Modifications of Tanabe-Sugano Diagram Induced by Radical Ligand Field: Ab Initio Inspection of a Fe(II)-Verdazyl Molecular Complex.

Quantum entanglement between the spin states of a metal center and radical ligands is suggested in an iron(II) [Fe(dipyvd)] compound (dipyvd = 1-isopropyl-3,5-dipyridil-6-oxoverdazyl). Wave function (Difference Dedicated Configuration Interaction, DDCI) inspections were carried out to stress the versatility of local spin states. We named this phenomenon , in reference to our previous work (see Roseiro et al., , e202200478) where we introduced the concept of as an extension of mesomerism to spin degrees of freedom. The construction of localized molecular orbitals allows for a reading of the wave functions and projections onto the local spin states. The low-energy spectrum is well-depicted by a Heisenberg picture. A 60 cm ferromagnetic interaction is calculated between the radical ligands with the = 0 and 1 states largely dominated by a local low-spin = 0. In contrast, the higher-lying = 2 states are superpositions of the local = 1 (17%, 62%) and = 2 (72%, 21%) spin states. Such mixing extends the traditional picture of a high-field Tanabe-Sugano diagram. Even in the absence of spin-orbit coupling, the avoided crossing between different local spin states is triggered by the field generated by radical ligands. This puzzling scenario emerges from versatile local spin states in compounds which extend the traditional views in molecular magnetism.