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 solutionElectronic supplementary information (ESI) available: Detailed experimental conditions, elemental analysis, 1H-NMR spectroscopy, magnetic susceptibility data and fitting, Mössbauer spectroscopy, high-field EPR spectroscopy of 2, and DFT calculations. CCDC 1006581. For ESI and crystallographic data in CIF or other electronic format see

Square-planar high-spin Fe( ii ) molecular compounds are rare and the only three non-macrocyclic or sterically-driven examples reported share a common FeO 4 core. Using an easily modifiable pincer-type ligand, the successful synthesis of the first compound of this type that breaks the FeO 4 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 Δ E Q value determined for this compound is rationalized on the basis of DFT calculations. Extensive spectroscopic evaluation of a novel ONO 3− trianionic pincer Fe( ii ) complex indicates the rare square-planar geometry and S = 2 spin state are retained in solution.