CHEMISTRY OF VARIABLE-VALENCE VOZ+ (Z = 2, 3) COMPLEXES - SYNTHESIS, STRUCTURE, AND METAL REDOX OF NEW VVO(ONO)(ON) AND VIVO(ONO)(NN) FAMILIES

In the title families the ONO ligands are deprotonated forms of N-(2-hydroxyphenyl)salicylaldimine (H-2amp), 2,2'-dihydroxyazobenzene (H-2azp), N-(2-carboxyphenyl)salicylaldimine (H-2amc), or 2-hydroxy-2'-carboxy-5-methylazobenzene (H-2azc). The ON ligand is deprotonated 8-quinolinol (Hhq), and the NN ligands are 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen). Reaction of VO(acac)2 with a mixture of H-2amp and bpy or Hhq in methanol affords V(IV)O(amp)(bpy) or V(V)O(amp)(hq) (oxidant is aerial oxygen). Complexes of azp2- and amc2- are similarly made, while those of azc2- are synthesized from preformed VO(azc).3H2O. In both VO(azc)(hq)-2MeOH and VO(azc)(bpy) the V(azc) and V(bidentate) fragments are respectively nonplanar and planar. The V-O distances within V(azc) are shorter in the former complex. Crystals of VO(azc)(hq).2MeOH are triclinic, space group P1BAR, with a = 8.104(3) angstrom, b = 12.217(4) angstrom, c = 12.573(5) angstrom, alpha = 100.62(3)-degrees, beta = 92.26(3)-degrees, gamma = 105.81(3)-degrees, V = 1176(1) angstrom3, Z = 2, R = 6.69%, and R(w) = 6.69%. Crystals of VO(azc)(bpy) are monoclinic, space group P2(1)/c, with a = 9.848(4) angstrom, b = 18.169(6) angstrom, c = 12.936(4) angstrom, beta = 11 1.78(3)-degrees, V = 2149(2) angstrom3, Z = 4, R = 6.25%, and R(w) = 6.39%. In VO(ONO)(NN) and electrogenerated VO(ONO)(ON)-the V-51 EPR hyperfine constants (A(av)) are slightly larger in the amc2- and azc2- (approximately 102 G) than in the amp2- and azp2- (approximately 99 G) complexes. The more nucleophilic phenolato function delocalizes electron density better. The VO3+-VO2+E1/2 values shift considerably to more negative values when neutral NN is replaced by anionic ON, which also provides better VO3+ binding via phenolato oxygen. For a given bidentate ligand E1/2 increases in the order amp2- < azp2- < amc2- < azc2- and correlates linearly with SIGMApK(a), which represents the sum of pK(a)'s of the variable N and 0 functions.