Synthesis, characterization, electro-optical studies and crystal structure of a chiral mesogenic compound

Abstract

A new series of chiral biphenyl derivatives presenting the following general sequence of phases Cr→S∗_c→N∗→I was synthesized and characterized. The mesomorphic properties were analyzed by optical microscopy, DSC and electro-optical measurements. This series presents a large temperature domain for the ferroelectric phase and large values for the spontaneous polarization (up to 200nC cm⁻²). For this series, the crystal structure of 4-[(2S)-2-chloro-3-methylbutanoyloxy] biphenyl-4-yl 4-undecyloxy-2,3-difluorobenzoate (C₃₅H₄₁O₅F₂Cl) is described. This compound crystallizes in the monoclinic system and P2₁ space group with two independent molecules per asymmetric unit (Z = 4). The cell parameters are the following: a = 6.764(5), b = 57.057(6), c = 8.597(2)Å and β = 99.08(1)°; λ(CuKα)' 1.54178 Å, R = 0.105 for 2987 observed reflections. The independent molecules A and B adopt a parallel head-to-head arrangement which gives rise to sheets parallel to the (xOz) plane with a thickness close to 28.5 Å and having a permanent dipole moment. The tilt angle within a sheet is close to 40°. Neighbouring sheets, generated by the 2₁ axis, are symmetric through the (xOz) plane with an opposite tilt direction and dipole moment. The molecular arrangement is antiferroelectric-like. The crystal cohesion can be attributed to dipole-dipole forces and van der Waals interactions. The structure of the present compound is compared to that of a similar compound which differs only by the replacement of one of the two terminal methyl groups with an ethyl group.