Synthesis of mono- and heterodinuclear complexes with unsymmetrical phenol-based dicompartmental ligand containing hexa- and tetradentate coordination sites: An unusual methyl elimination in coordination chemistry

Novel heterodinuclear complexes type [ZnIILMII](ClO4)2 where L is a phenol-based ligand with two contiguous hexa-(N4O2) and tetra-coordination (O2N2) sites and M = Cu or Ni were prepared by a stepwise procedure. The prepared mono- and dinuclear complexes were characterized by elemental analysis, molar conductance measurements, X-ray crystallography, IR, NMR and UV–Vis spectroscopies. Characterization results confirmed the expected C2 symmetrical geometry for the mononuclear zinc complex with trans-disposed pyridyl ligands. In contrast, the dinuclear complexes showed C1 symmetrical structures so that, the Zn(II) ion resided in the six-coordination site with cis-disposed pyridyl ligands and the tetradentate compartment is occupied by M(II) ion in a square planar geometry. An unusual methyl elimination was occurred upon the introduction of the M(II) ions into the O2N2 coordination site of the mononuclear complex. The reason for these phenomena is an inherent structural feature of the dinucleating macroacyclic ligand that is discussed.