Lewis bases, anion strength, coordination

Since anions are more adaptable in their bonding than cations, it is convenient to distinguish between the normal Lewis base strength, calculated by assuming that oxygen is 4-coordinate, and the maximum Lewis base strength, which equals the valence of the strongest bond that the undistorted anion can form. This is usually... 

The particular virtue of these definitions is that the Lewis acid and the Lewis base strengths are both estimates of the valence of the bond that links the cation with the anion. The most effective bonds will therefore occur between a cation whose Lewis acid strength (Sg) is close to the Lewis base strength (Sb) of the anion. This is known as the Valence Matching Principle. Compounds between badly matched ions, i.e. Be (Sa = 0.5 v.u.) and ClO j" (Sb = 0.08 v.u.), are difficult if not impossible to form as both the cation and the anion will be forced into unusual coordination. If they... 

Anion bonding strength, 5b The expected value of the valence of a bond formed by an anion. It can be estimated by dividing the anion s (negative) valence by its expected coordination number. This is the same as Lewis base strength Anion valence, Vb The valence of an atom when acting as an anion. is a negative number... 

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