Molecular structures of cycloborataphosphonianes. Part I. Crystal structure of 2,2,4,4-tetraiodo-1,1,3,3-tetraphenylcyclodiborataphosphoniane
The crystal structure of the title compound has been determined by the heavy-atom method from X-ray diffractometer intensity data and refined by least-squares methods to R0·064 for 3343 independent reflexions. The crystals are monoclinic with a= 12·34, b= 13·80 c= 17·56 Å, β= 111·8°, Z= 4, space-group P21/c. The dimeric molecules contain a non-planar, four-membered boron-phosphorus ring with approximate symmetry mm2 and a dihedral angle of 30°. The endocyclic bond angles are 88·2° at boron and 87·9° at phosphorus. Two different B–P bond lengths, 1·94 and 2·01 Å, are found. The mean B–I bond length is 2·21 Å. The complete molecule has an axis of approximate two-fold symmetry, in terms of which the tendency to form twinned crystals is explained.