A 2:1 co-crystal of 3,5-dibromo-4-cyanobenzoic acid and anthracene

Abstract

The title co-crystal, C 8 H 3 Br 2 NO 2 Á0.5C 14 H 10 , was self-assembled from a 2:1 mixture of the components in slowly evaporating dichloromethane. The molecules adopt a sheet structure parallel to (112) in which carboxy hydrogen-bonded dimers and anthracene molecules stagger in both dimensions. Within the sheets, six individual cyano acid molecules surround each anthracene molecule. Cyano acid molecules form one of the two possible R 2 2 (10) rings between neighboring cyano and bromo groups. Compared to the dichloro analog [Britton (2012). J. Chem. Crystallogr. 42,[851][852][853][854][855], the dihedral angle between the best-fit planes of acid and anthracene molecules has decreased from 7.1 to 0.9 (2) . Chemical contextDoyle Britton published roughly 30 crystallographic articles on solid-phase cyano-halo interactions from variously substituted halobenzonitriles and isocyanides. Britton postulated that 3,5-dichloro-4-cyanobenzoic acid might assemble into a honeycomb-like sheet structure (Fig. 1a) via a combination of carboxy hydrogen-bond dimerization and CNÁ Á ÁCl short contacts. In 2012, he found that the cyano acid molecules alone do not pack in this way, but slow evaporation of mixtures containing naphthalene or anthracene afforded 2:1 acid:hydrocarbon co-crystals roughly matching his proposed structure (Britton, 2012). However, no CNÁ Á ÁCl contacts were observed (Fig. 1b). Anthracene was the better fit, although it was too large to allow the ideal molecular arrangement. There is no obvious substitute for anthracene or naphthalene. Thus, we have prepared anthracene co-crystals with the dibromo analog in hopes that the larger Br bond and contact radii might close the CNÁ Á ÁX gaps observed with Cl. Structural commentaryThe benzene (C2-C5/C7/C8) and anthracene (C9-C15 and symmetry equivalents, Fig. 2) ring systems are nearly planar. The mean deviation of atoms from the planes of best fit are 0.0074 (17) Å and 0.0041 (14) Å , respectively, both of which are comparable to the corresponding values in the dichloro crystal. However, the dihedral angle between the carboxy group (O1-C1-O2) and the benzene ring is 3.2 (4) , compared with 7.2 in the dichloro analog. Supramolecular featuresThe dihedral angle between the benzene and anthracene planes is 0.9 (2) , which is much lower than 7.1 of the dichloro analog. As expected, R 2 2 (8) carboxy hydrogen-bonded dimers are observed (Table 1); these are located on an inversion center. R 2 2 (10) rings form about another inversion center based on C6 N1Á Á ÁBr2 contacts (Table 2); however, the corresponding N1Á Á ÁBr1 contacts are not observed (Fig. 3). Instead, 3.5534 (5) Å Br1Á Á ÁBr1 contacts form, slightly closer than the 3.70 Å non-bonded contact diameter of Br (Rowland & Taylor, 1996). In the title co-crystal, two corners of the anthracene molecule contact the cyano acid network (Fig. 3), whereas all four corners made contact in the Cl analog (Fig. 1b). Overall, substitution of Cl atoms with Br atoms has facilitated the formation of half of the envisioned CNÁ Á ...

Crystal structures of methyl 3,5-dibromo-4-cyanobenzoate and methyl 3,5-dibromo-4-isocyanobenzoate

“…Crystals of (VII) contain C(6) chains of C OÁ Á ÁBr contacts (Saeed et al, 2010), and crystals of (VIII) contain C(5) chains of BrÁ Á ÁBr contacts (Reinhold & Rosati, 1994). A co-crystal of cyano acid (IXa) with anthracene was recently reported by our group (Noland et al 2017a). The corresponding isocyano acid (IXb) was not observed, probably because of the acid sensitivity of isocyanides (Ugi et al, 1965), preventing crystallographic comparison of (IXa) and (IXb).…”

“…Methyl 4-amino-3,5-dibromobenzoate (RNH2) and methyl 3,5-dibromo-4-cyanobenzoate (RCN) were taken from material prepared in our recent study (Noland et al 2017a; Fig. 7).…”

3,5-Dibromo-4-carbamoylbenzoic acid 2-propanol monosolvate

“…1). The target was cyano acid (III), for a study in our laboratory involving co-crystals of (III) with anthracene (Noland et al, 2017).…”

“…3,5-Dibromo-4-carbamoylbenzoic acid (I): a portion of compound (II) (589 mg, Fig. 1) taken from our prior study (Noland et al, 2017) was placed in a round-bottomed flask with water (5 ml), 2-propanol (5 ml) and NaOH (186 mg). The resulting mixture was refluxed for 1 h, and then cooled to 290 K. Hydrochloric acid (6 M) was added dropwise until the pH of the mixture was less than 4.…”

Crystal structures of 2,6-dibromo-4-methylbenzonitrile and 2,6-dibromo-4-methylphenyl isocyanide

“…The chlorinated and brominated entries are either bis(carbonitriles) [(I), Fig. 1; Britton, 1981;Hirshfeld, 1984;van Rij & Britton, 1981] or 4-carboxy analogs [(II); Britton, 2012;Noland et al, 2017]. All of these 4-substituents have stronger interactions than a methyl group, and exhibit different packing motifs than RCN.…”