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

Even though they contain isosteric and isoelectronic molecules that both form C=O⋯Br contacts, the cyanide and isocyanide crystals are not isomorphous in any dimension.


Structural commentary
Molecules of RCN and RNC (Fig. 3) occupy general positions and have similar, typical geometry. Both benzene rings are nearly planar, with mean atomic deviations of 0.005 (2) and 0.002 (3) Å for RCN and RNC, respectively. The most prominent difference between the molecular conformations is the bond angles about the methoxy O atoms, which are 117.1 (2) for C8-O2-C9, and 114.8 (3) for C18-O12-C19. In RNC, the compression about O12 is probably caused by repulsion between methyl groups in adjacent molecules, rather than the N11 C17Á Á ÁC19 short contact (Table 1), because the C9-O2 and C19-O12 bond lengths are nearly identical.

Supramolecular features
Molecules of RCN form R 2 2 (10) inversion dimers based on C1 N1Á Á ÁBr2 short contacts (Table 1), similar to the centric contacts found in crystals of (II) and (IV)-(VI). Adjacent dimers are connected along [201] by C8 O1Á Á ÁBr6 contacts similar to those found in (VII). Adjacent dimers are mutually inclined by 44.03 (7) . The resulting sheet structure (Fig. 4) is staggered so that the methyl groups are spread apart to minimize steric congestion (Fig. 5). Crystals of RNC have a different packing motif, a slice of which is antiparallel ribbons parallel to [001] (Fig. 6). Each molecule of RNC participates in four short contacts between two pairs of molecules that are related by the (x + 1, y, z) translation, forming a threedimensional network. Contacted molecules are mutually inclined by 42.0 (1) . Half of the contacts are C18 O11Á Á ÁBr16 contacts, similar to those found in RCN and (VII). The other half are N11 C17Á Á ÁC19 contacts, instead of the anticipated N11 C17Á Á ÁBr12 contacts. It is interesting that the cyano group in RCN favors contacting a Br atom, but the isocyano group in RNC favors contacting the methoxy C atom. 3,5-Dibromobenzoates (VII) and (VIII) in the CSD. We recently reported (IXa); isocyano acid (IXb) was not observed.
Methyl 3,5-dibromo-4-isocyanobenzoate (RNC) was prepared from (RFA, 594 mg) by the dehydration procedure described by Britton et al. (2016), giving a brown powder (490 mg), which was crystallized as described below (453 mg Crystallization: Crystals of RCN and RNC were grown by slow evaporation of solutions in dichloromethane-pentane, followed by decantation, washing with pentane, and then drying at room temperature and reduced pressure (10 Pa, 4 h). RCN was obtained as colorless blocks, and RNC was obtained as colorless needles.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. A direct-methods solution was calculated, followed by full-matrix least squares/difference- A slice of a crystal of RNC parallel to (100), viewed nearly along [100].

Figure 7
The synthesis of RCN and RNC.

Methyl 3,5-dibromo-4-cyanobenzoate (RCN)
Crystal data Special details Experimental. Dr. K.J. Tritch / Prof. W.E. Noland Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.6370 (6)    where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.85 e Å −3 Δρ min = −0.65 e Å −3 Special details Experimental. Dr. K.J. Tritch / Prof. W.E. Noland Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refined as a 2-component pseudo-merohedral twin in an 0.67:0.33 ratio.