Reactions of a methylmercury zwitterionic thiolate complex [MeHg(Tab)]PF6 with various donor ligands: relevance to methylmercury detoxification

Abstract

Reaction of MeHgI with Ag₂O in H₂O followed by addition of equimolar TabHPF₆ in MeCN gave rise to a methylmercury zwitterionic thiolate complex [MeHg(Tab)]PF₆ (1) (TabH = 4-(trimethylammonio)benzenethiol) in a high yield. Treatment of 1 with KI and KSCN afforded an anion exchange product [MeHg(Tab)]I·0.25H₂O (2·0.25H₂O) and [MeHg(Tab)]SCN (3), respectively, while that of 1 with equimolar Tab resulted in the formation of another MeHg/Tab compound [MeHg(Tab)₂]PF₆ (4). The cation of 2 or 3 shows an approximately linear structure in which the central Hg(II) is coordinated by one C atom of one CH₃ group and one S atom of a Tab ligand. The Hg(II) center of the cation of 4 is trigonally coordinated by one C atom of the CH₃ group and two S atoms of two Tab ligands. The analogous reaction of 1 with NH₄SCN led to the cleavage of the Hg–C bond of 1 and the formation of a known four-coordinated Hg(II)/Tab complex [Hg(Tab)₂(SCN)₂] (5). When 4 was treated with 4,6-Me₂pymSH or EtSH, another four-coordinated Hg(II)/Tab complex [Hg(Tab)₄]₃(PF₆)₆ (6) was generated in a high yield. The Hg(II) center of each cation of 6 is tetrahedrally coordinated by four S atoms of four Tab ligands. The results suggested that cleavage of the Hg–C bond in the methylmercury complex 1 could be completed by increasing the coordination number of its Hg(II) center by S-donor ligands and protonating the methyl group by weak acids.