Hi Candidate,

CFSE refers to The crystal field stabilization energy (CFSE) is the stability that results from placing a transition metal ion in the crystal field generated by a set of ligands.

We can calculate the CFSE as -(5)(2/5)Δ _O + (2)*(3/5)Δ _O = -4/5 Δ _O . [CoF3(H2O) 3 ] is also an octahedral d 6 complex but it contains F, a weak field ligand. Its orbital occupancy is (t _2g ) ⁶ and it therefore has zero unpaired electron . In this case the CFSE is -(6)(2/5)Δ _O + (0)(3/5)Δ _O + P = -12/5 Δ _O + P, where P refers to the Pairing Energy which is equal to zero because of weak ligands.

Hope that you have got your answer. Have a Good Day!!