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. Besides, the crystal structure of both complexes present a graphitic - overlapping involving pairs of adjacent quinoxaline rings. But, the extention of the overlapping is less.