RELATIONSHIPS BETWEEN THE CRYSTALLINE AND THE SMECTIC-C STRUCTURES OFA BIFORKED MESOGEN

The crystal structure of a biforked mesogen containing thiobenzoate bi s(4-[4-(3,4-dinonyloxy)benzoylthio] phenyl)-trans-1,4-cyclohexanedicar boxylate) is described. This compound exhibits interesting nematic and smectic phases, The molecule crystallizes in the P (1) over bar space group (Z = 2) with one molecule per asymmetric unit, a = 9.202(4) Ang strom, b = 10.139(2) Angstrom, c = 38.089 Angstrom alpha = 96.05(1)deg rees, beta = 84.29(3)degrees, and gamma = 96.71(3)degrees. Molecules a dopt a zigzag conformation, with the four alkoxy chains stretched and approximately parallel to the (yet) plane; the mean axis of the alkoxy chains makes an angle close to 140 degrees with the central core, and the molecules are arranged in sheets of about 38 Angstrom thickness, as in a smectic C mesophase. The smectic C phase is analyzed by X-ray diffraction and dilatometry. The molecular arrangement in the mesophas e is found to be very similar to that in the crystal phase, suggesting that the structure at room-temperature predetermines the type of meso phase observed at high temperature with small variations of the struct ural parameters.