Abstract
The crystal structures of three hydrogen-bonded co-crystals of 4-alk-oxy-benzoic acid-1,2-bis-(pyridin-4-yl)ethane (2/1), namely, 2C9H10O3·C12H12N2, (I), 2C10H12O3·C12H12N2, (II), and 2C11H14O3·C12H12N2, (III), have been determined at 93, 290 and 93 K, respectively. In (I), the asymmetric unit consists of one 4-eth-oxy-benzoic acid mol-ecule and one half-mol-ecule of 1,2-bis-(pyridin-4-yl)ethane, which lies on an inversion centre. In (II) and (III), the asymmetric units each comprise two crystallographically independent 4-alk-oxy-benzoic acid mol-ecules and one 1,2-bis-(pyridin-4-yl)ethane mol-ecule. In each crystal, the two components are linked by O-H⋯N hydrogen bonds, forming a linear hydrogen-bonded 2:1unit of the acid and the base. Similar to the structure of 2:1 unit of (I), the units of (II) and (III) adopt nearly pseudo-inversion symmetry. The 2:1 units of (I), (II) and (III) are linked via C-H⋯O hydrogen bonds, forming tape structures.
Highlights
The crystal structures of three hydrogen-bonded co-crystals of 4-alkoxybenzoic acid–1,2-bis(pyridin-4-yl)ethane (2/1), namely, 2C 9 H 10 O 3 C 12 H 12 N 2, (I), 2C10H12O3C12H12N2, (II), and 2C11H14O3C12H12N2, (III), have been determined at 93, 290 and 93 K, respectively
In (I), the asymmetric unit consists of one 4-ethoxybenzoic acid molecule and one half-molecule of 1,2-bis(pyridin-4yl)ethane, which lies on an inversion centre
(differential scanning calorimetry) and polarizing microscope measurements show that the compounds of 4-methoxy, 4-ethoxy- and 4-n-propoxybenzoic acid have nematic phases at 419 (1), 421 (1) and 419 (1) K, respectively, while the compound of 4-n-butoxybenzoic acid exhibits a smectic A
Summary
Co-crystals of 4-alkoxybenzoic acid–4,40 -bipyridyl (2/1), in which the two acids and the base are held together by intermolecular O—H N hydrogen bonds, show thermotropic liquid crystallinity (Kato et al, 1990, 1993; Grunert et al., 1997). We have reported the crystal structures of the three compounds of 4-ethoxy-, 4-n-propoxy- and 4-n-butoxybenzoic acid (Tabuchi et al, 2015). As an expansion of our work on the structural characterization of hydrogen-bonded co-crystals which exhibit liquid phases, we have prepared compounds of 4-alkoxybenzoic acid–1,2-bis(pyridin-4-yl)ethane (2/1) and analyzed the crystal structures. The structure of 4-methoxybenzoic acid–1,2-bis(pyridin-4-yl)ethane (2/1) has been reported recently
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