As a consequence of the splitting of the energy of the d orbitals
into the t2g and eg sets in a ligand field, octahedral complexes of
certain of the transition metal ions, particularly those of the first
transition series with configurations d4 to d7, may exist in either
the high-spin (HS) or low-spin (LS) state, depending on the
nature of the ligand field about the metal ion.