COMPLEXES OF VANADIUM(III) AND VANADIUM(IV) CONTAINING BIPYRIDINE AND TETRACHLOROCATECHOLATE LIGANDS - INSIGHTS INTO THE TUNICATE VANADIUM(III) COORDINATION ENVIRONMENT

The reaction between V(acac)3, tetrachlorocatecbol, and bipyridine has been found to give V(bpy)(Cl4Cat)2. Crystallographic characterization on the complex [triclinic, space group P1BAR, a = 7.911 (2) angstrom, b = 8.982 (2) angstrom, c = 17.981 (3) angstrom, alpha = 80.05 (1)-degrees, beta = 88.60 (1)-degrees, gamma = 88.76 (2)-degrees, V = 1257.9 (5) angstrom3, Z = 2, D(calcd) = 1.845 g cm-3, R = 0.065 and R(w) = 0.076 for 2914 observed reflections] has shown that the complex molecule has a trigonal prismatic structure with a twist angle between triangular faces of 3.2-degrees. The complex appears to result from oxidation of V(III) species formed initially in the reaction. More immediate product isolation gave V(bpy)(acac)(Cl4Cat). Crystallographic characterization of a thin platelike crystal of the complex obtained as a dichloromethane solvate, V(bpy)(acac)(Cl4Cat).CH2Cl2 [monoclinic, P2(1)/n, a = 13.864 (3) angstrom, b = 8.407 (2) angstrom, c = 22.898 (5) angstrom, beta = 90.87 (2)-degrees, V = 2668.6 (10) angstrom3, Z = 4, D(calcd) = 1.581 g cm-3, R = 0.056 and R(w) = 0.074 for 896 observed reflections], has shown that the complex molecule is octahedral and monomeric in structure. Addition of the PPh4+ cation to the reaction mixture described above gave crystals of (PPh4)[V(bpy)(Cl4Cat)2], the V(III) analog of V(bpy)(Cl4Cat)2. The anion was also formed as the CoCp2+ salt by cobaltocene reduction of the neutral V(IV) complex. Electrochemical characterization on both V(bPY)(Cl4Cat)2 and V(bpy)(Cl4Cat)2- has shown that the V(III)/V(IV) couple occurs at -0.50 V (vs Fc/Fc+). Attempts at displacing the C14Cat ligands from both the V(III) and V(IV) forms of the complex with excess bipyridine failed. The implications of this observation to the characterization of tunicate V(III) are discussed.