Synthesis, X-ray crystal structures, spectroscopic and cyclic voltammetric studies of Cu(II) Schiff base complexes of pyridoxal

Abstract

Two mononuclear Cu(II) complexes, [Cu(L 1H 2)](ClO 4) 1.25Cl 0.75·1.25H 2O ( 1) and [Cu(L 2H 2)](ClO 4) 2 ( 2), of the pyridoxal Schiff base ligands N, N′-dipyridoxylethylenediimine (L 1H 2) and N, N′-dipyridoxyl-1,3-propanediimine (L 2H 2) are reported. X-ray crystal structures of both complexes are also reported. In both complexes the pyridoxal nitrogen atoms remain protonated. In the solid state, the tetradentate Schiff base ligand is virtually planar in 1, while in 2 the ligand conformation is like an inverted umbrella. In cyclic voltammetry experiments it is found that in these complexes the Cu(III) and Cu(I) states are more easily accessible than in their salen type analogs. The pyridoxal Schiff base complexes are also found to be resistant to oxidative electro-polymerization, unlike their corresponding salicyl aldehyde Schiff base complexes.