The pentaphenyl derivatives of Group 15 elements

The structures of these compounds have been determined by X-ray diffraction. The coordination geometries of the phosphorus atom in PPhs and the arsenic atom in AsPhs are both trigonal bipyramidal as expected, but the coordination geometry of the antimony atom in SbPhs is approximately square pyramidal (sqp). See Fig. 15.7. The symmetry of a perfect square pyramidal SbCs fragment is C4v. The fragment possesses a fourfold symmetry axis that coincides with one of the Sb-C bonds. The C atom on the symmetry axis is referred to as apical (ap). The four symmetry equivalent C atoms are referred to as basal (ba). 

The crystals of SbPhs had been obtained by crystallization from isooctane. When SbPhs is crystallized from cyclohexane, solvent molecules are incorporated in cavities between the pentaphenylantimony molecules the composition of the crystals is SbPhs 1/2 cyclo-CfUn- 

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