Two new polymorphs of 2,4,6-tri­bromo­benzo­nitrile have been found. Together with the known polymorph, they are polytypic. One new polytype is isostructural with the previously reported crystal structure of 1,3,5-tri­bromo-2-iso­cyano­benzene.

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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 ...

Melting points were measured with a Mel-Temp apparatus, and were not corrected or calibrated. Rf values obtained using SiO2 in 1:2 EtOAc:hexane. Infrared spectra were collected on a Thermo Fisher Scientific Nicolet iS5 spectrophotometer. 1 H NMR and 13 C NMR spectra were recorded on AV-500 Bruker Avance III HD, HD-500 Bruker Avance III HD, or AM-400 Bruker Avance III HD spectrometers at ambient temperature and are referenced to the solvent.Mass spectra were recorded on a Bruker Biotof II instrument using poly(ethylene glycol) as an internal calibrant, or on an Agilent 7890B gas chromatograph using an Agilent DB-5MS 250 µm capillary column with an Agilent 7200 GC/QTOF-MS detector calibrated with external perfluorotributylamine. Reagents and solvents were used as purchased. General procedures Method A: Reactions of indole with acetophenones in ethanolic HCl at RTIndole 1a (0.234 g, 2.00 mmol, 1 eq), naphthalene 10 (0.064 g, 0.50 mmol, 0.25 eq), and acetophenone 8a-h (3.00 mmol, 1.5 eq) were dissolved in ethanol (10 mL). Concentrated hydrochloric acid (1 mL) was added dropwise at room temperature. The resulting solution was allowed to stirred at RT for 5 d. The reaction mixture was neutralized using sat. sodium bicarbonate (25 mL) and the organic layer was extracted with dichloromethane (4 × 25 mL). The combined organic extracts were dried with magnesium sulfate, filtered, and excess solvent was removed with a rotary evaporator. The resulting mixtures were analyzed using 1 H NMR spectroscopy, with naphthalene as the internal integration standard. The crude mixture was dry-S2 loaded onto silica gel and the products were purified by column chromatography or MPLC using EtOAc:hexane as the eluent. Method B: Reactions of indole with acetophenones in ethanolic HCl at 40 o CThis procedure is identical with Method A, except reactions were stirred at 40 o C for 3 d before neutralization. Method C: Reactions of indole with acetophenones in refluxing acetic acidIndole 1a (1.171g, 10.00 mmol, 1eq) and acetophenone 8a-h (12.00 mmol, 1.2 eq) were dissolved in acetic acid (1 mL) and then refluxed overnight. The reaction mixture was neutralized using sat. sodium bicarbonate (10 mL) and the organic layer was extracted with dichloromethane (4 × 25 mL). The combined organic extracts were dried with magnesium sulfate, filtered, and excess solvent was removed with a rotary evaporator. The crude mixture was dry-loaded onto silica gel and purified by column chromatography using EtOAc:hexane as the eluent, giving products 11a-h. S32:1 condensation products: Bisindoles (11a-h) 3,3'-(1-phenylethane-1,1-diyl)bis(1H-indole) (11a) [46] was prepared by Method A from 8a (361 mg) as a white crystalline powder; 130 mg, 37% (calcd by 1 H NMR); mp 118-120 o C (lit.

The title crystals, C 7 H 2 I 3 N, are isomorphous. Both molecules lie across two crystallographic mirror planes and a twofold axis. The principal supramolecular interaction is centric R 2 2 (10) CN/NCÁ Á ÁI short contacts involving both ortho I atoms, with two contacts bisecting each cyano and isocyano group. These form ribbons along [010] and give rise to a planar sheet structure parallel to (100). All pairs of adjacent sheets have centric stacking, a mode not previously reported for sheets of this type. This study completes the series of homo-2,4,6-trihalobenzonitriles, in which I atoms give the strongest CNÁ Á ÁX and NCÁ Á ÁX interactions (X = F, Cl, Br, I).