Holding On-The Nature of Bonding in Metal Complexes

Various ways in which metal complexes can be represented, illustrated for the simple octahedral complex ion [IrClg]2-. 

Space-filling models, while giving a view closer to the actual situation for the molecular assembly, are difficult to visualize, even for very simple molecules, because atoms at the front tend to obscure those behind. As a consequence, the ball and stick models are met more often in formal presentations. 

Having established the basic concepts of coordination complexes, it is now time to attempt to understand how these complexes hold together, or bond. To pursue this aspect, we need to develop models for bonding that not only provide a satisfactory basis for dealing with the array of shapes that exist, but also can provide interpretation of the spectroscopic and other physical properties of this class of compounds. It is useful to introduce the core concepts and models that we use to interpret observations immediately, as they pervade discussion throughout the field. 

A simple valence bond description of bonding for the [Co(NH3)6]3+ complex ion. 

The higher stability of inner shell complexes that employ just the nine 3d—4s—4p orbital set suggests that there may be some special stability associated with the systems that employ nine orbitals that can accommodate no more than 18 electrons. There arose the 18-electron rule, which suggests that coordination complexes whose total number of valence 

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