Molecular and crystal structures of 4-acylphenyl 4′-alkyloxybenzoates

Abstract

The crystal structures of four liquid-crystal (LC) compounds belonging to 4-acylphenyl 4′-alkyloxybenzoates with the general formula C n H2n + 1-C(O)-C6H4-O-C(O)-C6H4-O-C m H2m + 1 numbered as 1/6, 1/7,2/7, and 3/7 (the numbers in the code indicate the ratios of the numbers of alkyl-chain units, n/m) are determined. Compounds 1/6 and 1/7 form smectic and nematic phases, but they are monotropic mesogens, whereas compounds 2/7 and 3/7 form only an enantiotropic smectic phase. Compound 3/7 crystallizes in two crystal modifications—triclinic with Z′ = 2 (3/7 tr ) and monoclinic with Z′ = 4 (sp. gr. P2, 3/7 mon ). All crystals consist of alternating aromatic and aliphatic regions and are characterized by the presence of weak directional interactions, such as C-H...O hydrogen bonds and π-stacking interactions. This provides the necessary conditions for the formation of a mesophase, and the existence of two types of structure-forming units is in line with the formation of a smectic phase. An explanation is proposed for the monotropic properties of 1/6 and 1/7.