Stereochemistry of Square Complexes

We have seen that a molecule or ion having in it a single atom bound to four different groups at the corners of a tetrahedron is, in general, asymmetric and may exist in two nonsuperimposible forms. On the other hand, if two of the four groups are the same or if two pairs of groups are bound tetraliedrally to the same atom, there will be only one form with 

If a complex has four groups at the corners of a square, the stereochemical situation is very different. Representing the central atom as M and the substituents as IF, X, Y, and Z, we can see that there are two forms apiece for complexes of the type MX 2Y2 and MX YZ hut three forms for the complex with four different groups. 

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