Manipulating the Relaxation of Quasi-D-4(d) Dysprosium Compounds through Alternation of the O-Donor Ligands

Three mononuclear Dy-III complexes with the same auxiliary ligand Lz (2,4-diamino-6-pyridyl-1,3,5-triazine), [Dy-(TTA)(3)Lz] (1Dy) (TTA = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate), [Dy(acac)(3)Lz]center dot CH3OH center dot 0.5H(2)O (2Dy) (acac = acetylacetonate), and [Dy(MQ)(2)Lz(2)]Br center dot CH3OH (3Dy) (HMQ = 2-methyl-8-quinolinol), have been synthesized through alteration of the ligands containing O donors. In all three complexes, the Dy-III ions are eight-coordinate and submitted to pseudo-D-4d symmetry in the first coordination sphere. It is noteworthy that the TTA ligands in 1Dy are easily substituted by other bidentate capping ligands with O donors, leading to distinct magnetic properties, which were studied experimentally and via ab initio calculations. All three complexes were found to exhibit single-molecule magnet behavior with U-eff of 22 cm(-1) (1Dy), 112 cm(-1) (2Dy), and 56 cm(-1) (3Dy) under zero applied dc field. Complex 1Dy demonstrates inferior SIM properties compared with 2Dy and 3Dy, which can be attributed to the strong electron-withdrawing effects of TTA ligands, as confirmed by theoretical calculations. However, butterfly-shaped magnetic hysteresis in 1Dy and 3Dy was observed at 1.9 K, while not in 2Dy.