Irving-Williams Stability Order for Transition Metals

Thermodynamic Stability Order:

$$\text{Stability of divalent } 3d \text{ metal complexes: } \text{Mn}^{2+} < \text{Fe}^{2+} < \text{Co}^{2+} < \text{Ni}^{2+} < \text{Cu}^{2+} > \text{Zn}^{2+}$$

Concept: The thermodynamic formation constant ($\beta_n$) for divalent high-spin $3d$ transition metal complexes increases steadily across the period regardless of ligand type, reaching a maximum at $$\text{Cu}^{2+}$$ due to ionic radius contraction combined with additional Jahn-Teller stabilization energy.

Notation:

• $$\text{Cu}^{2+}$$ = Possesses maximum stability among $$M^{2+}$$ cations due to high charge density and Jahn-Teller effect.