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-Me A) at pH 2.5 and in the presence of NaClO4 yields the compound [Hg(9-M eAH-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: monoc linic, P2(1)/a, a=16.438(6), b=14.381(5), c=10.210(4) Angstrom, beta=9 0.23(3)degrees, V=2414(3) Angstrom(3), Z=4. Hg is six-coordinate but d isplays a highly irregular coordination geometry with valence angles a t the mercury ranging from 68.2(3) to 159.2(4)degrees. There are no tw o ligand donor atoms that are at least approximately colinear with the heavy metal ion. This asymmetry appears to be a consequence of relati vely weak bonds between Hg(II) and the protonated adenine nucleobases (2.11(1) and 2.12(1) Angstrom). The findings are briefly discussed wit h regard to possible geometries of Hg(II)-DNA cross-links. (C) 1998 El sevier Science S.A.