Crystal structures of 2,4,6-triiodobenzonitrile and 2,4,6-triiodophenyl isocyanide

The title crystals are isomorphous, and form centrically stacked planar sheets formed by CN⋯I and NC⋯I short contacts.


Structural commentary
Molecules of I3CN and I3NC (Fig. 3) lie about a twofold axis and two orthogonal vertical mirror planes. Thus, they have crystallographically-imposed C 2v symmetry and are planar, with the para I atom (I4; I14) collinear with the CN and NC groups. All of the aryl bond angles are roughly 120 . The ortho I atoms (I2, I2 0 ; I12, I12 0 ) are scissored slightly toward the ipso C atom (C1; C11), which is probably caused by the intermolecular CNÁ Á ÁI and NCÁ Á ÁI short contacts. The bond lengths are typical for their respective functional groups.

Supramolecular features
Crystals of I3CN and I3NC are isomorphous. The CN and NC groups are bisected by C7 N7Á Á ÁI2 and N17 C17Á Á ÁI12 contacts (Table 1), forming ribbons of R 2 2 (10) rings parallel to (100) along [010]. Adjacent ribbons translate along [001]. The resulting planar sheet structure ( Fig. 4) matches that observed in Br3CN and the corresponding isocyanide (Br3NC) (Britton et al., 2016), and the 4-chloro (Britton, 2005)     The molecular structures of (a) I3CN and (b) I3NC, with atom labeling and displacement ellipsoids at the 50% probability level. Unlabeled atoms are generated by the symmetry operation (1 À x, 3 (Noland & Tritch, 2017) analogs of Br3CN. In crystals of I3CN and I3NC, all pairs of adjacent sheets have centric stacking along [100] (Fig. 5), with molecules stacked about a glide plane and an inversion center. In the polytypes of Br3CN and Br3NC, adjacent sheets had combinations of centric and translational stacking, but not solely centric stacking. The 4-chloro analog had translational stacking. The 4-nitro analog had glide stacking, with no inversion center between stacked molecules. Thus, the all-centric stacking of I3CN and I3NC can be regarded as a new polytype in this series.

Figure 4
A space-filling drawing of the sheet structure of I3NC, viewed along [100].

Figure 5
Two adjacent sheets in I3NC, viewed along [100], illustrating the centric stacking mode. Dashed magenta lines represent short contacts in the front layer. Molecules in the rear layer are drawn with smaller balls and sticks, lower opacity, and green dashed lines representing short contacts.
vessel over 2-4 d. After the transfer was complete, the reaction mixture was neutralized with NaHCO 3 solution, followed by reduction of excess iodine by washing with Na 2 S 2 O 3 solution. Dichloromethane (approx. 100 mL) was added, with stirring, until nearly all solids had dissolved. The organic portion was filtered through silica gel (3 cm H Â 4 cm D), and then the filter was washed with dichloromethane (3 Â 20 mL). The filtrate was placed in a loosely-covered beaker. After most of the dichloromethane had evaporated, beige needles were collected by suction filtration (4.48 g, 89%  Fig. 6) based on the Sandmeyer procedure described by Britton et al. (2016). Ethyl acetate (20 mL), toluene-4-sulfonic acid monohydrate (77 mg), and isoamyl nitrite (60 mL) were used in place of water, acetic and sulfuric acids, and sodium nitrite, respectively. The The synthesis of I3CN and I3NC. Crystallization: Crystals of I3CN and I3NC were prepared by slow evaporation of acetonitrile solutions at ambient temperature, followed by decantation and then washing with pentane.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. A direct-methods solution was calculated, followed by full-matrix least squares/difference-Fourier cycles. All H atoms were placed in calculated positions (C-H = 0.95 Å ) and refined as riding atoms with U iso (H) set to 1.2U eq (C).

2,4,6-Triiodobenzonitrile (I3CN)
Crystal data Extinction correction: SHELXL2014 (Sheldrick, 2015b), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.00199 (9) Special details 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.