Competition between Heisenberg Exchange, Double Exchange and Vibronic Coupling in the First Mixed-Valence Dimer with an Intermediate Spin Ground State

Very recently, the first dimer molecule with an intermediate spin ground state realised by delicate balancing of competing exchange interactions (Heisenberg and double) and vibronic coupling was published [Nat. Chem., 14, 328 (2022)]. This shows it is possible to balance exchange mechanisms and vibronic coupling in order to obtain desired properties, such as molecules which switch spin ground state by applying an electric field. We propose to make the first direct observation of an intermediate spin ground state and its spin dynamics with inelastic neutron scattering to accurately quantify the competition between Heisenberg and double exchange as well as the vibronic coupling. This will provide unprecedented insight into double exchange spin dynamics in molecules and validate existing computational approaches useful for predicting the properties of mixed-valence molecules.