Anastasios J. Tasiopoulos

A Mn17 octahedron with a giant ground-state spin: occurrence in discrete form and as multidimensional coordination polymers.

A [Mn(III)(11)Mn(II)(6)(mu(4)-O)(8)(mu(3)-L)(4)](25+) (L = N(3)(-) or OCN(-)) octahedral unit is reported, occurring within 1D (1)(infinity) and 2D (2)(infinity) 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.

Inducing Single-Molecule Magnetism in a Family of Loop-of-Loops Aggregates: Heterometallic Mn40Na4 Clusters and the Homometallic Mn44 Analogue

The syntheses, crystal structures, and magnetic properties of a new family of heterometallic Mn(40)Na(4) and homometallic Mn(44) loop-of-loops aggregates are reported. The reactions of [Mn(3)O(O(2)CMe)(6)(py)(3)]·py with 1,3-propanediol (pdH(2)) and 2-methyl-1,3-propanediol (mpdH(2)) in the presence of NaN(3) afforded [Mn(10)Na(μ(3)-O)(2)(O(2)CMe)(13)(pd)(6)(py)(2)](4) (1)(4) and [Mn(10)Na(μ(3)-O)(2)(O(2)CMe)(13)(mpd)(6)(py)(H(2)O)](4) (2)(4), respectively. Mn(40)Na(4) complexes (1)(4) and (2)(4) consist of four Mn(10) loops linked through Na(+) ions to give a supramolecular aggregate with a saddle-like topology. Magnetic characterization of compound (1)(4) showed that each Mn(10) loop has an S = 4 ground-state spin and displays frequency-dependent in-phase and out-of-phase ac susceptibility signals. It also exhibits hysteresis loops that, however, are not typical of single-molecule magnets (SMMs) due to the existence of interloop interactions between the neighboring Mn(10) units of (1)(4) through the diamagnetic Na(+) ions, and also intermolecular interactions between different Mn(40)Na(4) aggregates. The magnetically discrete Mn(44) analogue was targeted with high priority and finally prepared from the reaction of [Mn(3)O(O(2)CMe)(6)(py)(3)]·py with pdH(2) in the presence of Mn(ClO(4))(2)·6H(2)O. The loop-of-loops structure of [Mn(44)(μ(3)-O)(8)(O(2)CMe)(52)(pd)(24)(py)(8)](ClO(4))(OH)(3) (3) is essentially identical to those of (1)(4) and (2)(4), with the most significant difference being that the four Na(+) ions of (1)(4) and (2)(4) have been replaced with Mn(2+) ions. Compound 3 is thus best described magnetically as a Mn(44) cluster. In accord with this description and the stronger exchange coupling between the four Mn(10) loops expected through the connecting Mn(2+) ions, magnetic susceptibility measurements revealed that 3 has an S = 6 ground-state spin and displays frequency-dependent in-phase and out-of-phase ac signals. Magnetization vs dc field sweeps on single-crystals of 3 displayed scan rate- and temperature-dependent hysteresis loops confirming that complex 3 is a new SMM, and is thus the second largest Mn cluster and SMM reported to date.

Single-molecule magnets: a family of MnIII/CeIV complexes with a [Mn8CeO8]12+ core.

Four heterometallic, enneanuclear Mn8Ce clusters [Mn8CeO8(O2CMe)12(H2O)4] (4), [Mn8CeO8(O2CMe)12(py)4] (5), [Mn8CeO8(O2CPh)12(MeCN)4] [Mn8CeO8(O2CPh)12(dioxane)4] (6), and [Mn8CeO8(O2CCHPh2)12(H2O)4] (7) have been prepared by various methods. Their cores are essentially isostructural and comprise a nonplanar, saddlelike [MnIII8O8]8+ loop containing a central CeIV ion attached to the eight micro3-O2- ions. Peripheral ligation around the [Mn8CeO8]12+ core is provided by eight micro- and four micro3-O2CR- groups. Terminal ligation on four MnIII atoms is provided by H2O in 4 and 7, pyridine in 5, and MeCN/dioxane in 6. Solid-state magnetic susceptibility studies, fits of dc magnetization vs field and temperature data, and in-phase ac susceptibility studies in a zero dc field have established that complexes 4, 5, and 7 possess S=16, S=4 or 5, and S=6+/-1 spin ground states, respectively, but in all cases there are very low-lying excited states. The large variation in the ground-state spins for this isostructural family is rationalized as due to a combination of weak exchange interactions between the constituent MnIII atoms, and the presence of both nearest-neighbor and next-nearest-interactions of comparable magnitudes. Magnetization vs applied dc field sweeps on single crystals of 4.4H2O and 7.4H2O.3MeCN.2CH2Cl2 down to 0.04 K have established that these two complexes are new single-molecule magnets (SMMs). The former also shows an exchange-bias, a perturbation of its single-molecule properties from very weak intermolecular interactions mediated by hydrogen-bonding interactions with lattice-water molecules of crystallization.

Structural Motifs and Biological Studies of New Antimony(III) Iodide Complexes with Thiones

Eight new antimony(III) iodide complexes of the heterocyclic thioamides, 2-mercapto-1-methylimidazole (MMI), 2-mercaptobenzimidazole (MBZIM), 5-ethoxy-2-mercaptobenzimidazole (EtMBZIM), 2-mercaptothiazolidine (MTZD), 3-methyl-2-mercaptobenzothiazole (NMeMBZT), 2-mercapto-3,4,5,6-tetrahydropyrimidine (tHPMT), 2-mercaptopyridine (PYT), and 2-mercaptopyrimidine (PMT) of formulas {[SbI(3)(MMI)(2)].MeOH} (1), [SbI(3)(MBZIM)(2)] (2), {[SbI(2)(mu(2)-I)(EtMBZIM)(2)](2).H(2)O} (3), [SbI(3)(MTZD)] (4), [(NMeMBZT)SbI(2)(mu(2)-I)(2)(mu(2)-S-NMeMBZT)SbI(2) (NMeMBZT)] (5), {[SbI(3)(tHPMT)(3)].MeOH} (6), [SbI(3)(PYT)] (7), and [SbI(3)(PMT)(2)] (8), have been synthesized and characterized by elemental analysis, FT-IR spectroscopy, FT-Raman spectroscopy, and TG-DTA analysis. The crystal structures of 3, 4, 5, 6, and 7 were also determined by X-ray diffraction. The complexes show interesting structural motifs. Complex 6 is a monomer, with octahedral (Oh) geometry around the metal ion formed by three sulfur and three iodide atoms. Complexes 3 and 5 are dimers, with a square pyramidal (SP) geometry in each monomeric unit, while complexes 4 and 7 are polymers with pseudotrigonal bipyramidal (psi-TBP). Two or three sulfur atoms from thioamide ligands and three iodide atoms are bound to Sb atoms forming building blocks for the dimers and polymers. Strong intramolecular interactions between mu(2)-I and/or mu(2)-S and Sb atoms stabilize both structures. In dimer complex 5, two terminal iodide and one terminal sulfur atom are bonded to the Sb ion, while two mu(2)-I and one mu(2)-S bridging atoms bridge the metal ions forming psi-Oh geometry. Computational studies using multivariant linear regression (MLR) and artificial neural networks (ANN) and considering biological results (50% inhibitory concentration, IC(50)) as dependent variables derived a theoretical equation for IC(50) values of the complexes studied. The calculated IC(50) values are compared satisfactorily with the experimental inhibitory activity of the complexes measured. Complexes 3-7 were used to study their influence upon the catalytic peroxidation of linoleic acid by the enzyme Lipoxygenase (LOX). Compounds 1-8 were also tested for in vitro cytotoxicity, and they showed mostly a moderate cytostatic activity against a variety of tumor cell lines but comparable with those found for the antimony(III) chloride and bromide complexes, reported earlier [Ozturk et al. Inorg. Chem. 2007, 46, 2861-2866; Ozturk et al. Inorg. Chem. 2009, 48, 2233-2245].

Insertion of Functional Groups into a Nd3+ Metal–Organic Framework via Single-Crystal-to-Single-Crystal Coordinating Solvent Exchange

Single-crystal-to-single-crystal (SCSC) transformations represent some of the most fascinating phenomena in chemistry. They are not only intriguing from a basic science point of view but also provide a means to modify or tune the properties of the materials via the postsynthetic introduction of suitable guest molecules or organic functional groups into their structures. Here, we describe UCY-2, a new flexible Nd(3+) metal-organic framework (MOF), which exhibits a unique capability to undergo a plethora of SCSC transformations with some of them being very uncommon. These structural alterations involve the replacement of coordinating solvent molecules of UCY-2 by terminally ligating solvents and organic ligands with multiple functional groups including -OH, -SH, -NH-, and -NH(2) or their combinations, chelating ligands, anions, and two different organic compounds. The SCSC coordinating solvent exchange is thus demonstrated as a powerful method for the functionalization of MOFs.

New Antimony(III) Bromide Complexes with Thioamides : Synthesis, Characterization, and Cytostatic Properties

New antimony(III) bromide complexes with the heterocyclic thioamides, thiourea (TU), 2-mercapto-1-methylimidazole (MMI), 2-mercapto-benzimidazole (MBZIM), 2-mercapto-5-methyl-benzimidazole (MMBZIM), 5-ethoxy-2-mercapto-benzimidazole (EtMBZIM), 2-mercapto-3,4,5,6-tetrahydro-pyrimidine (tHPMT), 2-mercaptopyridine (PYT), 2-mercapto-thiazolidine (MTZD), 3-methyl-2-mercaptobenzothiazole (MMBZT), and 2-mercaptopyrimidine (PMTH) of formulas [SbBr(3)(TU)(2)] (1), [SbBr(3)(MMI)(2)] (2), {[SbBr(2)(MBZIM)(4)](+) [Br](-) H(2)O} (3), {[SbBr(2)(mu(2)-Br)(MMBZIM)(2)](2)} (4), {[SbBr(2)(mu(2)-Br)(EtMBZIM)(2)](2) MeOH} (5), {[SbBr(3)(mu(2)-S-tHPMT)(tHPMT)](n)} (6), {[SbBr(2)(mu(2)-Br)(PYT)(2))(n)} (7), {[SbBr(2)(mu(2)-Br)(MTZD)(2)](n)} (8), [SbBr(3)(MMBZT)(2)] (9), and {[SbBr(5)](2-)[(PMTH(2)(+))(2)]} (10) have been synthesized and characterized by elemental analysis, conductivity measurements, FTIR spectroscopy, FT-Raman spectroscopy, TG-DTA analysis, and X-ray powder diffraction. The crystal structures of 3, 4, 5, 6, 7, 8, and 10 were also determined by X-ray diffraction. In 3, four sulfur atoms from thione ligands and two bromide ions form an octahedral (O(h)) cationic [SbS(4)Br(2)](+) species in which the two bromide anions lie at axial positions. A third bromide counteranion neutralizes the whole complex. 4 and 5 are dimers, whereas 6, 7 and 8 are polymers, built up by monomeric units of square pyramidal (SP) geometry around the metal center, which were formed by two sulfur atoms of thioamide ligands and three bromide ions. Finally, 10 is ionic salt containing 1D polymeric network of {[SbBr(5)](2-)}(n) anions and (-)[(PMTH(2)(+))2] counter cations in the lattice. The complexes showed mostly a moderate cytostatic activity against a variety of tumor cell lines.

Synthesis, characterization and biological studies of new antimony(III) halide complexes with ω-thiocaprolactam.

Three new antimony(III) halide complexes (SbX(3), X=Cl, Br and I) with the heterocyclic thione ω-thiocaprolactam (1-azacycloheptane-2-thione, (Hthcl)) of formulae {[SbCl(2)(μ(2)-Cl)(Hthcl)(2)](n)} (1), {[(SbBr(2)(μ(2)-Br)(Hthcl)(2))(2)]} (2) and {[(SbI(2)(μ(2)-I)(Hthcl)(2))(2)]} (3) were synthesized from the reaction of antimony(III) halides with ω-thiocaprolactam in 1:2 stoichiometry. The complexes were characterized by elemental analysis, FT-IR spectroscopy, (1)H, (13)C NMR spectroscopy and Thermal Gravimetry-Differential Thermal Analysis (TG-DTA). Crystal structures of the ligand ω-thiocaprolactam and its complexes 1-3 were determined with single crystal X-ray diffraction analysis. Complexes 1-3 and ω-thiocaprolactam were evaluated for their in vitro cytotoxic activity against leiomyosarcoma (LMS) and human breast adenocarcinoma (MCF-7) tumor cell lines. Antimony complexes 1-3 exhibit strong antiproliferative activity against both cell lines tested. The higher such activity was found for 3 with IC(50) values of 0.12±0.04 μM (LMS) and 0.76±0.16 μM (MCF-7) which are 60 and 10 times respectively, stronger than that of cisplatin. The influence of these complexes 1-3 and ω-thiocaprolactam upon the catalytic peroxidation of linoleic acid to hyperoxolinoleic acid by the enzyme lipoxygenase (LOX) was kinetically and theoretically studied. The results were shown negligible inhibitory activity of 1-3 against LOX.

Synthesis, structural characterization and in vitro inhibitory studies against human breast cancer of the bis-(2,6-di-tert-butylphenol)tin(IV) dichloride and its complexes

Four new organotin(IV) complexes of bis-(2,6-di-tert-butylphenol)tin(IV) dichloride [(tert-Bu-)(2)(HO-Ph)](2)SnCl(2) (1) with the heterocyclic thioamides 2-mercapto-pyrimidine (PMTH), 2-mercapto-4-methyl-pyrimidine (MPMTH), 2-mercapto-pyridine (PYTH) and 2-mercapto-benzothiazole (MBZTH), of formulae {[(tert-Bu-)(2)(HO-Ph)](2)Sn(PMT)(2)} (2), {[(tert-Bu-)(2)(HO-Ph)](2)Sn(MPMT)(2)} (3), {[(tert-Bu-)(2)(HO-Ph)](2)SnCl(PYT)} (4) and {[(tert-Bu-)(2)(HO-Ph)](2)SnCl(MBZT)} (5), have been synthesized and characterized by elemental analysis, (1)H-, (13)C-, (119)Sn-NMR, EPR, FT-IR, Raman and Mössbauer spectroscopic techniques. The crystal and molecular structures of compounds 1–5 have been determined by X-ray diffraction. The geometries around the metal center adopted in complexes 1–5 varied between tetrahedral in 1, trigonal bipyramidal in 3, 4, 5 and distorted octahedral in 2. Two carbon atoms from aryl groups and two chlorine atoms form a distorted tetrahedron in the case of 1. Two carbon, two sulfur and two nitrogen atoms from thione ligands form a distorted octahedral geometry around tin(IV) with trans-C(2), cis-N(2), cis-S(2)-configurations in 2. However, in the case of 4 and 5 complexes two carbon, one sulfur, one nitrogen and one chloride atom form a distorted trigonal bipyramidal arrangement. Finally, in the case of 3 the trigonal bipyramidal geometry is achieved by two carbon, two sulfur and one nitrogen atom in a unique coordination mode of thioamides toward the tin(IV) cation. Compounds 1–5 were tested for their in vitro cytotoxicity against the human breast adenocarcinoma (MCF-7) cell line. Compound 3 exhibits strong cytotoxic activity against MCF-7 cells (IC(50) = 0.58 ± 0.1 μM).

Synthesis and Characterization of a Linear [Mn3(O2CMe)4(py)8]2+ Complex

Two new compounds that consist of the linear trinuclear manganese(II) cation [Mn3(O2CMe)4(py)8]2+ cocrystallizing with different counteranions (I3 −, [1]; ClO4 −, [2]) are reported. Complex 1 was prepared from the reaction of [Mn(O2CMe)2] · 4H2O with I2 in MeCO2H/py, whereas complex 2 was isolated from the reaction of [Mn3O(O2CMe)6(py)3] · py with [Mn(ClO4)2] · 6H2O in MeCN/py. The crystal structures of both compounds were determined by single crystal X-ray crystallography. Magnetic susceptibility studies that were performed in microcrystalline powder of 1 in the 2–300 K range revealed the presence of antiferromagnetic exchange interactions that resulted in an S = 5/2 ground spin state.

Rare Oxidation-State Combinations and Unusual Structural Motifs in Hexanuclear Mn Complexes Using 2-Pyridyloximate Ligands

The use of phenyl-2-pyridyl ketone oxime and di-2-pyridyl ketone oxime in Mn chemistry has led to hexanuclear clusters with unprecedented (Mn(II)(4)Mn(III)Mn(IV)) or extremely rare (Mn(II)Mn(III)(5) and Mn(II)(3)Mn(III)(3)) metal oxidation-state combinations and uncommon structural motifs.