Optically active co-ordination compounds. Part 43. Polysulphide complexes of platinum(IV)

Abstract

Brick-red [NH₄]₂[Pt(S₅)₃]·2H₂O crystallises from the reaction mixture obtained on adding K₂PtCl₆ to an aqueous ammonium polysulphide solution. Addition of concentrated hydrochloric acid results in the separation of maroon [NH₄]₂[PtS₁₇]·2H₂O. The physical properties (solubility, i.r., Raman, and electronic spectra, X-ray powder pattern) of the complexes are described. The [Pt(S₅)₃]^2– ion crystallises from solution as the racemate, whereas [PtS₁₇]^2– on crystallisation undergoes a second-order asymmetric transformation so that the solid contains an excess of the (–) enantiomer. The [Pt(S₅)₃]^2– ion was resolved by forming diastereoisomers with [ RuL₃]²⁺(L = 2,2′-bipyridyl or 1,10-phenanthroline). The circular dichroism spectra of both ions are described. The mechanism of racemisation is discussed.