Cobalt(II) is very stable in an aqueous solution, but it is easily oxidised to Cobalt(III) in the pr

Question

Cobalt(II) is very stable in an aqueous solution, but it is easily oxidised to Cobalt(III) in the presence of strong complexing agents. What is the reason for this?

Professor PC Thomas Classes · Answer

In the presence of strong ligands, the large Crystal Field Splitting Energy (CFSE) for the low-spin $d^6$ configuration of $	ext{Co}^{3+}$ more than compensates for the third ionisation enthalpy, making the oxidation of $	ext{Co}^{2+}$ to $	ext{Co}^{3+}$ highly favourable.