Question

Explain the following, giving two examples:

Coordination number

Answer 1

The coordination number (CN) of a metal ion in a complex can be defined as the number of ligand donor atoms to which the metal is directly bonded. For example, in the complex ions, [PtCl₆]²⁻ and [Ni(NH₃)₄]²⁺, the coordination numbers of Pt and Ni are 6 and 4, respectively. Similarly, in the complex ions, [Fe(C₂O₄)₃]³⁻ and [Co(en)₃]³⁺, the coordination number of both Fe and Co is 6 because \[\ce{C2O^{2−}4}\] and en (ethane-1, 2-diamine) are didentate ligands.