Homoleptic cyclohexanethiolato complexes of mercury(II)

Abstract

The complexes Hg(SR)₂1 and [NR′₄][Hg(SR)₃](R′= Et 2 or Me 3) have been obtained from the reaction of HgCl₂ with NaSR in acetonitrile, with [NR′₄]Cl also present for complexes 2 and 3; SR is cyclohexanethiolate. Complex 1 has a polymeric structure consisting of rather bent Hg(SR)₂ units [Hg–S 2.372(2) and 2.374(2)Å, S–Hg–S 160.4(1)°] linked together by weaker Hg–S bonds [3.004(2) and 2.959(2)Å]; the Hg atoms have highly distorted tetrahedral co-ordination and each thiolate acts as a very asymmetric bridge between two Hg atoms. Complex 2 contains Hg atoms in a distorted trigonal-planar co-ordination environment, the monomeric anions being well separated from each other. The distortion is mostly in-plane, producing one angle considerably less than, and one considerably greater than, the ideal 120°; the largest angle lies opposite the longest Hg–S bond, and the smallest angle opposite the shortest Hg–S bond. Proton and ¹³C NMR, far-IR and Raman, and low-energy UV spectroscopic data are discussed. The UV data afford additional support for the proposal of a trigonal-planar [Hg(CysS)₃]^– co-ordination environment for the metal receptor site of the MerR metalloregulatory protein. A correlation of co-ordination geometry, Hg–S bond lengths, and Hg–S stretching frequencies is developed for these and other homoleptic thiolate complexes of mercury.