Structural and coordinating properties of platinum(II) chloride complexes with polypyridyl ligands. Single crystal X-ray structure of [Pt(ddpq)Cl2]·H2O (ddpq=6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline)

The X-ray crystallographic study of the methylated complex [Pt(ddpq)Cl2] (ddpq=6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline) has been carried out and compared with that of the non-methylated derivative [Pt(dpq)Cl2] (dpq=2,3-di(2-pyridyl)quinoxaline). In both complexes the polypyridyl ligands are bonded bidentally by using their pyridyl nitrogen atoms. Also, the crystal structures of both complexes present a graphitic π–π overlapping involving pairs of adjacent quinoxaline rings. But, the extension of the overlapping is less in the methylated derivate than in the non-methylated one. Also, the complex [Pt(dhp)Cl2] (dhp=2,3-di(2-pyridyl)-5,6-dihydropyrazine) was synthesized to study the bonding feature by using a ligand containing a non-aromatic pyrazine moiety. In spite of forming species of similar formula to that of the dpq and ddpq ligands, [Pt(dhp)Cl2], the dhp ligand is bonded to the Pt(II) by using one pyridyl nitrogen and one dihydropyrazine nitrogen atom, as shown by 1H NMR spectroscopy.