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

Three mononuclear DyIII 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]·CH3 OH·0.5H2 O (2Dy) (acac = acetylacetonate), and [Dy(MQ)2 Lz2 ]Br·CH3 OH (3Dy) (HMQ = 2-methyl-8-quinolinol), have been synthesized through alteration of the ligands containing O donors. In all three complexes, the DyIII ions are eight-coordinate and submitted to pseudo- D4 d 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 Ueff 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.