A bis(9-methyladeninium) complex of Hg(II) with a highly irregular coordination geometry: [Hg(9-MeAH-N7)(2)(H2O)(NO3)(3)]ClO4

Reaction of Hg(NO3)(2) with the model nucleobase 9-methyladenine (9-MeA) at pH 2.5 and in the presence of NaClO4 yields the compound [Hg(9-MeAH-N7)(2)(H2O)(NO3)(3)]ClO4 with two 9-methyladeninium ligands bound to Hg(II) via the N7 positions. The X-ray structure is reported: monoclinic, P2(1)/a, a=16.438(6), b=14.381(5), c=10.210(4) Angstrom, beta=90.23(3)degrees, V=2414(3) Angstrom(3), Z=4. Hg is six-coordinate but displays a highly irregular coordination geometry with valence angles at the mercury ranging from 68.2(3) to 159.2(4)degrees. There are no two ligand donor atoms that are at least approximately colinear with the heavy metal ion. This asymmetry appears to be a consequence of relatively weak bonds between Hg(II) and the protonated adenine nucleobases (2.11(1) and 2.12(1) Angstrom). The findings are briefly discussed with regard to possible geometries of Hg(II)-DNA cross-links. (C) 1998 Elsevier Science S.A.