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

Graphical abstract Critical role of carboxylate bridging was examined for carboxylate coordination assisted aggregation in [Cu 4 (µ 4 –O)(µ–L1) 2 (µ 1,3 –O 2 CCH 3) 4 ]·H 2 O (2a) and [Cu 4 (µ 4 –O)(µ–L1) 2 (µ 1,3 –O 2 CC 2 H 5) 4 ]·H 2 O (2b) avoiding ligand imine arm hydrolysis. Highlights • New ligand HL1 has been examined for synthesis of CuII coordination aggregates. • Use of carboxylates give rise to µ 4 –oxido bridged [Cu 4 ] complexes 2a and 2b. • Partial ligand arm hydrolysis observed in absence of any carboxylates. • The Cu 2 based building blocks present in MeOH solution showed catecholase activity. • DNA binding ability of the synthesized complexes was checked. Abstract The dinuclear copper(II) complex [Cu 2 (µ–L2NH) 2 (OH 2) 2 ](ClO 4) 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 [Cu 4 (µ 4 –O)(µ–L1) 2 (µ 1,3 –O 2 CCH 3) 4 ]·H 2 O (2a) and [Cu 4 (µ 4 –O)(µ–L1) 2 (µ 1,3 –O 2 CC 2 H 5) 4 ]·H 2 O (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 H 2 O molecules, as hydrolytic nucleophiles, triggered imine arm hydrolysis and bridging carboxylate anions allowed transformation of copper(II) bound H 2 O molecule to μ 4 -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 Cu 2 -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. [ABSTRACT FROM AUTHOR]