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)

Abstract

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.

Key Words:

• Crystal structures
• molecular structures
• solid state polymorphism
• PCH8
• PCH9