9.18 What is crystal field splitting energy? How does the magnitude of decide the actual configuration of d orbitals in a coordination entity?
It is known that the degenerated d-orbitals split into two levels - eg and t2g . The splitting of the degenerate levels due to the presence of ligands is called the crystal-field splitting and the energy difference between the two levels (eg and t2g) is called the crystal-field splitting energy (CFSE).
The CFSE is denoted by Δo.
After splitting of orbitals, the filling of the electrons starts. After 1 electron has been filled in each of the three t2gorbitals, the fourth electron can enter the eg orbital ( t2g3 eg1 like electronic configuration) or the pairing of the electrons can take place in the t2g orbitals ( t2g4 eg0 like electronic configuration).
If the CFSE value or Δo value of a ligand is less than the pairing energy (P), then the electrons enter into the eg orbital. And, if the Δo value of a ligand is more than the pairing energy (P), then the electrons will enter the t2g orbital.