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

The crystal structures of title hydrogen-bonded co-crystals, 2C H O ·C H N , (I), and 2C H O ·C H N , (II), have been determined at 93 K. In (I), the asymmetric unit consists of one 4-( -pent-yloxy)benzoic acid mol-ecule and one half-mol-ecule of ( )-1,2-bis-(pyridin-4-yl)ethene, which lies about an inversion centre. The asymmetric unit of (II) comprises two crystallographically independent 4-( -hex-yloxy)benzoic acid mol-ecules and one 1,2-bis-(pyridin-4-yl)ethene mol-ecule. 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 C-H⋯π and π-π inter-actions [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 mol-ecule is orientationally disordered over two sets of sites approximately around the N⋯N mol-ecular axis, with an occupancy ratio of 0.647 (4):0.353 (4), and the average structure of the 2:1 unit adopts nearly pseudo- symmetry. Both compounds show liquid-crystal behaviour.