Synthesis, spectral and structural characterization of Cu(II) complexes of a tridentate NNO donor Schiff base carrying a pendant benzimidazolyl arm

Three new Cu(II) complexes of a Schiff base ligand, 2-[2-(1H-benzo[d]imidazol-2-yl]ethylimino)methyl]phenol, (HL), derived from 2-aminoethylbenzimidazolyl and salicylaldehyde have been synthesized and characterized by elemental analysis and electronic and IR spectroscopy. Results show that HL acts as tridentate ligand and coordinates through the imine nitrogen of benzimidazole ring, the azomethine nitrogen and a deprotonated phenolic oxygen of the Schiff base. One of the complex with the composition [Cu(L)CH3COO] has been structurally characterized. X-ray diffraction data reveals that the compound crystallizes in monoclinic space group P-21/c, with cell parameters of a = 12.8602(8) angstrom, b = 18.1466(10) angstrom, c = 8.1250(4) angstrom, a = 90 degrees, beta = 103.757(6)degrees, gamma = 90 degrees and Z = 4. The copper(II) ion adopts a distorted square planar geometry involving the N, N and O atoms of L and an O atom of acetate anion. The four bond distances are nearly equal. Kinetics of oxidation of dopamine using molecular oxygen as an oxidant and [Cu(L)CH3COO] as catalyst has also been studied spectrophotometrically. The complex catalyses the oxidation of dopamine to dopachrome or aminochrome in methanol.