Synthesis, characterization and electrochemical behavior of mononuclear, binuclear nickel(II) and heterobinuclear zinc(II)nickel(II) complexes derived from novel macrobicyclic tricompartmental ligands: kinetics of the catalytic hydrolysis of 4-nitrophenyl phosphate by the complexes

Abstract

Mononuclear, binuclear NiII and heterobinuclear ZnIINiII complexes have been derived from lateral macrobicyclic tricompartmental ligands embracing three different donor sets: (i) O2N2-donor set, derived from ether oxygens and tertiary amine nitrogens; (ii) N2O2-donor set, derived from tertiary amine nitrogens and phenolic oxygens; (iii) O2N2-donor set, derived from phenolic oxygens and azomethine nitrogens. Cyclic voltammograms of the mononuclear NiII complexes showed irreversible one-electron reduction processes in the −1.2 to −1.3 V region and an irreversible oxidation process in the range +0.8 V potential region. The binuclear complexes showed quasireversible two-step single electron reduction processes around the −1.3 and −1.7 V potential regions. The anodic potential region showed an irreversible oxidation process at +1.0 V. The heterobinuclear ZnIINiII complex showed an irreversible reduction of the NiII species at −1.55 V. The catalytic hydrolysis towards 4-nitrophenyl phosphate by the mononuclear, binuclear NiII complexes and the heterobinuclear complex were found to be appreciable. The pseudo-first order rate constant for the catalytic hydrolysis catalyzed by the binuclear and heterobinuclear complexes were found to be higher (9.8 × 10−4 s−1) than that of the corresponding mononuclear complexes (1.3 × 10−5 s−1), which ascertain the requirement of two metal ions in close proximity for the binding of the nucleophilic OH and the phosphate group.