Figure 3.

ΔE_π, the energy gap between the e_π*(d_xz,d_yz) and b₂(d_xy) orbitals, is a function of the electronic configuration: as electrons are added to e_π*(d_xz,d_yz), the M–oxo bond distance increases and ΔE_π decreases. The smaller energy gap, coupled with the relief of electron–electron repulsion upon electron unpairing, often produces a high-spin S = 3/2 ground state in the d³ configuration. The reduced M–oxo π-bond order in d³ and d⁴ configurations increases the basicity of M–oxo complexes.