Effect of alkyl group on the structure of heterodinuclear Zn(II)–Cu(II) and Zn(II)–Ni(II) complexes derived from unsymmetrical phenol-based dicompartmental macro-acyclic ligands

Abstract

A series of mono- and heterodinuclear macro-acyclic complexes of [ZnLCu(II)]2+ and [ZnLNi(II)]2+ were synthesized by a stepwise procedure. The phenol-based macro-acyclic dicompartmental ligands (L2−) possess contagious hexadentate (N4O2) and tetradentate (N2O2) coordination sites, where in the mononuclear complexes [ZnL(H+)2]2+ the latter site containing two alkyl-imine donor groups (ethyl or isopropyl) is attached to the azomethine moieties. The alkyl group(s) is eliminated upon introduction of the second metal (II) ion into N2O2 coordination site as a result of steric crowding of the alkyl groups along with the lack of flexibility associated with the imine groups. When the second metal ion is Cu(II) and R = isopropyl, the both of them are eliminated but when R = Et only one ethyl group is removed. However, in case of Ni(II) as the second metal ion, the both alkyl groups are eliminated regardless of the nature of the alkyl group. The origins of the structural variations are discussed. The prepared complexes were characterized by elemental analysis, molar conductance measurements, X-ray crystallography, IR, NMR and UV–Vis spectroscopies.