Formation and Structure of Complexes

I Lewis acid-base reactions are discussed in Section 16.3. 

Although the ion Fe(CN)g is a complex of Fe and CN ions, a solution of Fe(CN)g contains negligible concentration of CN . Therefore, a substance such as K4[Fe(CN)g] is relatively nontoxic, even though the free cyanide ion is a potent poison. 

A metal atom, particularly a transition-metal atom, often functions in chemical reactions as a Lewis acid, accepting electron pairs from molecules or ions. For example, Fe and H2O can bond to one another in a Lewis acid—base reaction. 

A pair of electrons on the oxygen atom of H2O forms a coordinate covalent bond to 

The Fe ion also undergoes a similar Lewis acid—base reaction with cyanide ions. In this case, the Fe ion bonds to the electron pair on the carbon atom of CN . 

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