Question:
Based on crystal field theory explain why Co(III) forms a paramagnetic octahedral complex with weak field ligands whereas it forms a diamagnetic octahedral complex with strong field ligands.
Solution:
The electronic configuration will be t42g e2g. It has 4 unpaired electron and paramagnetic. With weal ligand Δ0 < p. The configuration with strong field ligand will be
t62g e0g. the Δ0 > p and there won’t be any unpaired electron therefore diamagnetic.