Synthesis and X-ray crystal structure analysis of 1:1 and 1:2 complexes of cisplatin with the model nucleobase 9-methyladenine in its protonated form and a unique HNO3 adduct of cis-[(NH3)2Pt(9-MeAH-N7)2]4+

The 1:1 and 1:2 complexes of cis-(NH3)2PtII with 9-methyladeninium cations, 9-MeAH+, have been prepared and characterized by X-ray crystallography: cis-[(NH3)2Pt(9-MeAH-N7)Cl](NO3)2 (1) and cis-[(NH3)2Pt(9-MeAH-N7)2](NO3)4 · 2HNO3 · 2H2O (2). The pKa values for 9-MeAH+ in H2O are 1.7 in 1 as well as 0.4 (pKa1) and 1.3 (pKa2) for 2, as determined by pD dependent 1H NMR spectroscopy. Compound 2 is special in that it crystallizes with two equivalents of HNO3 per Pt entity. The HNO3 molecules are stacked in rectangular channels provided by cis-(NH3)2PtII units, 9-methyladeninium ligands and nitrate anions, which form a porous network of hydrogen bonds.