Question

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.

Answer 1

With weak field ligands, `Delta_(o) lt P`, (pairing energy) so, the electronic configuration of CO (III) will be `t_(2g)^(4) e_(g)^(2)` i.e., it has 4 unpaired electrons and is paramagnetic.