Displacement of ammonia from planar four-co-ordinate platinum(II) complexes by cyanide. The existence of a strong cis-labilising effect by CN–

Abstract

The reactions of [Pt(NH₃)₄]²⁺, cis- and trans-[Pt(NH₃)₂(CN)₂], cis- and trans-[Pt(NH₃)₂Cl₂], and [Pt(NH₃)Cl₃]^– with CN^– in basic aqueous solution have been studied. In all cases the final product is the [Pt(CN)₄]^2– ion but where hydroxo species are produced as intermediates the final conversion can be very slow. While the displacement of the first ammonia from [Pt(NH₃)₄]²⁺ is rate limiting, many of the other species react in an observable stepwise fashion. The individual stages have been characterised and examined. The similarity of the rate constants for the displacement of NH₃ from the cis- and trans-[Pt(NH₃)₂(CN)₂] isomers suggests that, at least in the reaction with CN^–, the cis effect of CN^– is comparable to its trans effect. Possible explanations are discussed.