Question

Explain the following:
$$Co^{2+}$$ is easily oxidised to $$Co^{3+}$$ in the presence of a strong ligand.

Answer 1

With the electronic configuration $$3d^2 4s^0, Co^{2+}$$ has three unpaired electrons. $$H_2O$$ being a weak ligand, the unpaired electrons present in $$3d$$ orbital of $$Co\ (II)$$ do not pair up. In the presence of strong ligands, two unpaired electrons in $$3d$$ orbitals pair up and the third unpaired $$e^-$$ shifts to higher energy orbital from where it can be easily lost and hence show an oxidation state of $$III$$.