PT(II) COMPLEXES OF AMINO-ACIDS AND PEPTIDES .3. X-RAY-DIFFRACTION STUDY OF [CL(PH3P)PT(H-AIB-O)]

The complex [Cl(Ph3P)Pt(H-Aib-0)], where Ph3P and H-Aib-0 are triphenylphosphine and alpha-aminoisobutyrate, respectively, has been synthesized and characterized in the solid state by X-ray diffraction analysis. It crystallizes as a monobydrate in the triclinic system, space group P1BAR with a=9.020, b=10.011, c=13.748 angstrom, alpha=91.74, beta=90.29, gamma=111.26-degrees and Z=2 molecules per unit cell. The crystal structure has been solved by the Patterson technique and refined to a final R factor of 0.038 for the 3826 observed reflections with I greater-than-or-equal-to 3.0 sigma(I). The Pt(II) atom displays the square planar coordination with the H-Aib-O- amino acid acting as a bidentate ligand. The N atom of the H-Aib-O- residue in trans position with respect to the P atom of the triphenylphosphine moiety and correspondingly the O atom of the carboxylate is trans to the chlorine atom. The observed distortions in the bond angles around the Pt(II) atom as well as the conformation assumed by the triphenylphosphine and the H-Aib-O- residue can be all explained on the basis of the need to release the intramolecular non-bonded interactions between atoms of the various ligands. Three intermolecular hydrogen bonds, involving as donors the cocrystallized water molecule and the two hydrogen atoms of the N-H groups and as acceptors the chlorine, the oxygen of the water molecule, and one of the oxygen atoms of the carboxylic acid group, together with van der Waals interactions between hydrophobic groups held the molecules in the crystal state.