Binding of Au3+ from solutions by nickel(II) and cadmium diisopropyl dithiophosphates: MAS 31P NMR, structure and thermal behavior of the polynuclear complex [Au2{S2P(O-iso-C3H7)2}2] n

The paper deals with reactions of freshly precipitated diisopropyl dithiophosphate (Dtph) complexes of nickel(II), [Ni{S2P(O-iso-C3H7)(2)}(2)] and cadmium, [Cd-2{S2P(O-iso-C3H7)(2)}(4)], with the [AuCl4](-) in 2M HCl, resulting in gold transition from the solution to the precipitate as polymeric gold(I) diisopropyl dithiophosphate. The reduction of gold(III) to gold(I) noted in both cases is due to oxidation of the relevant part of the Dtph group to bis(O,O'-di-(iso)-propoxythiophosphoryl) disulfide, (iso-C3H7O)(2)P(S)S-S(S)P(O-iso-C3H7)(2). The polynuclear gold(I) complex [Au-2{S2P(O-iso-C3H7)(2)}(2)] (n) (I) was isolated on a preparative scale from the chemisorption system and studied by MAS P-31 NMR and X-ray diffraction. The key structural unit of I is the non-centrosymmetric binuclear molecule [Au-2{S2P(O-iso-C3H7)(2)}(2)] in which the gold atoms are connected by two bridging Dtph groups. The structure contains two types of non-equivalent binuclear molecules related as conformational isomers. Owing to the relatively weak Au-Au contacts, the neighboring binuclear [Au-2{S2P(O-iso-C3H7)(2)}(2)] molecules are involved in an infinite polymeric chain with conformer alternation along the chain. To elucidate the conditions for the recovery of bound gold(I), the precipitates formed in the sorption systems were studied by simultaneous thermal analysis under argon. As the final product, thermolysis gives reduced metallic gold. The ability of dithiophosphate complexes to bind gold from a solution is much lower than that of dithiocarbamate complexes, which is due to oxidation of some Dtph groups to disulfide.