Crystal structure of an optically active non-symmetric liquid crystal dimer: cholesteryl 5-[4-(4-n-heptylphenylethynyl)phenoxy]pentanoate

Abstract

The crystal structure of cholesteryl 5-[4-(4-n-heptylphenylethynyl)phenoxy]- pentanoate (C₅₃H₇₆O₃) was determined by direct methods using single crystal X-ray diffraction data. It crystallises in the triclinic system with space group P1 and Z = 2. The unit cell parameters are: a = 10.6791(5), b = 13.0903(7), c = 18.6430(9)Å, α = 94.413(3), β = 98.222(3), γ = 112.987(3)°. The final reliability factor was R = 0.0510 for 7284 observed reflections and the goodness of fit was equal to 1.062. The asymmetric unit cell of the compound was found to contain two symmetry-independent molecules, A and B. In both molecules, the six-membered rings of the cholesterol moiety are conformationally very similar. However, pronounced differences were observed in the conformation of the five-membered ring, which is a half-chair in molecule A and assumes an envelope conformation in molecule B. In both molecules, the phenyl rings are planar. The dihedral angle between the two phenyl rings is 43.4(2) and 42.7(2)° for molecules A and B, respectively. The packing of molecules in the crystalline state was found to be a precursor to the smectic A phase structure. The crystal structure is stabilised by inter-molecular C–H…O and C−H…π interactions.

Keywords:

• non-symmetric dimer
• twist grain boundary
• blue phase
• crystal structure
• dihedral angle
• C−H…π interactions

Acknowledgements

The authors are thankful to the Head, Sophisticated Aalytical Instrument Facility, Indian Institute of Technology Madras, Chennai for extending the use of the intensity data collection facility.