Abstract Methylmercury(II) complexes of 1-methyladenine (1made) have been isolated from aqueous solution in the pH range 2–12 and structurally characterized by 1H NMR spectroscopy and X-ray analysis. The results establish N9 as the primary and N7 as the secondary binding site for CH 3Hg + with neutral 1-methyladenine. Crystal structure determinations for [1madeH]Cl and [1madeH 2]Cl 2 demonstrate that N9 is the first and N7 the second protonation site for 1-methyladenine. The cations [(HgCH 3)(1made)] +, [(HgCH 3)(1madeH)] 2+ and [(HgCH 3) 3(1made)] 3+ display N9-, N7- and N3,N7,N9-coordination, respectively. Metallation of the amino nitrogen N6 is observed for complexes crystallized from aqueous solution at pH values above 8. The complexes [(HgCH 3)(1madeH −1)]·H 2O and [(HgCH 3) 2(1madeH −1)][NO 3]·2H 2O exhibit N6- and N6,N9-coordination, respectively.