On trialkyl sulfonium salts of triiodomercury(II) and structure of the trimethyl salt

Abstract

The salt, [Me₃S][HgI₃], is a text book example of the relatively rare phenomenon of tricoordination among transition metal complexes of simple ligands. It was structurally characterized decades after P C Rây’s formulation of the [R₃S] [HgI₃] family of salts in 1930. We now report its structure at low temperature (150K). The [Me₃S]⁺ and [HgI₃]^{<span style="font-family:Symbol;mso-ascii-font-family:" times="" new="" roman";="" mso-hansi-font-family:"times="" roman";mso-char-type:symbol;mso-symbol-font-family:="" symbol"="" lang="EN-GB">- </span>}ions are respectively pyramidal and trigonal planar. The span of the three Hg-I distances and the three I-Hg-I angles are 2.69-2.74 Å and 110-125^o respectively. The Hg atom is 0.12 Å displaced from the plane of the iodine atoms. Weak supramolecular Hg---I interactions among adjacent molecules are present in the lattice and these influence the trend of bond lengths and angles in the [HgI₃]^-ion. The S-C distances and C-S-C angles in the cation span the ranges 1.75-1.81 Å and 100-103^o respectively.