Synthesis and characterization of mono- and heterodinuclear complexes of dinucleating macrocyclic ligand bearing hexa- and pentadentate coordination sites

Macrocyclic heterobinuclear Zn(II)–Cu(II) complexes with phenol based dicompartmental ligands possessing contiguous hexa- and penta-coordination sites were prepared by a stepwise procedure. The ligands include similar N4O2 and dissimilar N(imine)3O2 and N(amine)3O2 coordination sites sharing two phenolic oxygen atoms. The six-coordination site comprises two pyridyl pendant arms on the amine nitrogen atoms, while the five-coordination site consists of dipropylenetriamine moieties. The prepared mono- and dinuclear complexes were characterized by elemental analysis, molar conductance measurements, IR, NMR and UV-Vis spectroscopy techniques. Characterization results confirm that in the mononuclear macrocyclic zinc complexes two pyridyl moieties located in the expected trans positions and two protons occupied the N3O2 coordination site.  In contrast, the dinuclear macrocyclic Zn(II)-Cu(II) complexes the Zn(II) ions located in six coordination site with cis disposed pyridyl ligands and the penta-dantate compartment is occupied by Cu(II) ion in a square pyramidal geometry. The origins of the structural variations are discussed.