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

Abstract

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 (−ΔS_m) 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.