Effect of Ligands on Quantum Tunneling of Magnetization for Dysprosium C4v Single-Molecule Magnets with Theoretical Insights

Two mononuclear DyIII-based compounds formulated as Dy(L-pyra)2(NO3)(H2O)2·3H2O (1) and Dy(L-pyri)2(NO3)(CH3OH) (2) (HL-pyra = N3-(2-pyrazinyl)-3-pyridinecarboxamidrazone; HL-pyri = N3-(2-pyridoyl)-3-pyridinecarboxamidrazone) have been synthesized by modifying the ligands with different functional groups. In two compounds, DyIII centers all feature on N4O5 in a spherical capped square-antiprismatic geometry with C4v configuration. The magnetic studies showed that 1 and 2 display single-molecule magnet (SMM) behavior under a zero dc field with energy barriers of 175.44 and 322.96 K, respectively. Such an apparent dereference in magnetic properties was interpreted via ab initio calculations. Theoretical results support the axial coordination to be the key factor responsible for the difference between compounds 1 and 2. This work highlights the coordination mode and axial Dy–O bond length as important factors in constructing a high-performance DyIII-based SMM.