Lithium(I)-Incorporated Tetranuclear Dysprosium(III) Complexes with Single-Molecule Magnetic and Luminous Properties

Despite extensive research on dysprosium-based single-molecule magnets (SMMs), the deliberate incorporation of alkali-metal ions, such as lithium, as structure-directing components remains relatively unexplored. Herein, the reaction of an electron-rich lithiated Schiff-base ligand with DyCl$_3$ afforded tetranuclear heterometallic Li–Dy complexes featuring three types of E-bridging anions (E = ClO$_4$$^–$, CO$_3$$^{2–}$, C$_2$O$_4$$^{2–}$). Single-crystal X-ray diffraction analysis revealed distorted square-antiprismatic DyIII centers with N$_2$O$_6$ coordination environments and intramolecular Dy···Dy distances ranging from 3.58 to 3.94 Å. Magnetic investigations, supported by ab initio calculations, indicated weak antiferromagnetic (AFM) interactions between Dy$^{III}$ centers. All complexes exhibit zero-field single-molecule magnet (SMM) behavior, with low-temperature relaxation governed by quantum tunneling/direct processes and higher temperature relaxation involving Raman and Orbach mechanisms. The effective energy barriers for magnetization reversal (U$_{eff}$) range from 19 to 37 K. In addition, the complexes exhibit ligand-based green/yellow fluorescence, demonstrating the coexistence of SMM behavior and visible region emission in the heterometallic Li–Dy molecular framework.