A Simple Approach for Predicting the Spin State of Homoleptic Fe(II) Tris-diimine Complexes

We propose a simple
method for predicting the spin state of homoleptic
complexes of the Fe­(II) d6 ion with chelating diimine ligands.
The approach is based on the analysis of a single metric parameter
within a free (noncoordinated) ligand: the interatomic separation
between the N-donor metal-binding sites. An extensive analysis of
existing complexes allows the determination of critical N···N
distances that dictate the regions of stability for the high-spin
and low-spin complexes, as well as the intermediate range in which
the magnetic bistability (spin crossover) can be observed. The prediction
has been tested on several complexes that demonstrate the validity
of our method.