Mr. Kaviani,

You need the relationship total energy or only accounting for the free Gibbs energy as a function of the dielectric constant of the medium. There are given in discourse to Physical Chemistry I and II (BSc grad)

Dielectric constant will be important if the ligands and metal center are charged (high dielectric solvents will screen the electrostatic attraction between the oppositely charged species, decreasing the binding energy with respect to the binding energy in low dielectric solvents)

This may also be important if there are significant changes in the polarity of the species involved, even if there are no explicitly charged species.