ALKOXO BOUND MONOOXOVANADIUM(V) 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) {whe re L = Schiff base ligand possessing alkoxo group(s); HQ = 8-hydroxyqu inoline; salampr = cation of reduced Schiff base derived from salicyla ldehyde and 2-amino-2-methylpropan-1-ol}, bound to alkoxo, phenolate a nd 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 synthesi zed 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 o f V-O-phen bond distances of several VO3+ complexes vs the lmct showed a near linear correlation with a negative slope. The cyclic voltammog rams revealed a reversible V(V)/V(IV) couple with the reduction potent ials increasing to more negative ones as the number of alkoxo groups b ound to V increases from 1 to 2. Moreover, the cis-dioxo VO2+ complexe s are easier to reduce than their monooxo counterparts. The solution s tability of these complexes was studied in the presence of added water (1:4, water:solvent), where no decomposition was observed, unlike oth er Schiff base complexes of V. The conversion of the dioxo complexes t o their monooxo counterparts in the presence of catalytic amounts of a cid is also demonstrated. The reactivity of alkoxo bound V(V) complexe s is also reported. X-ray parameters are as follows. H(4)L(3): monocli nic space group, P2(1)/c; a = 10.480(3), b = 8.719(6), c = 12.954(8) A ngstrom; 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 = 1 2.988(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 = 1 2.971(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)Angs trom(3); Z = 2; R = 0.045, R(w) = 0.049.