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Mixed-valent polyoxometalate (POM) clusters are one of the most interesting host species, showing a wide range of structural features and properties. The facile preparation and functionalisation of a mixed-valent polyoxofluorovanadates is reported, where two electrons are trapped to antipodal sites of the clusters. The first members of this family of clusters with the general formula, [VV12VIV2O16(?-O)10(?3-O)10(?3-F)2(L)2]6?, where L: py=pyridine?(1) pyr=pyrazine?(2) im=imidazole?(3), are unique organic-inorganic hybrids with the addition of a N-donor ligand at either end of the polyoxofluorovanadate. The composition and connectivity of 1?3 were characterised by single-crystal X-ray diffraction and electrospray ionisation mass spectrometry. Electron paramagnetic resonance spectroscopy revealed that the two well-separated VIV ions in each cluster are fully uncoupled with J=0, giving a degenerate singlet?triplet ground state. This attenuation of the exchange interaction is probed with density functional theoretical calculations that reveal that the inclusion of the fluoride ion in the cluster produces a bond pathway biased toward destructive interference between competing ferromagnetic and antiferromagnetic interactions. These robust molecular materials are the ideal combination of desirable electronic properties, with an organic handle with which they can be integrated into spintronic circuitry for molecular devices. 24 15 3836 3845

Reaction of the cyclic ligand (2Z,6Z)-piperidine-2,6-dione dioxime with TiCl4 and KOH yielded the hexanuclear cluster K6[TiIV6(μ3-O)2(μ2-O)3(CH3O)6(μ2–η1,η1,η2-Hpidiox-O,N,O′)4(μ2–η1,η1,η2-pidiox-O,N,O′)2]·7.5CH3OH possessing a new {Ti6O5} structural motif. The cluster core {Ti6O5} is wrapped by external tripodal imide dioxime ligands, showing good solubility and stability and thus, allowing its solution to be studied by means of electrospray ionization mass spectrometry, electrochemistry and 2D NMR, c. w. EPR and UV-vis spectroscopies. Density Functional Theory (DFT) calculations reveal that the cyclo-Ti3 metallic cores exhibit metallaromaticity which is expected to contribute to the stabilization of this system. 48 17 5551 5559

The activation of dioxygen by metal ions is critical in chemical and bio-chemical processes. A scientific challenge is the elucidation of the activation site of dioxygen in some copper metalloproteins, which is either the metal center or the substrate. In an effort to address this challenge, we prepared a series of new copper(ii) complexes (1·2H2O, 2·CH3OH, 3) with bio-inspired amidate ligands and investigated their activity towards dioxygen activation. The secondary amine group ligated to copper(ii) of the complex 1·2H2O in methyl alcohol is oxidized (2e-) by air dioxygen in a stepwise fashion to an imine group, affording complex 2. The copper(ii) complex 2 in methyl alcohol induces the 4e- oxidation by air dioxygen of the imine functionality ligated to copper(ii) to an azinate group, resulting in the isolation of a dinuclear azinate copper(ii) compound (4). Experimental and computational studies, including X-band c. w. EPR, UV-vis and ESI-MS spectroscopy and density functional theory computations, indicate a direct attack of the dioxygen on the -HC[double bond, length as m-dash]N- group ligated to copper(ii), and a possible mechanism of the oxidation of the -HC[double bond, length as m-dash]N- functionality ligated to copper(ii) to an azinate group is provided. This unprecedented activation of dioxygen by a copper substrate paves the way for further exploration of the O2 activation mechanisms in enzymes and the development of effective catalysts in O2-involved green organic synthesis.

The development of ligands with high selectivity and affinity for uranium is critical in the extraction of uranium from human body, radioactive waste, and seawater. A scientific challenge is the improvement of the selectivity of chelators for uranium over other heavy metals, including iron and vanadium. Flat ligands with hard donor atoms that satisfy the geometric and electronic requirements of the UVIO22+ exhibit high selectivity for the uranyl moiety. The bis(hydroxylamino)(triazine) ligand, 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H2bihyat), a strong binder for hard metal ions (FeIII, TiIV, VV, and MoVI), reacted with [UVIO2(NO3)2(H2O)2]·4H2O in aqueous solution and resulted in the isolation of the complexes [UVIO2(bihyat)(H2O)], [UVIO2(bihyat)2]2–, and {[UVIO2(bihyat)(μ-OH)]}22–. These three species are in equilibrium in aqueous solution, and their abundance varies with the concentration of H2bihyat and the pH. Reaction of H2bihyat with [UVIO2(NO3)2(H2O)2]·4H2O in CH3CN gave the trinuclear complex [UVI3O6(bihyat)2(μ-bihyat)2]2–, which is the major species in organic solvents. The dynamics between the UVIO22+ and the free ligand H2bihyat in aqueous and dimethyl sulfoxide solutions the metal binding ability of the H2bihyat over pyridine-2,6-dicarboxylic acid (H2dipic) or glutarimidedioxime for UVIO22+, and the selectivity of the H2bihyat to bind UVIO22+ in comparison to VVO43– and FeIII in either UVIO22+/VVO43– or UVIO22+/FeIII solutions were examined by NMR and UV–vis spectroscopies. The results revealed that H2bihyat is a superior ligand for UVIO22+ with high selectivity compared to FeIII and VVO43–, which increases at higher pHs. Thus, this type of ligand might find applications in the extraction of uranium from the sea and its removal from the environment and the human body. 57 13 7631 7643

Although directly relevant to metal mediated biological nitrification and the coordination chemistry of peroxide, the transition metal complexes of hydroxylamines and their functionalized variants remain mainly unexplored except vanadium(V) and molybdenum(VI). Reaction of the chelating hydroxylamine ligand 3,3′-(hydroxyazanediyl)dipropanamide (Hhydia) with [MII(CH3COO)2]·xH2O (M = CoII, ZnII) in methyl alcohol solution yields the complexes [CoII(η1:η1-CH3COO)(η1-CH3COO)(Hhydia)], (1) and [ZnII(η1-CH3COO)2(Hhydia)], (4), while reaction of Hhydia with trans-[NiIICl2(H2O)4]·2H2O yields [NiII(Hhydia)2]Cl2 (3). The X-ray structure analysis of 1 and 4 revealed that the CoII and ZnII atoms are bonded to a neutral tridentate O,N,O-Hhydia ligand and a chelate and a monodentate acetate groups in a severely distorted octahedral geometry for 1 and two monodentate acetate groups for 4 in a highly distorted trigonal bipyramidal geometry (τ = 0.63). The X-ray structure analysis of 3 revealed that the nickel atom in [NiII(Hhydia)2]2+ is bonded to two neutral tridentate O,N,O-Hhydia ligands. The twist angle, θ, in [NiII(Hhydia)2]2+ is 55.1(2)°, that is, very close to an ideal octahedron. The metal/Hhydia complexes were studied by UV–Vis (cobalt and nickel compounds), NMR (zinc compounds), HR-MS spectroscopy. The 1H and 13C NMR spectra of the methyl alcohol or acetonitrile solutions of ZnII-Hhydia complexes show the existence of both the 1:1 and 1:2 metal:ligand species being in dynamic equilibrium. The exchange processes between the ZnII-Hhydia is through complete dissociation-association of the ligand from the complexes as it is evident from the 2D {1H} EXSY NMR spectroscopy. UV–Vis spectroscopy of the CoII-Hhydia in methyl alcohol also shows the existence of both the 1:1 and 1:2 metal:ligand species in contrast to 1:2 complex [NiII(Hhydia)2]2+ which is the only species found in solution. The NMR and UV–Vis observations are additionally supported by the HR-MS studies. 151 417 425

Reaction of hydroxylamine hydrochloride with prop-2-enamide in dichloromethane in the presence of triethylamine resulted in the isolation of the N,N′-disubstituted hydroxylamine-(diamido) ligand, 3,3′-(hydroxyazanediyl)dipropanamide (Hhydia). The ligand Hhydia was characterized by multinuclear NMR, high-resolution electrospray ionization mass spectrometry (ESI-MS), and X-ray structure analysis. Interaction of Hhydia with trans-[CrIIICl2(H2O)4]Cl·2H2O in ethanol yields the ionization isomers [CrIII(Hhydia)2]Cl3·2H2O(1·2H2O) and cis/trans-[CrIIICl2(Hhydia)2]Cl·2H2O (2·2H2O). The X-ray structure analysis of 1 revealed that the chromium atom in [CrIII(Hhydia)2]3+ is bonded to two neutral tridentate O,N,O-Hhydia ligands. The twist angle, Î, in [CrIII(Hhydia)2]3+ is 54.5(6)0, that is, very close to an ideal octahedron. The intramolecular hydrogen bonds developed between the N-OH group of the first ligand and the amidic oxygen atom of the second ligand and vice versa contribute to the overall stability of the cation [CrIII(Hhydia)2]3+. The reaction rate constant of the formation of Cr(III) complexes 1·2H2O and 2·2H2O was found to be 8.7(±0.8) × 10-5 M-1 s-1 at 25 °C in methyl alcohol and follows a first-order law kinetics based on the biologically relevant ligand Hhydia. The reaction rate constant is considerably faster in comparison with the corresponding water exchange rate constant for the hydrated chromium(III). The modification of the kinetics is of fundamental importance for the chromium(III) chemistry in biological systems. Ultraviolet-visible and electron paramagnetic resonance studies, both in solution and in the solid state, ESI-MS, and conductivity measurements support the fact that, irrespective of the solvent used in the interaction of Hhydia with trans-[CrIIICl2(H2O)4]Cl·2H2O, the ionization isomers[CrIII(Hhydia)2]Cl3·2H2O (1·2H2O) and cis/trans-[CrIIICl2(Hhydia)2]Cl·2H2O (2·2H2O) are produced.The reaction medium affects only the relevant percentage of the isomers in the solid state. The thermodynamic stability of the ionization isomers 1·2H2O and cis/trans-2·2H2O, their molecular structures as well as the vibrational spectra and the energetics of the CrIII- Hhydia/hydia- were studied by means of density functional theory calculations and found to be in excellent agreement with our experimental observations. © 2014 American Chemical Society. 53 21 11404 11414

Reaction of the oxidovanadium(IV)-LN-N species (LN-N is bipy = 2,2′-bipyridine or bipy-like molecules) with either BF4- or HF and/or KF results in the formation of compounds of the general formula cis-[VIV(=O)(F)(LN-N)2]+. Structural and spectroscopic (electron paramagnetic resonance) characterization shows that these compounds are in the tetravalent oxidation state containing a terminal fluorido ligand. Density functional theory calculations reveal that the VIV-F bond is mainly electrostatic, which is reinforced by reactivity studies that demonstrate the nucleophilicity of the fluoride ligand in a halogen exchange reaction and in fluorination of various organic substrates. © 2016 American Chemical Society. 55 4 1364 1366 Cited By :2

Corrosiveness is one of the main drawbacks of using the iodide/triiodide redox couple in dye-sensitized solar cells (DSSCs). Alternative redox couples including transition metal complexes have been investigated where surprisingly high efficiencies for the conversion of solar to electrical energy have been achieved. In this paper, we examined the development of a DSSC using an electrolyte based on square pyramidal oxidovanadium(IV/V) complexes. The oxidovanadium(IV) complex (Ph4P)2[VIVO(hybeb)] was combined with its oxidized analogue (Ph4P)[VVO(hybeb)] {where hybeb4- is the tetradentate diamidodiphenolate ligand [1-(2-hydroxybenzamido)-2-(2-pyridinecarboxamido)benzenato}and applied as a redox couple in the electrolyte of DSSCs. The complexes exhibit large electron exchange and transfer rates, which are evident from electron paramagnetic resonance spectroscopy and electrochemistry, rendering the oxidovanadium(IV/V) compounds suitable for redox mediators in DSSCs. The very large self-exchange rate constant offered an insight into the mechanism of the exchange reaction most likely mediated through an outer-sphere exchange mechanism. The [VIVO(hybeb)]2-/[VVO(hybeb)]- redox potential and the energy of highest occupied molecular orbital (HOMO) of the sensitizing dye N719 and the HOMO of [VIVO(hybeb)]2- were calculated by means of density functional theory electronic structure calculation methods. The complexes were applied as a new redox mediator in DSSCs, while the cell performance was studied in terms of the concentration of the reduced and oxidized form of the complexes. These studies were performed with the commercial Ru-based sensitizer N719 absorbed on a TiO2 semiconducting film in the DSSC. Maximum energy conversion efficiencies of 2% at simulated solar light (AM 1.5 1000 W m-2) with an open circuit voltage of 660 mV, a short-circuit current of 5.2 mA cm-2, and a fill factor of 0.58 were recorded without the presence of any additives in the electrolyte. © 2015 American Chemical Society. 54 8 3979 3988 Cited By :10

A simple donor atom additivity relationship has been used to calculate the donor atom electrochemical contribution (DEC) of the Oac (acetylacetonate-enolic oxygen), OPh (phenolic oxygen), SPh (mercaptophenol sulfur), Nam (deprotonate amide nitrogen), Nim (imine nitrogen) and Npy (pyridine nitrogen) to the redox processes of the square pyramidal vanadyl complexes. The study focuses on the amidate vanadyl complexes because of (a) their biological interest and (b) the existence of data from plethora complexes studied in great details. The electrochemical contributions for the vanadyl oxidation and reduction processes increase following the same order, OPh ~ Oac(enolic) Ph ~ Nam im py. These values predict the electrochemical potentials of square pyramidal vanadyl complexes with high accuracy. Octahedral complexes with the same equatorial environment show significant shift of the oxidation potentials to lower values. The DEC influence to the square pyramidal vanadyls' electrochemical potentials has been evaluated. © 2015 Elsevier Inc. All rights reserved. 147 39 43 Cited By :5

Reaction of [V(VI)OCl(2)(thf)(2)] with a bidentate nitrogen-donor ligand (L: phen=1,10-phenanthroline, 5-mephen=5-methyl-1,10-phenanthroline, bipy=2,2'-bipyridine, 5,5'-me(2)bipy=5,5'-dimethyl-2,2'-bipy) in methyl alcohol, in the presence of triethylamine, leads to the formation of hexameric [V(2) (IV)V(4) (V)] oxo-alkoxo-vanadates of the general formula [V(6)O(12)(mu(2)-OCH(3))(4)(L)(4)].x H(2)O [L=phen (1.4 H(2)O), 5-mephen (2.6 H(2)O), bipy (3.4 H(2)O), 5,5'-me(2)bipy (4.H(2)O)]. X-ray structure analysis of 1.2 H(2)O and 4.8 CH(3)OH revealed a pair of V(3)O(13)N(4) trimeric units sharing two corners, with a centrosymmetric planar V(6)-core. In addition, a fully oxidized V(V) species [V(V) (4)O(8)(OCH(3))(2)(mu(3)-OCH(3))(2)(5,5'-me(2)bipy)(2)].3 CH(3)OH (5.3 CH(3)OH) was isolated from the reaction mixture used for the synthesis of 4.H(2)O. The crystal structure of 5.3 CH(3)OH revealed a dicubane-like framework with two missing vertices. Electron paramagnetic resonance (EPR) and variable temperature magnetic susceptibility studies for the hexamers 1.4 H(2)O and 3.4 H(2)O showed the complete localization of the single 3d electrons on the V(IV) ions and unusual ferromagnetic interaction between the two paramagnetic vanadium(IV) ions separated by a distance of about 5.1 A. Furthermore, intermolecular antiferromagnetic interactions through pi-contacts of phenyl rings were observed for these species below 8 K. The ferromagnetic exchange coupling observed in the hexanuclear compounds 1.4 H(2)O and 3.4 H(2)O is also discussed using ab initio UHF calculations on a model compound. The value of the exchange coupling constant (3.7 cm(-1)) for this model compound, calculated using the broken symmetry approach, is in good agreement, both in sign and magnitude, with the experimental J values (6.00 cm(-1) for 1.4 H(2)O and 8.54 cm(-1) for 3.4 H(2)O).

The reaction of VCl(3) with 1,10-phenanthroline and a series of dipeptides (H(2)dip), having aliphatic as well as aromatic side chains, in methyl alcohol and in the presence of triethylamine affords vanadium(III) compounds of the general formula [V(III)(dip)(MeOH)(phen)]Cl. Aerial oxidation/hydrolysis of the vanadium(III) species gives their oxovanadium(IV) analogues of the general formula [V(IV)O(dip)(phen)]. X-ray crystallographic characterization of the [V(IV)O(dip)(phen)] compounds (where dip(2-)=Gly- L-Ala, Gly- L-Val and Gly- L-Phe) revealed that the vanadium atom possesses a severely distorted octahedral coordination and is ligated to a tridentate dip(2-) ligand at the N(amine) atom, the deprotonated N(peptide) atom and one of the O(carboxylate) atoms, as well as an oxo group and two phenanthroline nitrogen atoms. Circular dichroism characterization of the V(III)/V(IV)O(2+)-dipeptide compounds revealed a strong signal for the V(IV)O(2+) species in the visible range of the spectrum, with a characteristic pattern which may be exploited to identify the N(am), N(pep) and O(car) ligation of a peptide or a protein to V(IV)O(2+) center, and a weak Cotton effect of opposite sign to their vanadium(III) analogues. The visible spectra of the V(III)-dipeptide compounds revealed two d-d bands with high intensity, thus indicating that the covalency of the metal-donor atoms is significant, i.e. the vanadium d orbitals are significantly mixed with the ligand orbitals, and this is confirmed by the low values of their Racah B parameters. The high-intensity band of the V(IV)O(2+)-dipeptide compounds at approximately 460 nm implies also a strong covalency of the metal with the equatorial donor atoms and this was supported by the EPR spectra of these compounds. Moreover, the V(III)/V(IV)O(2+)-dipeptide complexes were characterized by EPR and IR spectroscopies as well as conductivity and magnetic susceptibility measurements.

The reaction of [VO(CH3COO)2(phen)] (phen = 1,10-phenanthroline) with the sulfhydryl-containing pseudopeptides (scp), N-(2-mercaptopropionyl)glycine (H3mpg), N-(2-mercaptopropionyl)cysteine (H4m2pc), N-(3-mercaptopropionyl)cysteine (H4m3pc) and the dipeptides glycylglycine (H2glygly) and glycyl-L-alanine (H2glyala), in the presence of triethylamine, results in the formation of the compounds Et3NH[VO(mpg)(phen)] (1), (Et3NH)2[VO(m2pc)] (4), [Et3NH)2[VO(m3pc)] (5), [VO(glygly)(phen)] · 2CH3OH (2 · 2CH3OH) and [VO(glyala)(phen)] · CH3OH (3 · CH3OH). Evidence for the molecular connectivity in 2 · CH3OH was established by X-ray crystallography, showing the vanadium(IV) atom ligated to a tridentate glygly2- ligand at the N(amine), N(peptide) and O(carboxylato) atoms. Combination of the correlation plot of the EPR parameters g(z) versus A(z), together with the additivity relationship supported the prediction of the equatorial donor atom sets of the V(IV)O2+ center at various pH values for the V(IV)O2+-glutathione system considered in this study. Model NMR studies (interaction of vanadium(V) with the scp H3mpg) showed that there is a possibility of vanadium(V) ligation to glutathione. (C) 2000 Elsevier Science Inc. 79 1-4 159 166 Cited By :29

Reaction of the N,N-disubstituted bis(hydroxylamino) ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H2bihyat) with cis-[MoVIO2(acac)2] in tetrahydrofuran resulted in isolation of the mononuclear compound cis-[MoVIO 2(bihyat)] (1). The treatment of Na2MoVIO 4·2H2O with the ligand H2bihyat in aqueous solution gave the dinuclear compounds cis-[MoVI 2O4(bihyat)2(H2O)2] (2) and trans-[MoVI2O4(bihyat)2(H 2O)2] (3) at pH values of 3.5 and 5.5, respectively. The structures for the three molybdenum(VI) compounds were determined by X-ray crystallography. Compound 1 has a square-pyramidal arrangement around molybdenum, while in the two dinuclear compounds, each molybdenum atom is in a distorted pentagonal-bipyramidal environment of two bridging and one terminal oxido groups, a tridentate (O,N,O) bihyat2- ligand that forms two five-membered chelate rings, and a water molecule trans to the terminal oxido group. The dinuclear compounds constitute rare examples containing the {Mo 2VIO2(μ2-O2)} 4+ moiety. The potentiometry revealed that the Mo VIbihyat2- species exhibit high hydrolytic stability in aqueous solution at a narrow range of pH values, 3-5. A subtle change in the coordination environment of the five-coordinate compound 1 with ligation of a weakly bound water molecule trans to the oxido ligand (1w) renders the equatorial oxido group in 1w more nucleophilic than that in 1, and this oxido group attacks a molybdenum atom and thus the dinuclear compounds 2 and 3 are formed. This process might be considered as the first step of the oxido group nucleophilic attack on organic substrates, resulting in oxidation of the substrate, in the active site of molybdenum enzymes such as xanthine oxidase. Theoretical calculations in the gas phase were performed to examine the influence of water on the dimerization process (1 → 2/3). In addition, the molecular structures, cis/trans geometrical isomerism for the dinuclear molybdenum(VI) species, vibrational spectra, and energetics of the metal-ligand interaction for the three molybdenum(VI) compounds 1-3 have been studied by means of density functional theory calculations. © 2012 American Chemical Society. 51 24 13138 13147 Cited By :3

Reaction of the ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5- triazine (H2bihyat) with NaVVO3 in aqueous solution followed by addition of either Ph4PCl or C(NH 2)3Cl, respectively, gave the mononuclear vanadium(V) compounds Ph4P[VVO2(bihyat)]·1.5H 2O (1) and C(NH2)3[VVO 2(bihyat)] (2). Treatment of VIVOSO4· 5H2O with the ligand H2bihyat in methyl alcohol under specific conditions gave the oxo-bridged dimer [VV2O 2(μ2-O)(bihyat)2] (3). The structures for 1 and 3 were determined by X-ray crystallography and indicate that these compounds have distorted square-pyramidal arrangement around vanadium. The ligand bihyat2- is bonded to vanadium atom in a tridentate fashion at the pyridine-like nitrogen atom and the two deprotonated hydroxylamino oxygen atoms. The high electron density of the triazine ring nitrogen atoms, which results from the resonative contribution of electrons of exocyclic nitrogen atoms (Scheme 4), leads to very strong V-N bonds. The cis-[VVO 2(bihyat)]- species exhibits high hydrolytic stability in aqueous solution over a wide pH range, 3.3-11.0, as it was evidenced by 1H and 51V NMR spectroscopy and potentiometry. The high affinity of the H2bihyat ligand for the VVO 2+ unit, its tridentate character, as well as its small size, paves the way for potential applications in medicine, analysis, and catalysis for the C(NH2)3[VVO 2(bihyat)] compound. The molecular structures, vibrational and electronic spectra, and the energetics of the metal-ligand interaction for compounds 1 and 3 have been studied by means of density functional calculations. © 2008 American Chemical Society. 47 24 11698 11710 Cited By :17

Reaction of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) in the mixed-solvent system H(2)O/CH(3)CN (pH = 5) resulted in the formation of the tetranuclear cluster (NH(4))(4)[Mo(4)(VI)SO(16)] x H(2)O (1), while the same reaction in acidic aqueous solution (pH = 5) yielded (NH(4))(4)[Mo(5)(VI)S(2)O(21)] x 3H(2)O (2). Compound {(H(2)bipy)(2)[Mo(5)(VI)S(2)O(21)] x H(2)O}(x) (3) was obtained from the reaction of aqueous acidic solution of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) (pH = 2.5) and 4,4'-bipyridine (4,4'-bipy). The mixed metal/sulfite species (NH(4))(7)[Co(III)(Mo(2)(V)O(4))(NH(3))(SO(3))(6)] x 4H(2)O (4) was synthesized by reacting Na(2)Mo(VI)O(4) x 2H(2)O with CoCl(2) x 6H(2)O and (NH(4))(2)SO(3) with precise control of pH (5.3) through a redox reaction. The X-ray crystal structures of compounds 1, 2, and 4 were determined. The structure of compound 1 consists of a ring of four alternately face- and edge-sharing Mo(VI)O(6) octahedra capped by the trigonal pyramidal sulfite anion, while at the base of the Mo(4) ring is an oxo group which is asymmetrically shared by all four molybdenum atoms. Compound 3 is based on the Strandberg-type heteropolyion [Mo(5)(VI)S(2)O(21)](4-), and these coordinatively saturated clusters are joined by diprotonated 4,4'-H(2)bipy(2+) through strong hydrogen bonds. Compound 3 crystallizes in the chiral space group C2. The structure of compound 4 consists of a novel trinuclear [Co(III)Mo(2)(V)SO(3)(2-)] cluster. The chiral compound 3 exhibits nonlinear optical (NLO) and photoluminescence properties. The assignment of the sulfite bands in the IR spectrum of 4 has been carried out by density functional calculations. The cobalt in 4 is a d(6) octahedral low-spin metal atom as it was evidenced by magnetic susceptibility measurements, cw EPR, BVS, and DFT calculations. The IR and solid-state UV-vis spectra as well as the thermogravimetric analyses of compounds 1-4 are also reported.

Reaction of VIVOCl2 in strongly acidic aqueous solution with either (NH4)2SO3 or Na2SO3 and Bu4NBr at ~70°C in the pH range 2.5-4.5 gives the clusters (NH4)2{[V4 IV(μ 4-O)2(μ 3-OH)2](VIVO)2(μ 3-SO3)4O4(H2O)2} and (n-Bu4N)2{[V4 IV(μ 4-O)2(μ 3-OH)2](VIVO)2(μ 3-SO3)4O4(H2O)2}, respectively. Reaction of NH4VVO3 with (NH4)2SO3 resulted in the isolation of the first compound. When the latter reaction is carried out in the presence of MgO, compound (NH4)[VIVO(SO3)1.5H2O]∞.2.5H2O was isolated instead. Compound (n-Bu4N)2{[V4 IV(μ 4-O)2(μ 3-OH)2](VIVO)2(μ 3-SO3)4O4(H2O)2} and (NH4)[VIVO(SO3)1.5H2O]∞.2.5H2O were characterized by X-ray structure analysis. The crystal structure of species (n-Bu4N)2{[V4 IV(μ 4-O)2(μ 3-OH)2](VIVO)2(μ 3-SO3)4O4(H2O)2} revealed a unprecedented hexanuclear cluster consisting of a cubane core [M4(μ 4-O)2(μ 3-OH)2] connected to two other metal atoms through the core oxo-groups and four μ 3-SO3 bridges. Compound (NH4)[VIVO(SO3)1.5H2O]∞.2.5H2O represents a rare example of an open-framework species prepared under mild conditions. Cyclic voltammetric examination of compound (n-Bu4N)2{[V4 IV(μ 4-O)2(μ 3-OH)2](VIVO)2(μ 3-SO3)4O4(H2O)2} revealed a redox process which was assigned to the oxidation of one core of vanadium(IV) to vanadium(V).

HYSCORE with a vanadium core: Examples of monomeric metal compounds containing the cis-[M(=O)(OH)]n+ unit, namely the VIVO2+ complexes [VIVO(OH)(bipy)2]BF4 (1 see picture) and [VIVO(OH)(phen)2]BF4·H2O (2·H2O), were isolated and structurally characterized. The continuous wave EPR and 2D ESEEM (HYSCORE hyperfine sublevel correlation) spectroscopy parameters obtained for 1 and 2 · H2O provide spectroscopic signatures that enable the assignment of the cis-[VIVO(OH)]+ center in biomolecules. 41 15 2797 2801 Cited By :19

Novel oxorhenium and oxotechnetium complexes based on the tetradentate 1-(2-hydroxybenzamido)-2-(pyridinecarboxamido)benzene, H3L, ligand have been synthesized and characterized herein. Thus, by reacting equimolar quantities of the triply deprotonated ligand L3- With the suitable MO3+ precursor, the following neutral MOL complexes could be easily produced following similar synthetic routes: M=Re (1), M=(TC)-T-99g (2) and M=Tc-99m (3). Complexes 1 and 2, prepared in macroscopic amounts, were chemically characterized and their structure determined by single-crystal X-ray analysis. They are isostructural metal chelates, adopting a distorted square pyramidal geometry around the metal. The N3O donor atom set of the tetradentate ligand defines the basal plane and the oxygen atom of the M=O core occupies the apex of the pyramid. Complex 3 forms quantitatively at tracer level by mixing the H3L ligand with (NaTcO4)-Tc-99m generator eluate in aqueous alkaline media and using tin chloride as reductant in the presence of citrate. Its structure was established by chromatographic comparison with prototypic complexes 1 and 2 using high-performance liquid chromatographic techniques. When challenged with excess glutathione in vitro, complex 3 is rapidly converted to hydrophilic unidentified metal species. Tissue distribution data after administration of complex 3 in vivo revealed a significant uptake and retention of this compound in brain tissue. Journal of Biological Inorganic Chemistry

33 5 845 846 Cited By :33

The complexes [VO(pycac)] and [VO(pycbac)] were prepared by the reaction of bis(pentane-2, 4-dionato)oxovanadium(IV) with either N-[2-(4-oxopent-2-en-2-ylamino)phenyl]pyridine-2-carboxamide (H2pycac) or 7V-[2-(4-phenyloxobut-2-en-2-ylamino)-phenyl]pyridine-2-carboxamide (H2pycbac) in a methanolic solution. Crystals of [VO(pycac)] crystallized from nitromethane were monoclinic, space group P21n with a = 7.5938 (1) Å, b = 30.161 (1) Å, c = 13.6982 (2) Å, β = 86.468 (1)°, Z=8, and Rw = 5.39%. Crystallization of [VO(pycac)] from chlorobenzene yielded triclinic crystals with a space group PI and a = 7.8558 (5) Å, b = 12.934 (1) Å, c = 15.675 (1) Å, α = 78.594 (2)°, β = 89.938 (2)°, γ = 88.097 (2)°, Z = 4, and Rw = 6.45%. [VO(pycbac)] crystals were monoclinic, space group P21/c with a = 6.5422 (4) k, b= 14.4786 (8) Å, c = 19.963 (1) Å, β = 93.461 (2)°, Z = 4, and Rw = 3.80%. The geometry about vanadium in each structure approximates a square pyramid with an average V=0 bond length of 1.595 Å with the metal ion 0.669 A above the basal plane. The average V-N(pyridine), V-N(amine), V-N(amide), and V-O bond lengths are 2.100, 2.045, 1.981, and 1.916 Å, respectively. The V-N(amide) and V-0 bond lengths constitute rare examples of such short V-N and V-0 distances that have been reported for oxovanadium(IV) complexes to date. In addition to the synthesis and crystallographic studies, we report the optical, infrared, magnetic, electron paramagnetic resonance, and electrochemical properties of these complexes. This study represents the first systematic study of oxovanadium containing a vanadium-amide bond. © 1992, American Chemical Society. All rights reserved. 31 12 2587 2594 Cited By :45

Reaction of H2pycac with bis(pentane-2,4-dionato)oxovanadium(IV) gives the title compound which is the first example of a vanadyl(iv) complex containing a vanadium-amide bond the X-ray crystal structure of the complex is reported. 23 1664 1665 Cited By :13

The tin(IV) complexes [SnX4L] [L = 2-(2-pyridyl)benzimidazole X = Cl, Br or I] and [SnMe2Cl2L] were prepared by a dehydration reaction of N-(2-aminophenyl)pyridine-2-carboxamide L′ with either SnX4 (X = Cl, Br or I) or SnMe2Cl2 in chloroform solution. The X-ray crystal structures of [SnMe2Cl2L] and [SnBr4L]·0.5MeNO2 show a distorted octahedral geometry around the tin(IV) atom in both molecules. The ligand L acts as a bidentate chelate with ligated atoms being the pyridine-type nitrogens of the heterocyclic rings. The chlorine atoms in [SnMe2Cl2L] are cis while the methyl groups are trans to each other, Infrared and Mössbauer spectra and a correlation of X-ray structural and anti-tumour (P388 lymphocytic leukaemia) data for the octahedral tin(IV) complexes are also reported. The X-ray structures are the first such reported for metal complexes containing 2-(2-pyridyl)benzimidazole. 18 2729 2733 Cited By :42