X-Ray and Thermoanalytical Investigations on Two Isomeric n-Pentylphenyl Cyano-Thiolbenzoates

The isomeric compounds 4-n-pentylphenyl 4′-cyanothiolbenzoate (NCSS) and 4-cyanophenyl 4′-n-pentylthiolbenzoate (5SCN) have been studied by X-ray diffraction and thermoanalytical methods. The crystal data are (NCSS): a = 31.020 (8), b = 8.366(2), c = 15.043(4) Å, β = 114.15(2)°; monoclinic, space group C2/c with eiet molecules in the unit cell and (5SCN): a = 37.128 (10), b = 6.055(2), c = 24.325(8) Å, β = 107.39(2)°; monoclinic, space group P2,/c with twelve molecules in the unit cell. The crystal structure of NCS5 has been solved by direct methods and refined to an R-value of 0.086. The molecule is in an extended form. The torsion angle between the two phenylrings is 69.0(5)°. The molecules are arranged parallel to each other, and perpendicular to [010], with y ∼ 0 or y ∼ ½ in a head-to-tail configuration. X-ray investigations have established different semibilayer structures for the nematic phases of the two isomeric compounds. The nematic phase of NCS5 has coexisting mass-density fluctuations (heavily damped) of two distinct wavelengths. Both compounds show solid state polymorphism. The transition temperatures and enthalpies are given. The binary phase diagram for NCS5 and 5SCN is described.