The Crystal and Molecular Structures of a Second Crystalline Modification of the Mesogenic trans-4- n -octyl-(4′-cyanophenyl)- cyclohexane (PCH8B) and of Two Crystalline Modifications of the Mesogenic trans-4- n -nonyl-(4′-cyanophenyl)- cyclohexanes (PCH9A, PCH9B)

The crystal and molecular structures of a new crystalline modification of the mesogenic PCH8 and of two solid modifications of PCH9 are described: PCH8B: Triclinic, space group P1, a = 6.369 (2), b = 11.907 (3). c = 13.119 (3) Å, α = 77.39 (1), β = 78.48 (1), γ = 77.68 (a)[ddot]; Z = 2; PCH9A: Monoclinic, space group P21/c, a = 21.562 (4), b = 5.158 (1), c = 19.326 (4) Å, β = 112.99 (1)[ddot], Z = 4; PCH9B: Triclinic, space group P1, a = 7.622 (2), b = 11.372 (3), c = 23.574 (6) Å, α = 94.20 (1), β = 95.68 (1), γ = 97.01 (l)[ddot], Z = 4. PCH9A is isostructural with PCH8A (Paulus and Haase),2 showing overlapping of the cyanophenyl groups in a head to tail manner. PCH8B and PCH9B are different from the A-modification and different from each other. PCH83 shows antiparallel CN‒CN correlation interpreted as dimers of infinite stacking, for PCH9B four molecules are showing antiparallel CN-CN clustering in form of an island. In all of the described modifications the alkylcyclohexyl groups are unflexible whereas the angle between the phenyl and the cyclohexyl groups is more flexible.