Crystal field splitting energy is the energy difference between the two levels of d-orbitals (t2g and eg) that split in the presence of ligands, according to the crystal field theory. The splitting is due to the repulsion between the electrons in the d-orbitals and the ligands, which causes the energy levels to split into two levels, t2g and eg. The energy difference between these two levels is called the crystal field splitting energy, Δ0/Crystal_Field_Theory/Crystal_Field_Theory). The crystal field splitting energy determines the electronic configuration of transition metal ions in coordination compounds.

The electronic configuration of d4 in terms of t2g and eg in an octahedral field can be determined using the crystal field theory. If Δ0 > P, the electrons are singly filled in the t2g energy levels first, and the remaining electrons are filled based on the crystal field splitting energy and pairing energy. Filling up of the remaining electrons takes place in two ways: (i) If the crystal field splitting energy (Δ0) is greater than that of the pairing energy (P), electrons will be filled in the eg orbitals. (ii) If the crystal field splitting energy (Δ0) is lesser than that of the pairing energy (P), electrons will be paired up in the t2g energy levels.