Synthesis and multinuclear magnetic resonance spectroscopy of the novel ionic Pt(II) mixed-ligands complexes cis- and trans-[Pt(pyrazine)2(Ypy)2](NO3)2 where Ypy = pyridine derivative

Novel ionic mixed-ligands complexes of the types cis- and trans-[Pt(pz)2(Ypy)2](NO3)2 (where Ypy is a pyridine derivative and pz = pyrazine) were synthesized and studied mainly in the solid state by IR spectroscopy and in aqueous solution by multinuclear (195Pt, 1H and 13C) magnetic resonance spectroscopy. The trans isomers with ligands containing a methyl group in ortho position on the pyridine ring could not be synthesized. The results of the solution NMR characterization have shown that the isolated compounds are pure. In 195Pt NMR, the cis complexes containing a methyl group in ortho positions were observed at lower field (average −2337 ppm) than the other cis compounds (average −2427 ppm), which is explained by the solvent effect. The trans isomers were observed at very slightly lower fields (average −2422 ppm) than the equivalent cis complexes (average −2427 ppm). In 1H NMR, the coupling constants 3J(195Pt–1HYpy) and 3J(195Pt–1Hpz) are larger in the cis compounds (∼40 Hz) than in the trans complexes (∼31 Hz). A few 4J(195Pt–1Hpz) were observed (∼16 Hz). In 13C NMR spectroscopy, the coupling constants 3J(195Pt–13Cpz) and 3J(195Pt–13CYpy) are also larger in the cis configuration (∼30 and ∼38 Hz, respectively) than in the trans isomers (∼20 Hz). One 4J(195Pt–13Cpz) could be calculated (17 Hz). The presence of the syn and anti rotamers were observed in all the cis complexes containing a pyridine derivative with a –CH3 group in ortho position. They were observed in 195Pt, 1H and 13C NMR spectroscopy. The proportion of the two rotamers is about 55% and 45%.