Ncert Exercises & Solutions

Q. 28 On the basis of crystal field theory explain why Co(III) forms paramagnetic

octahedral complex with weak field ligands whereas it forms diamagnetic

octahedral complex with strong field ligands.

With weak field ligands; $∆_{0} < P$ (pairing energy) so, the electronic configuration of Co (III)

will bet $t_{2 g}^{4} e_{g}^{2}$ i.e., it has 4 unpaired electrons and is paramagnetic.

With strong field ligands $∆_{0} < P$ (pairing energy), so pairing ocours thus, the electronic

configuration will be $t_{2 g}^{4} e_{g}^{2}$ . It has no unpaired electrons and is diamagnetic.