Magnetic Signatures of Hydroxyl- and Water-Terminated Neutral and Tetra-Anionic Mn12-Acetate

We investigate the energetics and magnetic signatures of the parent molecular magnet Mn₁₂-Acetate [Mn₁₂O₁₂(COOR)₁₆(H₂O)₄] and a chemically decomposed version of this structure, in which the four water molecules are converted to hydroxyl groups and hydrogen molecules. We determine electron addition and water decomposition energetics for this water-containing molecule using density-functional methods and include the recent Fermi-Löwdin-Orbital self-interaction correction. We find that it only costs 0.32 eV to add four electrons to the parent molecule. Furthermore, due to the strong Coulomb attractions between hydroxyl anions and the Mn cations, the energy cost for breaking the four coordinating water molecules into four coordinating hydroxyls and two hydrogen molecules is decreased in the tetra-anionic structure relative to the neutral structure. We calculate magnetic anisotropy barriers for the neutral molecule and the dehydrogenated tetra-anion and show that large changes in the magnetic anisotropy arise the strong attraction between the hydroxyl anions and four of the crown Mn cations. We suggest that the large changes in magnetic signals associated with the [Mn₁₂O₁₂(COOR)₁₆(HOH)₄] to [Mn₁₂O₁₂(COOR)₁₆(OH⁻)₄ + 2H₂] decomposition could provide a nondestructive spectroscopic method for learning about water decomposition mechanisms in a class of realizable model catalytic systems that have been synthesized recently. © 2019 Wiley Periodicals, Inc.