Synthesis and characterization of vanadyl(IV) complexes of Schiff bases derived from anthranilic acid and salicylaldehyde (or its derivatives) or acetylacetone. Single crystal X-ray structures of the oxidized products

Anhydrous, dimeric vanadyl(IV) complexes of Schiff bases derived from [1+1] condensation of salicylaldehyde (or its derivatives) and anthranilic acid, have been synthesized from CH3CN and were characterized by elemental analysis, FTIR, EPR, absorption, TGA, cyclic voltammetry and room temperature magnetic susceptibility measurements. These complexes were found to be oxidized by air in polar solvents like MeOH and DMF to V-V products. The E(1/2) values were found to be around 660 mV indicating that the carboxylate group favours vanadyl(IV) binding when compared to the alkoxo-bound vanadium complexes. Oxidative instability of these complexes are dependent on the substituent on the salicylaldehyde ring and follow an order, 5,6-benzo > H greater than or equal to 3-OMe in MeOH and DMF. Attempted recrystallization of the dimeric vanadyl(IV) complex from pyridine led to products of oxidation, polymerization and loss of Schiff base ligand. Single crystal X-ray diffraction showed the oxidation product to be a decavanadate with the pyridinium counter cation, [C5NH6](6) V10O28 . 2H(2)O. When the dinuclear vanadyl(IV) complex was recrystallized from MeOH, it gave a product of mononuclear carboxylate bound octahedral VO3+ moiety along with the presence of both MeOH and OMe units in the coordination sphere with a formula, VO(L)(OMe)(MeOH), where L = 1+1 Schiff base derived from 5,6-benzosalicylaldehyde and anthranilic acid, as studied through single crystal X-ray diffraction. Copyright (C) 199

MONONUCLEAR CIS-DIOXOVANADIUM(V) ANIONIC COMPLEXES [VO(2)L](-)(H(2)L=[1+1] SCHIFF-BASE DERIVED FROM SALICYLALDEHYDE (OR SUBSTITUTED DERIVATIVES) AND 2-AMINO-2-METHYLPROPAN-1-OL) - SYNTHESIS, STRUCTURE, SPECTROSCOPY, ELECTROCHEMISTRY AND REACTIVITY STUDIES

The compounds [H(3)NCMe(2)CH(2)OH][VO(2)L]{H(2)L = [1 + 1] Schiff base derived from salicylaldehyde (or substituted derivatives) and 2-amino-2-methylpropan-l-ol} have been synthesized in good yields by reaction of the Schiff base (formed in situ) and a further equivalent of the amino alcohol with [VO(acac)(2)](Hacac = acetylacetone). The structures of three of the complexes have been solved by single-crystal X-ray studies. All the compounds were also characterized by UV/VIS, FTIR and NMR spectroscopy and by cyclic voltammetry. The three structurally characterized mononuclear complexes contain the cis-dioxovanadium(V) moiety and exhibit distorted square-pyramidal geometry at vanadium which is-displaced from the equatorial plane by approximate to 0.5 Angstrom. The crystal and molecular structures of these compounds showed extensive hydrogen bonding between the anionic portion of the complexes and the counter-cations of the amino alcohol which resulted in some unusual metric features of interest to the binding of vanadium in biological systems. Two of the compounds showed the longest V=O distances reported so far for mononuclear cis-dioxovanadium(V) complexes. Three of the complexes undergo photoreduction in the solid state which is attributed to their intermolecular interactions in the crystal

Structure, characterization and photoreactivity of monomeric dioxovanadium(V) Schiff-base complexes of trigonal-bipyramidal geometry

Five mononuclear cis-dioxovanadium(v) complexes of tridentate Schiff bases derived from salicylaldehyde and its derivatives and 8-aminoquinoline have been synthesized and characterized. Single-crystal X-ray analyses were performed with [VO(2)L(1)] 1 and [VO(2)L(2)] 2 (L(1) and L(2) denote the [1 + 1] Schiff-base anions derived from salicylaldehyde or naphthaldehyde and 8-aminoquinoline). While the structure of 2 was refined to a final R = 0.074(R' = 0.055), that of 1 was refined only to R = 0.134(R' = 0.134) due to its poor diffraction quality. The complexes contain cis-oxo groups in the equatorial plane and a trigonal-bipyramidal geometry around the vanadium at which the Schiff base binds meridionally. Photoirradiation of these complexes in CH2Cl2 yielded chloride-bound VO3+ species, as studied using absorption and V-51 NMR spectroscopy. These species are convertible back to the dioxovanadium(v) complexes upon addition of water to the photoirradiated solution

Alkoxo bound monooxo- and dioxovanadium(V) complexes: Synthesis, characterization, x-ray crystal structures, and solution reactivity studies

A large variety of oxovanadium(V) complexes, mononuclear VO2+ and VO3+ in addition to the dinuclear VO3+, of the structural type (VOL)(2), (VOHL)(2), VOLHQ, K(VO(2)HL), K(VO(2)H(2)L), or (salampr) (VO(2)L) {where L = Schiff base ligand possessing alkoxo group(s); HQ = 8-hydroxyquinoline; salampr = cation of reduced Schiff base derived from salicylaldehyde and 2-amino-2-methylpropan-1-ol}, bound to alkoxo, phenolate and imine groups have been synthesized in high yields and characterized by several spectral and analytical methods, including single crystal X-ray studies. While the mononuclear VO2+ complexes have been synthesized at alkaline pH, the dinuclear VO3+ complexes have been synthesized under neutral conditions using alkoxo rich Schiff base ligands. The X-ray structures indicate that the cis-dioxo complexes showed longer V-O-alkoxo bond lengths compared to the monooxo counterparts. The plot of V-O-phen bond distances of several VO3+ complexes vs the lmct showed a near linear correlation with a negative slope. The cyclic voltammograms revealed a reversible V(V)/V(IV) couple with the reduction potentials increasing to more negative ones as the number of alkoxo groups bound to V increases from 1 to 2. Moreover, the cis-dioxo VO2+ complexes are easier to reduce than their monooxo counterparts. The solution stability of these complexes was studied in the presence of added water (1:4, water:solvent), where no decomposition was observed, unlike other Schiff base complexes of V. The conversion of the dioxo complexes to their monooxo counterparts in the presence of catalytic amounts of acid is also demonstrated. The reactivity of alkoxo bound V(V) complexes is also reported. X-ray parameters are as follows. H(4)L(3): monoclinic space group, P2(1)/c; a = 10.480(3), b = 8.719(6), c = 12.954(8) Angstrom; beta = 101.67(4)degrees; V = 1126(1) Angstrom(3); Z = 4; R = 0.060, R(w) = 0.058. Complex 1: monoclinic space group, P2(1)/n; a = 12.988(1), b = 9.306(2), c = 19.730(3) Angstrom; beta = 99.94(1)degrees; V = 2348.9(7) Angstrom(3); Z = 4; R = 0.031, R(w) = 0.027. Complex 2: monoclinic space group, P2(1)/n; a = 12.282(3), b = 11.664(2), c = 12.971(4) Angstrom; beta = 97.89(2)degrees; V = 1840.5(8) Angstrom; Z = 4; R = 0.035, R(w) = 0.038. Complex 5: monoclinic space group, P2(1)/c; a = 17.274(2), b = 6.384(2), c - 16.122(2) Angstrom; beta = 116.67(1)degrees; V = 1588.7(7) Angstrom(3); Z = 4; R = 0.039, R(w) = 0.043. Complex 8: monoclinic space group, P2(1)/c; a = 11.991(1), b = 11.696(4), c = 12.564(3) Angstrom; beta = 110.47(1)degrees; V = 1650.8(8)Angstrom(3); Z = 2; R = 0.045, R(w) = 0.049