CsH13Hg3NTO6, M r = 905.01, monoclinic, space group C2/c, a = 20.939 (7), b = 23.976 (3), c = 7.073 (6) A, fl = 94.29 (4) °, Z = 8, dc= 3.394 Mg m -3. The structure was refined on 1603 independent nonzero reflections to an R factor of 0-045. Ring sites N(3), N(7) and N(9) of a deprotonated adenine ligand are occupied by linearly coordinated methylmercury groups as observed in the corresponding perchlorate salt. Layers parallel to the ac plane contain parallel [adeninato(CH3Hg)3] 2+ cations bridged by nitrate ions interacting with the metal atoms. The remaining nitrate ions form strong hydrogen bonds with amino groups in the interlayer region.