)2(H2O)8]n (3), respectively, both containing PhPO32- groups from in situ oxidation of PhHPO2-. Complex 2 is molecular and consists of two Mn9 subunits linked by four additional Mn atoms. Complex 3 contains almost identical Mn22 units as 2, but they are linked into a one-dimensional chain structure. The Mn22 unit in both compounds is mixedvalence MnIII18, MnII4. Solid-state, variable-temperature dc magnetic susceptibility and magnetization measurements were performed on vacuum-dried samples of 2 and 3, indicating dominant antiferromagnetic interactions. A good fit of low-temperature magnetization data for 2 could not be obtained because of problems associated with lowlying excited states, as expected for a high nuclearity complex containing MnII atoms. An approximate fit using only data collected in small applied fields indicated an S = 7 or 8 ground state for 2. Solid-state ac susceptibility data established that the true ground state of 2 is S = 7 and that the connected Mn22 units of 3 are ferromagnetically coupled. Both 2 and 3 displayed weak out-of-phase ac signals indicative of slow magnetization relaxation. Singlecrystal magnetization versus applied dc field scans exhibited hysteresis loops for both compounds, establishing them as new single-molecule and single-chain magnets, respectively. Complex 2 also showed steps in its hysteresis loops characteristic of quantum tunneling of magnetization, the highest nuclearity molecule to show such QTM steps. Arrhenius plots constructed from dc magnetization versus time decay plots gave effective barriers to magnetization relaxation (Ueff) of 6 and 11 cm-1 for 2 and 3, respectively.




[29] “Switching on” the properties of single-molecule magnetism in triangular manganese(III) complexes

Th. C. Stamatatos, D. Foguet-Albiol, S.- C. Lee, C. C. Stoumpos, C. P. Raptopoulou, A. Terzis, W. Wernsdorfer, S. O. Hill, S. P. Perlepes, G. Christou


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[28] Mixed-valence cobalt(II/III) carboxylate clusters: CoII4CoIII2 and CoIICoIII2 complexes from the use of 2-(hydroxymethyl)pyridine

Th. C. Stamatatos, A. K. Boudalis, K. V. Pringouri, C. P. Raptopoulou, A. Terzis, J. Wolowska, E. J. L. McInnes, S. P. Perlepes


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Aerobic reactions of Co(O2CR)2 with 2-(hydroxymethyl)pyridine (hmpH), in the presence of ClO4 counterions give the hexanuclear, mixed-valence clusters [CoII4CoIII2(O2CR)4-(hmp)8](ClO4)2 [R = Me (1), Ph (2)] which possess the unprecedented [CoII4CoIII23-OR')4(µ-OR')4]6+ [R' = (2-pyridyl)- CH2-] core. Replacement of ClO4 by N3– in the reaction mixture that gives 1 leads to the linear complex [CoIII,II,III3-(O2CMe)2(N3)2(hmp)4] (3). Q-band EPR spectra and variabletemperature magnetic susceptibility studies for 1 and 2 provide strong evidence that the CoII ions are antiferromagnetically coupled.




[27] Ferromagnetic coupling in a 1D coordination polymer containing a symmetric [Cu(μ1,1-N3)2Cu(μ1,1-N3)2Cu]2+ core and based on an organic ligand obtained from the solid-state

Th. C. Stamatatos, G. S. Papaefstathiou, L. R. MacGillivray, A. Escuer, R. Vicente, E. Ruiz, S. P. Perlepes


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Addition of rctt-tetrakis(2-pyridyl)cyclobutane (2,2′-tpcb) in a CuII/N3- solution afforded the 1D coordination polymer [Cu3(N3)6(2,2′-tpcb)(DMF)2]n (1). The ligand 2,2′-tpcb serves as a tetradentate bis-chelating ligand by linking linear [(DMF)Cu(µ1,1-N3)2Cu(N3)21,1-N3)2Cu(DMF)] trinuclear units to produce a zigzag chain. Within each centrosymmetric trinuclear unit there exist two irregularly asymmetric end-on double azido-bridged [Cu(µ1,1-N3)2Cu]2+ cores, while one of the largest Cu−Nazide−Cu angles is observed. Magnetic susceptibility data, measured from 2 to 300 K, show bulk moderate ferromagnetic coupling within the magnetically isolated trinuclear units. These data were fitted to the appropriate equation derived from the Hamiltonian H = −J1(SA1SB + SA2SB) − J2SA1SA2, giving the parameters J1 = +70(3) cm-1, J2 = −3(2) cm-1, g = 2.12(1), with an intertrimer interaction parameter θ = −0.74(2) K. The coupling constants were correlated with the structural parameters. Density functional calculations reproduce very well the experimental J values and show that ferromagnetism for this complex is mainly due to the topology of the magnetic orbitals and the different coordination spheres of two neighboring CuII atoms, resulting in a small overlap of the orbitals possessing the unpaired electrons.




[26] The highest nuclearity metal oxime clusters: Ni14 and Ni12Na2 complexes from the use of 2-pyridinealdoximate and azide ligands

Th. C. Stamatatos, K. A. Abboud, S. P. Perlepes, G. Christou


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The reactions of 2-pyridinealdoxime [(py)CHNOH] with Ni(ClO4)2·6H2O in the presence of NaOH and NaN3 have led to NiII14 and NiII12Na2 clusters; the Ni14 compound is the biggest metal oxime cluster discovered to date, as well as the largest Ni azide cluster.




[25] “Squaring the circle”: Molecular squares and rectangles from chelate-induced structural transformations of known Fe10 and new Fe12 ferric wheels

Th. C. Stamatatos, A. G. Christou, C. M. Jones, B. J. O’Callaghan, K. A. Abboud, T. A. O’Brien, G. Christou


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[24] High-frequency EPR characterization of a triangular Mn3 single-molecule magnet

S.- C. Lee, Th. C. Stamatatos, S. Hill, S. P. Perlepes, G. Christou


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We present the results of a multi-high-frequency single-crystal EPR study of a recently discovered triangular trinuclear Mn complex, [Mn3O(O2CMe)3(mpko)3](ClO4) · 3CH2Cl2. The obtained data set confirm the findings of earlier magnetic measurements, which suggested that this complex is a single-molecule magnet with a spin ground state of S = 6. The zero-field splitting parameters obtained from the present EPR study are: D = -0.3 cm-1 , B04 = - 3 x 10-5 cm-1 and g = 2.00. We also find a significant transverse anisotropy which can be parameterized by a rhombic distortion with an E value of at least 0.015 cm-1.
© 2006 Elsevier Ltd. All rights reserved.




[23] New Mn3 structural motifs in manganese single-molecule magnetism from the use of 2-pyridyloximate ligands

Th. C. Stamatatos, D. Foguet-Albiol, C. C. Stoumpos, C. P. Raptopoulou, A. Terzis, W. Wernsdorfer, S. P. Perlepes, G. Christou


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The use of 2-pyridyl oximes (L’H) in reactions with [MnIII3 O(O2CR)6(py)3](ClO4) has led to complexes [MnIII3O(O2CR)3L'3](ClO4). Ferromagnetic exchange interactions between the three MnIII ions in the complexes lead to spin ground states of S = 6. The complexes display the temperature- and scan rate-dependent hysteresis loops that are indicative of single-molecule magnetism behaviour.
© 2006 Elsevier Ltd. All rights reserved.




[22] A new Mn25 single-molecule magnet with an S = 61/2 ground state arising from ligand-induced ‘spin-tweaking’ in a high-spin molecule

Th. C. Stamatatos, K. A. Abboud, W. Wernsdorfer, G. Christou


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Reactivity studies of a [Mn25]2+ cage of full formula [MnII6 MnIII18MnIVO18(OH)2(N3)12(pdm)6(pdmH)6]2+ (1) involving replacement of azide groups with hmp- ones have led to a new, isostructural [Mn25O18(OH)(OMe)(hmp)6(pdm)6(pdmH)6]8+ (2) cluster with new and impressive magnetic properties. The successful ligand (hmp-)-induced structural distortion of the preformed Mn25 cluster (1) with an S = 51/2 ground-state causes the ground-state spin to increase remarkably (~20%) to S = 61/2. Hysteresis loops are seen below ~1.0 K whose coercivities increase with increasing sweep rate and with decreasing temperature. This confirms 2 to be an SMM, possessing one of the highest S values ever reported.
© 2006 Elsevier Ltd. All rights reserved.




[21] A general synthetic route for the preparation of high-spin molecules: Replacement of bridging hydroxo ligands in molecular clusters by end-on azido ligands

G. S. Papaefstathiou, A. K. Boudalis, Th. C. Stamatatos, C. J. Milios, C. G. Efthymiou, C. P. Raptopoulou, A. Terzis, V. Psycharis, Y. Sanakis, R. Vicente, A. Escuer, J.- P. Tuchagues, S. P. Perlepes


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A general method of increasing the ground-state total spin value of a polynuclear 3d-metal complex is illustrated through selected examples from cobalt(II) and nickel(II) cluster chemistry that involves the dianion of the gem-diol form of di-2-pyridyl ketone and carboxylate ions as organic ligands. The approach is based on the replacement of hydroxo bridges, that most often propagate antiferromagnetic exchange interactions, by the end-on azido ligand, which is a ferromagnetic coupler.
© 2006 Elsevier Ltd. All rights reserved.




[20] Ferromagnetically-coupled decanuclear, mixed-valence [Mn10O4(N3)4(hmp)12]2+ [hmpH = 2-(hydroxymethyl)pyridine] clusters with rare T symmetry and an S = 22 ground state

Th. C. Stamatatos, K. A. Abboud, W. Wernsdorfer, G. Christou


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[19] 2-Pyridyloximate clusters of cobalt and nickel

Th. C. Stamatatos, C. Papatriantafyllopoulou, E. Katsoulakou, C. P. Raptopoulou, S. P. Perlepes


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The use of 2-pyridyloximate(-1) ligands, (py)C(R)NO- [R = H, Ph, 2-pyridyl (py)] in cobalt and nickel(II) chemistry has been investigated and led to four families of clusters. A representative member of each family, namely [CoIICoIII2 {(py)C(ph)NO}6](PF6)2 (1), [CoII2 CoIII2 (OH)2(O2CMe)2{(py)2CNO}4(MeOH)2](ClO4)2 (2), [Ni9(OH)4{(py)CHNO}10(H2O)8]{N(CN)2}3(ClO4) [3{N(CN)2}3(ClO4)] and [Ni4(O2CMe)4{(py)C(ph)NO}4(MeOH)2] (4) is briefly structurally and magnetically described.
© 2006 Elsevier Ltd. All rights reserved.




[18] “Spin tweaking” of a high-spin molecule: An Mn25 single-molecule magnet with an S = 61/2 ground state

Th. C. Stamatatos, K. A. Abboud, W. Wernsdorfer, G. Christou


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[17] Initial use of di-2-pyridyl ketone oxime in chromium carboxylate chemistry: Triangular {CrIII33-O)}7+ compounds and unexpected formation of a carboxylate-free dichromium(II,II) complex

K. V. Pringouri, C. P. Raptopoulou, A. Escuer, Th. C. Stamatatos


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A systematic investigation of the [Cr3O(O2CCMe3)6(H2O)3](O2CCMe3)/(py)2CNOH [(py)2CNOH = di-2-pyridyl ketone oxime] reaction system is described, involving the determination of the influence of the CrIII:(py)2CNOH ratio, the temperature and the presence of counterions on the identity of the reaction products. As a consequence, complexes [Cr2{(py)2CNO}4] · 2H2O (1 · 2H2O), [Cr3OCl(O2CCMe3)4{(py)2CNO}2] · 2Me2CO (2 · 2Me2CO) and [Cr3O(O2CCMe3)4{(py)2CNO}2(H2O)](NO3) · H2O · 0.5Me2CO (3 · H2O · 0.5Me2CO) have been isolated and structurally characterized by single-crystal X-ray studies. (py)2CNO- behaves as a N,N'-bidentate chelating and/or N,N',O-tridentate bridging ligand binding through one 2-pyridyl and the oximate nitrogen atoms, and/or the oximate oxygen atom. 1 is a relatively stable air-stable dinuclear Cr(II) complex with no metal–metal bonding arising, from the ligand-assisted reduction of the 'basic carboxylate' Cr(III) triangle. The structures of 2 and 3 consist of similar neutral and cationic triangles of CrIII ions, respectively, centered by a triply bridging oxo ligand and with two edge-bridging oximate groups from the two 2.1110 (py)2CNO- ligands. Variable-temperature magnetic susceptibility studies and EPR data for 2 reveal an antiferromagnetically-coupled system with an ST = 3/2 ground state. Solid-state IR and ligand field spectra of 2 are briefly discussed in terms of its structure.




[16] Acetate/di-2-pyridyl ketone oximate “blend” as a source of high-nuclearity nickel(II) clusters: Dependence of the nuclearity on the nature of the inorganic anion present

Th. C. Stamatatos, E. Diamantopoulou, C. P. Raptopoulou, V. Psycharis, A. Escuer, S. P. Perlepes


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The use of di-2-pyridyl ketone oxime [(py)2CNOH] in reactions with Ni(O2CMe)2‚4H2O, in the presence or absence of extra inorganic anions (N3- and SCN-) has led to Ni4, Ni5, and Ni7 clusters; the magnetic study of the heptanuclear nickel(II) complex reveals an S = 3 ground state.




[15] A family of 3D coordination polymers composed of Mn19 magnetic units

E. E. Moushi, Th. C. Stamatatos, W. Wernsdorfer, V. Nastopoulos, G. Christou, A. J. Tasiopoulos


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[14] Reversible size modification of iron and gallium molecular wheels: A Ga10 “gallic wheel” and large Ga18 and Fe18 wheels

P. King, Th. C. Stamatatos, K. A. Abboud, G. Christou


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[13] An unusual dichromium(II,II) compound bearing di-2-pyridyl ketone oximate ligands and prepared by the ligand-assisted reduction of a trichromium(III,III,III) complex in air

Th. C. Stamatatos, K. V. Pringouri, C. P. Raptopoulou, R. Vicente, V. Psycharis, A. Escuer, S. P. Perlepes


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The reaction of the oxide-centred triangular, trichromium(III,III,III) complex [Cr3O(O2CCMe3)6(H2O)3](O2CCMe3) with di-2-pyridyl ketone oxime, (py)2CNOH, in MeCN under aerobic and refluxing conditions yields the pivalate-free, dichromium(II,II) complex [Cr2{(py)2CNO}4] · 2H2O (1·2H2O). The dinuclear complex can also be prepared by the reaction of [Cr(CO)6] with (py)2CNOH in refluxing MeCN/H2O in air. The two high-spin CrII atoms are doubly bridged by two 2.1110 oximate ligands, while a chelating 1.0110 (py)2CNO- ion completes distorted trigonal bipyramidal coordination at each metal centre. The dimers are stabilized by intramolecular stacking interactions between the terminal (py)2CNO- ligands, and the structural effects of these interactions are discussed.
© 2006 Elsevier B.V. All rights reserved.




[12] Formation of the {CuII33-OH)}5+ core in copper(II) carboxylate chemistry via use of di-2-pyridyl ketone oxime [(py)2CNOH]: [Cu3(OH)(O2CR)2{(py)2CNO}3] (R = Me, Ph)

Th. C. Stamatatos, J. C. Vlahopoulou, Y. Sanakis, C. P. Raptopoulou, V. Psycharis, A. K. Boudalis, S. P. Perlepes


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Reactions of [Cu2(O2CMe)4(H2O)2] or Cu(O2CPh)2 · 2H2O with 2 or 1, respectively, molar equivalents of di-2-pyridyl ketone oxime, (py)2CNOH, in MeCN-based solvent mixtures yield complexes [CuII33- OH)(O2CR)2{(py)2CNO}3] (1, R = Me; 2, R = Ph). Crystal structures of these compounds show similar triangles of CuII ions, centered by a triply bridging hydroxo ligand and with three edge-bridging oximate groups from the three 2.1110 (py)2CNO- ions. Preliminary variable-temperature magnetic susceptibility studies and EPR data at 4.2 K for 1 reveal an antiferromagnetically-coupled system showing antisymmetric exchange.
© 2006 Elsevier B.V. All rights reserved.




[11] Reactivity and structural and physical studies of tetranuclear iron(III) clusters containing the [Fe43-O)2]8+ “butterfly” core: An FeIII4 cluster with an S = 1 ground state

Th. C. Stamatatos, A. K. Boudalis, Y. Sanakis, C. P. Raptopoulou


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[10] High-nuclearity, high-symmetry, high-spin molecules: A mixed-valence Mn10 cage possessing rare T symmetry and an S = 22 ground state

Th. C. Stamatatos, K. A. Abboud, W. Wernsdorfer, G. Christou


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[9] Enneanuclear Ni(II) complexes from the use of the flexible ligand 2-pyridinealdoxime: The nature of the inorganic anion does not affect the chemical and structural identity of the cationic cluster

Th. C. Stamatatos, E. Diamantopoulou, A. Tasiopoulos, V. Psycharis, R. Vicente, C. P. Raptopoulou, V. Nastopoulos, A. Escuer, S. P. Perlepes


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The use of 2-pyridinealdoximate(-1) [(py)CHNO-] in nickel(II) chemistry has been further investigated. The synthetic investigation has led to two new salts of the very recently reported (in the form of its tetraperchlorate salt, 1) enneanuclear cation [Ni93-OH)22-OH)23- (py)CHNO}42-(py)CHNO}62-OH2)2(H2O)6]4+. The two new cationic clusters [Ni9(OH)4{(py)CHNO}10(H2O)8](SCN)2(OH)2 · 9.91H2O (2 · 9.91H2O) and [Ni9(OH)4{(py)CHNO}10(H2O)8]{N(CN)2}3(ClO4) · 11.11H2O (3 · 11.11H2O) have been structurally characterized by single-crystal X-ray crystallography at 100 K. The nature of the inorganic anions (Cl-/SCN-,N(CN)2-/ClO4-) present in the reaction mixtures does not affect the chemical and structural identity of the enneanuclear cation. Characteristic IR data are discussed in terms of the nature of bonding and the structures of the complexes. The variable-temperature magnetic susceptibility data of 1, which had also been obtained by our group, were simulated by means of a 3-J model, which is compared with the 2-J model reported for this cluster by Chaudhuri and co-workers [S. Khanra, T. Weyhermüller, E. Rentschler, P. Chaudhuri, Inorg. Chem. 44 (2005) 8176]. The ground-state total spin of the cluster is ST = 1.




[8] 4-(Hydroxymethyl)pyridine and pyrimidine in manganese benzoate chemistry: Preparation and characterization of hexanuclear clusters featuring the {MnII4MnIII24-O)2}10+ core

Th. C. Stamatatos, D. Foguet-Albiol, S. P. Perlepes, C. P. Raptopoulou, A. Terzis, C. S. Patrickios, G. Christou, A. J. Tasiopoulos


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The use of 4-(hydroxymethyl)pyridine (4hmpH) and pyrimidine (pym) in manganese benzoate chemistry has been investigated. The reactions of 4hmpH and pym with Mn(O2CPh)2 · 2H2O in MeCN affords the complexes [Mn6O2(O2CPh)10(4hmpH)3 (MeCN)] (1) and [Mn6O2(O2CPh)10(pym)2(MeCN)2] (2), respectively. Complex 1 contains a {Mn6O2}10+ core that can be conveniently described as two edge-sharing Mn4 tetrahedra at the center of each of which is a μ4-O2- ion. Peripheral ligation to the octahedrally coordinated Mn centres is provided by 10 bridging PhCO2- ligands, three N-monodentate ligands and one terminal MeCN group. The complex is mixed-valence (MnII4MnIII2) and the MnIII ions are assigned as the two central metal centres bridged by two O2- ions. The molecular structure of 2 is very similar to that of 1, except that the terminal ligands are two monodentate pym molecules and two MeCN groups. IR data are discussed in terms of the nature of bonding and the known structures. Complexes 1 and 2 were characterized by variable-temperature ac and dc magnetic susceptibility data and found to possess a total spin ground state of 0. The ST = 0 ground state is explained in terms of the strong antiferromagnetic coupling within the central Mn2IIIO2 unit.
© 2005 Elsevier Ltd. All rights reserved.




[7] The coordination chemistry of pyridyl oximes

C. J. Milios, Th. C. Stamatatos, S. P. Perlepes,


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The coordination chemistry of pyridyl oximes is reviewed. Simple pyridyl oximes have the general formula (py)C(R)NOH, where py is a pyridyl group (2-, 3- or 4-) attached to the oxime carbon atom and R can be a donor or a non-donor group. There are also ligands containing more pyridyl and/or oxime groups. The coordination chemistry of twenty-three such ligands is described, including 2-acetylpyridine N-oxide oxime (which strictly speaking is not a pyridyl oxime) and of four polydentate ligands containing pyridyl groups that are not directly attached to the oxime carbon. References are given to methods for the synthesis of the ligands that are not available in the market. The coordination chemistry of each ligand with all metals is detailed, with emphasis being placed on structural features and physical properties (mainly magnetic) of the resulting metal complexes. This report shows that the anions of pyridyl oximes are versatile ligands for a variety of objectives/advantages, including μ2 and μ3 behavior, preparation of polynuclear complexes (clusters) and coordination polymers, mixed-metal chemistry and interesting magnetic characteristics. The activation of 2-pyridyl oximes by 3d-metal centers towards further reactions seems to be an emergent area of synthetic chemistry.
©2005 Elsevier Ltd. All rights reserved.




[6] Initial example of a triangular single-molecule magnet from ligand-induced structural distortion of a [MnIII3O]7+ complex

Th. C. Stamatatos, D. Foguet-Albiol, C. C. Stoumpos, C. P. Raptopoulou, A. Terzis, W. Wernsdorfer, S. P. Perlepes, G. Christou


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[5] The first cobalt metallacrowns: Preparation and characterization of mixed-valence cobalt(II/III), inverse 12-metallacrown-4 complexes

Th. C. Stamatatos, S. Dionyssopoulou, G. Efthymiou, P. Kyritsis, C. P. Raptopoulou, A. Terzis, R. Vicente, A. Escuer, S. P. Perlepes


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Aerobic reactions of Co(O2CMe)2·4H2O with di-2-pyridyl ketone oxime (Hpko) in the presence of counterions (ClO4-, PF6-) give the tetranuclear, mixed-valence cobalt(II/III) clusters [CoII2-CoIII2(OR)2(O2CMe)2(pko)4S2]X2 [R = H, S = MeOH, X = ClO4 (1); R = Me, S = EtOH, X = PF6 (2)] depending on the solvent mixture. Complexes 1 and 2 are the first Co members in the family of metallacrowns adopting the extremely rare inverse 12-metallacrown-4 motif.




[4] Old ligands with new coordination chemistry: Linear trinuclear mixed oxidation state cobalt(III/II/III) complexes and their mononuclear “ligand” cobalt(III) complexes featuring 2-pyridyloximates

Th. C. Stamatatos, A. Bell, P. Cooper, A. Terzis, C. P. Raptopoulou, S. L. Heath, R. E. P. Winpenny, S. P. Perlepes


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Reaction schemes involving 2-pyridyloximes, (py)C(R)NOH, CoII sources and counterions X- in various solvents lead to the new family of linear trinuclear clusters [Co3III,II,III{(py)C(R)NO}6]X2 (py = 2-pyridyl group; R = H, Me, Ph; X = ClO4, PF6). The outer metal centres are low spin, octahedral CoIII ions and are coordinated by three N,N'-bound 2-pyridyloximato ligands; each of these outer CoIII complexes acts as a tridentate chelating "ligand" to the central CoII ion, which adopts an octahedral geometry with six oxygen donor atoms. The CoIII "ligands" have been individually prepared and the reaction of [CoIII{(py)C(Me)NO}3] with Co(ClO4)2 · 6H2O leads to the isolation of [Co3III,II,III{(py)C(Me)NO}6](ClO4)2.
© 2005 Elsevier B.V. All rights reserved.




[3] Copper(II) chloride/1-methylbenzotriazole chemistry: Influence of various synthetic parameters on the product identity, structural and magnetic characterization, and quantum-chemical studies

K. Skorda, Th. C. Stamatatos, A. P. Vafiadis, A. T. Lithoxoidou, A. Terzis, S. P. Perlepes, J. Mrozinski, C. P. Raptopoulou, J. C. Plakatouras, E. G. Bakalbassis


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A systematic investigation of the CuCl2/Mebta (Mebta = 1-methylbenzotriazole) reaction system is described, involving the determination of the influence of the CuII:Mebta ratio, the nature of solvent and the presence of counterions on the identity of the reaction products. As a consequence, complexes [Cu2Cl4(Mebta)4] (1), [CuCl2(Mebta)2] (2), {[Cu2Cl4(Mebta)2]}n (3), [Cu4OCl6- (Mebta)4] · 0.25H2O (4 · 0.25H2O) and [Cu2Cl2(Mebta)6](ClO4)2 (5) have been isolated and structurally characterized by single-crystal X-ray studies. Mebta behaves as a monodentate ligand binding through N(3). 1 is a dinuclear complex, the structure of 2 consists of discrete monomeric units, and that of 3 is composed of linear, well-separated polymeric chains of CuII atoms. The molecules of 4 · 0.25H2O have a central μ4-oxide ion surrounded tetrahedrally by four CuII atoms. In the cations of 5 the two CuII centres are asymmetrically bridged by two chloro ligands, with three Mebta molecules completing five coordination at each metal. Complexes were characterized by spectroscopic (IR, far-IR, solution UV/Vis) and thermal decomposition (TG, DTG, and DTA) techniques. Variable-temperature magnetic susceptibility data for 1, 3 and 5 showed intramolecular (1, 5) and intrachain (3) ferromagnetic exchange interactions. Estimates of the J parameters, experimentally derived, were in close agreement with a new magneto-structural criterion developed by us, holding for bis(μ-chloro) copper(II) dimers. A comparison between the CuCl2/Mebta and CuBr2/Mebta systems is also presented.
© 2004 Elsevier B.V. All rights reserved.




[2] Phenyl 2-pyridyl ketone and its oxime in manganese carboxylate chemistry: Synthesis, characterization, X-ray studies and magnetic properties of mononuclear, trinuclear and octanuclear complexes

C. J. Milios, Th. C. Stamatatos, P. Kyritsis, A. Terzis, C. P. Raptopoulou, R. Vicente, A. Escuer, S. P. Perlepes


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The use of phenyl 2-pyridyl ketone [(ph)(2-py)CO] and its oxime [(ph)(2-py)CNOH] in manganese benzoate chemistry has been investigated. The reaction of an excess of (ph)(2-py)CNOH with Mn(O2CPh)2·2H2O affords the mononuclear complex [MnII(O2CPh)2{(ph)(2-py)CNOH}2]·1.2H2O (1·1.2H2O) in high yield. The MnIIion is coordinated by two monodentate benzoates and two N,N'-bidentate chelating (ph)(2-py)CNOH molecules in a cis-cis-trans fashion. The comproportionation reaction between Mn(O2CPh)2·2H2O and NnBu4MnO4 (3:1) in the presence of (ph)(2-py)CNOH in MeCN/EtOH/CH2Cl2 leads to the isolation of the mixed-valent cluster [Mn8O2(OH)2(O2CPh)10{(ph)(2-py)CNO}4]· 4CH2Cl2 (2·4CH2Cl2) in about 55% yield. A second synthetic procedure that leads to pure 2 involves the reaction between the known starting material (NnBu4)[Mn4IIIO2(O2CPh)9-(H2O)] and four equivalents of the oxime ligand in CH2Cl2. The centrosymmetric octanuclear molecule contains four MnII and four MnIII ions held together by two μ4-O2− ligands and two μ3-OH ions to give the unprecedented [Mn84- Ο)23-ΟΗ)2]14+ core, with peripheral ligation provided by ten PhCO2− (two η1, four syn,syn η112 and four η123) and four η1112 (ph)(2-py)CNO ions. The 1:1 reaction between Mn(O2CPh)2·2H2O and the ketone (ph)(2-py)CO affords the trinuclear complex [Mn3(O2CPh)6{(ph)(2-py)CO}2] (3) in more than 80% yield. As judged from single-crystal Xray crystallography, the complex adopts a linear structure with one η122 and two η112 benzoates spanning each pair of metal ions. The terminal MnII ions are capped by bidentate chelating (ph)(2-py)CO ligands. The three complexes have been characterised by IR spectroscopy. The CV study of complex 2 in CH2Cl2 reveals irreversible reduction and oxidation processes. The magnetic properties of 2 and 3 have been studied by variable-temperature dc magneticsusceptibility techniques. As the temperature approaches zero, the value of the χMΤ product for 2 approaches zero and, thus, the octanuclear complex has an S = 0 ground state. This S = 0 ground state is explained in terms of the magnetic behaviour of the central, butterfly-like [Mn4 III3-O)2]8+ subcore. The results for 3 reveal weak antiferromagnetic coupling, with J = −2.7 cm−1 for adjacent MnII ions.
( © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)




[1] Cadmium carboxylate chemistry: Preparation, crystal structure, thermal and spectroscopic characterization of the one-dimensional polymer [Cd(O2CMe)(O2CPh)(H2O)2]n

Th. C. Stamatatos, E. Katsoulakou, V. Nastopoulos, C. P. Raptopoulou, E. Manessi-Zoupa, S. P. Perlepes


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Compound [Cd(O2CMe)(O2CPh)(H2O)2]n (1) was initially obtained in a serendipitous way during efforts to prepare a CdII/PhCO2 /bepy complex (bepy = 2-benzoylpyridine). With the identity of 1 established by single-crystal X-ray crystallography, a rational preparative route to this complex was designed and carried out by reacting Cd(O2CMe)2·2H2O with a slight excess of PhCOOH in MeCN under reflux. The crystal structure of 1 consists of isolated zig-zag chains. The CdII atom is coordinated to five carboxylate and two aqua oxygen atoms creating a distorted, capped trigonal prismatic coordination polyhedron. The acetate group exhibits the η122 coordination mode, while the benzoate ligand is chelating. There is an extensive hydrogen-bonding network which reinforces the chains and also links them generating sheets. The new complex was characterized by IR, far-IR, Raman, CP MAS and solution 113Cd NMR spectroscopy. The spectroscopic data are discussed in terms of the nature of bonding and the known structure. An anhydrous compound with the empirical formula Cd(O2CMe)(O2CPh) was isolated during the thermal decomposition of 1; the vibrational study of this thermally stable intermediate supports an 1D polymeric structure with 6-coordinate CdII ions.