Binuclear chelates of diethylenetriamine-Pentaacetic acid with chromium(III) and oxovanadium(IV) ions

The reactions of diethylenetriaminepentaacetic acid (DTPA=H₅L) or chromium(III)-DTPA, a ‘chelating agent’, with oxovanadium(IV) were investigated in aqueous solution by potentiometric methods. Homo- and hetero-binuclear species were evidenced as well as mixed complexes with hydrogen or hydroxide ions. The stability constants for these equilibria were calculated in 1.0 mol 1^?1 NaClO₄ solution at 20?C. The mononuclear (VO)H₃L·H₂O and the heterobinuclear (VO)CrL·5H₂O complexes were also obtained as solid compounds and were characterized by IR spectroscopy and thermoanalytical techniques (TG and DSC).     

Sulphoxide complexes of oxovanadium(IV) chloride and oxovanadium(IV) sulphate

Summary Ten complexes of VOCl₂ and VOSO₄ with several aliphatic and aromatic sulphoxides were prepared and studied systematically. Three were reported previously, and we have extended studies of them. The isolated complexes were characterized by elemental analysis, conductivity, thermal analysis, i.r. and electronic spectroscopy.     

Thermoanalytical studies of oxovanadium(IV)hydroxamate complexes

The thermal decomposition behavior of oxovanadium(IV)hydroxamate complexes of composition [VO(acac)(C₆H₅C(O)NHO)] (I), [VO(C₆H₅C(O)NHO)₂] (II), [VO(acac)(4-ClC₆H₄C(O)NHO)] (III), [VO(4-ClC₆H₄C(O)NHO)₂] (IV) (where acac = (CH₃COCHCOCH₃ ^–) synthesized from the reactions of VO(acac)₂ with equi- and bimolar amounts of potassium benzohydroxamate and potassium 4-chlorobenzohydroxamate in THF + MeOH solvent medium has been studied by TG and DTA techniques. TG curves indicated that complexes I, II, and IV undergo decomposition in single step to yield VO₂ as the final residue, while complex III decomposes in two steps to yield VO(acac) as the likely intermediate and VO₂ as the ultimate product of decomposition. The formation of VO₂ has been authenticated by IR and XRD studies. From the initial decomposition temperatures, the order of thermal stability for the complexes has been inferred as IV > I > III > II.     

Synthesis and properties of the binuclear vanadium(III) and oxovanadium(IV) chelates with tetradentate schiff bases

The complexes of vanadium(III) and oxovanadium(IV) with Schiff bases derived from some aliphatic diamines and 2-hydroxy-1-naphthaldehyde were prepared and characterized by elemental analysis, IR, electronic and EPR spectra. The binuclear V^III complexes have the [V₂(μ-oxo)(μ-aquo)] core in distorted octahedral environments. The VO^IV complexes form monomeric, dimeric or polymeric complexes by ligand bridging. The structures are dependent on the length of the carbon chain linking the imine groups. A complex EPR signal is observed for [VO(naphbu)]₂ in chloroform solution at room temperature, its isotropic spectrum exhibits a 15 line hyperfine signal at g_av = 2.014 and the hyperfine coupling constant is 50 G, suggesting that the centres are weakly coupled. The reactions of the binuclear V^III complexes with dioxygen and VO^IV complexes with thionylchloride were also studied.     

Binary and ternary complexes of oxovanadium(IV) and homobinuclear double-bridged oxovanadium(IV) complexes

Summary Binary and ternary complexes of oxovanadium(IV) with salicylaldehyde and/or 2-hydroxy-1-naphthaldehyde were prepared and additional homobinuclear doublybridged oxovanadium(IV) complexes were obtained from the reaction products ofmeta-orpara-phenylenediamine withortho-hydroxy aromatic aldehydes (bridging Schiff base). The complexes were characterised by elemental analysis, and by spectral and magnetic studies.     

Synthesis and magnetic studies of phthalato-bridged oxovanadium(IV) binuclear complexes

Six new μ-phthalato binuclear oxovanadium(IV) complexes, namely [(VO)₂(PHTH)-(L)₂]SO₄ (L denotes 2,2′-bipyridine (bpy); 1,10-phenanthroline (phen); 4,4′-dimethyl-2,2′-bipyridine (Me₂ bpy); 5-nitro-1,10-phenanthroline (NO₂-phen); 5-chloro-1,10-phenanthroline (Cl-phen) and 5-methyl-1,10-phenanthroline (CH₃-phen), where PHTH is the phthalate dianion), have been synthesized and characterized by elemental analyses, IR, electronic spectra, magnetic moments at room temperature and molar conductivity measurements. The temperature dependence of the magnetic susceptibility of complexes [(VO)₂(PHTH)(phen)₂]SO₄ (1) and [(VO)₂(PHTH)(CH₃-phen)₂]SO₄ (2) was measured in 4—300 K range and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, ?=?2J?₁·?₂, giving the exchange integrals J=?12.8 cm^?1 for 1 and J=?7.9 cm^?l for 2. This indicates an antiferromagnetic spin-exchange interaction between the metal ions within each molecule.     

Vanadium (III), oxovanadium (IV) and oxovanadium (V) trifluoro-methanesulfonates

V(SO₃CF₃)₃, VO(SO₃CF₃)₂ and VO(SO₃CF₃)₃ have been prepared by reacting V(O₂CCF₃)₃, VO(O₂CCF₃)₂ and VOC1₃ with HSO₃CF₃. The i.r. data suggest a bridging bidentate nature for SO₃CF₃ groups. The diffuse reflectance spectrum of V(SO₃CF₃)₃ suggests hexacoordination of vanadium, whilst that of VO(SO₃CF₃)₂ is comparable to either five or six coordinated oxovanadium (IV) systems. The magnetic moments of V(SO₃CF₃)₃ and VO(SO₃CF₃)₂ are slightly lower than the spin-only values. Thermal decomposition of these triflates is simple. All the three triflates form coordination complexes with pyridine, 2, 2′-bipyridyl and triphenylphosphine oxide.     

Complexes of oxovanadium(IV) with polyaminocarboxylic acids

The stability constants for a series of oxovanadium(IV) complexes of polyaminocarboxylic acids were determined by potentiometry. The values obtained are almost equal to those of the corresponding nickel(II) complexes. The complexes formed by terdentate and quadridentate ligands contain 2 and 1 co-ordinated water molecules, respectively. These dissociate at pH ~4 in the first case, to give dimers-(VO)(2)(OH)(2)L(2),-and at about pH ~7, in the second case, to give the mononuclear hydroxo species VO(OH)L. Hydrolysis of the 1:1 aquo-complexes is preferred to the formation of 2:1 ligand: metal complexes even in the presence of a 10-fold molar excess of ligand. These results are of interest for better understanding of the behaviour of oxovanadium(IV) in biological systems.     

Spectrophotometric and potentiometric determination of the protonation constants of dithiocarbazates and studies on some of their metallic chelates

The protonation constants of 2-methyldithiocarbazate, 3,3-dimethyldithiocarbazate and 3-methyl-3-phenyldithiocarbazate, have been determined potentiometrically (I = 1.00M) and spectrophotometrically (I = 0.01M) at 25 degrees in aqueous solution. The analytical properties of the reagents have been studied, and also the compositions of some of their insoluble metallic chelates.     

pH-Metric studies on the binary and ternary complexes of oxovanadium(IV)

The interaction of oxovanadium(IV) with some hydroxy acids, salicylic (SA), 5-sulphosalicylic (SSA) and 8-hydroxyquinoline-5-sulphonic (HQSA) acids, has been studied potentiometrically. Further, pH-metric studies of the ternary systems, VO²⁺?HQSA-dicarboxylic or hydroxy acids (where dicarboxylic acids = phthalic and maleic acids and hydroxy acids =SA andSSA) have been carried out and the formation of 1∶1∶1 mixed complexes inferred from the potentiometric curves. The equilibrium, chelate formation and hydrolysis constants have been calculated in the case of binary systems. The ternary complexes have been found to be more stable as indicated by their formation constants.     

Synthesis,physico-chemical and biological studies on oxovanadium(IV) derivatives of mercaptotriazoles

Summary Complexes of 3-methyl- or 3-ethyl-4-amino-5-thiolato-1,2,4-triazole (LH) and its Schiff base derivatives with oxovanadium(IV), of the types [VOL₂(H₂O)], [VOL₂-(H₂O)] and [VOL(H₂O)₂] (where LH = Schiff bases derived from condensation of LH with benzaldehyde, 2-chlorobenzaldehyde, 4-methoxybenzaldehyde or acetophenone; LH₂ = Schiff bases derived from condensation of LH with salicylaldehyde or o-hydroxyacetophenone) have been prepared and characterized by elemental analyses, electrical conductance, magnetic moments and spectral data. The thermal behaviour of selected complexes was investigated by t.g., d.t.g. and d.s.c. techniques. The antifungal and antiviral activities of the Schiff bases and their corresponding complexes were also investigated.Author to whom all correspondence should be directed.     

Complexes of oxovanadium(IV) with cyclic nitrogen-containing ligands

Summary Five complexes were prepared containing VOSO₄ and the ligands 4-aminopyridine (4-APY), 3-aminopyridine (3-APY), 2-aminopyridine (2-APY), 2-aminopyrimidine (2-APYM), and aniline (AN). Complexes of 4-APY and AN did not react with orthophenanthroline (o-phen) and dipyridyl (dipy); the others did react, however, giving similar products. Spectroscopic evidence shows that bonding occurs preferably through an endocyclic nitrogen whenever the ligand possesses more than one type of nitrogen atom.The shift in (VO) upon complexation seems to depend both on the basicity of the ligands as well as on the coordination number of the metal atom. The electronic spectra show two absorptions for the complexes with monodentate ligands and three absorptions for those with bidentate ligands. The former are thought to haveC ₁ symmetry whereas the latter are likely to beC _s species.     

Spectrophotometric determination of hydrogen peroxide by using the cleavage of Eriochrome black T in the presence of peroxidase

A new hydrogen donor for peroxidase, Eriochrome black T, was reported for the first time. Steady-state catalytic velocity depends upon enzyme and substrate concentrations, and a Michaelis-Menten K(m) value of 1.72x10(-5) mol l(-1) and a V(max) value of 4.43x10(-3) s(-1) were measured at pH 8.6. Trace amount of hydrogen peroxide (2x10(-7)-1.0x10(-5) mol l(-1)) was determined in aqueous solution by using the cleavage of Eriochrome black T catalyzed by peroxidase. The method is simple and practical, with high sensitivity and enzymatic activity.     

Interactions between oxovanadium (IV), glycylvaline and imidazoles: An aqueous potentiometric and spectroscopic study

Speciation has been determined in aqueous oxovanadium, glycylvaline and imidazoles at 25 ± 1°C and μ = 0.1M NaClO₄ using a combination of potentiometry, and visible and EPR spectroscopy. Results of potentiometric and spectroscopic methods are consistent. Calculations of stability constants have been made using the SCOGS computer program.     

Mixed-ligand and binuclear complexes of oxovanadium(IV)

Summary Mixed ligand complexes of the type [VOLA]ClO₄ where L=5-bromosalicylaldehyde (L) or 5-nitrosalicylaldehyde (L) and A=2, 2-dipyridyl (A) or 1, 10-phenanthroline (A) have been prepared. Treatment of the mononuclear complexes, [VOLA]ClO₄, withp-phenylenediamine (ppd) orm-phenylenediamine (mpd) yielded homobinuclear [VOLA-NC₆H₄N-LAVO](ClO₄)₂, complexes, which were characterised by elemental analyses, spectra, magnetic susceptibility and molar conductance measurements.     

Ferromagnetic oxovanadium(IV) complexes chelated with tetrahalosalen ligands

Five oxovanadium(IV) complexes [VO(X₄salen)] have been prepared and characterized, where each benzene ring was substituted with two halogen atoms in salen (H₂salen = N,N′-disalicylideneethylenediamine). The X-ray diffraction study on 3,3′,5,5′-tetrachloro-, 3,3′,5,5′-tetrabromo-, and 4,4′,6,6′-tetrachlorosalen derivatives clarified their polymeric structure with the (-VO-)_n repeating unit. The interatomic V···V distances are 3.710(3), 3.695(3), and 3.749(3) Å, respectively, being shorter than that of known [VO(salpn)] (3.83 Å; H₂salpn = N,N′-disalicylidenepropylenediamine). The exchange coupling parameters (J) were determined by fitting the magnetic susceptibility data to the one-dimensional ferromagnetic model, giving 2J/k_B = 8.2-16 K, which are the largest in the [VO(salen)] and [VO(salpn)] family.     

Epr studies of copper(II) and oxovanadium(IV) dithiophosphate complexes in the solid state

A single crystal of Cu(dtp)₂ and numerous powdered copper(II) and oxovanadium(IV) dithiophosphate complexes magnetically diluted in the corresponding Ni and In complexes have been prepared and studied by EPR. It was shown that the values of A(³¹P) for all complexes are isotropic.Some assumptions about the origin of superhyperfine splitting in the EPR spectra of the complexes are discussed.     

Thermal decomposition of oxovanadium(IV) complexes with substituted pyridines

The kinetics of decomposition of solid complexes of bis(dibenzoylmethanato) oxovanadium(IV) with pyridine and several methyl, dimethyl and aminopyridines has been studied using differential scanning calorimetry. Activation energies have been determined and, in general show an increase with increasing basicity of the ligands. A linear relationship exists between pK_b values of the bases and the temperatures for the decomposition, except for the complexes obtained with 4 aminopyridine and 4 methylpyridine. These complexes are less stable than expected from the basicity of the ligands. These observations are discussed in terms of the nature of the metalligand bond.     

Spectroscopic and equilibrium studies of adduct formation between sulfoxides and bis(2,4-pentanedionato)oxovanadium(IV)

The adducts formed between VO(acac)₂ and a number of alkyl and aryl sulfoxides in dichloromethane were investigated by means of visible and IR spectroscopy. The sulfoxides all interact with the vanadium of the VO(acac)₂ via their oxygen atoms to form weak adducts with formation constants (2.4 < K_f < 6.4) which show a linear correlation with the pKa values found for these sulfoxides in aqueous H₂SO₄.