Pt(II) Complexes of Amino Acids and Peptides. II. Structural Analysis of trans-[Cl2-Pt-(H-Aib-OH)2] and trans-[Pt-(H-Aib-O-)2]

The trans-[Cl2-Pt-(H-Aib-OH)2] and trans-[Pt-(H-Aib-O-)2] complexes have been synthesized and characterized in solution and in the solid state. Their crystal and molecular structures have been determined by X-ray diffraction analyses. The complexes show a distorted planar coordination around the heavy atom. The organic moiety in the two complexes shows different conformations: in trans-[Pt-(H-Aib-O-)2] the amino acid residue, acting as a bidentate, is forced to assume an unusual conformation. On the other hand, in trans-[Cl2-Pt-(H-Aib-OH)2], in which the amino acid acts as a monodentate ligand, the alpha-aminoisobutyric acid assumes an extended conformation, which in general for alpha-monosubstituted amino acid residues coordinated to the platinum should be the preferred conformation. In both crystal structures hydrogen bonds are formed between the donor and acceptor groups with further stabilization deriving from van der Waals interactions between hydrophobic moieties.