Studies on five-co-ordinate d8 metal ions. Part 3. Stability constants for the reversible formation of five-co-ordinate complexes from the bis(2,2′bipyridine)- and bis(1,10-phenanthroline)-platinum(II) cations

Abstract

The dipositive ions bis(1,10-phenanthroline)platinum(II) and bis(2,2′-bipyridine)platinum(II) both add nucleophiles reversibly in aqueous solution giving five-co-ordinate products. The stability constants for complex formation with 12 different nucleophiles (Nu) have been determined at 23.0 ± 0.5 °C. It has been shown that the stability constants for the phenanthroline (K_phen) and the bipyridine (K_bipy) complexes correlate according to the expression log₁₀K_phen= 1.01 (log₁₀K_bipy)– 1.21. These series of stability constants were compared with rate and stability data from the literature; the values correlate only with the equilibrium constants for the reaction [PtCl₂(C₂H₄)(H₂O)]+ Nu ⇌[PtCl₂(C₂H₄)(Nu)]+ H₂O. In all cases a slow substitution reaction followed the rapid equilibrium. This substitution was faster for the bipyridine complexes than for the phenanthroline complexes.