Chemisorption binding of gold(III) from solutions with bismuth dipropyldithiocarbamate: Supramolecular self-assembly (role of the secondary Au…S and aurophilic interactions) and thermal behavior of the solvated heteropolynuclear ionic type complex ([Au{S2CN(C3H7)2}2]3[Bi2Cl9] • 0.5CO(CH3)2 • 0.5HCl) n

Abstract

The reaction of binuclear bismuth(III) N,N-dipropyldithiocarbamate [Bi2{S2CN(C3H7)2}6] with a solution of AuCl3 in 2 M HCl was studied. Crystallization of the heterogeneous reaction products from an acetone solution afforded the polymeric solvated heteropolynuclear gold(III)–bismuth complex, ([Au{S2CN(C3H7)2}2]3[Bi2Cl9] · 1/2CO(CH3)2 · 1/2HCl)n (I). According to X-ray diffraction data (CIF file CCDC no. 1050766), the structure of I comprises four isomeric [Au{S2CN(C3H7)2}2]+ cations in 1: 1: 2: 2 ratio, namely: cation “A” with the Au(1) atom, cation “B” with the Au(2) atom, cation “C” with the Au(3) atom, and cation “D” with the Au(4) atom, and the discrete binuclear [Bi2Cl9]3– anions. The isomeric gold(III) complex cations are involved in the construction of two types of cationic triads, [“C”···“A”···“C”] and [“D”···“B”···“D”], through secondary bonds and short Au···S contacts. The cation types differ by both the nature of binding and the Au–Au distances. The weak aurophilic binding between the cationic triads (Au···Au 3.5416(2) A) gives rise to zigzag-like polymeric chains (···[“C”···“A”···“C”]···[“D”···“B”···“D”]···)n extended along the y axis. In turn, the [Bi2Cl9]3– anions located on one side of polymer chains are held by the secondary Cl···S bonds. The outer-sphere CO(CH3)2 and HCl solvate molecules joined by hydrogen bonds are located in the space between bismuth anions. The thermal behavior of I was studied by simultaneous thermal analysis. The thermal destruction of the complex includes desolvation and thermolysis of the dithiocarbamate moiety and [Bi2Cl9]3– with liberation of gold metal and bismuth chloride (which is subsequently evaporated) and partial formation of Bi2S3. In the temperature range of 712–828°C, bismuth sulfide is oxidized to (BiO)2SO4, which decomposes above 828°C to give Bi2O3. Bismuth(III) oxide and reduced gold are the final products of thermal transformations.