New semiconductors obtained by reaction of 4-imidazoline-2-selone derivatives with TCNQ.: Characterization and X-ray structure of (C9H12N4Se)2+(TCNQ)32-

The charge transfer complexes I, II and III of three new electron donors, 1,1'-ethylenebis(3-methyl-4-imidazoline-2-selone) 1, 1,1'-methylenebis(3-methyl-4-imidazoline-2-selone) 2 and 1,3-dimethyl-4-imidazoline-2-selone 3, with TCNQ have been synthesized. We report the X-ray crystal structure of II, (C9H12N4Se)(TCNQ)(3), which crystallizes in the triclinic system, space group P1, with one molecule per unit cell and a = 7.563(7), b = 10.371(6), c = 13.575(5) Angstrom, alpha = 95.00(2), beta = 95.54(2), gamma = 109.74(2)degrees. The comparison with the already described crystal structure of I and a detailed spectroscopic characterization of all three complexes, allows us to show that the change of the donor yields compounds characterized by quite different charge distributions and stack types. The semiconducting properties, ranging from similar to 10(-2) to 6 x 10(-4) S cm(-1), are most likely due to the TCNQ stacks, where two negative charges are distributed among three TCNQ units. At room temperature, the charge is fully delocalized along the TCNQ stack of I, the semiconductor with the highest conductivity, whereas in II and III the charge is unevenly distributed among the TCNQ units. The donors show a strong tendency to form stable dications: in I and III they give rise to mixed-valence cations and a new dication with elimination of an Se atom is formed in II.