Rapid Equilibrium between Trigonal-bipyramidal and Square-pyramidal Geometries of 1-Popanethiolato Platinum(II) Complex with Tris[2-(diphenylphosphino)ethyl]phosphine

The rapid equilibrium between five-coordinate trigonal-bipyramidal [Pt(pt)(pp3)]+ (pt = 1-propanethiolate, pp3 = tris[2-(diphenylphosphino)ethyl]phosphine) and square-pyramidal [PtI(pt)(pp3)] with an axially coordinated I- and dissociated terminal phosphino group was clearly observed in the presence of a large excess of I- at low temperatures. Such a square-pyramidal intermediate is expected to be formed in the course of substitution reactions of trigonal-bipyramidal Pt(II) complexes.