Six-coordinate Vanadium Research Articles

A new synthetic smectite-like vanadosilicate containing V3+ in the framework

A new synthetic smectite-like vanadosilicate, named Vanadosilicate Araraquara Madrid (VAM), containing V3+ was prepared by a hydrothermal method and its behavior as catalyst for methanol oxidation was investigated by X-ray Absorption Spectroscopy (XAS) under operando conditions. The samples were characterized by powder X-ray Diffraction (XRD), Scanning and Transmission Electronic Microscopy (SEM and TEM), CHN chemical analysis, as well as Nuclear Magnetic Resonance spectroscopy, Ultraviolet–visible spectroscopy (UV–Vis) and XAS. The use of VCl3 as a source of vanadium in low oxidation state (V3+) together with a mixture of hexamethyleneimine (HMI) and N,N,N-trimethyl-1-adamantamonium hydroxide (TMAdaOH) and the preparation of the synthesis mixture under inert atmosphere are mandatory for an efficient formation of this smectite-like vanadosilicate. XRD analyses show the synthetic smectite-like vanadosilicate to be impurity free and dioctahedral smectite peaks were observed. TEM observations together with EDS analyses indicate that the chemical composition is consistent with the dioctahedral structure. XAS measurements have revealed that six-coordinated vanadium is present on VAM, in an environmental similar to that reported for roscoelite mineral. The catalytic properties of this material were evaluated during methanol transformation under operando conditions. The reaction mechanism under different atmospheres was investigated and the results indicated that the process under He leads to the formation of H2 and CO, while the presence of oxygen shifts the mechanism toward the partial oxidation of methanol.

Di-μ-oxidovanadium(V) di-nuclear complexes: Synthesis, X-ray, DFT modeling, Hirshfeld surface analysis and antioxidant activity

In this work, two di-μ-oxidovanadium(V) complexes, [(L1H)VO(μ-O)]2 (C1) and [(L2H)VO(μ-O)]2 (C2), with tridentate Schiff base ligands, [N-(2-hydroxyethylamino)ethyl]-5-methoxysalicylaldimine (L1H) and 2-[(2-(2-Hydroxyethylamino) ethylimino)methyl] phenol (L2H), respectively, were prepared and characterized by various spectroscopic techniques. The X-ray diffraction of C1 showed six-coordinate vanadium in a distorted octahedral geometry with the imine, phenolate and amine donors of the ligand and two oxo-group bonds. Density functional theory (DFT) was carried out using B3LYP level with the 6-31G basis set in order to predict the molecular structure of C1, delineate its vibrational wavenumbers and define the theoretical NMR shifts, which were performed with the GIAO approach. Thereafter, Hirshfeld surface (HS) and 2D fingerprint analysis were used to investigate the intermolecular contacts in the C1 complex. The DPPH free radical scavenging assay was used to evaluate the antioxidant activity of both C1 and C2 complexes.

Crystal structure and catalytic properties of a vanadium complex cis-[VO2(Him-py)(im-py)]2·3H2O

The coordination behavior of Him-py (2-(1H-imidazol-2-yl)pyridine) toward vanadium has been explored. The six-coordinate complex, cis-[VO2(Him-py)(im-py)]2·3H2O (1), was synthesized by the coordination reaction of NH4VO3 and Him-py in the aqueous methanol solution, which was characterized by single-crystal X-ray technology. It belongs to the monoclinic space group P21/n with a = 8.0756(6), b = 19.3531(15), c = 11.4433(8), β = 106.905(2), V = 1711.2(2), and Z = 2. The crystal structure shows that the six-coordinate vanadium is bonded to two cis-oxido ligands and two bidentate ligands, Him-py and im-py. Interestingly, when crystals of 1 were immersed in H2O2, a peroxovanadium compound, (H2im-py)[OV(O2)2(Him-py)] (2), was obtained, which crystallizes in the orthorhombic space group Fdd2 with a = 22.600(2), b = 22.7259(13), c = 18.0146(11), V = 9252.4(12), and Z = 16, and consists of a seven-coordinate peroxovanadate(V) ion, one Him-py and one H2im-py ligand. Moreover, we also studied the catalytic activity of 1 in the oxidative bromination of phenol/aniline-like compounds towards mimicking bromoperoxidase reactivity.

Vanadium chlorides supported by BIAN (BIAN = bis(arylimo)-acenaphthene) ligands: Synthesis, characterization, and catalysis on ethylene polymerization

Several vanadium chlorides bearing bis(arylimino)-acenaphthene (BIAN) ligands, (2,6-Me2C6H3-BIAN)V(THF)Cl3 (1), (2,6-Et2C6H3-BIAN)V(THF)Cl3 (2), (2,6-iPr2C6H3-BIAN)V(THF)Cl3 (3), [3,5-(CF3)2C6H3-BIAN]V(THF)Cl3 (4), [4-OMe-C6H4-BIAN]V(THF)Cl3 (5), and [2,6-(Ph2CH)2-4-OMeC6H2-BIAN]V.(THF)Cl3 (6) were synthesized by direct reaction of VCl3(THF)3 with corresponding BIAN ligands. All these complexes were characterized by elemental analyses, and FT-IR spectroscopy. The molecular structures of 1, 2, and 4 were identified by X-ray crystallography, in which the six-coordinated vanadium metal centers were in distorted octahedral geometry with the oxygen atom of the coordinated THF, two nitrogen atoms of the diimine ligand and one chlorine atom in the same plane. When activated with AlEt2Cl these vanadium complexes showed high catalytic activities for ethylene polymerization affording linear polyethylene with high molecular weight. However, when MAO was used as co-catalyst, ultra high molecular-weight polymers were obtained albeit with decreased activity.

Complexes of vanadium(IV) oxide difluoride with neutral N- and O-donor ligands

A convenient new synthesis for complexes of VOF2 with N-donor ligands is via the reaction of VF4 with the ligand in water, either under reflux or using hydrothermal conditions. The complexes, mer-[VOF2(terpy)]·3H2O (terpy=2,2′6′,2‴-terpyridyl), [VOF2(bipy)(H2O)], [VOF2(phen)(H2O)], [VOF2(py)2(H2O)], [VOF2(py)2(H2O)]·H2O, [V2O2F4(py)4] and [pyH]2[V2O2F6(H2O)2], along with the O-donor, pyridine N-oxide (pyNO) complex, [V2O2F4(H2O)2(pyNO)2], have been isolated and characterised. The controlled hydrolysis of VF4 in water produces the hydrate [VOF2(H2O)2]·H2O. The complex [VOF2(Me3tacn)] (Me3tacn=1,4,7-trimethyl-1,4,7-triazacyclononane) was prepared by the reaction of [VOF2(py)2(H2O)] and Me3tacn in MeCN. The new complexes have been characterised by microanalysis and single crystal X-ray diffraction. Powder X-ray diffraction (PXRD) data were recorded for the bulk samples and compared with the PXRD patterns simulated from the single crystal data to confirm that the latter were representative of the bulk products. All the complexes contain six-coordinate vanadium(IV), with extensive H-bonding and (in the pyridyl ligand complexes) π-stacking interactions present. IR and UV–visible spectroscopic data and magnetic measurements are also reported and discussed. Attempts to obtain phosphine oxide or ether complexes by similar routes were unsuccessful. Unless the temperature is carefully controlled, the hydrothermal route yields mixtures of VIV and VV complexes.

Aerobic Oxidation of β-1 Lignin Model Compounds with Copper and Oxovanadium Catalysts

The reactivity of homogeneous oxovanadium and copper catalysts toward aerobic oxidation of phenolic and nonphenolic β-1 lignin model compounds has been investigated. Aerobic oxidation of diastereomeric, nonphenolic β-1 lignin models (1T, 1E) using the six-coordinate vanadium complex (HQ)2VV(O)(OiPr) (HQ = 8-oxyquinolinate) as a precatalyst in pyridine afforded ketone (3) and dehydrated ketone (4) derived from oxidation of the secondary alcohol. In contrast, using CuOTf/2,6-lutidine/TEMPO (OTf = trifluoromethanesulfonate, TEMPO = 2,2,6,6-tetramethyl-piperidin-1-yl-oxyl) in toluene for the same reaction afforded 3,5-dimethoxybenzaldehyde (5) and 4-methoxybenzaldehyde (6) as major products resulting from Cα–Cβ bond cleavage. Reactions of the corresponding phenolic lignin model compounds (2T, 2E) with 10 mol % CuOTf/2,6-lutidine/TEMPO gave ketone (9) as the major product, whereas 10 mol % (HQ)2VV(O)(OiPr) or a stoichiometric amount of CuOTf/2,6-lutidine/TEMPO yielded 2,6-dimethoxybenzoquinone (10) as the majo...

New Polymorph of InVO4: A High-Pressure Structure with Six-Coordinated Vanadium

A new wolframite-type polymorph of InVO4 is identified under compression near 7 GPa by in situ high-pressure (HP) X-ray diffraction (XRD) and Raman spectroscopic investigations on the stable orthorhombic InVO4. The structural transition is accompanied by a large volume collapse (ΔV/V = -14%) and a drastic increase in bulk modulus (from 69 to 168 GPa). Both techniques also show the existence of a third phase coexisting with the low- and high-pressure phases in a limited pressure range close to the transition pressure. XRD studies revealed a highly anisotropic compression in orthorhombic InVO4. In addition, the compressibility becomes nonlinear in the HP polymorph. The volume collapse in the lattice is related to an increase of the polyhedral coordination around the vanadium atoms. The transformation is not fully reversible. The drastic change in the polyhedral arrangement observed at the transition is indicative of a reconstructive phase transformation. The HP phase here found is the only modification of InVO4 reported to date with 6-fold coordinated vanadium atoms. Finally, Raman frequencies and pressure coefficients in the low- and high-pressure phases of InVO4 are reported.

Five- and six-coordinate vanadium(V) complexes with tridentate Schiff base ligands derived from S(+)-isoleucinol: Synthesis, characterization and catalytic activity in the oxidation of sulfides and olefins

A series of vanadium(V) complexes with chiral tridentate Schiff base ligands, obtained by a single condensation of S(+)-isoleucinol with salicylaldehyde and its derivatives, and also six-coordinate complexes with additional monoanionic bidentate benzohydroxamate co-ligand, were prepared. The complexes were characterized by elemental analysis and by their IR, CD, UV–Vis, one- (1H, 51V) and two-dimensional (COSY, gHSQC and NOESY) NMR spectra. The X-ray analysis of the complex, (benzohydroxamato-κ2O,O′){S(+)-2-[(1-oxido-3-methylpentyl)iminomethyl]phenolato-κ3N,O,O′}oxidovanadium(V), 1b, revealed a distorted octahedral VO(ONO)(OO) geometry. The five-coordinate vanadium(V) complexes have ability to catalyze the oxidation of sulfides [PhSR (R=Me, Bz)] using aqueous 30% H2O2 in good yields and enantiomeric excesses. Catalytic activity of these complexes were also tested in the oxidation of styrene and cyclohexene, using aqueous 30% H2O2 or tert-butyl hydroperoxide (TBHP) as oxidant.

Synthesis, characterization, and crystal structure of a new three-dimensional phosphate with large cavities and polynuclear vanadium

Abstract A new three-dimensional phosphate by the synergy of five-coordinated and six-coordinated vanadium, has been obtained. Compared with other V–P–O systems, large cavity and polynuclear transition metal are co-existed in the new compound, which is rarely reported.

Insulin-enhancing activity of a dinuclear vanadium complex: 5-chloro-salicylaldhyde ethylenediamine oxovanadium(V) and its permeability and cytotoxicity

A new insulin-enhancing oxovanadium complex 5-chloro-salicylaldhyde ethylenediamine oxovanadium (V) ([V 2O 2(μ-O) 2L 2]) has been synthesized. The complex was characterized by a variety of physical methods, including X-ray crystallography. The X-ray diffraction analysis show a dinuclear complex of two six-coordinate vanadium centers doubly bridged by the oxygen atoms of the Schiff base ligand with a V 2O 2 diamond core. The complex was administered intragastrically to STZ-diabetic rats for 2 weeks. The biological activity results show that the complex at the dose of 10.0 and 20.0 mg V kg − 1 , could significantly decrease the blood glucose level and ameliorate impaired glucose tolerance in STZ-diabetic rats. That results suggested that the complex exerts an antidiabetic effect in STZ-diabetic rats. Furthermore, the complex ([V 2O 2(μ-O) 2L 2]) had permeability above 10 − 5 cm/s. The experimental results suggested that the vanadium complex permeates via a passive diffusion mechanism. It was also suggested the complex with salen-type ligands has good lipophilic properties and better oral administration. The cytotoxicity of the complex ([V 2O 2(μ-O) 2L 2]) on Caco-2 cells was measured by a decrease of cell viability using the MTT assay suggesting that the chlorine atom at C4 of complex [V 2O 2(μ-O) 2L 2] increased cytotoxicity for vanadium complexes.

Unexpected Synthesis of an Unsymmetrical μ-Oxido Divanadium(V) Compound through a Reductive Cleavage of a N−O Bond and Cleavage-Hydrolysis of a C−N Bond of an N,N-Disubstituted Bis-(hydroxylamino) Ligand

Reaction of the N,N-disubstituted bis-(hydroxylamino) ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine, H(2)bihyat, with V(IV)OSO(4).5H(2)O in water for 6 h followed by the addition of methyl alcohol resulted in the isolation of the unsymmetrical mu-oxido divanadium(V) compound [V(V)(2)O(2)(mu(2)-O)(bihyat)(hyta)(hyto)].3H(2)O (1.3H(2)O) and of the methylhydroxylamido derivative [V(V)O(bihyat)(CH(3)NHO)].H(2)O (2.H(2)O). The N,N-disubstituted mono(hydroxylamino) ligands Hhyta, Hhyto, and CH(3)NHOH were formed by the decomposition of the ligand H(2)bihyat in the presence of vanadium. The structures of compounds 1.3H(2)O and 2.H(2)O were determined by X-ray crystallography. The structure of 1.3H(2)O consists of one five-coordinate vanadium(V) atom and one six-coordinate vanadium(V) atom bridged by an oxido group and ligated to a tridentate bihyat(2-) and two bidentate hyta(-) and hyto(-) ligands, respectively. The two terminal oxido groups in 1.3H(2)O are syn-directed, lying on the same side of the V-O-V plane. The coordination environment of the vanadium atom in 2.H(2)O approximates to a highly distorted pentagonal pyramid with the oxido ligand occupying the apical position. Compounds 1.3H(2)O and 2.H(2)O were studied by multinuclear NMR ((1)H, (13)C, and (51)V) to elucidate their solution structures. The (51)V NMR of 1.3H(2)O in anhydrous CD(2)Cl(2) gave two signals at -199 and -508 ppm, which were assigned to the five- and six-coordinate vanadium(V) atoms, respectively. The resonance of the five-coordinate vanadium nucleus, in a field much lower than that expected from Rehder's [Inorg. Chem., 1988, 27, 584-587] referencing scale, was attributed to the low-energy ligand-to-metal charge transfer transition at 605 nm [epsilon(M) = 5050 M(-1) cm(-1)] of 1.3H(2)O according to Pecoraro et al. [J. Am. Chem. Soc., 1992, 114, 9925-9933]. Electrospray ionization-mass spectrometry studies were used to follow the decomposition products of H(2)bihyat in the presence of vanadium.

Aerobic oxidation of alcohols and alkylaromatics with dioxygen catalysed by N-hydroxyphthalimide with vanadium co-catalysts

[Bu4N]VO3 or a combination of vanadium complexes with chloride salts are attractive co-catalysts for oxidation reactions of organic compounds with dioxygen catalysed by N-hydroxyphthalimide. The role of the chloride additive relates to the formation of more labile six-coordinate vanadium complexes. The same effect is also observed with amines. Two catalytic systems based on NHPI/VO(acac)2 with LiCl or [Bu4N]Cl and NHPI/[Bu4N]VO3 are most effective in oxidation reactions of primary and secondary alcohols, but oxidation of alkylaromatics proceeds with conversion rates of from 14.4% in the case of toluene to 67.0% in the case of ethylbenzene and with different selectivities, dependent on the structure of the substrate.

Chlorination of a Pyrazole Ligand in Vanadium(V)alkoxo Complexes(1).

VOCl3 reacts with pyrazolylpyridines in the presence of tBuOH to give new six-coordinate vanadium oxoalkoxo complexes. Changing from tBuOH to tBuOOH does not lead to the corresponding tbutylperoxo complexes but to oxidation of Cl-, which finally results in chlorination of the pyrazole fragment of the chelate ligand. These new V(V) complexes catalyze the epoxidation of allylic alcohols and unfunctionalized olefins in the presence of tBuOOH.

Vibrational modes and structure of vanadium(V) complexes in M2SO4–V2O5 (M=K or Cs) molten salt mixtures

Raman spectra of the M2SO4–V2O5 (M=K or Cs) binary molten salt systems have been recorded at temperatures up to 570°C under an oxygen atmosphere and at different compositions in the range 0.25⩽X(V2O5)⩽0.50. 33 mol% V2O5 mixtures contain VV polymeric complexes consisted of VO3- and VO2(SO4)23- units participating in chain-like or network-like configurations, while VO2SO4- units were also detected in the K2SO4–V2O5 system. The spectral changes occurring upon addition of V2O5 up to X(V2O5)=0.50 are interpreted to indicate: (i) a gradual transformation of VO2(SO4)23- units, where vanadium is six-coordinated, to VO2SO4-, where vanadium is four-coordinated and (ii) extensive linking of polymeric chains giving rise to large and complex three-dimensional networks. The most characteristic bands observed for the various units comprising the polymeric complexes in the K2SO4–V2O5 system are assigned as follows: (i) for VO2(SO4)23- at 1042 (terminal VO stretches of six-coordinated vanadium), 940 (terminal S–O stretches of sulfate), 880 (bridging S–O), 668, 408 and 227 cm-1; (ii) for VO3- units at 950 (terminal VO stretches of four-coordinated vanadium), 486 and 365 cm-1 and (iii) for VO2SO4- units at 983 (terminal VO stretches of four-coordinated vanadium) and 862 cm-1 (bridging S–O). Similar values have been found for the band wavenumbers in the Cs2SO4–V2O5 system. The spectral data are discussed in terms of possible structural models. The spectral changes upon freezing the Cs2SO4–V2O5 molten mixtures with 0.33⩽X(V2O5)⩽0.50 indicate formation of the 1:1 V2O5·Cs2SO4 solid. This conclusion is confirmed also by powder XRD spectroscopy. For the first time, high-temperature vibrational spectroscopy has been used to establish the structural and vibrational properties of M2SO4–V2O5 (M=K or Cs) molten salt mixtures.

Solution and Solid State Properties of [N-(2-Hydroxyethyl)iminodiacetato]vanadium(IV), -(V), and -(IV/V) Complexes(1).

A mononuclear vanadium(IV), a mononuclear vanadium(V), and a binuclear mixed valence vanadium(IV/V) complex with the ligand N-(2-hydroxyethyl)iminodiacetic acid (H(3)hida) have been structurally characterized. Crystal data for [VO(Hhida)(H(2)O)].CH(3)OH (1): orthorhombic; P2(1)2(1)2(1); a= 6.940(2), b = 9.745(3), c= 18.539(4) Å; Z = 4. Crystal data for Na[V(O)(2)(Hhida)(2)].4H(2)O (2): monoclinic; P2(1)/c; a = 6.333(2), b = 18.796(2), c = 11.5040(10) Å; beta = 102.53(2) degrees; Z = 4. Crystal data for (NH(4))[V(2)(O)(2)(&mgr;-O)(Hhida)(2)].H(2)O (3): monoclinic; C2/c; a = 18.880(2), b= 7.395(2), c = 16.010(2) Å; beta = 106.33(2) degrees; Z = 4. The mononuclear vanadium(IV) and vanadium(V) complexes are formed from the monoprotonated Hhida(2)(-) ligand, and their structural and magnetic characteristics are as expected for six-coordinate vanadium complexes. An interesting structural feature in these complexes is the fact that the two carboxylate moieties are coordinated trans to one another, whereas the carboxylate moieties are coordinated in a cis fashion in previously characterized complexes. The aqueous solution properties of the vanadium(IV) and -(V) complexes are consistent with their structures. The vanadium(V) complex was previously characterized; in the current study structural characterization in the solid state is provided. X-ray crystallography and magnetic methods show that the mixed valence complex contains two indistinguishable vanadium atoms; the thermal ellipsoid of the bridging oxygen atom suggests a type III complex in the solid state. Magnetic methods show that the mixed valence complex contains a free electron. Characterization of aqueous solutions of the mixed valence complex by UV/vis and EPR spectroscopies suggests that the complex may be described as a type II complex. The Hhida(2)(-) complexes have some similarities, but also some significant differences, with complexes of related ligands, such as nitrilotriacetate (nta), N-(2-pyridylmethyl)iminodiacetate (pmida), and N-(S)-[1-(2-pyridyl)ethyl]iminodiacetate (s-peida). Perhaps most importantly, the mixed valence Hhida(2)(-) complex is significantly less stable than the corresponding pmida and s-peida complexes of similar overall charge but very similar in stability to the nta and V(2)O(3)(3+) complexes with higher charges. Thus, there is the potential for designing stable mixed valence dimers.

Reactions of vanadate with N,N- dimethylhydroxylamine: aqueous equilibria and the crystal structure of the uncharged oxygenbridged dimer of bis(N,N-dimethylhydroxamido)hydroxooxovanadate

51V nuclear magnetic resonance spectroscopy has been utilized in the investigation of the reactions of vanadate with N,N-dimethylhydroxylamine in aqueous medium. The major components of the reaction products were mono- and bisliganded mononuclear vanadate compounds with 51V chemical shifts near −630 and −740 ppm, respectively. Variation of the concentration of the reactants enabled the determination of stoichiometry and formation constants of the products. The two major signals near −740 ppm were assigned to two stereoisomers of a bisligand product. The proton stoichiometrics and pKa values of the major products were determined from pH variation studies. A crystalline product of the type [V(O)(ONMe2)2]2O was isolated from the reaction of vanadate with dimethylhydroxylamine and its structure determined from X-ray diffraction studies. The compound possesses a dimeric oxo-bridge structure with a six-coordinate vanadium core. The arrangement about each vanadium may be described as approximately tetrahedral considering the center of the N—O bond in each dimethylhydroxamide ligand as one vertex. Hydrolysis of the crystalline solid in D2O provided two isomers that corresponded to the two bisligand products. A variable temperature 1H NMR study in D2O and 50% D2O/(CD3)2CO mixture revealed the existence of reasonably fast chemical exchange between the two predominant isomers. The nature of coordination of these and related compounds is discussed. Crystal structure of [V(O)(ONMe2)2]2O: orthorhombic, space group P22121;Z = 2;a = 7.0955(9) Å; b = 10.2313(12) Å; c = 11.5942(11) Å; V = 841.69 Å3; T = 213 K; RF = 0.021 for 1141 data (I0 ≥ 2.5σ(I0) ) and 137 variables. Keywords: bis(N,N-dimethylhydroxamido)hydroxooxovanadate, vanadate, dimethylhydroxylamine, vanadium NMR, aqueous equilibria, peroxovanadate.

Electrochemistry of vanadium complexes of o-N-salicylideneaminoethylphenol. A well characterized cyclic mechanism for the gain or loss of vanadyl oxygen

The electrochemistry of two vanadium complexes of o-N-salicylideneaminoethylphenol, VO(HSalamp) 2 ( 1) and [VO(Salamp)] 2O ( 2), is reported. The oxidation of 1, V(V)/V(IV), is completely reversible. The electrochemical properties of V(IV)/V(III) of 1 are complex and the results support a well characterized cyclic scheme mechanism. The redox reactions are accompanied by the conversions between five-coordinate oxovanadium(IV) complex and six-coordinate vanadium(III) complex by losing or gaining vanadyl oxygen. Oxidation-state-dependent change in coordination environment was also seen in the electrochemical behaviour of the complex 2.

Synthesis, Structures, and Spectroscopic Characterization of a Series of N,N‘-Dimethyl-2,11-diaza[3.3](2,6)pyridinophane Vanadium(III), -(IV), and -(V) Complexes

Three vanadium-containing complexes, [(L-N4Me2)VCl2](BPh4) (1), [(L-N4Me2)VClO](ClO4) (2), and [(L-N4Me2)VO2](BPh4) (3) where L-N4Me2 is the tetradentate ligand N,N‘-dimethyl-2,11-diaza[3.3](2,6)pyridinophane, have been prepared and characterized by X-ray diffraction and electrochemical methods as well as by IR, 1H-NMR, EPR, and electronic absorption spectroscopy. Complex 1 crystallizes in monoclinic space group P21/n (No. 14) with a = 16.940(4) Å, b = 9.902(3) Å, c = 21.936(8) Å, β = 108.21(2)°, V = 3495(2) Å3, and Z = 4, complex 2 in orthorhombic space group P212121 (No. 19) with a = 10.163(2) Å, b = 13.351(3) Å, c = 14.762(3) Å, V = 2003(1) Å3 and Z = 4, and complex 3 in monoclinic space group P21/c (No. 14) with a = 14.349(3) Å, b =14.040(5) Å, c = 18.131(10) Å, β = 110.62(3)°, V = 3419(2) Å3, and Z = 4. In all these complexes a distorted cis-octahedral coordination geometry is found with the cis coordination sites occupied either by terminal chloro and/or oxo ligands. Thus, a rather unique series of mononuclear complexes has been established where, for example, in reaction with air consecutive replacements of both chloride ions by oxo donors increases the oxidation state of the six-coordinate vanadium ion from III over IV to V while the residual coordination environment remains preserved. Interestingly, in each complex the electronic properties of the cis donor atom set stabilize only one specific oxidation state of the vanadium ion in order to warrant the isolation of the complex.

Pentadecavanadate, V15O429–, a new highly condensed fully oxidized isopolyvanadate with kinetic stability in water

The X-ray structure of the new fully oxidized isopolyvanadate, (TMA)3H6VV15O42·2.5H2O 1(TMA = tetramethyl-ammonium), prepared by reaction of H2O2 with VOSO4·4H2O shows a bicapped Keggin structure with four-, five- and six-coordinate vanadium atoms; 51V NMR indicates that the same structure has considerable kinetic stability in water at ca. pH 3.5 but is thermodynamically unstable with respect to the conventional VV10O286– structure.

NMR quadrupole interactions in vanadium phosphate glass

By means of absorption and dispersion mode spectra at frequencies of the 51V nucleus from 1.78 to 20 MHz, three unique vanadium sites in vanadium phosphate glass have been identified. The relative occupation of these sites is found to be compositionally dependent. Two of these sites have lower-bound quadrupole coupling constant values of 1.8 and 0.4 MHz which can be assigned to four- and six-coordinated vanadium respectively. These results agree well with the structural model of vanadium phosphate glass based on alpha -VPO5 proposed by Calvo and Jordan (1976) which predicts three different coordinations of vanadium in the glass.