Effect of Ligands on Quantum Tunneling of Magnetization for Dysprosium C_4v Single-Molecule Magnets with Theoretical Insights

Abstract

Two mononuclear Dy III -based compounds formulated as [Dy(L-pyra) HL-pyri = N 3 -(2-pyridoyl)-3-pyridinecarboxamidrazone) have been synthesized by modifying the ligands with different functional groups. In two compounds, Dy III centers all feature on N 4 O 5 in a spherical capped square-antiprismatic geometry with C 4v 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 Dy III -based SMM.

Structures and Single-Molecule Magnet Behavior of Dy3 and Dy4 Clusters Constructed by Different Dysprosium(III) Salts

“…Using the obtained parameters, we fitted both the Orbach and Raman processes (τ –1 = CT n + τ 0 –1 exp(− U eff / kT )) over the entire temperature region (10.0–30.0 K). Thus, the excellent fit to the overall relaxation was obtained, and parameters were obtained: U eff = 197.44 K (137.22 cm –1 ), τ 0 = 3.03 × 10 –7 s, C = 8.69 × 10 –5 s –1 ·K – n , n = 5.07, R 2 = 0.999, where the n value and τ 0 were consistent with normal value (1 < n < 6 and 10 –5 < τ 0 < 10 –12 ). − To further study the relaxation process of 2 , an asymmetric Cole–Cole graph based on the generalized Debye model was used to extract τ and the corresponding distribution (α) for each temperature (Figure d and Table S8). The α value was obtained in the wide range of 0.06 to 0.51, with a large relaxation time distribution, which confirmed that there might be multiple relaxation processes in 2 . , …”