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

[Mn3O(OAc)(7)(HOAc)](6)center dot xAcOH (x=6-9) represents a rare example of a compound containing molecular Mn-18-rings. These are formed by Mn-3(mu(3)-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 [Mn-3(mu(3)-O)(mu(2)-OAc)(6)(AcOH)]-units, designated in short as Mn-3-units, that are interconnected by acetate anions via the other two Mn atoms to form Mn-18-rings. Magnetic measurements show weak ferromagnetic interactions between them that are suppressed in strong magnetic field. Quantum-chemical calculations on Mn-3 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 Mn-3-units within the Mn-18-ring allowed to simulate the magnetic susceptibility versus temperature dependence in terms of basically uncoupled magnetic moments of each Mn-3-unit within the ring.

Automated summary

[Mn3O(OAc)(7)(HOAc)](6)·xAcOH (x=6-9) is a rare compound containing molecular Mn-18 rings. The Mn-18 rings are formed by Mn-3(mu(3)-O) subunits, in which high-spin Mn(III) centers are bridged by acetate anions (AcO-) pairs. The magnetic measurements show weak ferromagnetic interactions between the Mn-3 units within the Mn-18 rings, which can be simulated as basically uncoupled magnetic moments of each Mn-3 unit within the ring.