Molecular Metals Based on 1,2,7,8-Tetrahydrodicyclopenta[cd:lm]perylene and Iodine; (CPP)2(I2)1-delta

Jorge Manuel Ferreira Morgado; Isabel C. Santos; Rui Teives; Marc Fourmigué; Pedro Matias; Luís Filipe Coelho Veiros; Maria José Calhorda; Maria Teresa Duarte; Luís Joaquim; Manuel Almeida

Informações chave

Autores:

Jorge Manuel Ferreira Morgado (Jorge Manuel Ferreira Morgado); Isabel C. Santos; Rui Teives (Rui Teives Henriques); Marc Fourmigué; Pedro Matias; Luís Filipe Coelho Veiros (Luís Filipe Coelho Veiros); Maria José Calhorda; Maria Teresa Duarte (Maria Teresa Nogueira Leal da Silva Duarte); Luís Joaquim (Luís Joaquim Alcácer); Manuel Almeida

Publicado em

1994

Resumo

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 generalformula (CPP)2(I3)1-delta, delta = 0-0.13, are reported. Single crystals, obtained either by electrocrystallization or by diffusion-controlled iodine oxidation of CPP, present two types of morphologies, elongated diamond or thinner needle-shaped crystals, both with a monoclinic cell, space group P21/a, a = 4.3757(9), b = 19.3681(11), c = 10.0860(11) A, beta = 98.050(8) deg, V = 846.4(2) A3, Z = 2. The structure of the diamond-shaped crystals was solved by X-ray diffraction to a final R(F) = 0.096, Rw(F) = 0.069. It consists of regular stacks of CPP molecules along a with a 3.41 A 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 unspecified and slightly different iodine content. Band structure calculations in this structure by the extended Huckel method indicate a onedimensional conduction band 0.55 eV wide. These thin needle crystals present, at room temperature, an electrical conductivity along the a axis sigma(a)(RT) = 200 S/cm and thermopower S(a)(RT) = 30 microV/K, while for the diamond-shaped crystals sigma(a)(RT) = 2 S/cm and S(a)(RT) = -8 microV/K. These transport coefficients for both types of crystals indicate a metallic behavior from room temperature down to ca. 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 with a width of ca. 6 G in the range 80-300 K and without significant differences between the two types of crystals. Static magnetic 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 transition where it vanishes, ascribed tothe conduction electrons in the CPP stacks.