A 2:1 co-crystal of 3,5-di-bromo-4-cyano-benzoic acid and anthracene.

The title co-crystal, C8H3Br2NO2·0.5C14H10, was self-assembled from a 2:1 mixture of the components in slowly evaporating di-chloro-methane. The mol-ecules adopt a sheet structure parallel to (1-12) in which carb-oxy hydrogen-bonded dimers and anthracene mol-ecules stagger in both dimensions. Within the sheets, six individual cyano acid mol-ecules surround each anthracene mol-ecule. Cyano acid mol-ecules form one of the two possible R22(10) rings between neighboring cyano and bromo groups. Compared to the di-chloro analog [Britton (2012 ▸). J. Chem. Crystallogr.42, 851-855], the dihedral angle between the best-fit planes of acid and anthracene mol-ecules has decreased from 7.1 to 0.9 (2)°.

Crystal structures of 2,6-di-bromo-4-methyl-benzo-nitrile and 2,6-di-bromo-4-methyl-phenyl isocyanide.

In the title crystals, C8H5Br2N, which are isomorphous, the steric bulk of the methyl group causes neighboring mol-ecules to become mutually inclined. This prevents the formation of planar or nearly planar sheets, which were observed in the tri-chloro and tri-bromo analogs. Instead of CN/NC⋯Br contacts, tetra-meric Br⋯Br contacts are observed. These contacts form tetra-gonally puckered sheets parallel to (001). The CN/NC and methyl groups are grouped at the peaks and troughs. Both mol-ecules lie across crystallographic mirror planes; thus, the methyl H atoms are disordered over two sets of sites with equal occupancy. The title nitrile is a redetermination. The refinement converged at R[F2 > 2σ(F2)] = 0.020, whereas the original determination [Gleason & Britton, (1976 ▸). Cryst. Struct. Commun.5, 229-232] had R = 0.112.