A Stable Molecular Entity Derived from Rare Iron(II) Minerals: The Square‐Planar High‐Spin‐d⁶ FeIIO₄ Chromophore

The odd couple: The red chromophore of both the rare silicate mineral gillespite (BaFeSi4O10; see picture, left, on sanbornite, BaSi2O5) and the bis(meso-oxolanediolato)ferrate(II) anion in its lithium salt (right) is the square-planar, high-spin-d6 ferrous center. The unusual combination of structure and spin state for the FeO4 moiety is not forced by a rigid environment of the central metal, but rather results from an intrinsically stable entity.