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 bett2g4eg2i.e.,  it has 4 unpaired electrons and is paramagnetic.

With strong field ligands0<P  (pairing energy), so pairing ocours thus, the electronic

configuration will be t2g4eg2. It has no unpaired electrons and is diamagnetic.