How High the Spin? Allowed and Forbidden Spin States in Transition‐Metal Chemistry

How high is high and how low is low? With respect to transition-metal complexes of different coordination numbers and stereochemistry, high-, low-, and intermediate-spin states may mean different things. The hybridization of the d orbitals, similar to the deformation of a balloon subjected to pressure (see picture), provides a rationale for the splitting of the d manifold and, hence, for the allowed spin states in a given complex.