Solid State Polymorphism in 4-Cyano-4'-n-Propylbiphenyl and X-Ray Structure Determination of the Higher Melting Modification

Abstract

DSC and thermomicroscopic analysis of 4-cyano-4'-n-propylbiphenyl (CB 3) revealed solid crystalline polymorphism. Thus the compound exhibits two solid phases subsequent to appropriate thermal treatment. The melting points are K_I: 338.4 (5) K and K_II: 326.3(3) K. The enthalpies of fusion for K_I and K_II are 19.9(5) kJ/mol and 16.7(7) kJ/mol, respectively. The compound also possesses a monotropic nematic phase, its clearing point being 303.3(2) K and ΔH _N-I = 0.3(2) kJ/mol. The crystals of the higher melting modification are monoclinic, with a = 6.259 (3) Å, b = 19.1216 (9) Å, c = 11.0473 (5) Å and β = 103.39 (2) °. The space group is P2₁/c. For 1014 nonzero reflections, R = 0.051, R _w = 0.042. The dihedral angle between the phenyl rings was found to be 42.8°.