Gold(III) preconcentration from acid solutions by cadmium diisopropyldithiocarbamate: Gold(III)-binding species, supramolecular structure, and thermal properties of the heteropolynuclear complex ([Au{S2CN(iso-C3H7)2}2]2[CdCl4] · 1/2C3H6O) n

Abstract

The reaction of binuclear cadmium diisopropyldithiocarbamate with a solution of AuCl3 in 2 M HCl was studied. The heterogeneous reaction of gold(III) binding follows a chemisorption scenario (in combination with partial ion exchange) and yields a heteropolynuclear gold(III)-cadmium complex. The molecular and crystal structure of a solvated species of the compound, namely ([Au{S2CN(iso-C3H7)2}2]2[CdCl4] · 1/2C3H6O)n (I), was solved by X-ray crystallography. The structure of complex I contains (in the ratio 1: 1) structurally nonequivalent molecular cations [Au{S2CN(iso-C3H7)2}2]+; the differences between these cations allow them to be classified as conformational isomers (cations A and B). The specifics of the supramolecular organization of complex I consist of the alternation of layers of [Au2{S2CN(iso-C3H7)2}4]2+ binuclear cations (formed by cations A), ([Au{S2CN(iso-C3H7)2}2]+)n polymer chains (formed by cations B), and [CdCl4]2− anions. The chemisorption capacity of the precursor cadmium diisopropyldithiocarbamate as calculated from the gold(III) binding reaction is 423.5 mg Au3+ per gram of sorbent. The thermal properties of complex I were studied by simultaneous thermal analysis (STA) in order for the parameters of sorbed gold recovery to be determined. The multistep thermal destruction process involves desorption of solvating acetone molecules, thermolysis of the dithiocarbamate part of the complex and [CdCl4]2− with release of metallic gold and cadmium chloride and formation of CdS, as well as vaporization of CdCl2 and CdS. The only final product of thermal conversions is reduced metallic gold.