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Oxovanadium(IV) complexes, [VO(J-R)], where H2J-R is a Jager-type ligand with bridging group R (ethylene o-phenylene or 4-methyl-o-phenylene), have been synthesized. Condensations of the complexes with diamines give products but as sticky, insoluble materials. An alternative method has been used to obtain cyclic oxovanadium(IV) complexes.

Reactions of arylazobenzaldoxime, RC(=NOH)NNPh (HL), where R = CH3, Ph, ρ-ClC6H4, ρ-(CH3O)C6H4, ρ-(CH3)C6H4, ρ-(O2N)C6H4, with vanadyl sulfate pentahydrate in methanol/sodium methoxide yielded complexes with the general formula [VO(L)2].nH2O where n = 1–2. These complexes were characterized by elemental analyses, conductivity measurements, magnetic susceptibility, IR and 1H NMR data. Dimeric structures with strong vanadium-vanadium interaction have been proposed.

Fluoro-substitution in the phenyl ring of some β-(4-alkoxyphenyl)-dialdehydes markedly affects the mesophase behaviour of their copper(II) and oxovanadium(IV) complexes. Fluoro-substitution in the 2-position of the octyl and decyl copper(II) derivatives lowers melting and clearing temperatures, whereas substitution in the 3-position lowers only the former. Fluoro-substitution in the 2-position ofthe corresponding oxovanadium(IV) complexes usually lowers the melting point, but inhibits mesophase formation.

New tetradentate Schiff base−oxovanadium(IV) complexes, [VO{3-Xsal-(R,R)-2,4-ptn}] (H2{3-Xsal(R,R)-2,4-ptn}: N,N‘-di-3-Xsalicylidene-(R,R)-2,4-pentanediamine; X = EtO (ethoxy), MeO (methoxy), and H) were prepared and characterized. Only an orange polymeric form was obtained for the 3-methoxy and nonsubstituted (X = H) complexes. Both orange polymeric (1) and green monomeric (2) crystals were obtained for the 3-ethoxy substituted complex. X-ray structure analyses of 1 and 2 were carried out. Crystal data: [VO{3-EtOsal-(R,R)-2,4-ptn}]·H2O (1), VO6N2C23H30, orthorhombic, P212121, a = 13.764(4) A, b = 21.544(4) A, c = 7.682(5) A, Z = 4; [VO{3-EtOsal-(R,R)-2,4-ptn}] (2), VO5N2C23H28, orthorhombic, P212121, a = 10.393(2) A, b = 22.278(2) A, c = 9.886(2) A, Z = 4. The orange crystals (1) have water of crystallization, and the complexes take a polynuclear linear chain structure (···VO···VO···) with a six-membered N−N chelate ring in a chair form. The green crystals (2) have no water of crystallization, and the ...

In the reaction of bis(1,3-di­phenyl-1,3-propane­dionato)­oxovanadium(IV) with pyridine, a 1:1 adduct is formed, viz bis(1,3-di­phenyl-1,3-propane­dionato-κ2O,O′)­oxo­(pyridine-κN)­vanadium(IV), [V(C15H10O2)2O(C5H5N)]. The V atom is surrounded by one pyridine ligand, two 1,3-di­phenyl-1,3-propandionate (dbm) ligands and one oxo group. The complex exhibits a distorted octahedral coordination, with the oxo group and pyridine ligand in a cis configuration. Pairs of mol­ecules of the adduct are connected by an intermolecular C41—H41⋯O1(−x, 2 − y, 1 − z) contact of 3.171 (3) A and thus form dimers in the solid state.

The synthesis and characterization of the title VIV complex of a salicyl­ald­imine, [V(C20H14N2O4)O]·2C2H6OS·2H2O, is described. The reaction of 2,4-di­hydroxy­benz­aldehyde and 1,2-phenyl­enedi­amine with vanadyl sulfate produces a monomeric VIV complex. Its structure reveals that the vanadium(IV) ion is pentacoordinated and situated in a distorted square-pyramidal environment.

The oxovanadium(IV) complexes LVO and L′VO (L = dianion of 5,14-dihydro-6,8,15.17- tetramethyldibenzo[b.i][1,4.8,11]tetraazacyclotetradecine. H2L, and L′ = dianion of 5,14-dihydro-6,15-dimethyl-8,17-diphenyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine, H2L′) are redox active as indicated by cyclovoltammetric measurements and confirmed by preparative methods: Reversible oxidation to the corresponding oxovanadium (V) cations is observed at ca. 0.35 V vs. SCE in CH2Cl2, and these cations are prepared in high yield by oxidation of the oxovanadium(IV) precursors with [(C5H5)2Fe]SbF6 (reversible by addition of cobaltocene). Irreversible reduction waves are observed for both complexes in the range -1 .9 to 2.1 V vs. SCE in CH2Cl2. Preparative reduction of LVO with Na/K alloy affords very unstable anionic oxovanadium(IV) complexes containing a deprotonated or reduced ligand, while with Li[B(C2H5)3H] in THF the Lewis acid/Lewis base adduct LVOxB(C2H3)3 is isolated. Spectroscopic data including ESR [vanadium(IV)] and 51V NMR [vanadium(V)] are given and discussed. The complexes LVO and [LVO]SbF6 have been characterized by single crystal Xray structure determinations.

A series of novel hexa-coordinated mixed-ligand complexes of oxovanadium(IV) of the general formula [VO(acac)2(L)], where acacH-acetylacetone and L = MPHP, DMMASPHP, ADMPHP, CODPHS, 2, 6-XYL, 2-HMP, 3-HMP or 4-HMP has been synthesized. The complexes have been obtained by refluxing the parent compound [VO(acac)2] with the corresponding ligand, L, in alcohol. The complexes, are thermally stable and behave as non-electrolytes. A distorted trans-octahedral structure has been proposed for these complexes.

The coordination structures of various species in aqueous solutions of oxo-vanadium(IV) + derivatives of l -histidine (1) and related ligands (3-methyl- l -histidine, 1-methyl- l -histidine, l -histidine methyl ester, l -histidinol, Nα- acetyl- l -histidine and histamine) have been studied by investigating the pH dependence of the circular dichroism, isotropic absorption and electron spin resonance spectra, and are compared with the structures of the corresponding complexes of l -histidine. Comparison of the spectroscopic results for all systems studied indicates coordination geometries.

A vanadium(IV) complex VO(sal-glygly)(H 2 O) n ( 1 )(sal-glygly  N-salicylideneglycylglycinate; n = 1.5−3.0) has been isolated from relatively concentrated solutions containing oxovanadium(IV), glycylglycine and salicylaldehyde, and characterized by elemental analysis, thermal (TG and DSC), magnetic and spectroscopic techniques. From similar but dilute solutions the decavanadate, (NH 4 ) 4 (Na) 2 [V 10 O 28 ]·10H 2 O ( 2 ) was isolated after ageing: its structure has been determined by X-ray diffraction analysis. The NH 4 + cations were formed by deamination of the glycylglycine present in solution.

{N, N'-Disalicylidene-(R, R)-1, 2-Biphenyl-1, 2-ethanediamine}oxovanadium(IV) crystallized in two different forms, green (from chlorinated solvents) and orange (from acetonitrile). X-ray structure analyses revealed that the green form contains mononuclear square pyramidal molecules of the complex, while the orange form has a polynuclear linear chain structure. The green crystals turn orange when heated at 120°C for a few minutes. The orange crystals turn green when exposed to chloroform vapor, and the green crystals turn orange when exposed to acetonitrile vapor. The orange complex shows piezochromism (mechanochromism); its color changes to green on grinding.

We studied functional properties of tracheal smooth muscle cells in rats with diabetes mellitus. Reactivity of tracheal smooth muscles increased in rats with experimental alloxan-induced diabetes mellitus. A new complex compound of oxovanadium (IV) and isonicotinic acid hydrazide affected reactivity of tracheal smooth muscles in albino rats with experimental type I diabetes mellitus. This new organic vanadium-containing compound reduced contractility of tracheal smooth muscles in rats and potentiated relaxation of smooth muscle cells in the trachea in response to exogenous nitric oxide.

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Curcumin (Hcur) as a cellular imaging and PDT agent shows remarkable photocytotoxicity in HeLa cells in visible light of 400-700 nm giving IC(50) = 8.2 ± 0.2 μM and its degradation is arrested on formation of photocytotoxic dipyridophenazine (dppz) complex [VO(cur)(dppz)Cl] (IC(50) = 3.3 ± 0.4 μM), while both are less toxic in the dark.

New mixed-ligand complexes of oxovanadium(IV) of the general formula [VO(C2O4)(o-PDA)], where o-PDA = o-phenylenediamine, and [VO(C2O4)(L)2], where L = N-methylaniline (NMA), N,N′-dimethylaniline (NNDMA), N,N′-diethylaniline (NNDEA), o-toluidine (o-TD), m-toluldine (m-TD), o-anisldine (o-ANS), m-anisidine (m-ANS), o-phenetidine (o-PD) or m-phenetidine (m-TD) have been synthesized by refluxing (oxalato) (diaquo)oxovanadium(IV) with the said aromatic amines. The resulting complexes have been characterized on the basis of elemental analyses, vanadium determination, molar conductances, magnetic measurements and infrared spectral studies. Rectangular-pyramidal structures are likely for these complexes. Referee I: D. H. Williams Referee II: J. H. Worrell

The isomerization between the two diastereomers of [VIVO{3-MeOsal,sal-(RR)-chxn}] (H2{3-MeOsal,sal-(RR)-chxn} = N-salicylidene-N′-3-methoxysalicylidene-(RR)-1,2-cyclohexanediamine) in acetonitrile-water(95:5 v/v) was observed under aerobic conditions. The reaction was accelerated by the addition of [VVO(salen)]ClO4 (H2salen = N,N′-disalicylidene-1,2-ethanediamine), but the complex did not isomerize in dry acetonitrile. The mechanism of the isomerization was investigated.

V02+ forms complexes of composition VO(L1)EtOH), VO(HL1)2 and VO(HL2)(H2O) with the ithium or sodium salts of 6-droxymethyl-pyridine-2-arboxylic acid (H2L1) and 4,8-hydroxyquinoline-2-carboxylic acid (H3L2). VCl2(salen/salphen) and VCl2(napgly/ nappa) (napgly and nappa are the Schiff bases derived from o-ydroxynaphthaldehyde and glycine or phenylalanine, respectively), prepared from the oxo precursor and SOCl2, react with Li2L1 and the lithium salts of benzilic acid (H2L3) and ortho-ydroxybenzoic acid (H2L4) to yield the non-oxo (“bare”) complexes V(salen)L1 , V(salen)L3, V(salphen)L3, V(salen)L4, V(napgly)L1, V(nappa)L1, and V(nappa)L4. The complexes have been characterized by IR, EPR and elemental analyses. VOCl2(salen) crystallizes in the monoclinic space group Cc, a = 14.579(3), b = 9.537(2), c = 13.453(3) Å, β=120.92(3)°. The molecule exhibits gross distor­tions from octahedral geometry. An improved synthesis for H2L1 is described.

Oxovanadium(IV) complexes of types [VO(L)2(H2O)] and [VO(L′)(H2O)2] (LH = 4-amino-3-mercapto-6-methyl-5-oxo-1,2,4 triazine and its Schiff bases derived from benzaldehyde, 2-chlorobenzaldehyde, 4-methoxybenzaldehyde; L′H2 = Schiff bases derived from 4-amino-3-mercapto-6-methyl-5-oxo-1,2,4 -triazine and salicylaldehyde or o-hydroxyacetophenone) have been synthesized and characterized by elemental analyses, electrical conductance, room temperature magnetic moments, and spectral (electronic, IR and ESR) studies. The complexes are hexa-coordinate and have a distorted octahedral structure. The thermal behaviour of the complexes under nonisothermal condition was investigated by TG and DTG techniques. Referee I: E. A. Mintz Referee II: G. Gordon

We have observed that the presence of some oxovanadium(IV) complexes has a considerable effect on the electrochemical behaviour (O2 → O−2) of the dioxygen molecule, and concluded that there is a weak interaction between the dioxygen molecule and the oxovanadium(IV) ion in the solution. This interaction leads to the shift of reduction potential of the dioxygen molecule to a more positive region than that of the free dioxygen molecule.

Oxovanadium(IV) and oxozirconium(IV) chloride complexes with pyridinaldazine (PAA), pyrrolaldazine (PyAA-H2), furanaldazine (FAA), and thiophenaldazine (TAA) of the composition (MO)m(L)yCln.x-H2O, where M = V, Zr;L = PAA, PyAA-H2, FAA, TAA; m = 1–3; y = 1–3; n = 2, 4, 6; x = 1, 3, 6, 8 have been prepared by the reaction of VOCl2.2H2O or ZrOCl2.6H2O with PAA, PyAA-H2, FAA or TAA and characterized by spectral data, electrical conductance, magnetic susceptibility, thermal and elemental analyses.

In the presence of a catalytic amount of oxovanadium(IV) complexes coordinated with 1,3-diketone ligands, fused aromatic compounds such as naphthalenes and naphthol derivatives are smoothly oxygenated into the corresponding 1,4-naphthoquinones by combined use of molecular oxygen and crotonaldehyde under an atmospheric pressure.

Electrochemical confirmation that (N,N'-ethylenebis(salicylideneaminato))oxovanadium(IV), VO(salen), reacts with trifluoromethanesulfonic acid (CF 3 SO 3 H) or triphenylmethyl tetrafluoroborate (Ph 3 C(BF 4 )) to form a deoxygenated complex, V IV (salen) 2+ , and a μ-oxodinuclear complex, [(salen)VOV(salen)]X 2 , (X=CF 3 SO 3 - or BF 4 - ) is presented. Cyclic voltammograms of VO(salen) in the presence of CF 3 SO 3 H or Ph 3 C(BF 4 ) exhibit reversiblewaves with formal potentials near 0.5 and 0.8 V (vs Ag/AgCl)

The crystal structure of the title compound, [VO(C5H9O3)2(C5H8N2)], has been obtained from single-crystal X-ray diffraction data measured at 150 K. The title compound provides a potential synthon for complexes that model V-containing haloperoxidases. The complex is pseudo-octa­hedral and the metal–oxo bond length is 1.595 (2) A.

The oxovanadium(IV) complex of oxodiacetic acid (H(2)ODA) and o-phenanthroline of stoichiometry [VO(ODA)(ophen)]·1.5H(2)O, which presents the interesting tridentate OOO coordination, was thoroughly characterized by infrared, Raman, and electronic spectroscopies. The biological activity of the complex on the cell proliferation was tested on osteoblast-like cells (MC3T3E1 osteoblastic mouse calvaria-derived cells and UMR106 rat osteosarcoma-derived cells) in culture. The complex caused inhibition of cellular proliferation in both osteoblast cell lines in culture, but the cytotoxicity was stronger in the normal (MC3T3E1) than in the tumoral (UMR106) osteoblasts.

The green crystals of the title compound, [V(C(22)H(18)N(2)O(2))O], represent a mononuclear oxovanadium complex. The central V(IV) centre has a distorted square-pyramidal coordination. Two N atoms and two O atoms of the Schiff base ligand define the base of the pyramid, and the oxide O atom is in the apical position. Density functional theory (DFT) calculations were performed to analyse the changes in the geometry of the ligand during the complex formation. The most significant changes are observed in the values of the torsion angles in the vicinity of the donor N atoms. The HOMA index (Harmonic Oscillator Model of Aromaticity) has been calculated to compare the aromaticity of the benzene rings in the complex and its ligand.

Solvated oxovanadium(IV) complexes of Schiff bases derived from aromatic diamines and 2-hydroxy-1-naphthaldehyde have been prepared from ethanolic medium. The elemental analyses reveal that the complexes have the ratio 1:1, 2:2 and 1:2 (ligand:metal) composition which are nonelectrolyte inDMF. The coordination number six (octahedral geometry) is proposed for the complexes prepared. This is based on the results of IR, electronic and EPR spectra. TGA as well as DTA studies and the electrical properties and (I–V) characteristics for the metal complexes were investigated.

Five new cyclohexylamine and morpholine adducts of oxovanadium(IV) dithiocarboxylates have been isolated. The compounds have been characterized by analytical, magnetochemical, IR and visible-UV spectral methods and are assigned the formula [VO(RCS2)2 B] (B= cyclohexylamine or morpholine and R = n-pentyl, n-hexyl, iso-octyl, cyclohexyl or phenyl). The effect of adduct formation on the πv=0 bond is discussed in terms of the O, V-S and V-N stretching freguencies and d-d transitions.

The synthesis and crystallographic characterization of three oxovanadium(IV) complexes as solvates are reported: (a) [{HB(Me 2 pz) 3 }VOCl(Me 2 pzH)].2MeCN (I.2MeCN), (b) [{HB(Me 2 pz) 3 }VO(benzoate)(Me 2 pzH)].0.4toluene (II-0.4toluene), and (c) [{HB(Me 2 pz) 3 }VO(μ-malonate)VO(Me 2 pzH){HB(Me 2 pz) 3 }]-2toluene (III.2toluene), where Me 2 pz=3,5-dimethylpyrazolyl.

With the goal of making vanadyl-specific ligands, the synthesis of a series of tetraanionic diamidate-diphenolate ligands and their respective oxovanadium(IV) complexes is reported. The strongly σ-donating ligands are constructed on a disubstituted propanediamide backbone, which stabilizes the highly oxidized vanadium(IV) center as evidenced by the remarkably low potential of -0.047 V (vs SCE) for the reversible VO 3+ /VO 2+ redox couple of the oxovanadium(IV) dianion complex.

The two new Schiff base complexes of oxovanadium (IV) [VO(acac-en)] (acac-en = bisacetylactone-ethylenediimino) and [VO(sal-o-phdn)] (sal-o-phdn = N,N′-o-phenylenebis (salicylideneiminato) have been prepared. The infrared spectra of the solid complexes have been obtained and assigned on the bases of Cs symmetry. A polymeric chain structure with V-O-V bridge has been adopted for the both complexes.

Complex formation between oxovanadium(IV) and a series of aliphatic mercaptocarboxylic acids (mercaptoacetic, 2- and 3-mercaptopropionic, 2-mercaptosuccinic, and meso-2,3-dimercaptosuccinic) was studied in aqueous solution by potentiometric and spectroscopic (EPR and electronic absorption) techniques. A comparison with the complexes of the corresponding hydroxycarboxylic acid analogues was also made. The most interesting finding is that VO2+ has a similar affinity to the rather soft thiolate-S donors as to the hard alcoholate-O donors, if these donors are in chelatable position with a hard carboxylate group. The bidentate mercaptocarboxylates form (CO2–, S–)-co-ordinated mono and bis complexes, while bis complex formation is rather hindered with the tridentate 2-mercaptosuccinic acid. Due to the high denticity of the ligand, 2,3-dimercaptosuccinic acid readily forms oligomeric species via the co-ordination of all potential donor groups.

By combined use of molecular oxygen (oxidant) and secondary or primary alcohol (reductant) in the presence of a catalytic amount of bis(2-alkyl-1,3-diketonato)oxovanadium(IV) complexes, norbornene analogues are monooxygenated into the corresponding epoxides in good yields.

In the presence of a catalytic amount of bis(1,3-diketonato)oxovanadium(IV) complex, epoxidation of α,β-unsaturated carboxamides with molecular oxygen and an aldehyde proceeds smoothly at room temperature to give the corresponding 2,3-epoxycarboxamides in good yields.

In the presence of a catalytic amount of oxovanadium(IV) complexes coordinated with 1,3-diketone ligands, fused aromatic compounds such as naphthalenes and naphthol derivatives are smoothly oxygenated into the corresponding 1,4-naphthoquinones by combined use of molecular oxygen and crotonaldehyde under an atmospheric pressure.

A vanadyl complex, bis(6-methylpicolinato)oxovanadium(IV), VO(6MPA), with VO(N2O2) coordination mode, was found to exhibit a normoglycemic effect on KKAy mice with hereditary noninsulin-dependent diabetes mellitus with daily oral administration.

Several novel chiral oxovanadium(IV) complexes have been designed and prepared for the asymmetric catalytic oxidative coupling of 2-naphthols with high enantioselectivities of 83-98% ee.

Complex formation between oxovanadium(IV) and a series of hydroxamic or hydroxamic-like ligands (acetohydroxamic, benzohydroxamic, 2-hydroxypyridine-N-oxide and N-phenyl-benzohydroxamic acids) has been investigated in solution by EPR spectroscopy. VO(IV) complexes involving the ligand-to-metal molar ratio of 2:1 have also been isolated in the solid state. The results show that the simple hydroxamic ligands (acetohydroxamic and benzohydroxamic acids) can undergo two deprotonation processes and thus act as either hydroxamato(1−) or hydroximato(2−) ligands. A similar dissociation pattern is not possible for N-phenyl-benzohydroxamic acid and the hydroxamic-like ligand 2-hydroxypyridine-N-oxide, which are able to yield only a hydroxamato(1−) coordinating anion. All the ligands form hexa-coordinate tris-chelated complexes of V(IV) after displacing the oxo group from VO(IV).

Oxovanadium(IV) phosphates show a diversity of magnetic behaviours that cannot be deduced from their respective structural features only. In part, this is due to the involvement of phosphate bridges in the spin transfer between V(IV) centres, and 31P solid state nuclear magnetic resonance becomes a key tool in determining the exchange mechanisms. The magnetic properties of a wide set of vanadium(IV) containing derivatives can be explained by realizing that a good overlap of the magnetic orbits may be achieved through paths involving phosphorus d orbitals.

EPR spectra of oxovanadium(IV) complexes of some bidentate Schiff bases have been described. Various epr parameters and bonding coefficients have been calculated and discussed.

We report the synthesis and study of bis(xylene-dithiocarboxylate)oxovanadiuum(IV) and its adducts with cyclohexylaraine, piperidine, morpholine, piperazine and pyrrolidine. The compounds have been characterized by analytical, magnetochemical, IR and visible-UV spectral methods and analytical data, and are assigned respectively to the formula VO(C8H9CS2)2 and VO(C8H9CS2)2 B. The effect of adduct formation on the πv=o bond are discussed in terms of the IR (V=o, V-S and V-N stretching frequencies) and electronic spectra (d-d transitions).