Controlled syntheses of heterodinuclear complexes of a dicompartmental macro-acyclic ligand with hexa and tetra coordination sites

Abstract

Two phenol-based unsymmetrical dinucleating macro-acyclic ligands (LH 2), which can contiguously accommodate two metal ions, one in a hexa-coordinate (N4O2) site and the other in a tetra-coordinate (N2O2) site, and their heterodinuclear complexes [ZnLMII]2+, where M = Cu or Ni, were prepared using a stepwise method. One of the ligand systems (L3H2) comprises an ethylenediamine link in the N4O2 compartment, whereas the other (L6H2) includes an 1,3-diaminopropane link. Both ligands contain two methyl arms attached to the nitrogen atoms in the N2O2 coordination site. The mononuclear complex of the type [ZnL3(H+)2]2+ has a C 2-symmetrical structure. When a second metal is incorporated, however, the resultant heterodinuclear complexes [ZnL3M II]2+ provide a non-symmetrical structure due to the occurrence of geometrical isomerization. In contrast, the mononuclear complex of the type [ZnL6(H+)2]2+ demonstrated a mixture of topological isomers and the structures of the resultant heterodinuclear complexes [ZnL6MII]2+, remained constant without a change in the structures with respect to the mononuclear complex. The origins of the structural variations are discussed. The structures of the complexes were studied by NMR, IR, UV-Vis spectroscopies and X-ray crystallography. © 2012 Published by Elsevier Ltd. All rights reserved.