[Pt(bipy)(ONO₂)₂] and [{(bipy)Pt(μ-O₂NO)₂Pt(bipy)}₂](NO₃)₄ : Empirically identical but structurally distinct complexes obtained from a basic aqueous solution of [Pt(bipy)₂ ](NO₃)₂

Abstract

Vapour diffusion of acetonitrile into a basic aqueous solution of [Pt(bipy)2](NO3)2·H2O results in slow crystallisation of a mixture of the monomeric complex [Pt(bipy)(ONO2)2]·5.25H2O and the tetrameric complex [{(bipy)Pt(μ-O2NO)2Pt(bipy)}2](NO3)4·8.5H2O, the structures of which were confirmed by X-ray crystallography. Calculations on the tetrameric complex show that the central Pt–Pt bond is weak, as evidenced by the fact that inclusion of dispersion forces is required to prevent the cation from dissociating into two [(bipy)Pt(μ-O2NO)2Pt(bipy)]2+ dimers. Isolation of the monomeric and tetrameric complexes shows that one of the bipy ligands in the [Pt(bipy)2]2+ cation is easily displaced in basic aqueous solution. This displacement may be a consequence of OH− attack at the Pt ion.