Reactions of the methylmercury cation with xanthine and crystal structures of μ-(xanthinato-N3,N7,N9)tris(methylmercury(II)) nitrate and μ-(xanthinato-N1,N3,N7,N9)tetrakis(methylmercury(II)) nitrate

Abstract

Compounds of the types [(CH3Hg)3X], [(CH3Hg)4X]Z, and [(CH3Hg)3(HX)]Z (where Z = NO3−, ClO4−) were obtained by reacting the methylmercury cation with xanthine (H3X) in aqueous media. The three acidic protons of H3X at N(1), N(3), and N(7) are substituted by CH3Hg+ groups in [(CH3Hg)3X]•2H2O. Crystals of [(CH3Hg)3(HX)]NO3•H2O belong to the triclinic [Formula: see text] space group, with a = 7.319(3), b = 9.466(8), c = 12.004(3) Å, α = 96,06(5), β = 95.00(3), γ = 97.69(5)°, and Z = 2. The structure was refined on 1610 nonzero reflections to an R factor of 0.038. The CH3Hg+ groups are linearly coordinated to N(3), N(7), and N(9) of a dianionic xanthine retaining its N(1)—H proton (mean Hg—N = 2.07(3) Å). The [(CH3Hg)4X]NO3 compound is monoclinic, space group C2/c, a = 24.55(2), b = 17.016(4), c = 19.108(9) Å, β = 110.26(5)°, Z = 16. The structure was refined on 1418 nonzero reflections to R = 0.046. The two independent [(CH3Hg)4X]+ ions possess methylmercury groups linearly coordinated to the four nitrogen atoms of the X3− anion (mean Hg—N = 2.07(5) Å). The compounds prepared were characterized by ir spectroscopy, and by 1H and 13C nmr. The [(CH3Hg)3X]•2H2O and [(CH3Hg)4X]Z compounds were found to remain undissociated in DMSO solution. The [(CH3Hg)3(HX)]+ salts disproportionated to some extent into [(CH3Hg)4X]+ and a lower complex which was identified as the N(7),N(9)-bonded [(CH3Hg)2(H2X)]+ ion.