MONONUCLEAR AND POLYNUCLEAR GUANINE COMPLEXES OF PLATINUM(II) - SYNTHESES AND CRYSTAL AND MOLECULAR-STRUCTURES OF BIS(9-METHYLGUANINE-N(7))BIS (TRIMETHYLPHOSPHINE)PLATINUM(II) DINITRATE AND )HEXAKIS(CIS-BIS-(TRIMETHYLPHOSPHINE)PLATINUM(II)) HEXANITRATE

The synthesis and characterization of the guanine complexes cis-[(PMe( 3))(2)Pt(9-MeGu)(2)](NO3)(2) and cis-[(PMe(3))(2)Pt(9-MeGu(-H))]6NO3)( 6) (9-MeCu and 9-MeGu(-H) are the neutral and the N(1)-deprotonated 9- methylguanine, respectively) are reported. The mononuclear derivative is formed by reacting 2 equiv of nucleobase with an aqueous solution o f cis-[(PMe(3))(2)Pt(NO3)(2)] at autogenous pH, and it crystallizes fr om methanol in the tetragonal system, space group P4(1)2(1)2, with the following cell dimensions: a = b = 11.106(4) Angstrom, 48.89(3) Angst rom, Z = 8. The structure was solved using 3562 observed reflections a nd refined to R = 3.98 and R(w) = 5.02%. The nucleobases are N(7)-bond ed to the metal center of the cis-(PMe(3))(2)Pt unit (Pt-P = 2.250(4) Angstrom (average); Pt-N(7) = 2.11(1) Angstrom P-Pt-P = 96.2(2)degrees ; N-Pt-N = 83.2(5)degrees) in a head-to-tail arrangement. The two puri ne rings are almost perpendicular to the metal-coordination plane (dih edral angles 83.6 and 101.7 degrees) and form an intraligand dihedral angle of 77.6 degrees. The hexanuclear complex is formed when equimola r amounts of cis-[(PMe(3))(2)Pt(NO3)(2)] and 9-MeCu are reacted at neu tral pH. Crystallization of the crude product from water affords color less prisms which crystallize as cis-[(PMe(3))(2)Pt(9-MeGu(-H))](6)(NO 3)(6) . 18H(2)O, in the hexagonal system, space group R (3) over bar, with the following cell dimensions: a = b = 23.178 (3) Angstrom, c = 2 4.937(3) Angstrom, Z = 3. The structure was solved using 2094 independ ent observed reflections and refined to R = 5.64 and R(w) = 5.97%. The compound contains the cyclic cation cis-[(PMe(3))(2)Pt(9-MeGu(-H))](6 +)(6) in which six cis-(PMe(3))(2)Pt units are symmetrically bridged b y deprotonated guanine ligands through their N(1) and N(7) atoms. The hexamer, with an S-3 symmetry, exhibits the purine rings alternatively disposed above and below the mean plane passing through the metal ato ms and forming with this plane an angle of 50 degrees. The adjacent pl atinum atoms are disposed alternatively in two parallel planes, slight ly separated (0.34 Angstrom), at a minimum distance of 6.5 Angstrom. E ach metal atom is in a distorted square-planar arrangement defined by the phosphorus atoms of two PMe(3) moieties [(Pt-P = 2.245(7) Angstrom (average); P-Pt-P = 94.9(2)degrees] and the N(1) [Pt-N(1) = 2.12(2)An gstrom] and N(7)' [Pt-N(7)' = 2.09(1) Angstrom; N(1)-Pt-N(7) = 83.4(5) degrees] atoms of two deprotonated guanine ligands. Both complexes hav e been further characterized by H-1 and P-31 NMR spectroscopy.