Effect of Substituents in Equatorial Hexaazamacrocyclic Schiff Base Ligands on the Construction and Magnetism of Pseudo D6h Single-Ion Magnets

Three mononuclear DyIII compounds DyL1(Ph3SiO)2BPh4·MeCN·2H2O (1), DyL2(Ph3SiO)2BPh4·C2H5OH·H2O (2), and DyL3(Ph3SiO)(OAc)BPh4·CH3OH·3H2O (3) and their corresponding YIII diluted analogues Dy0.0967Y0.9033L1(Ph3SiO)2BPh4·MeCN·2H2O (1@Y), Dy0.2668Y0.7332L2(Ph3SiO)2BPh4·C2H5OH·H2O (2@Y), and Dy0.1260Y0.8740L3(Ph3SiO)(OAc)BPh4·CH3OH·3H2O (3@Y) were synthesized with hexaazamacrocyclic Schiff base ligands as an equatorial ligand. The substituents in the equatorial hexaazamacrocyclic Schiff base ligand show a significant effect on the replacement of the axial ligands. Compounds 1, 2, and 3 are typical zero dc field single-molecule magnets with effective energy barriers (Ueff) of 1092(6), 946.1(7), and 150.1(9) K, respectively. Although the effective energy barriers of 1 and 2 are close, the magnetic hysteresis remains open up to 20 K for 1, twice as large as that of 2 (10 K), which is different from the previously reported compounds, probably due to nonplanarity N6 in the equator. Ab initio calculations indicate that the ground states of compounds 1 and 2 exhibit high anisotropy and pure second and third excited states, while compound 3 exhibits pure ground-state anisotropy and highly mixed excited states, leading to the easy occurrence of quantum tunneling of magnetization between the ground and excited states in compound 3. This work indicates that the substituents in equatorial hexaazamacrocyclic Schiff base ligands have a significant effect on the construction and magnetic properties of DyIII SIMs with D6h symmetry.