Synthesis and structure of methylmercury(II) complexes of 9-methylguanine, including the X-ray structural analysis of (9-methylguanine)-methylmercury(II) nitrate

Abstract

Methylmercury(II) nitrate reacts with 9-methylguanine (9-MeGua) in water to form solid complexes of stoicheiometry [HgMe(9-MeGuaH_–1)], [HgMe(9-MeGua)][NO₃], [HgMe(9-MeGua)][NO₃]·H₂O, and [(HgMe)₂(9-MeGuaH_–1)][NO₃]. Comparison of i.r. spectra of the solid complexes and ¹H n.m.r. spectra of [²H₆]dimethyl sulphoxide-soluble (ionic) complexes with spectra of analogous guanosine (Guo) complexes indicates that complexes of 9-MeGua and Guo with similar stoicheiometry have the same mode of binding of Hg^IIMe to the purine ring. The spectra indicate that [HgMe(9-MeGuaH_–1)] and [(HgMe)₂(9-MeGuaH_–1)][NO₃] have Hg^IIMe bonded to N(1) and both N(1) and N(7), respectively, and the complexes [HgMe(9-MeGua)][NO₃] and [HgMe(9-MeGua)][NO₃]·H₂O have Hg^IIMe bonded to N(7) with retention of a proton at N(1). Crystals of [HgMe(9-MeGua)][NO₃] are monoclinic, with a= 4.196(1), b= 15.060(4), c= 18.288(5)Å, β= 90.17(2)°, Z= 4, and space group P2₁/c. The structure has been solved by conventional Patterson and Fourier methods and refined by least-squares techniques to R 0.061 for 1 152 reflections collected by diffractometer. The complex has Hg^IIMe bound to N(7) with Hg–C 2.06(2), Hg–N(7) 2.09(2)Å, and C–Hg–N(7) 175(1)°. Mercury interacts weakly with nearby nitrate ions, with Hg ⋯ 0 2.75(2) and 2.99(2)Å; the purine ring is planar with the Hg^IIMe group slightly tilted from this plane, Hg being –0.168(1) and the carbon atom –0.411(25)Å from the plane.