A ligand exchange reaction, where the structural type of the metal complex remains the same. $$\ce{ML_{n} + X -> ML_{n-1}X + L + \Delta\textit{E}}$$ Although these types of reactions are not necessarily isodesmic reactions, a substantial degree of error cancellation for the calculated energy, $\Delta E$, is achieved because the coordination sphere of the metal atom $\ce{M}$ is conserved.