A comparative study of mesogenic structures. The crystal structures of bis[(4-butoxycarbonyl)-phenyl]terephthalate and bis[(4-vaIeroyloxy)-phenyl]terephthalate

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Abstract
Smectogenic bis[(4-butoxycarbonyl)-phenyl]terephthalate (B-A) and Hematogenic bis[(4-valeroyloxy)-phenyl]terephthalate (V-A) have been synthesized and their crystal and molecular structure have been determined, at room temperature, by direct methods. Crystals of B-A are triclinic, space group P1, a = 5·914(1) Å, b = 8·532(1)Å, c = 13·647(2)Å, α=102·07(1)°, β = 92·73(2)°, γ = 73·21(2)° with one molecule per unit cell. Crystals of V-A are monoclinic, space group P21/c, a = 32·318(5)Å, b = 5·350(3)Å, c = 7·987(2)Å, β = 92·84(2)° with two molecules per unit cell. The structures were refined by the full matrix least squares method, to R = 0·050 for B-A and R = 0·071 for V-A. Molecules of B-A and V-A are centrosymmetric (point group Ci) and show some differences in the structure of the phenyl terephthalate moiety, which are probably due to the different electron withdrawing effects of the terminal substituents linked to the phenyl rings. The crystal packing of the two compounds is different. Molecules of V-A are packed in layers with their long molecular axes normal to the layer surface, while in B-A molecular layers are formed in which the long molecular axes are highly tilted with respect to the layer normal.