The crystal structure of benzene iododichloride

The crystal of benzene iododichloride, C6HsIC12, is monoclinic.The unit cell, containing 8 molecules, has the dimensions a--~ 15.6, b = 5.45, c : 19.6 /~, fl = 90 ° 30' and the space group is B2~/a.An alternative space group is P21/a, with unit cell dimensions a----15.6,b----5.45,c----12.3/~, fl----128 ° 30'.The method of double Fourier synthesis was applied, using first Cu Ka and later Mo Ka radiation, and the projections of the electron density on the a c and b c planes were made.The IC1 z group is linear and symmetrical, and its direction is approximately at right angles to the plane of the benzene ring.The line joining the I, C~ and C4 atoms is approximately parallel to the a c plane.The I-C1 distance is 2.45 A, the C-I distance is 2.00 A. The angle Cl~-I-C1 is 86 °.The closest approach between I and C1 in adjacent molecules is 3.40 /~, between I and I 4.70 /~, between C1 and C1 4-44 A, between I and CH 4.08 /~, between C1 and CH 3-77 /~ and between CH and CH 3-55 A. The main binding forces in the crystal are evidently between neighbouring iododichloride groups. Physical and X-ray data