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).

Yohei Tabuchi,Hiroyuki Ishida,Kazuma Gotoh

doi:10.1107/s2056989016017655

Yohei Tabuchi, Hiroyuki Ishida + Show 1 more

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https://doi.org/10.1107/s2056989016017655

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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-pent-yloxy)benzoic acid mol-ecule and one half-mol-ecule 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-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 via 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-C2 symmetry. Both compounds show liquid-crystal behaviour.

Highlights

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
Consists of one 4-pentyloxybenzoic 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) is composed of two crystallographically independent 4-hexyloxybenzoic acid molecules and one (E)-1,2-bis(pyridin-4-yl)ethene molecule, and the two acids and the base are linked by O—H N hydrogen bonds (Table 2), forming a linear hydrogen-bonded 2:1 aggregate with trans-zigzag alkyl chains

Summary

Chemical context

1) and 4-alkylbenzoic acid [CH3(CH2)nC6H4CO2H, n = 3, 4, 7]–(E)-1,2-bis(pyridin-4-yl)ethene (2/1), in which the two acid molecules and the base molecule are held together through intermolecular hydrogen bonds, show thermotropic liquid crystallinity (Kato et al, 1990, 1993). Of these co-crystals, crystal structures of 4,40 -bipyridyl with 4-methoxybenzoic acid (Mukherjee & Desiraju, 2014; Ramon et al, 2014), 4-ethoxy-, 4-n-propoxy- and 4-n-butoxybenzoic acid (Tabuchi et al., 2015a) have been reported.

Structural commentary

Supramolecular features

Synthesis and crystallization

Phase transitions

Refinement