A high-spin square-planar Fe(ii) complex stabilized by a trianionic pincer-type ligand and conclusive evidence for retention of geometry and spin state in solution

Abstract

Square-planar high-spin Fe(II) molecular compounds are rare and the only three non-macrocyclic or sterically-driven examples reported share a common FeO₄ core. Using an easily modifiable pincer-type ligand, the successful synthesis of the first compound of this type that breaks the FeO₄ motif was achieved. In addition, we present the first evidence that geometry and spin state persist in solution. Extensive characterization includes the first high-field EPR and variable field/temperature Mössbauer spectra for this class of compounds. Analysis of the spectroscopic data indicates this complex exhibits a large and positive zero-field splitting tensor. Furthermore, the unusually small ΔE_Q value determined for this compound is rationalized on the basis of DFT calculations.