Tin in Coordination Numbers Above Four

Since the dominant higher-coordination chemistry is that of tin, we survey this first. The range of structural studies is so wide that it is possible only to generalize and look at recent and representative examples. Intramolecular coordination in organotin compounds has been extensively reviewed up to 1992113. 

As the number of organic groups bonded to tin increases, the acceptor power decreases. Thus we find the frequency of different coordination numbers varies broadly as follows  

For five-coordination, the usual geometry is trigonal bipyramidal. This varies from fully symmetrical, as in Pt SnF, to extremely distorted. At the limit the shape can equally well be described as capped tetrahedral or distorted square pyramid. 

TABLE 5. Representative tin-element bond lengths in different coordinations (pm) 

In interpreting such values, both the experimental uncertainties and the empirical basis of van der Waals radii need to be taken into account. 

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