Fixation modes of gold(III) from solutions using cadmium(II) dithiocarbamates. Preparation, supramolecular structure and thermal behaviour of polynuclear and heteropolynuclear gold(III) complexes: Bis(N,N- dialkyldithiocarbamato-S,S′)gold(III) polychlorometallates

Article abstract of DOI:10.1016/j.poly.2012.03.043

Four novel heteropolynuclear and polynuclear complexes of the general formulae [Au(S₂CNR₂)₂]₂X (X = [CdCl₄]^2-, R = CH₃ (1); X = [Cd ₂Cl₆]^2-, R = C₃H₇ (2)) and [Au(S₂CNR₂)₂][AuCl₄] (R = iso-C₃H₇ (3); R = iso-C₄H₉ (4)) were prepared using heterogeneous reactions between appropriate freshly precipitated binuclear cadmium(II) dialkyldithiocarbamates and AuCl₃ in 2 M hydrochloric acid. The isolated complexes were studied by ¹³C CP/MAS NMR spectroscopy, single-crystal X-ray diffraction and simultaneous thermal analysis (STA) under an argon atmosphere. In all molecular structures (1-4), one of the gold atoms coordinates two dialkyldithiocarbamate ligands in the S,S′-bidentate mode, forming a square-planar coordination polygon [AuS₄], while the other gold atom (in 3 and 4) has four neighbouring chlorine atoms [AuCl₄]. At the supramolecular level, compounds 1 and 2 comprise binuclear cations, [Au₂{S₂CN(CH ₃)₂}₄]²⁺ and polynuclear chains, ([Au{S₂CN(C₃H₇)₂}₂] ⁺)_n in a combination with [CdCl₄]^2- and [Cd₂Cl₆]^2- anions, respectively. Unexpected structural distinctions at the supramolecular level were discovered for the chemically related compounds 3 and 4. In these ionic complexes, there are either cationic trinuclear formations, {[Au{S₂CN(iso-C₃H ₇)₂}₂]₂[AuCl₄]} ⁺, or polynuclear chains, ([Au{S₂CN(iso-C ₄H₉)₂}₂]⁺)_n, both combined with [AuCl₄]^- anions, in the structural basis of compounds 3 and 4, respectively.