SYNTHESIS, CHARACTERIZATION, ELECTROOPTICAL STUDIES AND CRYSTAL-STRUCTURE OF A CHIRAL MESOGENIC COMPOUND

A new series of chiral biphenyl derivatives presenting the following g eneral sequence of phases Cr-->S-c-->N*-->I was synthesized and chara cterized. The mesomorphic properties were analyzed by optical microsco py, DSC and electro-optical measurements. This series presents a large temperature domain for the ferroelectric phase and large values for t he spontaneous polarization (up to 200 nC cm(-2)). For this series, th e crystal structure of 4-[(2S)-2-chloro-3-methylbutanoyloxy]biphenyl-4 -yl 4-undecyloxy-2,3-difluorobenzoate (C35H41O5F2Cl) is described. Thi s compound crystallizes in the monoclinic system and P2(1) space group with two independent molecules per asymmetric unit (Z=4). The cell pa rameters are the following: a=6.764(5), b=57.057(6), c=8.597(2) Angstr om and beta=99.08(1)degrees; lambda(CuK alpha)=1.54178 Angstrom, 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 p arallel to the (x0z) plane with a thickness close to 28.5 Angstrom and having a permanent dipole moment. The tilt angle within a sheet is cl ose to 40 degrees. Neighbouring sheets, generated by the 2(1) axis, ar e symmetric through the (xOz) plane with an opposite tilt direction an d 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 comp ared to that of a similar compound which differs only by the replaceme nt of one of the two terminal methyl groups with an ethyl group.