Abstract

The five binuclear nickel(II) complexes have been synthesized by the Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-1,4,8,11-tetraazacyclo-tetradecane (PC) with appropriate aliphatic diamines and nickel(II) perchlorate. All the five complexes were characterized by elemental and spectral analysis. The electronic spectra of the complexes show three d-d transition in the range of 550-1055 nm due to (3)A(2g) -> T-3(2g)(F), (3)A(2g) -> T-3(1g)(F) and (3)A(2g) -> T-3(1g)(P). These spin allowed electronic transitions are characteristic of an octahedral Ni2+ center. Electrochemical studies of the complexes show two irreversible one electron reduction waves at cathodic region. The reduction potential of the complexes shifts towards anodically upon increasing the chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves at anodic region. The oxidation potential of the complexes shift towards anodically upon increasing the chain length of the macrocyclic ring. The catalytic activities of the complexes were observed to be increase with increase the macrocyclic ring size. The observed rate constant values for the catalytic hydrolysis of 4-nitrophenyl phosphate are in the range of 5.85 x 10(-3) to 9.14 x 10(-3) min(-1). All the complexes were screened for antimicrobial activity. (C) 2010 Elsevier B.V. All rights reserved.