Basic Schemes of o-Bonding Single Bonds

Since the apex angles in pyramidal phosphorus compounds are usually nearer to 100° than 90°, the bonds are best described as mainly p with some sp character. In such cases the lone pair becomes involved in the bonding to some degree. 

The axial (apical) bonds in trigonal bipyramidal molecules are generally slightly weaker than the equatorial bonds involving the same kinds of atoms. Snch systems may be regarded as sp hybridised to give three bonds at 120%, and pd hybridised to give two colinear axial bonds. 

TABLE 3.10 Hybridised Orbitals Orbitals No. of Bonds Angles (°) Configuration Symmetry 

In order to achieve a system of minimum energy, mutual repulsion of ligand gronps should lead to a situation in which each is as equidistant as possible from all the others. 

In compounds where the phosphorus coordination number exceeds 6 and may be as high as 10, as in some metal phosphides (Chapter 8), the bonding may be only partially covalent. 

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