The splitting can be further de-/increased by ligands that exhibit strong π-bonding or πbackbonding, respectively. This is especially relevant for transition metal complexes with 4-7 electrons within their d-orbitals, because the size of their CFSE relative to the spin pairing energy (SPE) determines whether a high spin (hs) or low spin (ls) complex is formed. The first three electrons introduced into an octahedrally coordinated TM will always be placed separately into the three t 2g states. If the CFSE is small compared to the energy necessary for pairing electrons within one state, it is more beneficial to start filling the e g states with single electrons before pairing electrons within one orbital. The result is a high spin configuration. Conversely, if the CFSE is large in relation to the SPE, it would minimize the energy to place the fourth electron into one of the t 2g states, paying the price for pairing the electrons rather than gaining less by placing it into a higher orbital, resulting in a low spin configuration.