What is crystal field splitting energy ? How does the magnitude of `Delta_(0)` decide the actual configuration of d orbitals in a coordination entity?

Explanation

During the formation of coordination entity, when ligands approach the centre metal ion, d - orbital of metals do not remain degenerate but 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 (represented as `Delta_(0)` for octahedral field ).
If `Delta_(0) lt P` (pairing energy), the 4th electron of a `d^(4)`- system occupies one of the higher energy d - orbitals (i.e., `e_(g)` - orbitals) giving the configuration `t_(2)^(3)e_(g)^(1)` thus forming high spin complexes. Such ligands for which `Delta_(0)lt P` are called weak - field ligands.
If `Delta_(0) gt P`, the 4th electron pairs up in one of the lower energy d- orbitals (i.e., `t_(2g)` orbitals) leading to the configuration `t_(2)^(4)e_(g)^(0)` thereby forming low spin complexes.
Such ligands for which `Delta_(0)gt P` are called strong - field ligands.