Explain the difference between a weak field ligand and a strong field ligand.

Explanation

A ligand with small value of crystal field splitting energy (CFSE) is called a weak field ligand and a ligand with large value of CFSE is called a strong field ligand. In case of a weak field ligand, CFSE is less then pairing energy, as such pairing does not take place and as such outer orbital low spin complexes are formed. On the other hand in case of a strong field ligand CFSE is more than pairing energy, as such pairing of unpaired electron takes place and as such inner orbital or high spin complexes are formed.