Regulating the luminescent and magnetic properties of rare-earth complexes with β-diketonate coligands

Eleven dinuclear rare-earth (RE) complexes, [RE2(dbm)2L2(DMF)2]·2CH3OH (RE = Y (1), Nd (2), Dy (6), Er (7)), [RE2(dbm)2L2(CH3OH)2]·nCH3OH (RE = Eu (3), Gd (4), Tb (5), Yb (8)) and [RE2(acac)2L2(CH3OH)2] (RE = Dy (9), Er (10), Yb (11)) (H2L = N′-(2-hydroxybenzylidene)-2-(hydroxyimino)-propanohydrazide, dbm− = 1,3-diphenyl-1,3-propanedionate, acac− = acetylacetonate, DMF = N,N-dimethylformamide) have been synthesized, and structurally and magnetically characterized. The rare-earth ions of the eleven complexes are all located in an eight-coordinated environment. The luminescence spectra in methanol solution show that complexes 3, 5 and 6 exhibit the typical emissions of the RE(III) ions, while complex 1 exhibits an emission peak similar to that of the H2L ligand. And for complexes 2, 7, 8 and 11, all of them show near-infrared fluorescent characteristic peaks. Magnetic studies reveal that complex 4 can act as a cryogenic magnetic refrigerant with the maximum magnetic entropy change (−ΔSm) of 25.79 J kg−1 K−1 at 7 T and 2 K. Complex 9 shows slow magnetic relaxation behavior with an energy barrier of 23.78 K and the pre-exponential factor of 1.74 × 10−6 s, while complex 6 does not exhibit excellent SMM behavior. Besides, complex 9 presents multiple relaxation processes when subjected to an additional dc magnetic field of 2000 Oe. The distinct magnetic relaxation behaviors of the two Dy2 complexes originate from the different coordination environment around the Dy(III) ions. These results mean that the luminescence and magnetic properties of rare-earth complexes can be finely tuned by altering the β-diketonate ligands.