X-ray Photographic Studies of Liquid Crystals: III. Structure Determination of the Smectic Phase of 4-Butyloxybenzal- 4′-Ethylaniline

A new type of smectic phase (smectic H) is described, using microscopic and X-ray data. The structure of this phase can be assigned a three dimensional monoclinic lattice, with a = 10.32 Å, b = 4.986 Å, c = 20.73 Å, and β = 123.8°, probably space group P21, or Pa. The ab plane is parallel to the smectic layers; the thickness of the layers is 17.27 Å. The molecules are most probably approximately parallel to the c axis, thus making an angle of 56.2° with the smectic layers and forming continuous columns of molecules parallel to the c axis. In planes perpendicular to the c axis the arrangement of the molecular axes is approximately hexagonal, with a spacing of 4.97 Å. Successive layers of molecules parallel to the bc plane are shifted 2.87 Å with respect to each other in the direction of the c axis. The most probable arrangement of the molecular planes is a herringbone-type packing. It appears that within the regular three-dimensional structure there are a considerable number of columns of molecules displaced parallel to the c-axis, thus giving rise to continuous diffuse planes in the reciprocal lattice.