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

Two mononuclear Cu(II) complexes, [Cu(L1H2)](ClO4)1.25Cl0.75·1.25H2O (1) and [Cu(L2H2)](ClO4)2 (2), of the pyridoxal Schiff base ligands N,N′-dipyridoxylethylenediimine (L1H2) and N,N′-dipyridoxyl-1,3-propanediimine (L2H2) 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.

Graphical abstractSynthesis, X-ray crystal structures and spectroscopic properties of two mononuclear Cu(II) complexes, Cu(L1H2)(ClO4)1.25Cl0.75·1.25H2O (1) and [Cu(L2H2)](ClO4)2 (2), of pyridoxal Schiff base ligands N,N′-dipyridoxylethylenediimine (L1H2) and N,N′-dipyridoxyl-1,3-propanediimine (L2H2) are reported. 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 electropolymerization, unlike their corresponding salicyl aldehyde Schiff base complexes.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Cu(II) complexes of pyridoxal Schiff bases of diamines can have different conformations of the Schiff base, depending on the number of carbon atoms separating the nitrogen atoms of the diamine. ► Such a difference in conformation also affects the ability of the complexes to accommodate water of crystallization in their lattice. ► Cyclic voltammetry experiments show that the Cu(III) and Cu(I) states are more easily accessible in these complexes than in their salen type analogs; the pyridoxal Schiff base complexes are also found to be resistant to oxidative electropolymerization, unlike their corresponding salicyl aldehyde Schiff base complexes.