On the importance of H-bonding interactions in organic ammonium tetrathiotungstates

Abstract

Four new organic ammonium tetrathiotungstates (N-Me-enH2)[WS4] (1), (N,N'-dm-1,3-pnH2)[WS4] (2), (1,4-bnH2)[WS4] (3), and (mipaH)2[WS4] (4), (N-Me-enH2 = N-methylethylenediammonium, N,N'-dm-1,3-pnH2 = N,N'-dimethyl-1,3-propanediammonium, 1,4-bnH2 = 1,4-butanediammonium, and mipaH = monoisopropylammonium) were synthesized by the base promoted cation exchange reaction and characterized by elemental analysis, infrared, Raman, UV-Vis and 1H NMR spectroscopy as well as single crystal X-ray crystallography. The structures of 1-4 consist of [WS4]2- tetrahedra which are linked to the organic ammonium cations via N-H...S hydrogen bonding. The strength and number of the S...H interactions affect the W-S bond lengths as evidenced by distinct short and long W-S bonds. The IR spectra exhibit splitting of the W-S vibrations, which can be attributed to the distortion of the [WS4]2- tetrahedron. From a comparative study of several known tetrathiotungstates it is observed that a difference of more than 0.033 Angstrom between the longest and shortest W-S bonds in a tetrathiotungstate will result in the splitting of the asymmetric stretching vibration of the W-S bond.