Geometrical Types and Isomers

remember that coordination number is equivalent to Werner s secondary valence. 

Several different types of isomers arise in transition-metal coordination compounds, and these are described below. 

Linkage isomerism This is a special type of structural isomerism in which the differences arise from a particular ligand which may coordinate to a metal ion in more than one way. In Table 1-3 we indicated that a ligand such as thiocyanate could bond to a metal through either the nitrogen or the sulfur atom, and the complex ions [Co(NH3)5(ACS)]2+ and [Co(NH3)5(5CN)]2+ are related as linkage isomers. 

Geometrical isomerism This is an important topic which played a crucial role in the development of coordination chemistry. Werner used the number of isomers 

A planar complex of the type [Pt(NH3)2Cl2] can exist in two forms depending upon the relative spatial orientation of the two chloride ligands. They can be at 90° to each other to give the cis form (1.1), or at 180° to give the trans isomer (1.2). 

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