Adenine acidification as a consequence of simultaneous Pt-II binding to N1 and N7 facilitates deprotonation of the exocyclic N(6)H-2 group and permits Pt-II migration from N1 to N6 under mild conditions. Starting from the trinuclear complex cis-[(NH3)(2)Pt(N1-9-MeA-N7)(2){Pt(NH3)(3))}(2)](6+) (3), stepwise migration of cis-(NH3)(2)Pt-II takes place in the alkaline aqueous solution to give initially cis-[(NH3)(2)Pt(N1-9-MeA-N7)(N6-9-MeA(-)-N7){Pt(NH3)(3)}(2)](5+) (4) and eventually cis-[(NH3)(2)Pt(N6-9-MeA(-)-N7)(2){Pt(NH3)(3)}(2)](4+) (5) (with 9-MeA = neutral 9-methyladenine, 9-MeA(-) = 9-methyladenine monoanion, deprotonated at N6). The migration process has been studied by H-1 NMR spectroscopy, and relevant acid-base equilibria have been determined. 5 has been crystallized as its nitrate salt and has been characterized by X-ray crystallography. The precursor of 3, [(NH3)(3)Pt (9-MeA-N7)]Cl-2 center dot 2H(2)O (2) has likewise been studied by X-ray analysis.