Ligand substitution is the process in which one ligand in a coordination complex is replaced by another ligand. The effect of ligand substitution on the thermodynamic stability of a coordination complex depends on the nature of the incoming ligand, the leaving ligand, and the metal center. The stability of a coordination complex can be quantified using stability constants K , which are equilibrium constants for the formation of the complex from its constituent ions.In general, ligand substitution can either increase or decrease the thermodynamic stability of a coordination complex, depending on the relative strengths of the metal-ligand bonds formed and broken during the reaction. The strength of the metal-ligand bond is influenced by factors such as the charge, size, and electronic properties of the ligand and the metal ion.Here are two examples of ligand substitution reactions and their respective stability constants to illustrate the effect of ligand substitution on the thermodynamic stability of coordination complexes:1. Substitution of water ligands by ethylenediamine en in the hexaaquacopper II complex:[Cu H2O 6] + 3en [Cu en 3] + 6H2OThe stability constant for the formation of the [Cu en 3] complex is much larger than that for the [Cu H2O 6] complex log K = 18.7 for [Cu en 3] vs. log K = 6.0 for [Cu H2O 6] . This indicates that the [Cu en 3] complex is more thermodynamically stable than the [Cu H2O 6] complex. The increased stability is due to the stronger metal-ligand bonds formed between the copper II ion and the ethylenediamine ligands, which are bidentate and can form chelate rings, compared to the weaker bonds formed with water ligands.2. Substitution of chloride ligands by thiocyanate ligands in the tetrachloropalladate II complex:[PdCl4] + 2SCN [Pd SCN 2Cl2] + 2ClThe stability constant for the formation of the [Pd SCN 2Cl2] complex is smaller than that for the [PdCl4] complex log K = 3.2 for [Pd SCN 2Cl2] vs. log K = 5.0 for [PdCl4] . This indicates that the [Pd SCN 2Cl2] complex is less thermodynamically stable than the [PdCl4] complex. The decreased stability is due to the weaker metal-ligand bonds formed between the palladium II ion and the thiocyanate ligands compared to the stronger bonds formed with chloride ligands.In conclusion, the effect of ligand substitution on the thermodynamic stability of a coordination complex depends on the nature of the incoming and leaving ligands and the metal center. The stability of the complex can either increase or decrease, as demonstrated by the examples provided.