Inhibition of ligand arm hydrolysis and carboxylate coordination directed formation of μ4-oxido-bridged [Cu4] complexes: Synthesis, X-ray structure and functional activity

Abstract

The dinuclear copper(II) complex [Cu2(µ–L2NH)2(OH2)2](ClO4)4 (1) was obtained following one imine side arm hydrolysis of HL1 (2,6-bis-[{3-(diethylamino)propylimino}methyl]-4-methylphenol). Introduction of carboxylates inhibited the hydrolysis and resulted in two tetranuclear copper(II) complexes [Cu4(µ4–O)(µ–L1)2(µ1,3–O2CCH3)4]·H2O (2a) and [Cu4(µ4–O)(µ–L1)2(µ1,3–O2CC2H5)4]·H2O (2b). Use of perchlorate and carboxylate salts of copper(II) for the reactions under study with HL1 has directed these reactions. Perchlorate anions in presence of H2O molecules, as hydrolytic nucleophiles, triggered imine arm hydrolysis and bridging carboxylate anions allowed transformation of copper(II) bound H2O molecule to μ4-oxido central nucleating group via hydroxido-bridge. The complexes were obtained from simultaneous chelation and bridging by the hydrolyzed and as used ligand anions L2NH− and HL1− respectively. These complexes have been characterized in the solid state by X-ray crystallography and FT-IR spectroscopy. Solution phase stability of Cu2-based fragments was studied by UV–vis absorption spectroscopy. Solution properties have been examined for substrate binding in catechol oxidase activity and binding affinity for biomacromolecules like DNA and Human Serum Albumin.