A new polymorphic modification and chemisorption activity of mercury(II) N,N-di-iso-propyldithiocarbamate: Synthesis and characterisation of the heteronuclear double complex of ([Au{S2CN(iso-C3H7)2}2]2[Hg2Cl6]·OC(CH3)2)n

Abstract

A new crystalline modification (γ-form, 1) of the mercury(II) N,N-di-iso-propyldithiocarbamate (Hg-iso-PDtc) has been identified and structurally characterised using single-crystal X-ray diffraction analysis. The crystal structure of 1 is presented by centrosymmetric binuclear molecules of [Hg2{S2CN(iso-C3H7)2}4], in which the mercury atoms are interconnected by two tridentate bridging iso-PDtc ligands. The chemisorption activity of the freshly precipitated Hg-iso-PDtc was tested with respect to gold(III) in a 2M HCl solution. The novel heteronuclear gold(III)–mercury(II) double complex was found to be the sole gold-containing product of the chemisorption. The isolated compound was crystallised as a solvated form, ([Au{S2CN(iso-C3H7)2}2]2[Hg2Cl6]·OC(CH3)2)n (2). It was revealed that compound 2 adopts a polymeric structure comprising two types (‘A’ and ‘B’) of isomeric gold(III) cations [Au{S2CN(iso-C3H7)2}2]+ and centrosymmetric binuclear mercury(II) anions [Hg2Cl6]2–. The supramolecular self-organisation of 2 occurs due to the relatively weak Au···S secondary interactions between neighbouring isomeric [Au{S2CN(iso-C3H7)2}2]+ cations resulting in the formation of linear cation-cationic chains of (⋯‘A’⋯‘B’⋯‘A’⋯‘B’⋯)n. The thermal behaviour of polycrystalline samples of Hg-iso-PDtc and 2 was studied by simultaneous thermal analysis (STA). It was shown that thermal decomposition is accompanied by the formation of HgS (for the original mercury(II) complex) or quantitative reduction of gold(III) to elemental gold and formation of HgCl2 along with its partial transformation to HgS (for 2).