Counter-ion influence on the coordination mode of the 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (bpo) ligand in mercury(II) coordination polymers, [Hg(bpo)(n)X-2]: X = I-, Br-, SCN-, N-3(-) and NO2-; spectroscopic, thermal, fluorescence and structural studies

A series of new mercury(II)-organic polymeric complexes generated from 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (bpo) as an angular dipyridyl derivative ligand, [ Hg(bpo)(n)X-2]: X = SCN- (1), I- (2), Br- (3), NO2- (4) and N-3(-) (5), was prepared from reactions of the ligand bpo with different mercury(II) salts. All these compounds were characterized by elemental analysis, IR-, H-1 NMR-, and C-13 NMR spectroscopies and structurally determined by X-ray single-crystal diffraction. The thermal stabilities of compounds 1-5 and also the reported compound, [Hg(mu-bpo) I-2]center dot CH3CN (6), were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). Solid-state luminescent spectra of the compounds 1-6 indicate intense fluorescent emissions at ca. 470 nm. The results show the influence of the counter-ions on the coordination mode of the bpo ligand in the mercury ion as a soft acid that is capable of forming compounds with four-, five-and six coordination numbers and, consequently, acting in different forms of coordination polymers, containing both discrete and divergent (from one-dimensional, 1-D to two-dimensional, 2-D) coordination frameworks.