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)nX2]: X = I−, Br−, SCN−, N3− and NO2−; spectroscopic, thermal, fluorescence and structural studies

Abstract

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)_nX₂]: X = SCN⁻ (1), I⁻ (2), Br⁻ (3), NO₂⁻ (4) and N₃⁻ (5), was prepared from reactions of the ligand bpo with different mercury(II) salts. All these compounds were characterized by elemental analysis, IR-, ¹H NMR-, and ¹³C NMR spectroscopies and structurally determined by X-ray single-crystal diffraction. The thermal stabilities of compounds 1–5 and also the reported compound, [Hg(μ-bpo)I₂]·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.