A Fixation Mode of Gold(III) in the [Zn2{S2CN(iso-C3H7)2}4]- [AuCl4]~-/2 M HCl Chemisorption System: Supramolecular Structure and Thermal Behavior of the Heteropolynuclear Complex ([H3O][Au3{S2CN(iso-C3H7)2}6][ZnCl4]2 · H2O)_n

摘要

The interaction of freshly precipitated binuclear zinc dithiocarbamate [Zn2{S2CN(iso-C3H7)2}4] with solutions of AuCl3 in 2 M HC1 is studied. The heterogeneous reaction includes the chemisorption of gold(III) and the partial ion exchange to form a polynuclear ionic gold(III)—zinc complex. The molecular and supramolecular structures of the individual fixation mode of gold(III), coordination compound (H3O[Au3{S2CN(iso-C3H7)2}6][ZnCl4]2 · H2O)_n (I), are determined by X-ray diffraction analysis. Compound I includes three complex cations [Au{S2CN(iso-C3H7)2}2]~+, two of which (noncentrosymmetric, A) are structurally nonequivalent with respect to the third cation (centrosymmetric, B). The structural self-organization of compound I includes the formation of linear trinuclear fragments [Au3{S2CN(iso-C3H7)2}6]~(3+) by three cations (2A and B) due to nonsymmetric secondary Au—S bonds. The interaction between the [Au3{S2CN(iso-C3H7)2}6]~(3+) fragments results in the formation of zigzag polymer chains ([Au3{S2CN(iso-C3H7)2}6]~(3+))_n. The outer-sphere water molecule and the hydronium ion are involved in the pairwise linkage of the [ZnCl4]~(2-) anions due to hydrogen bonds Cl···O. The chemisorption capacity of the zinc dithiocarbamate complex calculated from the reaction of gold(III) fixation is 471.2 mg of gold per 1 g of the sorbent. The conditions for the isolation of chemisorbed gold are determined by the simultaneous thermal analysis of the thermal behavior of compound I. The multistage thermal destruction includes two steps of dehydration of the complex, the thermolysis of the dithiocarbamate moiety and [ZnCl4]~(2-) (with the release of metallic gold and zinc chloride and the partial formation of ZnS), and the evaporation of ZnCl2. The final products of the thermal transformations are metallic gold and ZnS.