Synthesis and characterization of the novel Pt(II) complexes of the types cis- and trans-Pt(Ypy)(pyrazine)Cl 2, K 2[Cl 3Pt(μ-pyrazine)PtCl 3] and trans, trans-(Ypy)Cl 2Pt(μ-pyrazine)Pt(Ypy)Cl 2 (Ypy = pyridine derivative)

Abstract

New types of Pt(II) mixed-ligand complexes containing a pyridine derivative (Ypy) and pyrazine (pz) were synthesized. The compounds were characterized by infrared spectroscopy and by multinuclear ( 1H, 13C and 195Pt) magnetic resonance. The complexes cis-Pt(Ypy)(pz)Cl 2 were synthesized from the reaction of K[Pt(Ypy)Cl 3] with pyrazine (1:1 proportion) in water. When the reaction was carried on in a 2:1 ratio, a mixture of compounds was obtained, which was refluxed in CH 2Cl 2 for several days. The final product was found to be pure and it was identified as trans, trans-Cl 2(Ypy)Pt(μ-pyrazine)Pt(Ypy)Cl 2. The cis monomers isomerize to the trans isomers in organic solvents. Different methyl derivatives of pyridine were studied in order to determine the influence of substitution in ortho position on the pyridine ligand in the complexes. In IR spectroscopy, the cis monomers showed two ν(Pt–Cl) bands, while the trans monomers and dinuclear species showed only one ν(Pt–Cl) band. The NMR results were interpreted in relation to the solvent effect, which seems important in these complexes. The 195Pt NMR signals of the cis monomers were found at slightly higher fields than those of the corresponding trans isomers. The coupling constants J( 195Pt– 1H) and J( 195Pt– 13C) are larger in the cis geometry. The δ( 195Pt) of the dinuclear species were found close to those of the trans monomers and the coupling constants are similar to those of the trans monomers, strongly suggesting a trans–trans configuration for the dinuclear compounds. The pyrazine-bridged complex K 2[Cl 3Pt(μ-pz)PtCl 3] was also synthesized and spectroscopically studied. The crystal structures of the compounds cis-Pt(3,5-lut)(pz)Cl 2 and trans-Pt(2,4,6-col)(pz)Cl 2 were determined by X-ray diffraction methods.