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)

The crystal structures of title hydrogen-bonded co-crystals, 2C(12)H(16)O(3)·C(12)H(10)N(2), (I), and 2C(13)H(18)O(3)·C(12)H(10)N(2), (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-C (2) symmetry. Both compounds show liquid-crystal behaviour.