The crown ether influence on ligand exchange reactions of Na2PtCl6 with glycine and D-(+)-alanine; synthesis and characterization of platinum(IV) amino acid complexes

The reaction of Na2PtCl6 with glycine in water yields cis-[PtCl2(gly)2] (1). [Na(18-cr-6)]2[PtCl6]·3H2O reacts with glycine and D-(+)-alanine in water to give [Na(18-cr-6)(H2O)2][PtCl4(gly)]·(18-cr-6) (2) and [Na(18-cr-6)][PtCl4(ala)] (3), respectively. Cis-[PtCl4(glyH)2]·2(18-cr-6) (4) and cis-[PtCl4(alaH)2]·(18-cr-6) (5), respectively, are formed when the reaction mixture is irradiated with light from a halogen lamp. All complexes were characterized by microanalysis as well as by NMR, IR and Raman spectroscopy revealing that in complexes 1–3 the glycinato and alaninato ligands act as N,O-chelate ligands whereas in complexes 4 and 5 the amino acids act as N-donor ligands. The molecular structure of 1 (orthorhombic, Pbca, a=10.163(2), b=11.028(2), c=16.310(4) A, Z=8, R1=0.0413, wR2=0.0953) exhibits a distorted octahedral coordinated Pt atom with a cis-PtCl2 unit and two N,O-coordinated glycinato ligands (OC-6-32). The complex is stabilized by intramolecular hydrogen bonds between the amino group and the C–O group as well as the chloro ligand. The crystal structure of 2 (orthorhombic, Pnma, a=23.262(9), b=11.149(4), c=15.834(5) A, Z=4, R1=0.067, wR2=0.1644) shows a [PtCl4(gly)]− unit and an [Na(18-cr-6)(H2O)2]+ unit linked via hydrogen bridges with a further crown ether molecule.