Synthesis, x-ray structures, spectroscopic and thermal characterization of two new organic ammonium tetrathiotungstates

Abstract

Two new tetrathiotungstates (pipH2)[WS4] (1) and (trenH2)[WS4] . H2O (2) (pip = piperazine and tren = tris(2-aminoethyl)amine) were synthesized and characterized by elemental analysis, infrared, Raman, UV-Visible and 1H NMR spectroscopy, single crystal X-ray crystallography, and thermoanalysis. In 1 and 2 the amines pip and tren are diprotonated and they are linked to the [WS4]2- tetrahedra via weak N-H...S (1, 2) and N-H...O (2) hydrogen bonds. In 2 the H atoms of the H2O molecule have also contacts to S atoms. The strength and number of the S...H interactions affect the W-S bond lengths and a relatively long W-S bond of 2.2147(7) Angstrom is observed in 1 while the longest W-S bond in 2 is 2.1997(6) Angstrom. The different degree of distortion of the [WS4]2- anions is reflected in the IR and Raman spectra. The compounds decompose upon heating in an inert atmosphere to form amorphous WS2.1C1.2N0.3 and WS2.1C3N0.8 respectively, and the C and N content of the decomposition products is determined by the C and N content of the amines. In contrast to other tetrathiotungstates, the thermal reaction of both compounds do not proceed via amorphous WS3 as an intermediate phase. Compound 2 can be reversibly de- and re-hydrated, and the process of re-hydration proceeds presumably via dissolution-re-crystallization mechanism.