Crystal structure and smectic orientation of a mesogenic compound

The structure of the mesogenic compound 3-Cyanobenzyi-2,5-bis(4-n-octyloxybenzoyl-oxy)benzoate (3CNBOB) was investigated by single and melt crystal methods. Using a single crystal of 3CNBOB at 20degreesC, the unit cell structure was determined as triclinic with two molecules in a unit cell of dimensions: a = 8.792 Angstrom, b = 11.760 Angstrom, c = 19.121 Angstrom, alpha = 96.61degrees, beta = 90.56degrees, and gamma = 90.28degrees. Three benzene rings of the compound exhibit pi-pi interactions in the crystalline form. The 3CNBOB showed a liquid crystalline state in the region of 82.9 to 101.5degreesC. Melt crystallization was observed by in-situ x-ray diffraction using a temperature slope apparatus. A smectic phase appeared in the liquid crystalline region near the boundary to the crystalline phase. The smectic molecules showed spontaneous orientation aligned with their long axes parallel to the crystallizing plane. There were two crystalline states in the bulk material. The room-temperature crystalline form was the same as the one observed using the single crystal. The high-temperature crystalline state developed from the smectic state. During the smectic-crystalline transition, the packing became denser and the spontaneous orientation decreased.