Structural Analysis by X-Ray Diffraction of a Polar Mesogen 4-Cyanobiphenyl-4′-heptylbiphenyl Carboxylate

Abstract

Crystal and molecular structure of a compound 4-cyanobiphenyl-4′-heptylbiphenyl carboxylate (7CBB), which exhibit both monolayer smectic A and nematic phases, have been determined by direct methods using single crystal X-ray diffraction data. The structure is monoclinic with the space group P2₁/c and Z = 4. The unit cell parameters are a = 16.9550(5) Å, b = 5.5912(18) Å, c = 27.5390(9) Å, α = 90.000°, β = 93.986(6)°, and γ = 90.000°. Packing of the molecules is found to be precursor to SmC phase, although SmA₁ phase is observed on melting. Several strong van der Waals interactions are observed in the core part of the neighboring molecular pairs. Crystal to mesophase transition is probably of reconstitutive nature. Geometry, packing, and nature of crystal-mesophase transition are compared to those in 6CBB.

Keywords:

• crystal and molecular structure
• crystal-mesogen transition
• molecular packing
• reconstitutive transition
• smectogen
• van der Waals interaction

ACKNOWLEDGMENT

Authors thankfully acknowledge financial support for the work under the Indo-Polish Bilateral cooperation scheme.