Question

What is crystal field splitting energy? How does the magnitude of ${\Delta }_0$ decide the actual configuration of d-orbitals in a coordination entity?

Answer 1

When ligands approach a transition metal ion, the d-orbitals split into two sets $\left(t_{2g}and{e}_g\right)$, 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, ${\Delta }_0$ for octahedral field $\left(and{\Delta }_{l}fortetrahedralfield\right)$
If ${\Delta }_0<p$ (pairing energy), the 4th electron enters one of the $e_g$ orbitals giving the configuration $t_2^3{e}_g^{}1$ thereby forming high spin complex. Such ligands for which ${\Delta }_0<p$ are known as weak field lignds.
If ${\Delta }_0>p,$ the 4th electron pairs up in one of the $t_{2g}$ orbitals giving the configuration $t_2^4{e}_g^0,$ thus forming low spin complexes. Such ligands for which ${\Delta }_0>p$ are called strong field ligands.