The effect of magnetic coupling along the magnetic axis on slow magnetic relaxation in Dy complexes with configuration based on an aggregation-induced-emission-active ligand.

The adjustment of crystal symmetry and intramolecular magnetic coupling is of great importance for the construction of high-performance single-molecule magnets. By using an aggregation-induced-emission-active pyridine-carbohydrazone-based Schiff base ligand and phosphine oxides, four dinuclear and one one-dimensional Dy-based complexes, [Dy(TPE-pc)(BuPO)Cl]·2CHCN·2HO (1), [Dy(TPE-pc)(CyPO)Cl] (2), [Dy(TPE-pc)(MePA)Cl]·2CHOH (3), [Dy(TPE-pc)(PhPO)Cl] (4) and [Dy(TPE-pc)(DPPO)Cl] (5) (HTPE-pc = ()-'-(2-hydroxy-5-(1,2,2-triphenylvinyl)benzylidene)picolinohydrazide, MePA = -phenyl-',''-bis(morpholinyl) phosphoric triamide, DPPO = piperazine-1,4-diylbis(diphenyl phosphine oxide)), were isolated. All complexes are made up of an enol oxygen-bridged Dy unit, where Dy ions possess a pentagonal bipyramidal geometry with pseudo symmetry. Magnetic measurements reveal that intramolecular Dy-Dy couplings are ferromagnetic and all complexes display a significant slow magnetic relaxation phenomenon below 30 K under a zero dc field. calculations indicate that the anisotropic magnetic axes of all Dy ions are approximately perpendicular to the higher-order symmetric axes in all complexes, and that Dy-Dy magnetic couplings along the magnetic axes effectively suppress the ground state quantum tunneling effect of magnetization and promote the occurrence of slow magnetic relaxation. Raman relaxation prevails in all complexes. In addition, the HTPE-pc ligand shows an aggregation-induced emission (AIE) effect; however, all complexes exhibit an aggregation-caused quenching (ACQ) phenomenon.