Abstract
The asymmetric unit of the title 2:1 co-crystal, 2C8H8O2·C14H14N4O2, comprises an acid mol-ecule in a general position and half a di-amide mol-ecule, the latter being located about a centre of inversion. In the acid, the carb-oxy-lic acid group is twisted out of the plane of the benzene ring to which it is attached [dihedral angle = 28.51 (8)°] and the carbonyl O atom and methyl group lie approximately to the same side of the mol-ecule [hy-droxy-O-C-C-C(H) torsion angle = -27.92 (17)°]. In the di-amide, the central C4N2O2 core is almost planar (r.m.s. deviation = 0.031 Å), and the pyridyl rings are perpendicular, lying to either side of the central plane [central residue/pyridyl dihedral angle = 88.60 (5)°]. In the mol-ecular packing, three-mol-ecule aggregates are formed via hy-droxy-O-H⋯N(pyrid-yl) hydrogen bonds. These are connected into a supra-molecular layer parallel to (12[Formula: see text]) via amide-N-H⋯O(carbon-yl) hydrogen bonds, as well as methyl-ene-C-H⋯O(amide) inter-actions. Significant π-π inter-actions occur between benzene/benzene, pyrid-yl/benzene and pyrid-yl/pyridyl rings within and between layers to consolidate the three-dimensional packing.
Highlights
The asymmetric unit of the title 2:1 co-crystal, 2C8H8O2ÁC14H14N4O2, comprises an acid molecule in a general position and half a diamide molecule, the latter being located about a centre of inversion
Systematic work on synthon propensities in multi-component crystals have revealed that carboxylic acids have a great likelihood of forming hydroxy-O—HÁ Á ÁN hydrogen bonds when co-crystallized with molecules with pyridyl residues (Shattock et al, 2008)
Recent systematic work in this phenomenon relates to molecules shown in Scheme 1, where isomeric molecules with two pyridyl rings separated by a diamide residue have been cocrystallized with various carboxylic acids (Arman, Miller et al, 2012; Arman et al, 2013, Syed et al, 2016; Jotani et al, 2016)
Summary
Multi-component crystals, incorporating co-crystals, salts and co-crystal salts, attract continuing interest for a wide variety of applications as this technology may be employed, for example, to provide additives to promote the growth of crystals, to stabilize unusual and unstable coformers, to generate new luminescent materials, to separate enantiomers, to facilitate absolute structure determination where the molecule of concern does not have a significant anomalous scatterer, etc. (Aakeroy, 2015; Tiekink, 2012). Controlled/designed crystallization of multicomponent crystals requires reliable synthon formation between the various components and that, is the challenge of crystal engineering, let alone engineering small aggregates within crystals (Tiekink, 2014). Systematic work on synthon propensities in multi-component crystals have revealed that carboxylic acids have a great likelihood of forming hydroxy-O—HÁ Á ÁN hydrogen bonds when co-crystallized with molecules with pyridyl residues (Shattock et al, 2008). Recent systematic work in this phenomenon relates to molecules shown in Scheme 1, where isomeric molecules with two pyridyl rings separated by a diamide residue have been cocrystallized with various carboxylic acids (Arman, Miller et al, 2012; Arman et al, 2013, Syed et al, 2016; Jotani et al, 2016). The central C4N2O2 core is essentially planar with an r.m.s. deviation (O1, N2, C6, C7 and symmetry equivalents) = 0.031 A
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