NEW SEMICONDUCTORS OBTAINED BY REACTION OF 4-IMIDAZOLINE-2-SELONE DERIVATIVES WITH TCNQ - CHARACTERIZATION AND X-RAY STRUCTURE OF (C9H12N4SE)(2-)()(TCNQ)(3)(2)

The charge transfer complexes I, II and III of three new electron dono rs, 1,1'-ethylenebis(3-methyl-4-imidazoline-2-selone) 1, 1,1'-methylen ebis(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 crys tal structure of II, (C9H12N4Se)(TCNQ)(3), which crystallizes in the t riclinic 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 alr eady described crystal structure of I and a detailed spectroscopic cha racterization of all three complexes, allows us to show that the chang e of the donor yields compounds characterized by quite different charg e distributions and stack types. The semiconducting properties, rangin g from similar to 10(-2) to 6 x 10(-4) S cm(-1), are most likely due t o the TCNQ stacks, where two negative charges are distributed among th ree TCNQ units. At room temperature, the charge is fully delocalized a long the TCNQ stack of I, the semiconductor with the highest conductiv ity, whereas in II and III the charge is unevenly distributed among th e TCNQ units. The donors show a strong tendency to form stable dicatio ns: in I and III they give rise to mixed-valence cations and a new dic ation with elimination of an Se atom is formed in II.