MOLECULAR-METALS BASED ON 1,2,7,8-TETRAHYDRODICYCLOPENTA[CD-LM]PERYLENE AND IODINE, (CPP)2(I3)1-DELTA

The synthesis and characterization of molecular metals derived from 1, 2,7,8-tetrahydrodicyclopenta[cd:lm]perylene (CPP) by partial oxidation with iodine and with general formula (CPP)2(I3)1-delta, delta = 0-0.1 3, are reported. Single crystals, obtained either by electrocrystalliz ation or by diffusion-controlled iodine oxidation of CPP, present two types of morphologies, elongated diamond or thinner needle-shaped crys tals, both with a monoclinic cell, space group P2(1)/a, a = 4.3757(9), b = 19.3681(11), c = 10.0860(11) angstrom, beta = 98.050(8)-degrees, V = 846.4(2) angstrom3, Z = 2. The structure of the diamond-shaped cry stals was solved by X-ray diffraction to a final R(F) = 0.096, R(w)(F) = 0.069. It consists of regular stacks of CPP molecules along a with a 3.41 angstrom spacing and uncorrected one-dimensional chains of I3- located in channels between four CPP stacks corresponding to (CPP)2(I3 )0.892. The thin needle crystals have the same unit cell but an unspec ified and slightly different iodine content. Band structure calculatio ns in this structure by the extended Huckel method indicate a one-dime nsional conduction band 0.55 eV wide. These thin needle crystals prese nt, at room temperature, an electrical conductivity along the a axis s igma(a)(RT) = 200 S/cm and thermopower S(a)(RT) = 30 muV/K, while for the diamond-shaped crystals sigma(a)(RT) = 2 S/cm and S(a)(RT) = -8 mu V/K. These transport coefficients for both types of crystals indicate a metallic behavior from room temperature down to almost-equal-to 63 K , where a metal-to-insulator (M-I) transition takes place. EPR studies in single crystals show an almost isotropic line at g = 2.0044 and wi th a width of almost-equal-to 6 G in the range 80-300 K and without si gnificant differences between the two types of crystals. Static magnet ic susceptibility measurements in polycrystalline samples of the thin needles show a paramagnetic contribution of chi(P)(RT) = (1.2 -/+ 0.4) x 10(-4) emu/mol slightly decreasing upon cooling until the M-I trans ition where it vanishes, ascribed to the conduction electrons in the C PP stacks.