Fluorescent metal-organic polymers of zinc and cadmium from hydrothermal in situ acylation reaction.

A series of metal-organic complexes based on d(10) metals and the ligand H(4)bbh (H(4)bbh = benzene-1, 2, 4, 5-biformhydrazide), formed through hydrothermal in situ acylate reaction of H(4)bta (H(4)bta = benzene-1, 2, 4, 5-tetracarboxylic acid) with hydrazine hydrate (N(2)H(4)·H(2)O), have been prepared and structurally characterized by single-crystal X-ray diffraction. Compounds Zn(μ(2)-H(2)bbh)(phen)(H(2)O) (1) (phen = 1, 10-phenanthroline) and Zn(μ(2)-H(2)bbh)(2, 2'-bpy) (2) (2, 2'-bpy = 2, 2'-bipyridine) are both dinuclear complexes in which bridging ligands H(2)bbh(2-) display different μ(2)- coordination modes. Zn(μ(2)-H(2)bbh)(1/2)(μ(2)-H(2)bbh)(1/2)(H(2)O) (3) exhibits a two-dimensional (2-D) layer structure containing simultaneously two kinds of different coordination modes of H(2)bbh(2-): μ(2)-bidentate and μ(4)-tetradentate. Cd(μ(3)-H(2)bbh)(phen) (4) consists of one-dimensional (1-D) double-metal chains. The crystal structures of these compounds are stabilized by hydrogen bonds and π···π interactions, forming three-dimensional supramolecular networks. All of the compounds were characterized by IR, UV-vis spectra and elemental analysis and they show good fluorescence properties in the solid state at room temperature. In order to understand the emission mechanism, we carried out TDDFT calculations on the excited electronic states of compound 2.