Impact of Solvents on Slow Magnetic Relaxations in Binuclear Dy III Complexes with the AIE-Active Ligand

Magnetic anisotropy is a key factor for high-performance single-molecule magnets. To investigate the influence of solvent molecules on magnetic anisotropy and at the same time explore rare earth ion luminescent materials, we synthesized series of TPE-based binuclear Dy III complexes [Dy 2 (TPE-prmd) 2 (tfa) 2 (MeOH) 2 ]·2CH 2 Cl 2 ·2CH 3 OH ( 1, H 2 TPE-prmd = ( E )- N ′-(2-hydroxy-5-(1,2,2-triphenylvinyl)benzylidene)pyrimidine-2-carbohydrazide, H 2 tfa = 1,1,1-trifluoroacetylacetonate), [Dy 2 (TPE-prmd) 2 (tfa) 2 (MeOH) 2 ]·4CHCl 3 ( 2 ), and [Dy 2 (TPE-prmd) 2 (tfa) 2 (DMF) 2 ] ( 3 ) by using an aggregation-induced-emission-active tetraphenylethylene (TPE) derivative of the H 2 TPE-prmd ligand to react with Dy(tfa) 3 ·6H 2 O under three different kinds of solvents. Single crystal X-ray diffraction analysis suggests that all complexes are made up of symmetrical enol oxygen-bridged Dy 2 units where Dy III ions are eight-coordinated with a hula-looplike geometry. The remarkable structural difference among them is that coordinated MeOH molecule and tfa anion are arranged side by side in 1 and 2, while the DMF molecule and tfa anion are set face-to-face in 3 . Fluorescence studies show the H 2 TPE-prmd ligand presents obvious aggregation-induced emission (AIE) effect, while all complexes eventually exhibit aggregation-caused quenching (ACQ) phenomenon and no characteristic emission peak of Dy III ions is found. Magnetic measurements reveal that strong Dy···Dy ferromagnetic couplings are operated in the Dy 2 unit of 1–3 . All complexes display significant slow magnetic relaxation behavior under zero dc field. Among three complexes, 3 possesses the highest effective energy barrier of 205.06 K for magnetic reversal. Theoretical calculations and magneto-structural studies suggest that the higher effective energy barrier in 3 is attributed to the larger magnetic anisotropy stemming from higher symmetry of Dy III ions in magnetism and stronger intramolecular magnetic couplings.