A Fixation Mode of Gold(III) in the Course of the Chemisorption Interaction with Cadmium cyclo-Hexamethylene Dithiocarbamate: Structural Organization and Thermal Behavior of the Heteropolynuclear Complex ([Au{S2CN(CH2)6}2]2[CdCl4] · 3/4H2O)_n (An Example of the Complicated Supramolecular Structure)

摘要

The chemisorption interaction of binuclear cadmium cyc/o-hexamethylene dithiocarbamate with H[AuCl4] in a solution of 2 M HC1 is studied. The state of the chemisorbent is monitored by ~(113)Cd and ~(13)C MAS NMR spectroscopy. The result of the heterogeneous reaction, including the chemisorption of gold(III) from a solution and partial ion exchange, is the formation of the heteropolynuclear gold(III)-cadmium complex. The crystal, molecular, and supramolecular structures of the hydrated form of the synthesized coordination compound ([Au{S2CN(CH2)6}2]2[CdCl4] · 3/4H2O)_n (I) are determined by X-ray diffraction analysis. Compound I includes three structurally nonequivalent complex cations [Au{S2CN(CH2)6}2]~+. The character of structural differences between them indicate that they correlate as conformers: cations (A), (B), and (C) are present in the ratio 2:1:1. The isomeric cations perform different functions in the self-organization of the chemical system into unusually complicated supramolecular structure I. Cations (A) form centrosym-metric dimers [Au2{S2CN(CH2)6}4]~(2+), which are involved together with cations (B) in the formation of polymeric chains ([Au2{S2CN(CH2)6}4]~(2+) · [Au{S2CN(CH2)6}2]~+)_n alternating along the chain length. Cations (C) are structurally isolated, as well as anions [CdCl4]~(2-). The chemisorption capacity of the cadmium cyc/o-hexamethylene dithiocarbamate complex calculated from the reaction of Au(III) binding is 427.2 mg of gold per 1 g of the sorbent. To establish the optimum conditions for the regeneration of bound gold, the thermal behavior of I is studied by simultaneous thermal analysis (STA). The multistage process of chemical destruction includes the desorption of hydrate water, the thermolysis of the dithiocarbamate part of the complex and [CdCl4]~(2-) (with the release of metallic gold and cadmium chloride and the partial formation of CdS), and the evaporation of CdCl2 and CdS. The final product of thermal transformations is reduced metallic gold.