Synthesis, crystal structure and properties of the zinc complexes with unsymmetrical tridentate ligands

Two complexes of zinc (II) with mixed-ligand, [Zn2(phen)2(HL1)2] (ClO4)2 (1) and [Zn2(phen)2(HL2)2] (ClO4)2(2) (H2L1&z.dbnd6;N–(2-hydroxybenzyl) ethanolamine and H2L2=N–(2-hydroxybenzyl) propanolamine), and another zinc complex ZnL1 (3) were synthesized and characterized by elemental analysis, IR spectra, thermal analysis, fluorescence and 1H NMR. The crystal structure of (1) has a centrosymmetric di-phenoxo-bridged dizinc (II) core and each zinc center is laid in a slightly distorted trigonal bipyramidal geometry. A 2D supramolecular structure is formed approximately along bc plane in terms of the action of multiple N–H⋯O and O–H⋯O hydrogen bonds between the (HL1)− ligands and the π⋯π stacking interactions between the phenanthroline ligands. Thermal behavior, studied by TG and DTA in nitrogen atmosphere, indicates that phen is eliminated at higher temperature than (HL1)− and (HL2)−. Several possible mechanisms for the fluorescence quenching of the metal complexes are proposed. [Copyright &y& Elsevier]