SYNTHESIS AND CHARACTERIZATION OF AMINO-A CID COMPLEXES OF PLATINUM(IV) STABILIZED BY CROWN-ETHERS

Crown ether complexed pentachloro(aqua)platinic acid, (H3O)[PtCl5(H2O) ]. 2(18-cr-6). 6H(2)O (1) reacts with glycine, L-alanine, and DL-2-ami nobutyric acid to give cis-[PtCl4(O-glyH)(H2O)].(18-cr-6). H2O (4a)(1) and cis-[PtCl6]. 2(18-cr-6) (amacH = glyH 5a, alaH 5b abuH 5c). The c rown ether complexed hexachloroplatinic acid, (H3O)(2)[PtCl6]. 2(18-cr -6) (2), reacts with glycine to afford (glyH(2))[PtCl4(N, O-gly)]. 2(1 8-cr-6). 1.25H(2)O (6). The structures of 4b and 6 were determined by X-ray diffraction. The alanine ligand in 4b is a zwitterion that is co ordinated to platinum by one oxygen atom of the carboxylate group only . The other oxygen atom is engaged in a strong hydrogen bond to the ci s-coordinated aqua ligand. The glycinato ligand in 6 is N,O-coordinate d at platinum forming an anion [PtCl4(N,O-gly)](-). The other oxygen a tom of the carboxylate group is involved in a strong hydrogen bridge t o the cation (glyH(2))(+). In both complexes hydrogen bridges are form ed between the -N+H3 and -NH2 groups of the amino acid ligands and the oxygen atoms of the crown ether molecules.