Exchange Interactions and Magnetic Properties of a Molecular Mn18‐Ring Complex

Abstract

Abstract[Mn3O(OAc)7(HOAc)]6 ⋅ x AcOH (x=6–9) represents a rare example of a compound containing molecular Mn18‐rings. These are formed by Mn3(μ3‐O) subunits in which the high‐spin Mn(III) centers are bridged by three pairs of acetate anions (AcO−). An AcOH molecule coordinates to one of the Mn atoms leading to [Mn3(μ3‐O)(μ2‐OAc)6(AcOH)]‐units, designated in short as Mn3‐units, that are interconnected by acetate anions via the other two Mn atoms to form Mn18‐rings. Magnetic measurements show weak ferromagnetic interactions between them that are suppressed in strong magnetic field. Quantum‐chemical calculations on Mn3 model complexes using independently DFT and ab‐initio multi reference methods (CASSCF/NEVPT2) show a correlation between the orientation of the pseudo‐Jahn‐Teller axes of pairs of Mn(III) magnetic centers and corresponding exchange coupling energies. Weak coupling between Mn3‐units within the Mn18‐ring allowed to simulate the magnetic susceptibility versus temperature dependence in terms of basically uncoupled magnetic moments of each Mn3‐unit within the ring.