The Crystal and Molecular Structure of 8, 8-Dicyanoheptafulvene

Abstract

Abstract Crystals of 8, 8-dicyanoheptafulvene, C10H6N2, are monoclinic, with two molecules in a unit cell with the dimensions a=7.84, b=13.14, c=3.99 Å, and β=97.9°; the space group is P21⁄m. The intensities were recorded on multiple-film equi-inclination Weissenberg photographs and measured visually against a standard scale. A trial structure was constructed from the Patterson projections, P(u, v) and P(u, w), and a Harker section, P(u, 1/2, w). The atomic coordinates and anisotropic temperature factors were refined by the least-squares method. The final R factor for (hkl) reflections is 0.107. A considerable bond alternation in the conjugated seven-membered ring has been observed. The average long and short bond lengths in the ring are 1.44 and 1.34 Å respectively. The shortest C=C bond measures 1.31 Å, which is shorter than that in ethylene. The exocyclic C=C bond length is 1.42 Å, suggesting a considerable dipolar resonance structure, one which may be responsible for the stability of the compound. The C≡N bond length is 1.13 Å. The molecule deviates slightly from being planar; it lies nearly parallel to the (101) plane. All the intermolecular separations correspond to normal van der Waals interactions; the perpendicular distance between the molecular planes is 3.4Å. The thermal motion was interpreted in terms of rigid body vibrations, and the bond lengths and angles were corrected for the rotational oscillations.