Synthesis, structural and mass spectrometric investigations of pyridinium bis(thiosalicylato)mercurate(II)

Abstract

This work investigates the synthesis and structural properties of a hydrogen-bonded salt of the [Hg(SC6H4-2-CO2)2]2− ion. The known bis(thiosalicylato)mercury(II) complex [Hg(SC6H4-2-CO2H)2], dissolves in pyridine (py), from which the crystalline pyridinium salt (pyH)2[Hg(SC6H4-2-CO2)2] can be isolated. Single crystal X-ray crystallography reveals two distinct three-molecule aggregates, namely {Hg[SC6H4-2-C(=O)OH]2(NC5H5)2} and {Hg[SC6H4-2-C(=O)O]2(HNC5H5)2}, which differ in the location of the acidic hydrogen atoms, i.e. either compound-bound for the former species or located on the pyridinium cations in the latter. The thiolate ligands are S,O-chelating and the resultant O2S2 four-coordinate geometries are each based on a distorted disphenoidal geometry. The three-molecule aggregates are sustained by hydroxylOH⋯N(pyridine) hydrogen bonds in the case of {Hg[SC6H4-2-C(=O)OH]2(NC5H5)2} whereas the second aggregate features charge-assisted pyridiniumNH⋯O(carboxylate) hydrogen bonds. (pyH)2[Hg(SC6H4-2-CO2)2] was also characterised by negative-ion ESI mass spectrometry, where it showed appreciable stability towards capillary exit voltage-induced fragmentation. In contrast, the S-bonded monodentate thiosalicylate complexes RHg(SC6H4-2-CO2)− (R = Et, Ph or ferrocenyl) undergo facile decarboxylation at relatively low voltages, with the phenyl and ferrocenyl complexes subsequently forming RHgS− as an additional fragment ion at high voltages. Aggregate ions formed with the sodium counter-cations of the type [(RHgSC6H4-2-CO2)nNan−1]− show appreciable stability towards fragmentation.