Interchange between coordinated and lattice solvents generates the highest energy barrier within nine-coordinated DyIII single molecule magnets

Abstract

It is crucial to promote axiality to enhance easy-axis magnetic anisotropy. Two mononuclear Dy^III compounds, in which each Dy^III is nine-coordinated, namely, [(C₁₂H₁₀N₅O)Dy(NO₃)₂(H₂O)₂]·C₂H₅OH (1) and [(C₁₂H₁₀N₅O)Dy(NO₃)₂(C₂H₅OH)₂]·H₂O (2) (HL = N³-(2-pyridoyl)-4-pyridinecarboxamidrazone), have been prepared through controlling the amount of C₂H₅OH and H₂O solvents. Geometry modulations were realized by interchanging coordinated and lattice solvents, thus achieving a structure closer to the configuration of a capped square antiprism for 2 compared to that for 1. Notably, magnetic studies revealed that compound 1 displays no slow relaxation of magnetization while compound 2 exhibits single-molecule magnet (SMM) behaviour in the absence of a static magnetic field, with the highest energy barrier (203.11 K) of nine-coordinated Dy^III SMMs. Ab initio calculations were performed to elucidate such a distinct performance, demonstrating that the combination of the larger charge distribution along the magnetic axis and the lower charge distribution in the equatorial plane generates a strong easy-axis ligand field to enhance magnetic properties, which is further associated with the structural symmetry. In addition, a possible coordination mode is proposed to realize high axis anisotropy for nine-coordinated Dy^III compounds. This work presents an effective method to modulate the dynamic magnetic relaxation of the Dy^III SMMs through interchange between coordinated and lattice solvents.