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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

Partial oxidation of an aqueous solution of CoIICl 2·6H2O with (NH4)6[Mo 7VIO24]·4H2O in the presence of (NH4)2SO3·H2O and LiCl, at pH ≈ 5.3, leads to isolation of the octanuclear cluster (NH 4)11(Li⊂[Co4IICo 4III(SO3)16(NH3) 8]·10H2O), 1. The structure of the anion of 1 consists of a central [Co4II], almost ideal square planar unit, and a pair of symmetry-related CoIII dimers above and below the Co4II plane grafting onto the tetramer by 16 bridging sulfite groups. The [Co8(SO3)16(NH 3)8]12- cluster encapsulates a lithium cation which lies at the center of the Co4II square. © 2008 American Chemical Society. 47 11 4451 4453 Cited By :19

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).

Reaction of the non-oxo VIV species [VIVCl2(LOO)2] [LOO = acetylacetonate (acac-) or benzoylacetonate (bzac-)] with a chelate nitrogen-donor ligand LNN in acetonitrile leads to the reduction of VIV to VIII and the formation of the mononuclear VIII compounds of the general formula [VIIICl2(LOO)(LNN)] (LOO and LNN are acac- and bipy for 1 acac- and 5,5′-me2bipy for 2 acac- and 4,4′-tb2bipy for 3 acac- and phen for 4 bzac- and bipy for 5 bzac- and phen for 6). The reduction of the VIV complexes was monitored by GC-MS and 1H NMR spectroscopy. Both one- and two-dimensional (2D COSY and 2D EXSY) 1H NMR techniques were used to assign the observed 1H NMR resonances of 1-6 in CD2Cl2 or CDCl3 solution. It appeared that in solution these VIII complexes form two isomers which are in equilibrium: cis-[VIIICl2(LOO)(LNN)] ⇌ trans-[VIIICl2(LOO)(LNN)]. 2D EXSY cross-peaks were clearly observed between bipy- and acac-hydrogen atoms of the two geometrical isomers of 1-3 as well as between bipy and acac- protons of the cis isomer, indicating a dynamic process that corresponds to cis-trans isomerization and a cis-cis racemization. The thermodynamic and kinetic parameters of the equilibrium between these two isomers were calculated for compounds 1 and 2 by using variable temperature (VT) NMR data. Both cis-trans isomerization and cis-cis racemization processes probably proceed with an intramolecular twist mechanism involving a trigonal prismatic transition state. Density functional calculations (DFT) also indicated such a rearrangement mechanism. 42 15 4640 4649 Cited By :7

Reaction of the p-hydroquinone derivative H2Na4bicah·4H2O with either VIVOSO4·3H2O and NaVVO3 in equivalent quantities or with NaVVO3 yields the tetranuclear VIVO2+ macrocycle-semiquinonate compound Na6{(VIVO)4-(μ2-O) 2[μ2-bicas·(-5)-N,O,O,O]2}·Na 2SO4·20H2O (1·Na2SO4·20H2O) and the dinuclear cis-VVO2+-hydroquinone species Na4{(VVO2)2[μ2- bicah(-6)-N,O,O,O]}·11H2O (2·11H2O) respectively. Compounds 1·Na2SO4·20H2O and 2·11H2O were characterized by X-ray structure analysis and ab initio calculations. 23 2786 2787 Cited By :21

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

The first polyoxomolybdenum carbonate has been synthesized and its single crystal structure as well as its IR, UV-vis and 13C NMR spectra have been determined. 23 3419 3420 Cited By :29

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

Valuable analogues of the VIVO2+ - glutathione complex have been synthesized and characterized. The reaction of [VIVO(CH3COO)2(phen)] (phen = 1,10-phenanthroline) with the sulfhydryl-containing pseudopeptides (scp) N-(2-mercaptopropionyl)cysteine (H4m2pc), and N-(3-mercaptopropionyl)cysteine (H4m3pc) in the presence of triethylamine gives the oxovanadium(IV) compounds [(Et3NH)2][VO(m2pc)] (1) and [(Et3NH)2][VO(m3pc)] (2), while reaction of [VOCl2(phen)] with the scp N-(2-mercaptopropionyl)glycine (H3mpg) 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)] (3), [VO(glygly)-(phen)]·2CH3OH (4·2CH3OH), and [VO(glyala)(phen)]·CH3OH (5·CH3OH). Complex [VOCl2(phen)(CH3OH)] (7) was prepared by the reaction of [VOCl2(thf)2] with phen in a methanolic solution. The X-ray structure of 3 shows that the vanadium(IV) atom is ligated to a tridentate mpg3- ligand at the Sthiolato, Npeptide and Ocarboxylato atoms. The X-ray structure of 7 is also reported. The optical, infrared, magnetic, electron paramagnetic resonance, and electrochemical properties of compounds 1-5· CH3OH and 7 were studied. Combination of the correlation plots of the EPR parameters gz versus Az, or the groundstate orbital population (β*)2 versus Az, together with the additivity relationship, Az,calcd = ΣniAzi/4, were shown to provide a powerful tool for probing the equatorial donor atoms in an oxovanadium(IV) compound and consequently in biomolecules. Thus, these methods provide valuable evidence for the assignment of the equatorial donor atoms for the VIVO2+ center of the VIVO2+ - glutathione system at various pH values. Model NMR studies (interaction of vanadium(V) with H3mpg) showed that there is a possibility of vanadium(V) ligation to glutathione. The contribution of a deprotonated peptide(amide) nitrogen to Az is not a fixed quantity (it varies from 29 to 43 × 10-4 cm-1), but is influenced by the presence of the three other donor atoms in the equatorial plane and, in particular, their charge. 5 3 910 921 Cited By :92

a = 12.668(5) Å, b = 8.084(3) Å, c = 17.222(6) Å, α = 108.148(12)° A series of vanadium(III) and oxovanadium(IV/V) compounds with the ligands, N-(2-nitrophenyl)pyridine-2-carboxamide (Hpycan), N-(phenyl)pyridine-2-carboxamide (Hpheca), and N-(2-pyridyl)acetamide (Hpyra), containing the amide functionality, was prepared and characterized both in solution and in solid state. All vanadium compounds contain a vanadium - amide oxygen bond. Crystal data for [VOCl2(OC2H5)(Hpheca)] (4) are monoclinic P21la Z = 4. In addition to the synthesis and crystallographic studies, the optical, infrared, and magnetic properties of these compounds are reported. Electron paramagnetic resonance [of oxovanadium(IV) species] and 1H, 13C{'H}, and 51V nuclear magnetic resonance [of oxovanadium(V) compounds] properties are reported as well. 37 26 6785 6794 Cited By :18

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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