Synthesis, Crystal Structure and Catecholase Activity of Copper(II) Complexes with N,N,N-Tridentate Schiff Base Ligand

Four complexes, [Cu(L-1)Cl-2](1),[Cu(L-1)(SCN)(2)](2),[Cu(L-1)bpy](ClO4)(2)center dot CH3OH(3) and [Cu(L-2)bpy](ClO4)(2)(4),were synthesized via the reaction of the N,N,N-tridentate Schiff base ligands, 2-[(1H-benzimidazol-2-yl-ethylimino)-methyl]pyridine(L-1) or 2- [(1H-benzimidazol-2-yl-propylimino)-methyl]pyridine (L-2) with Cu(II) salts(where bpy=2,2'-bipyridine). The complexes were characterized by means of elemental analysis, infrared spectroscopy, powder X-ray diffraction, single-crystal X-ray diffraction, thermal gravimetric analysis and cyclic voltammetry. In the solid state, complexes 1 similar to 4 are mononuclear Cu(II) complexes and the Cu(II) ions exhibit distorted square pyramidal coordination geometry with tau values ranging from 0.088 to 0.340. Catecholase activity of the complexes has been studied using 3,5-di-tertbutyl catechol(3,5-DTBC) as model substrate, and kinetic parameters were calculated using the Michaelis-Menten model and Lineweaver-Burk plot. The results demonstrate that all complexes exhibit catecholase activity, with the catechol oxidation rates following the order of 2>3 approximate to 4>1. The oxidation rates depend on the distortion of the Cu(II)coordination environment, the bond lengths of the leaving group of Cu(II)ions and the steric hindrance of the complexes.