Role of co-ligand and solvent on properties of V(IV) oxido complexes with ONO Schiff bases

Four complexes of V(IV/V) of octahedral geometry, with tridentate ONO Schiff base ligand, oxido and bidentate (maltol, 1,10-phenantroline or 2,2'-bipyridine) co-ligands are described. The Schiff bases were formed from 3,5-di-tert-butyl-2-hydroxybenzaldehyde and hydrazides (benzhydrazide, 2-hydroxybenzhydrazide and phenylacetic hydrazide). The X-ray single-crystal structures of all complexes revealed that they are a mixture of 1:1 isomers with the different position of 5- and 6-membered ring of ONO ligand versus V=O, excluding 1. The position of the V=O band in 1R spectra was found to be dependent on the V=O and trans located donor atom bond distances. Two complexes, 3 and 3a, were isolated as unsolvated and solvated ones, the coordination of solvent molecule drastically changed the structure parameters. The cyclic voltammetry measurements show irreversible processes for vanadium redox system and reversible ones for co-ligands. The stability of complexes in solution is discussed. (C) 2018 Elsevier B.V. All rights reserved.