CRYSTAL-STRUCTURE OF BIS[4-(4'-CARBOXY-BUTANOYLOXY)-ACETOPHENON]AZINE

Bis[4-(4'-carboxy-butanoyloxy)-acetophenon]azine (C26H28O8N2) is a dicarboxylic acid that can be considered as a model for semiflexible mesogenic polyesters having formula [-COO-R-OOC-(CH2)2n-]x with R = -phi-C(CH3)=N-N=C(CH3)-phi- (-phi- = p-phenylene). It has been synthesized and its crystal structure has been determined by direct methods. Crystals are triclinic, space group P1BAR, a = 6.306(2), b = 7.738(2), c = 25.982(6) angstrom, alpha = 96.93(2)degrees, beta = 93.16(4)degrees, gamma = 93.93(3)degrees with two molecules in the unit cell. The structure was refined by full matrix least squares methods to R = 0.084 for 1962 observed reflections, having I > 2.5 sigma(I). The structure is affected by positional disorder on one of the two terminal chains of the molecule. The conformation around the central =N-N= bond of the crystallographic independent molecule is not trans planar. The average planes of the phenyl rings belonging to the same molecule make a dihedral angle of 62.6-degrees. Molecules are linked through hydrogen bonds between carboxylic groups and form parallel rows having linear symmetry ti.