SYNTHESIS AND STRUCTURE OF METHYLMERCURY(II) COMPLEXES OF 9-METHYLGUANINE, INCLUDING THE X-RAY STRUCTURAL-ANALYSIS OF "(9-METHYLGUANINE)-METHYLMERCURY(II) NITRATE

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 ⋯ O 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.