MIXED PLATINUM(II)-MERCURY(II) CYTOSINE NUCLEOBASE COMPLEXES WITH METAL-METAL BONDS

Reaction of trans-[a2PtL2]2+ (a = NH3 or CH3NH2; L = 1-methylcytosine, C5H7N30, or 1,5-dimethylcytosine, C6H9N30) with HgO in water yields novel heteronuclear Pt-Hg compounds containing two bridging cytosyl ligands L-, binding to Pt via N3 and to Hg via the deprotonated exocyclic amino group N4. Three representative examples have been characterized by X-ray crystallography: trans-[(CH3NH2)2Pt(I-MeC-)2Hg](NO3)2 (1d), trans-[(CH3NH2)2Pt(1,5-DiMeC-)2Hg](NO3)2.O-5H2O (2d), and trans-[(CH3NH2)2Pt(1-MeC-)2Hg]Cl(NO3) (1e). Crystal data are as follows: ld, triclinic system, space group P1BAR, a = 10. 1 57(4) angstrom, b = 10.494(4) angstrom, c = 11.452(4) angstrom, alpha = 101.33(2)-degrees, beta = 102.44(2)-degrees, gamma = 104.65(2)-degrees, V = 1111.8(7) angstrom3, Z = 2; le, monoclinic system, space group C2/m, a = 13.876(4) angstrom, b = 16.254(3) angstrom, c = 10.358(3) angstrom, beta = 11 2.02(1)0, V = 2166(l) angstrom3, Z = 4; 2d, monoclinic system, space group P2(1)/n, a = 8.614(3) angstrom, b = 20.610(6) angstrom, c = 13.984(5) angstrom, beta = 97.67(2)-degrees, V = 2461 (2) angstrom3, Z = 4. In all three compounds, Pt displays a square-pyramidal coordination sphere, with Hg in the apical position. Hg has severely distorted coordinations with two short Hg-N(4) distances, a Hg-Pt contact, and longer Hg-O3N- distances in ld (distorted octadedron) and 2d (distorted bipyramid), whereas in le the coordination around Hg is completed by Cl- (distorted bipyramid). Pt-Hg separations are 2.785(l) angstrom (1d), 2.765(1) angstrom (2d), and 2.835(1) angstrom (1e), and interactions are interpreted in terms of weak Pt-Hg bonds. The Pt-195 NMR spectra of the Pt-Hg compounds display Hg-199 satellites due to 1J coupling, consistent with Pt-Hg bonding. H-1 NMR spectra of the various Pt-Hg compounds show Pt-195 and Hg-199 coupling, as determined by decoupling and spectral editing techniques. Unlike related Pt-Pt compounds, the mixed-metal Pt-Hg species, when reacted with a large variety of N and S donor ligands X, tend to decompose with formation of trans-[a2PtL2]2+ and HgX2.