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

Two complexes of zinc (II) with mixed-ligand, [Zn-2(phen)(2)(HL1)(2)] (ClO4)(2) (1) and [Zn-2(phen)(2)(HL2)(2)] (ClO4)(2)(2) (H2L1=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 H-1 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 be plane in terms of the action of multiple N-(HO)-O-... and O-(HO)-O-... hydrogen bonds between the (HL1)(-) ligands and the pi(...)pi 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. (C) 2003 Published by Elsevier Science B.V.