Crystal structures of hydrogen-bonded co-crystals as liquid crystal precursors: 4-(n-pentyloxy)benzoic acid–(E)-1,2-bis(pyridin-4-yl)ethene (2/1) and 4-(n-hexyloxy)benzoic acid–(E)-1,2-bis(pyridin-4-yl)ethene (2/1)

Abstract

The crystal structures of title hydrogen-bonded co-crystals, 2C12H16O3·C12H10N2, (I), and 2C13H18O3·C12H10N2, (II), have been determined at 93 K. In (I), the asymmetric unit consists of one 4-(n-pentyloxy)benzoic acid molecule and one half-molecule of (E)-1,2-bis(pyridin-4-yl)ethene, which lies about an inversion centre. The asymmetric unit of (II) comprises two crystallographically independent 4-(n-hexyloxy)benzoic acid molecules and one 1,2-bis(pyridin-4-yl)ethene molecule. In each crystal, the acid and base components are linked by O—H...N hydrogen bonds, forming a linear hydrogen-bonded 2:1 unit of the acid and the base. The 2:1 units are linked via C—H...π and π–π interactions [centroid–centroid distances of 3.661 (2) and 3.909 (2) Å for (I), and 3.546 (2)–3.725 (4) Å for (II)], forming column structures. In (II), the base molecule is orientationally disordered over two sets of sites approximately around the N...N molecular axis, with an occupancy ratio of 0.647 (4):0.353 (4), and the average structure of the 2:1 unit adopts nearly pseudo-C2 symmetry. Both compounds show liquid-crystal behaviour.

Keywords

• crystal structure
• (E)-1,2-bis(pyridin-4-yl)ethene
• 4-(n-pentyloxy)benzoic acid
• 4-(n-hexyloxy)benzoic acid hydrogen-bonded liquid crystal