Complexes of methylmercury(II) with 1-methylcytosine and crystal structure of μ-(1-methylcytosinato-N3,N4)bis(methylmercury(II)) nitrate

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Abstract
Two types of solid complexes are isolated by reaction of CH3HgX (X = NO3 and ClO4) with 1-methylcytosine (MCy). The CH3Hg+ ion is probably bonded to N(3) in the [CH3Hg(MCy)]X compounds. Mercury binding to N(3) and the deprotonated amino group in [(CH3Hg)2(MCy—H)]X is confirmed by X-ray work on the nitrate salt. The crystals are orthorhombic, space group Pbca, with a = 12.014, b = 13.573, c = 16.353 Å, and Z = 8. The structure was refined on 962 independent reflections to an R factor of 0.038. The CH3Hg+ groups are arranged in a syn configuration and the angles around the mercury-bonded nitrogen atoms are severely distorted to prevent short Hg … Hg contacts. N(3)-coordination in the 1:1 complexes introduces minor changes in the infrared spectra, but the substitution of an amino proton in the 1:2 compounds produces important modifications. 1H nmr data in DMSO-d6 are reported for both types of compounds. This work emphasizes the important acidity enhancement experienced by the amino protons upon initial coordination to N(3), which facilitates further reaction of CH3Hg+ by proton displacement even in acidic media.