Q28Short answer
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.
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With weak field ligands; ∆O < p, the electronic configuration of Co (III) will 4 2 be t 2g e g and it has 4 unpaired electrons and is paramagnetic. With strong 6 0 field ligands, ∆0 > p, the electronic configuration will be t 2g e g. It has no unpaired electrons and is diamagnetic.