What is crystal field splitting energy ? How does the magnitude of `Delta_0` decide the actual configuration of d - orbitals in a co-ordination entity ?

Explanation

When ligands approach a transition metal ion, the d-orbitals split into two sets, one with lower energy and the other with higher energy. The difference of energy between the two sets of orbitals is called crystal field splitting energy `(Delta_0)` in case of octahedral field.
If `Delta_0 lt P` (pairing energy), the `4^(th)` electron enters one of the eg orbitals giving the configuration `t_(2g)^4 e_g^1` thereby forming high spin complexes. Such ligands for which `Delta_0 lt P` are called weak field ligands.
If` Delta_0 gt P`, the `4^(th)` electron pairs up in one of the `t_(2g)` orbitals giving the configuration `t_(2g)^(4) e_g^1` thus forming low spin complexes. Such ligands for which `Delta_0 gt` Pare called strong field ligands.