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.