Mononuclear Oxovanadium Research Articles

Oxovanadium and copper complexes of new unsymmetrically tetradentate ligands: X- ray structure, theoretical and NLO properties, catalytic oxidation and bromoperoxidase activities

A series of mononuclear oxovanadium VOLBz, VOLT and copper CuLBz, CuLT complexes containing unsymmetrical tetradentate Schiff base ligands were synthesized and fully characterized by conventional spectroscopic techniques such as FT-IR, UV–vis, 1HNMR and mass spectrometry (MS). Crystal structure data of CuLT, solved by X-ray diffraction, shows a monoclinic system with Cc space group and Z = 4 molecules per unit cell. The central copper ion adopts a nearly ideal square planar coordination geometry. Cyclic voltammetry of oxovanadium and copper complexes revealed quasi reversible redox couples corresponding to VOIV/VOV and CuI/CuII redox processes, respectively. The quantum calculations, performed by DFT and TD-DFT theory at the M062X/6-311**G/SDD level, agree well with the experimental data. The results show that the copper and the oxovanadium compounds have larger static and dynamic hyperpolarizability values than the urea. For instance, the β0 value of H2LT is about 68 times larger than that of the urea. The results predict that the studied compounds have the ability to be excellent second and third-order NLO materials. The prepared complexes catalyzed effectively homogeneous oxidation reaction of cyclohexene in the presence of H2O2 as oxidant. Higher conversion of 98% is attained using CuLBz as catalyst. The bromoperoxidase activity is explored in the oxidative bromination of phenol red as a trap employing the studied complexes which can be considered as potential functional models of bromoperoxidase, CuLBz catalyst exhibits the better catalytic activity, the reaction rate constant k is equal to 2.203×105 (mol L-1)-2s-1.

Spectroscopic characterization of a mononuclear oxovanadium (IV) Schiff base complex. Oxidation catalysis applications and antibacterial activities

Herein we describe the chemical synthesis of a new oxovanadium (IV) complex of an N,N-bis(1-naphthalidimine)-o phenylenediamine (VOL). The structure has been characterized by various physiochemical and spectroscopic techniques. The single crystal X-ray diffraction confirms a tetra-coordinate chelated and a planar geometry of the complex by ONNO donor sets of the ligand. Hirshfeld's surface analysis indicates that the most important inter-molecular contact within crystal packing is C-H⋯O interaction. Density Functional Theory (DFT) calculations have been used to optimize the structure and discuss the chemical reactivity through the Frontier Molecular Orbitals (FMOs). The electrochemical properties of the complex were studied by cyclic voltammetry which shows a reversible VIV/VV redox process which is consistent with the hydrodynamic voltammograms. The complex was used as catalyst for the selective oxidation of cyclohexene to the corresponding 2-cyclohexene-1-one in DMF. Finally, antibacterial activity was determined using 3 Gram negative and 2 Gram positive bacteria using disk diffusion method, it was found to be more effective against Gram positive than the Gram negative bacteria.

Synthesis and molecular structural studies of racemic chiral-at-vanadium(V) complexes using an unsymmetric achiral phenolic bidentate ligand.

Mononuclear oxovanadium(V) complexes [V(O)XL (1: X = Ot-Bu, 2: X = Cl)] [H2L: 2,2'-methylene bis(4,6-di-tert-butylphenol)(4'-tert-butyl-6'-(1-adamantyl)phenol)] directed towards asymmetric catalysis have been synthesised as racemic compounds using an unsymmetric and achiral phenolic bidentate ligand (H2L), and NMR and UV-vis absorption spectroscopies, single-crystal X-ray diffraction, and IR spectroscopy revealed their racemic chiral-at-vanadium structures in solution and in the crystal. In addition, theoretical calculations revealed that the HOMO-LUMO energy gap is smaller for unsymmetric ligands, which promotes d-orbital splitting of the metal centre.

SYNTHESIS, PHYSICOCHEMICAL STUDIES AND BIOLOGICAL APPLICATIONSOF OXOVANADIUM(IV) COMPLEXES WITH SCHIFF BASES DERIVED FROM 3-PHENYL-4-AMINO-5-MERCAPTO-1, 2, 4-TRIAZOLES AND BENZIL

A series of some mononuclear oxovanadium(IV) complexes have been synthesized by the reactions of oxovanadium(IV) sulfate with Schiff base ligands derived from 3-(phenyl / substituted phenyl)-4-amino-5-mercapto-1, 2, 4-triazoles of aromatic carboxylic acids and benzyl. The complexes were analyzed by different spectroscopic methods (FTIR, UV-Vis., EPR), X-ray diffraction (XRD) analysis, elemental analysis, conductivity measurement, and cyclic voltammetry (CV) analysis. The non-electrolytic nature of the complexes was determined on the basis of the molar conductance values. The powder X-ray diffraction pattern has also been used to determine crystal size and type. On the basis of the physicochemical data, the tentative square- pyramidal geometry of the complexes has been proposed. In vitro antibacterial andantidiabeticproperties by alpha amylase inhibition activities of the selected complexes have also been determined.

Oxovanadium(IV) Complexes with Triazole Based Schiff Base Ligands: Synthesis, Characterization and Antibacterial Study

Schiff bases have been synthesized by the reaction of triazole containing primary amine with aromatic carbonyl compounds. The Schiff bases prepared, act as ligand when these are made in contact with oxovanadium (VO2+) ion. Some new mononuclear oxovanadium(IV) complexes have been synthesized by the reaction of Schiff base ligands with vanadyl sulphate (VOSO4.xH2O) and the complexes are analyzed by different spectroscopic methods; [fourier-transform infrared (FTIR), ultraviolet-visible (UV-Vis.), electron paramagnetic resonance (EPR)], X-ray diffraction (XRD) analysis, elemental analysis, and conductivity measurement. The complexes have been well characterized based on analytical data. The electrolytic nature of the complexes was determined based on the molar conductance values. The powder XRD pattern has been used to determine crystal size and type. The synthesized Schiff base ligands and oxovanadium(IV) complexes were found to be stable in air and moisture at room temperature. On the basis of the physicochemical data, the tentative geometry of the complexes has been proposed. Antibacterial sensitivity of the ligand and its metal complexes have been assayed in vitro against bacterial pathogens viz. growth inhibitory activity of ligands and complexes against pathogens has also been determined.

Oxovanadium(V) and Dioxomolybdenum(VI) Complexes of Amide-Imine Conjugates: Structures, Catalytic and Antitumor Activities.

Three new amide-imine conjugates, namely [(E)-2-hydroxy-N'-((2-hydroxynaphthalen-1-yl)methylene)benzohydrazide] (SALNP), [(E)-N'-(4-(diethylamino)-2-hydroxybenzylidene)-2-hydroxybenzohydrazide] (SALSD), and [(E)-N'-(3-ethoxy-4-hydroxybenzylidene)-2-hydroxybenzohydrazide] (SALVN), derived by reacting 2-hydroxybenzohydrazide (SAL) with three different aldehyde, 2-hydroxynapthaldehyde, 4-(diethylamino)-2-hydroxybenzaldehyde, and 3-ethoxy-4-hydroxybenzaldehyde, respectively. Three mononuclear oxovanadium(V) and two μoxo-bridged dinuclear molybdenum(VI) complexes have been synthesized using SALNP and SALSD. Besides, SALVN is used to prepare oxovanadium(V) and dioxomolybdenum(VI) complexes. All five metal complexes along with three amide-imine conjugates are characterized by single crystal XRD analysis. Some of them have been explored as catalyst for oxidation of alkyl benzene and styrene. Antitumor activities of the metal complexes along with ligands have been studied on Dalton lymphoma (DL) and 2PK3 murine lymphoma cells.

Oxovanadium(V) complexes with tripodal bisphenolate and monophenolate ligands: Syntheses, structures and catalytic activities

The reactions between [VO(acac)2] (acac– = acetylacetonate) and the tripodal amino bisphenols 6,6′-(((2-morpholinoethyl)azanediyl)bis(methylene))bis(2,4-di-tert-butylphenol) (H2L1) and 6,6′-(((thiophen-2-ylmethyl)azanediyl)bis(methylene))bis(2,4-di-tert-butylphenol) (H2L2) as well as the tetradentate amino phenol 2,2′-((3,5-di-tert-butyl-2-hydroxybenzyl)azanediyl)bis(ethan-1-ol) (H3L3) afford the complexes [VO(L1)(OMe)] (1), [VO(L2)(acac)] (2) and [VO(L3)] (3), correspondingly. Complexes 1 and 3 can also be prepared using VOSO4·xH2O or [VO(OPr)3] as vanadium precursors. When [VO(acac)2] or VOSO4·xH2O is used, mononuclear oxovanadium(V) complexes are formed upon oxidation of the metal precursor. Single crystal X-ray structure analysis show that complexes 1 and 2 have distorted octahedral coordination spheres, in which the amino bisphenolate coordinates in a tetradentate or tridentate manner, respectively, and the coordination spheres are completed by methoxy or acetylacetonato ligands. Complex 3 has a slightly distorted trigonal bipyramidal geometry with an NO4 coordination environment. All three complexes can catalyze epoxidation of cis-cyclooctene at 50 °C with tert-butyl hydroperoxide (TBHP) or H2O2 as an oxygen source, and sulfoxidation of thioanisole or methyl-p-tolylsulfide proceeds at 25 °C using the same oxidants.

Syntheses, Crystal Structures, and Antimicrobial Activities of Oxovanadium(V) Complexes with Tridentate Schiff base Ligand

Two structurally similar new oxovanadium complexes, [VO(L)(L1)] (I) and [VO(L)(L2)] (II), where L is the dianionic form of 3-((3-bromo-2-hydroxyphenyl)-{[1-(3-bromo-2-hydroxyphenyl)methylidene]amino}methyl)pentane-2,4-dione (H2L), L1 is the deprotonated form of 8-hydroxyquinoline, L2 is 2,2'-bipyridine, were prepared and characterized by spectroscopic and single crystal X-ray diffraction (СIF files CCDC nos. 1566824 (I), 1566825 (II)). Complex I crystallizes as the monoclinic space group P21/c with unit cell dimensions a = 11.265(1), b = 18.179(2), c = 13.461(2) A, β = 103.376(3)°, V = 2681.8(5) A3, Z = 4, R1 = 0.0659, wR2 = 0.1318, GOOF = 1.003. Complex II crystallizes as the orthorhombic space group Pbca with unit cell dimensions a = 19.958(1), b = 13.600(1), c = 22.8713(2) A, V = 6192.3(8) A3, Z = 8, R1 = 0.0550, wR2 = 0.1008, GOOF = 1.074. X-ray analysis indicates that the complexes are mononuclear oxovanadium(V) species with the V atoms in octahedral coordination. The complexes were evaluated for their antibacterial (Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas fluorescence) and antifungal (Candida albicans and Aspergillus niger) activities by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) method. Interestingly, complex II has strong activity against S. aureus.

Characterization and X-Ray Structures of Oxovanadium(V) Complexes Derived from Hydrazone Ligands

The reaction of [VO(acac)2] (where acac = acetylacetonate), benzohydroxamic acid (HL) with N′-(3,5-dichloro-2-hydroxybenzylidene)nicotinohydrazide (H2L1) and N′-(2-hydroxy-4-methoxybenzylidene)-3-nitrobenzohydrazide (H2L2) in methanol affords methanol-coordinated mononuclear oxovanadium(V) complexes [VOL1L] (1) and [VOL2L]·MeOH (2), respectively. Crystal and molecular structures of the complexes are determined by the single crystal X-ray diffraction method. The complexes were further characterized by the elemental analysis and FT-IR spectra. Single crystal X-ray structural studies indicate that the hydrazone ligands coordinate to the VO core through enolate oxygen, phenolate oxygen, and azomethine nitrogen atoms, and the benzohydroxamate ligands coordinate to the VO core through the carbonyl oxygen and hydroxy oxygen atoms. The V atoms in the complexes are in the octahedral coordination. The thermal stability of the complexes are also studied.

Mononuclear oxovanadium(IV) Schiff base complex: Synthesis, spectroscopy, electrochemistry, DFT calculation and catalytic activity

A new complex of oxovanadium, VOL has been synthesized from Schiff base ligand obtained by the condensation of o-phenylenediamine and 5-bromo-salicylaldehyde. All new compounds have been characterized by 1H NMR, IR spectra, UV–Vis spectroscopy, elemental analysis and mass spectrometry. The molar conductance data revealed that the metal complex is a non-electrolyte. Thermal analysis techniques (TGA/DTA) of the ligand and the complex were performed. The proposed structures for the free ligand and the corresponding vanadium complex were corroborated by the use of geometry optimization and conformational analysis. The solid state structure of complex VOL was fully determined by single crystal X-ray diffraction analysis.Similar electrochemical behavior for both the ligand and the corresponding complex have been observed by cyclic voltammetry (CV). The complex gave a metal-based one-electron quasi-reversible redox couple at 606 mV/SCE corresponding to the VOIV/VOV redox process which was consistent with the hydrodynamic voltammograms. Additional peaks in the CVs that were growing with the scan rate have been attributed to consecutive one-electron reduction of the ligand. The catalytic activity of the oxovanadium Schiff base complex VOL was tested in the oxidation reaction of cyclohexene. The efficiency of the catalyst was influenced by the nature of the oxidant. The results showed that the complex was highly active and selective for cyclohexenone in optimized conditions.

Paramagnetic Mononuclear Oxovanadium(IV) Complex as Oxidation Catalyst

Paramagnetic Mononuclear Oxovanadium(IV) Complex as Oxidation Catalyst

Oxovanadium(IV), cerium(III), thorium(IV) and dioxouranium(VI) complexes of 1-ethyl-4-hydroxy-3-(nitroacetyl)quinolin-2(1H)-one: Synthesis, spectral, thermal, fluorescence, DFT calculations, antimicrobial and antitumor studies

A new series of mononuclear oxovanadium(IV), cerium(III), thorium(IV) and dioxouranium(VI) complexes of a quinolinone ligand; 1-ethyl-4-hydroxy-3-(nitroacetyl)quinolin-2(1H)-one (H2L) have been synthesized. The metal complexes were characterized by different techniques such as elemental and thermal analyses, IR, 1H NMR, electronic, ESR, mass spectra and powder XRD, TEM in addition to magnetic susceptibility and conductivity measurements. The quinolinone ligand acts as a dibasic bidentate ligand forming mononuclear complexes, which can be formulated as: [(L)VO(H2O)2]·0.5H2O, [(L)M(NO3)x(H2O)y]·nH2O; M = Ce or Th, x = 1 or 2, y = 3 or 4 and n = 2 or 7 and [(L)UO2(H2O)x(MeOH)y]·nH2O; x = 2 or 3, y = 0 or 1 and n = 0.5 or 2.5. The photoluminescent properties of the prepared complexes were studied. The ligand and its thorium(IV) complex are characterized by an intense green emission. Kinetic parameters (Ea, A, ΔH, ΔS and ΔG) of the thermal decomposition stages have been evaluated using Coats–Redfern equations. The geometry of the ligand and its oxovanadium(IV) complex has been optimized using density functional theory (DFT). Total energy, energy of HOMO and LUMO, dipole moment and structure activity relationship were performed and confirmed practical antimicrobial and antitumor results. The antimicrobial activity of the ligand and its metal complexes was conducted against the microorganisms S. aureus, K. pnemonia, E. coli, P. vulgaris and C. albicans and the MIC values were determined. The antitumor activity of the ligand and its metal complexes was investigated against human Hepatocelluar carcinoma and human breast cancer cell lines.

Mononuclear oxovanadium(Iv) complex containing VO(ONS) basic core: Synthesis, structure, thermal gravimetric analysis, and catalytic property

ABSTRACTReaction of vanadyl(IV)-acetylacetonate with 3-ethoxy-2-hydroxybenzaldehyde 4-methylthiosemicarbazone and 2,2′-bipyridyl in methanol affords a mononuclear oxovanadium(IV) complex containing VO(ONS) basic core. The complex has been characterized by various physicochemical techniques (UV–Vis, IR, and elemental analysis), and single-crystal X-ray diffraction. X-ray crystal structure determination reveals that the complex crystallizes as triclinic space group P, with unit cell dimensions a = 10.073(2) Å, b = 11.272(3) Å, c = 11.338(3) Å, α = 87.291(2)°, β = 83.440(2)°, γ = 64.003(2)°, V = 1149.5(5) Å3, Z = 2, R1 = 0.0356, wR2 = 0.0867, S = 1.052. The V atom in the complex is octahedrally coordinated, with the tridentate ONS ligand occupying the meridional sites. The nitrogen donor of 2,2′-bipyridyl ligand, occupying an apical position has a trans-labilizing influence, resulting in elongation of the V=O terminal bond. Thermal gravimetric analysis was performed to understand the stability of the complex. The complex shows high catalytic property and selectivity in the epoxidation of cyclohexene with t-butylhydroperoxide as oxidant.

Substituent group effects on the self-assembly of oxovanadium(V) complexes with hydrazone ligands bearing benzoic acid (1-methyl-3-oxobutylidene)hydrazide backbones

An oxo-bridged dinuclear oxovanadium(V) complex, [V2O2(μ-O)(L1)2] (1) [H2L1 = 3-nitrobenzoic acid (1-methyl-3-oxobutylidene)hydrazide], and a mononuclear oxovanadium(V) complex, [VO(OMe)(L2)] (2) [H2L2 = 3-hydroxynaphthalene-2-carboxylic acid (1-methyl-3-oxobutylidene)hydrazide], were prepared by the reactions of [VO(acac)2] with H2L1 and H2L2, respectively, in methanol. Both complexes were characterized by elemental analysis, IR spectra, and single crystal X-ray crystallography. The crystal of 1 crystallizes in the monoclinic space group P2/n, with a = 13.116(3) A, b = 7.597(2) A, c = 13.927(2) A, β = 104.851(2)°, V = 1341.4(5) A3, Z = 2. The crystal of 2 crystallizes in the triclinic space group \(P\overline 1 \), with a = 7.897(2) A, b = 9.690(2) A, c = 11.576(3) A, α = 86.405(2)°, β = 70.597(2)°, γ = 85.991(2)°, V = = 832.7(3) A3, Z = 2. The V atoms in the complexes have square pyramidal environment. The substituent groups attached to the aromatic rings can influence the self-assembly of the complexes.

Synthesis, characterization and crystal structures of oxovanadium(V) complexes derived from similar aroylhydrazone ligands

Reaction of [VO(acac)2] (acac = acetylacetonate) with N’-(5-chloro-2-hydroxybenzylidene)-3-methoxybenzohydrazide (H2L1) and N’-(2-hydroxy-4-methoxybenzylidene)-4-nitrobenzohydrazide (H2L2) in methanol affords methanol-coordinated mononuclear oxovanadium(V) complexes, [VOL1(OMe)(MeOH)] (1) and [VOL2(OMe)(MeOH)] (2), respectively. The complexes were characterized by elemental analysis, FT-IR, 1H NMR and 13C NMR spectra. Crystal and molecular structures of the complexes were determined by single crystal X-ray diffraction method. Single crystal X-ray structural studies indicate that the hydrazone ligands coordinate to the VO core through enolate oxygen, phenolate oxygen and azomethine nitrogen. The V atoms in the complexes are in octahedral coordination. Thermal stabilities of the complexes have also been studied. KEY WORDS: Oxovanadium complex, Aroylhydrazone ligand, Crystal structure, X-ray diffraction, Thermal property Bull. Chem. Soc. Ethiop. 2015, 29(3), 423-430. DOI: http://dx.doi.org/10.4314/bcse.v29i3.10

Synthesis and X-ray structures of di- and mono-nuclear oxovanadium(V) complexes derived from aroylhydrazones

A new methanolato-bridged dinuclear oxovanadium(V) complex [VO(L)(OMe)]2 (I) derived from N'-(2-hydroxy-5-methylbenzylidene)-2-methylbenzohydrazide (H2L) and a new mononuclear oxovanadium(V) complex [VO(L')(OMe)(MeOH)] (II) derived from 3-chloro-N'-(2-hydroxy-3-methylbenzylidene)benzohydrazide (H2L') were prepared and characterized by infrared spectra and single crystal X-ray determination (CIF files CCDC nos. 974793 (I) and 974792 (II)). Complex I crystallizes as triclinic space group P\(\overline 1 \) with unit cell dimensions a = 8.5063(4), b = 9.5367(4), c = 11.2445(5) A, α = 71.740(1)°, β = 72.341(1)°, γ = 74.509(1)°, V = 810.37(6) A3, Z = 1, R1 = 0.0527, wR2 = 0.1316, S = 0.969. The complex possesses a crystallographic inversion center symmetry between two V atoms. Complex II crystallizes as triclinic space group P\(\overline 1 \) with unit cell dimensions a = 7.4257(3), b = 9.9475(4), c = 13.1021(5) A, α = 71.954(1)°, β = 85.657(1)°, γ = 84.127(1)°, V = 914.38(6) A3, Z = 2, R1 = 0.0365, wR2 = 0.0957, S = 1.039. The tridentate aroylhydrazone ligands coordinate to the V center through azomethine nitrogen, phenolate oxygen, and enolate oxygen. The V atoms in the complexes are in octahedral coordination. Crystal structures of the complexes are stabilized by hydrogen bonds and π···π interactions.

Synthesis, crystal structure, and preliminary antibacterial activity of oxovanadium(V) complex with hydrazone ligand

A new mononuclear oxovanadium(V) complex, [VOL(OMe)(MeOH)] (I), where L is the dianionic form of (1H-indol-3-yl)acetic acid [1-(2-hydroxynaphthalen-1-yl)methylidene]hydrazine, has been synthesized and characterized by physico-chemical methods and single crystal X-ray determination, (CIF file CCDC no. 858861). The complex crystallizes in the triclinic space group \(P\bar 1\) with unit cell dimensions a = 10.117(1), b = 10.609(2), c = 11.454(2) A, α = 99.228(2)°, β = 112.250(2)°, γ = 100.561(2)°, V = 1082.3(3)A3, Z = 2, R1 = 0.0512, and wR2 = 0.1045. The V atom in complex I is in an octahedral coordination. Thermal analysis and preliminary antibacterial activity of complex I were studied.

Pyridoxal based ONS and ONO vanadium(V) complexes: Structural analysis and catalytic application in organic solvent free epoxidation

A series of dinuclear and mononuclear oxovanadium(V) complexes containing tridentate Schiff base ligands derived from pyridoxal and appropriate thiosemicarbazide or hydrazide are reported. The compounds were characterised by elemental analysis, thermogravimetric analysis, IR and NMR spectroscopy. The molecular structure of the dioxido-vanadium(V) complex [VO2(HL5)]·MeOH·H2O (H2L5=pyridoxal benzhydrazido ligand), determined by X-ray crystallography, reveals an unexpected distorted trigonal bipyramidal arrangement of the VO2 moiety. A DFT study of this molecule and of the related [VO2(H2L5)] complex of VIV reveals a moderate effect of the oxidation state change on the bond distances and angles, pointing to solvation as the cause of the structural distortion. All complexes were tested as (pre) catalysts for olefin epoxidation by aqueous tert-butylhydroxyperoxide (TBHP) under solvent-free conditions. Low vanadium loadings (0.05% vs. olefin) resulted in good cyclooctene conversions and TOFs. The lifetime of one catalyst was explored through repeated runs with recovery/recycling. DFT calculations have also addressed the olefin epoxidation mechanism, which reveals the possible direct O atom transfer from the activated tert-butoxido (tBuOO–) ligand, without the need to generate a peroxido (O22–) ligand.

Synthesis and X-ray Structures of Di- and Mono-Nuclear Oxovanadium(V) Complexes Derived from Aroylhydrazones

Synthesis and X-ray Structures of Di- and Mono-Nuclear Oxovanadium(V) Complexes Derived from Aroylhydrazones

Synthesis, structural characterization and spectroscopy studies of new oxovanadium(IV, V) complexes with hydrazone ligands

The reaction of vanadyl acetoacetonate, VO(acac)2, with 2-hydroxybenzaldehyde hydrazone in ethanol gave the mononuclear oxovanadium(IV) complex [VO(salh1)2] (1). However, when the hydrazides 3-hydroxy-2-naphthoic acid hydrazide (h2) and 5-phenylisoxazole-3-carboxylicacidhydrazide (h3) were used, the mononuclear oxoethoxovanadium(V) complexes [VO(acanh2)(OEt)] (2) and [VO(acanh3)(OEt)] (3) were isolated, respectively. The reaction with benzene-1,4-dicarbohydrazide (h4) in a water–ethanol solution gave polynuclear {[VO(μ-EtO)2](μ-acanh4)}n (4). The complexes were characterized by elemental analysis, IR, UV–Vis and 51V NMR spectra. Magnetic susceptibility measurements indicated the +5 vanadium oxidation state in 2, 3 and 4 and +4 in 1. X-ray single crystal diffraction studies revealed that the vanadium(V) center has a distorted square pyramidal geometry in 2 and 3, and a distorted octahedral geometry in 4, with an O3N coordination environment around the V(V) acceptor center. Complex 4 is a polymeric compound with dihydrazide ligand as a linker and each two vanadium ions are connected via two μ-ethoxo bridges.