The ability of cis-{Pt(NH3)(2)(L)}(2+/+), a molecular fragment of the anticancer drug cisplatin, to bind to purines and CO by pi-back-donation from Pt to the ligand was examined computationally. Optimized geometries and computed vibrational frequencies suggest that cis-{Pt(NH3)(2)(L)}(2+/+) (L = Cl, H2O, NH3) is a poor g-donor and that pi-back-donation does not play an important role for Pt(II)-ligand interactions in general.