The Crystal Structure of Chloranil and Bromanil

抄録

The Crystal structure of chloranil and bromanil has been determined by X-ray diffraction technique based on the two-dimensional Fourier analysis. Chloranil and bromanil are isomorphous. The cell constants are: a₀=8.86₂, b₀=5.83₇, c₀=8.76₃Å, β=72.6° for chloranil and a₀=8.62₄, b₀=6.17₃, c₀=9.02₇Å, β=74.2° for bromanil. There are two molecules in the unit cell and the space group is P 2₁⁄a (C_2h⁵). The crystal consists of two layers of substituted halogen atoms which are parallel to the (001) plane, and the skeletons consisting of oxygen and carbon atoms lie between these two layers. The juxtaposition of molecules is such that the dipole interactions between C=O bonds stabilize the structure. There is definite localization of the double bonds in the benzene ring. In the molecule the adjacent halogen and oxygen atoms protrude respectively up and down from the plane of the benzene ring making a puckered form. The thermal motions of the molecules in this crystal have been analysed from the anisotropic thermal parameters of chlorine and oxygen atoms. A theoretical analysis shows that the puckered form is more stable, as a molecule, than the planar form. A clear correspondence is found between this fact and the anisotropic thermal motions of Cl and O atoms.