SYNTHESIS, CRYSTAL-STRUCTURE, AND C-13 NMR-SPECTRA OF ALPHA-PYRROLIDONATO-BRIDGED HEAD-TO-HEAD [PTIII2(NH3)4(C4H6NO)2(NO2)(NO3)](NO3)2.H2O AND ELECTROCHEMICAL STUDY ON CONVERSION OF THE BINUCLEAR PLATINUM(III) COMPLEX INTO A TETRANUCLEAR PLATINUM(III) COMPLEX

The alpha-pyrrolidonate-bridged binuclear Pt(III) complex [Pt(III)2(NH3)4(C4H6NO)2(NO2)(NO3)](NO3)2.H2O was prepared by oxidation of [Pt(II)2Pt(III)2(NH3)8(C4H6NO)4](NO3)6.2H2O with HNO3. The crystal structure, C-13 and Pt-195 NMR and UV-vis spectra, and the electrochemical properties are reported. The crystal is monoclinic, P2(1)/c, with the cell dimensions a = 10.019 (2) angstrom, b = 25.196 (6) angstrom, c = 9.714 (4) angstrom, beta = 112.39 (2)-degrees, Z = 4, and V = 2267 (1) angstrom 3. The two Pt(III) atoms are bridged by two alpha-pyrrolidonate ligands in a head-to-head manner. Each Pt(III) atom is also coordinated by two NH3 groups in cis position. One of the Pt atoms is axially coordinated by NO2- and the other is by NO3-. Cyclic voltammogram of the compound in 0.05 M H2SO4 shows an irreversible redox wave at E(pc) = 0.12 V and E(pa) = 0.70 V vs SCE; however, the wave gradually changes to E(pc) = 0.48 V and E(pa) = 0.55 V after repetitive cyclic scans. This change corresponds to the electrochemical reduction of the compound to [Pt(II)2(NH3)4(C4H6NO)2]2+, which is then electrochemically oxidized not to the original compound but to [Pt(III)4-(NH3)8(C4H6NO)4]8+. Therefore, on repeated scans, the original binuclear Pt(III) compound is gradually converted to a tetranuclear Pt(III) compound.