I. The Crystal Structure of a New Dimer of Triphenylfluorocyclobutadiene. II. A Low Temperature Refinement of the Cyanuric Triazide Structure

I. The Crystal Structure of a New Dimer of Triphenylfluorocyclobutadiene The crystal structure of thermal isomer of the “head-to-head” dimer of triphenylfluorocyclobutadiene was determined by the direct method. The Σ2 relationship involving the low angle reflections with the largest E’s were found and solved for the signs by the symbolic method of Zachariasen. The structure was seen in the electron density map and the E-map, and was refined antisotropically by the method of least squares. The residual R was 0.065. The structure is a gem-difluorohexaphenyldihydropentalene. All of the phenyl groups are planar as it is the cyclopentadiene ring of the dihydropentalene skeleton. Overcrowding at the position of the flourines causes some deviations from the normal bond angles in the cyclopentene ring. The list of observed and calculated structure factors on pages 32-34 will not be legible on the microfilm. Photographic copies may be obtained from the California Institute of Technology. II. A Low Temperature Refinement of the Cyanuric Triazide Structure The structure of cyanuric triazide was refined anisotropically by the method of least squares. Three-dimensional intensity data, which has been collected photographically with MoKα radiation at -110˚C, were used in the refinement. The residual R was reduced to 0.081. The structure is completely planar, and there is no significant bond alternation in the cyanuric ring. The packing of the molecules causes the azide groups to deviate from linearity by 8 degrees.