What is crystal field splitting energy? How does the magnitude of `triangle_(0)` decide the actual configuration of d orbitals in a coordination 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 `(triangle_0` for octahedral field).
If `triangle_0ltP` (pairing energy) the 4th electron enters one of the `e_(g)` orbitals giving the configuration `t_(2g)^(3)e_(g)^(1)` thus forming high spin complexes. Such ligands for which `triangle_0ltP` are called weak field ligands.
If `triangle_0gtP`, the 4th electron pairs up in one of the `t_(2g)` orbitals giving the configuration `t_(2g)^(4)e_(g)^(0)` thereby forming low spin complexes. Such ligands for which `triangle_0gtP` are called strong field ligands.