Stabilization of unusual electronic configurations of transition elements in elongated six-coordinated oxygen sites of a K2NiF4 structure

The A′_xA_2?xLi_0.5M_0.5O₄ matrix deriving from the K₂NiF₄ structure has an elongated MO₆ octahedron; it has been used to stabilize anisotropic electronic configurations such as high-spin Fe⁴⁺, low-spin Co⁴⁺, medium-spin Co³⁺, low-spin Ni³⁺, or low-spin Cu³⁺. The choice of ions to be stabilized was based on a simple model for predicting the electronic configuration of a dⁿ ion in a tetragonally distorted octahedral environment.