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Abstract
The crystal and molecular structure of 4,4′di-n-heptyloxyazoxybenzen (HOAB), which melts to give a smectic C phase has been determined by direct methods. The compound crystallizes in space group P1 with a=7.782(2), b=8.589(2), c=18.896(3)Å, α=87.01(2)°, β=97.50(2)° γ=96.43(2)°. The structure was refined by full-matrix least-squares calculations to R=0.053 for 3053 observed reflections The molecules are in their most extended trans conformation, they are nearly planar and are packed in alternate sheets in which all the molecular long axes are either in head or tail orientation. The packing is also layer-like with the molecules making an angle of approximately 35° relative to the layers, which are the 001 (ab) planes. The long axes of the molecules are in a distorted hexagonal arrangement but the orientation of all molecules about these axes is closely similar.
The relationship between the molecular packing in the crystal and smectic C phases is discussed.
