Electrochemistry, protein binding and crystal structures of platinum(II) and platinum(IV) carboxylato complexes

The crystal structures of the platinum(II) complexes [Pt(ox)(en)] (ox = oxalato, en = ethane-1,2-diamine) and [Pt(ethmal)(en)] (ethmal = ethylmalonato), and of their platinum(IV) analogues, trans-[Pt(OH)(2)(ox)(en)].H2O and trans-[Pt(ethmal)(OH)(2)(en)], have been determined. All crystallize in the monoclinic space group P2(1)/c, with the exception of trans-[Pt-IV(OH)(2)(ox)(en)].H2O which crystallizes in C2/c. The ethylmalonato ligand in [Pt II (ethmal)( en)] adopts a pseudo-boat conformation. Changes in the fold angles of the boat occur on oxidation and introduction of the trans hydroxo ligands. The cathodic forward half-wave potentials of the platinum(IV) complexes (including trans-[Pt(mal)(OH)(2)(en)], mal = malonato) are reported and reveal that these complexes are more difficult to reduce than analogous complexes with equatorial chloro ligands. The binding of trans-[Pt(OH)(2)(ox)(en)].H2O and trans-[Pt(mal)(OH)(2)(en)] to mouse albumin was investigated with no binding observed after 6 h and a very small amount observed for the latter complex after 24 h.