Crystal structures and photophysical properties of mono- and dinuclear ZnII complexes flanked by tri-ethyl-ammonium.

Abstract

Two new zinc(II) complexes, tri-ethyl-ammonium di-chlorido-[2-(4-nitro-phen-yl)-4-phenyl-quinolin-8-olato]zinc(II), (C₆H₁₆N){Zn(C₂₁H₁₃N₂O₃)Cl₂] (ZnOQ), and bis-(tri-ethyl-ammonium) {2,2'-[1,4-phenyl-enebis(nitrilo-methyl-idyne)]diphenolato}bis-[di-chlorido-zinc(II)], (C₆H₁₆N)₂[Zn₂(C₂₀H₁₄N₂O₂)Cl₄] (ZnBS), were synthesized and their structures were determined using ESI-MS spectrometry, ¹H NMR spectroscopy, and single-crystal X-ray diffraction. The results showed that the ligands 2-(4-nitro-phen-yl)-4-phenyl-quinolin-8-ol (HOQ) and N,N'-bis-(2-hy-droxy-benzyl-idene)benzene-1,4-di-amine (H₂BS) were deprotonated by tri-ethyl-amine, forming the counter-ion Et₃NH⁺, which inter-acts via an N-H⋯O hydrogen bond with the ligand. The Zn^II atoms have a distorted trigonal-pyramidal (ZnOQ) and distorted tetra-hedral (ZnBS) geometries with a coord-ination number of four, coordinating with the ligands via N and O atoms. The N atoms coordinating with Zn^II correspond to the heterocyclic nitro-gen for the HOQ ligand, while for the H₂BS ligand, it is the nitro-gen of the imine (CH=N). The crystal packing of ZnOQ is characterized by C-H⋯π inter-actions, while that of ZnBS by C-H⋯Cl inter-actions. The emission spectra showed that ZnBS complex exhibits green fluorescence in the solid state with a small band-gap energy, and the ZnOQ complex does exhibit non-fluorescence.