Orbital order

Cations with d-electrons in orbitally degenerate energy levels may exhibit electronic ordering effects that are formally equivalent to antiferromagnetism. Consider the example of Cu²⁺, a 3d⁹ cation, octahedrally coordinated by oxygen.
This cation has its ninth electron in an e^↓_g level, where the d_z² and d_x²−y² orbitals are degenerate. However, d⁹ is a Jahn–Teller ion, which tends to elongate or flatten the octahedron in order to stabilize one orbital or the other. It may be energetically favourable to alternate the configurations, so that the distortions of neighbouring octahedra match. There is then G-type orbital order, where there are two sublattices, composed of ions with electrons in d_z² or d_x²−y² orbitals.