The molecular and crystal structure of alpha,omega-bis[4-(4 '-butyloxybenzylideneimino-phenyl)]octane (4O.8.O4) and alpha,omega-bis [4-(4 '-pentyloxybenzylideneiminophenyl)]octane (5O.8.O5)

The crystal and molecular structures of alpha,omega-bis[4-(4'-butyloxybenzy lideneiminophenyl)]octane (4O.8.O4) and the homologue alpha,omega-bis[4-(4' -pentyloxybenzylideneiminophenyl)]octane (5O.8.O5) have been determined at room temperature, the starting model obtained by direct methods. These two dimesogenic compounds possess besides two crystalline phases (KI, KII) also SmG phases. The crystals KI of the compound 4O.8.O4 belong to the triclini c system with space group P-1, a = 5.484(3), b = 11.826(8), c = 28.03(3) An gstrom, alpha = 95.77(5), beta = 92.39(5), gamma = 96.44(5)degrees with two molecules per unit cell. The compound 5O.8.O5 crystallizes in the monoclin ic system with space group P2(1)/n (KI), a = 5.571(2), b = 7.460(2), c = 89 .55(3) Angstrom, beta = 90.92(2)degrees with four molecules per unit cell. The structures were refined by full-matrix least-squares calculations to R = 0.069 for 6647/(3340 unique) observed reflections for 4O.8.O4 and to R = 0.106 for 3760/(3329 unique) reflections for 5O.8.O5. The conformations of the two compounds differ considerably. Nevertheless, t he molecules exhibit straight and S-shaped extended forms, respectively. Fo r both compounds the molecular packing consists of layers parallel to the a ,b-plane, piled up in c*-direction with minimal interdigitation of the wing groups.