Synthesis and characterization of mononuclear copper(II) complexes of pyridine 2-carboxamide: Their application as catalyst in peroxidative oxidation and antimicrobial agents

Abstract

Four water soluble copper(II) complexes, [Cu(HL)2(H2O)2]Cl2 (1), [Cu(HL)2(ClO4)2] (2), [Cu(HL)2(SCN)2] (3) and [CuL2]⋅8H2O (4), where HL is pyridine 2–carboxamide, have been synthesized and characterized by various spectroscopic techniques. Structures have been determined by single crystal X-ray crystallography. The pH induced inter-conversion of Cu(HL)2(H2O)2]Cl2 (1) and [CuL2]⋅8H2O (4) through co-ordination mode switching was investigated thoroughly with the help of absorption spectroscopy. Complexes 1–3 were found to be active catalysts for the oxidation of toluene, ethyl benzene and cyclohexane in the presence of hydrogen peroxide as the oxidant under mild conditions. Toluene was oxidized to benzyl alcohol and benzaldehyde, ethyl benzene was oxidized to 1-phenylethanol and acetophenone and cyclohexane was oxidized to yield cyclohexanol and cyclohexanone Antimicrobial activities have been investigated with these copper(II) complexes against gram + ve bacteria, gram −ve bacterial and fungal species. X-ray structural characterization, pH-induced co-ordination mode switching phenomenon, peroxidative oxidation catalysis and antimicrobial activity of water soluble, discrete mononuclear complexes of copper(II) using the simplest pyridine 2–carboxamide ligand (HL) and its deprotonated form have been investigated thoroughly.