Question

Which of the following complexes is most stable?
(1) ${[M{(N{H_3})_6}]^{2 + }}$
(2) ${[M{(N{H_3})_6}]^{3 + }}$
(3) ${[Me{n_2}{(N{H_3})_2}]^{3 + }}$
(4) ${[M{(en)_3}]^{3 + }}$

Answer 1

Hint:In the coordination complex the central metal atom is surrounded by electron-donating ligands. The stability of the coordination depends on many factors including the charge on the complex and the type of ligand attached.

Complete step by step answer:
The stability of the coordination complex depends on the charge on the complex, greater is the charge on the complex, the more stable is the complex and vice versa. The main reason for the stability of the coordination complex is the type of ligands attached to it. If the metal atom is attached with the chelating ligand, more stable will be the complex.
-The chelating ligands are defined as the ligand which can bond with the central metal atom from two or more sites.
-Ammonia is a non-chelating ligand, it can bind with the central atom from one side and ethylene diamine is a chelating ligand that binds with the central metal atom from two sides.
-The complex ${[M{(N{H_3})_6}]^{2 + }}$ has +2 charge, therefore it is least stable among the given complex and the central metal is attached to the six ammonia ligand which is non-chelating.
-The complex ${[M{(N{H_3})_6}]^{3 + }}$ has +3 charge. The central metal is attached to the six ammonia ligands which are non-chelating.
-The complex ${[Me{n_2}{(N{H_3})_2}]^{3 + }}$ has +3 charge. The central metal atom is attached to two ammonia ligands and two ethylenediamine ligands. As ethylene diamine is a chelating ligand it will bind with the central atom from two sides.
-The complex ${[M{(en)_3}]^{3 + }}$ has +3 charge. The central metal atom is attached with three ethylene diamine ligands. As it is a chelating ligand. Therefore, it is the most stable complex among the other complexes.
Therefore, the correct option is 4.

Note:
The other factors which affect the stability of the coordination complex or coordination complex ion are size and charge of the ligands, size of metal ion, electronegativity, and charge distribution, nature of the ligand.