A NOVEL BINDING MODE OF THE N(6)-DEPROTONATED ADENINE - SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION AND X-RAY STRUCTURE OF BIS(MU-9-ETHYLADENINATO-N1,N6) BIS(BIS(TRIMETHYLPHOSPHINE)PLATINUM(II) DINITRATE

9-Ethyladenine (9-EtAd) reacts with cis-[(PMe3)2Pt(mu-OH)]2(NO3)2 in a queous solution at ambient temperature to give the adduct cis-[(PMe3)2 Pt(mu-9-EtAd(-H))]2(NO3)2 which has been characterized in the solid st ate by single-crystal X-ray analysis. The complex crystallizes in the triclinic system, space group P1BAR, with a=10.359(5), b=11.224(5), c= 21.056(9) angstrom, alpha=85.09(3), beta=88.69(4), gamma=83.90(4)degre es, Z=2. The structure was solved from 3455 reflections to R=0.075. Th e molecular structure of the cationic complex exhibits two cis-(PMe3)2 Pt units which are bridged by two NH2-deprotonated adenine molecules t hrough the N(1) and N(6) atoms (mean Pt-N distance of 2.10 angstrom) i n a head-to-tail fashion. The two purine rings are virtually perpendic ular (dihedral angle of 101.4-degrees) and each ring forms with the pl atinum coordination planes angles of 87.6 and 89.3-degrees. The comple x has been characterized in solution by H-1 and P-31 NMR spectroscopy. The H(2) and H(8) resonances, which are indistinguisbable in the prot on spectrum of the free base, appear well differentiated upon platinat ion of the nucleobase, with the H(2) proton coupled to the metal centr e (3J(PtH) 15.5 Hz). The presence of long-range platinum-phosphorus in teractions in the P-31 spectrum indicates that the dinuclear structure found in the solid state is maintained in solution.