The crystal structure of p-chloriodoxybenzene

Para-chlor-iodoxy benzene (ClC₆H₄IO₂) is monoclinic. The cell, containing four molecules, has the dimensions a= 14.4 A., b = 6.50 A., c = 8.11 A. and [beta] = 98½°. The space group is P2₁/c. The method of triple Fourier series has been applied to determine the electron density in a series of planes parallel to the ab plane. The plane containing the iodoxy group is very nearly perpendicular to the plane of the benzene ring. The I-O distances are nearly equal, being 1.60 and 1.65 A., with the angle O-I-O = 103°. The I-C distance is 1.93 A., the C-Cl distance is 1.80 A., and the benzene ring is a regular hexagon of side 1.41 A. The closest approach between I and O in adjacent molecules is 2.72 A., that between I and I is 3.60 A., that between Cl and C1 is 3.75 A., and that between CH and CH is 3.9 A. The main binding forces in the crystal are evidently between neighbouring iodoxy groups.