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

Eleven dinuclear rare-earth (RE) complexes, [RE 2 (dbm) 2 L 2 (DMF) 2 ]·2CH 3 OH (RE = Y ( 1 ), Nd ( 2 ), Dy ( 6 ), Er ( 7 )), [RE 2 (dbm) 2 L 2 (CH 3 OH) 2 ]· n CH 3 OH (RE = Eu ( 3 ), Gd ( 4 ), Tb ( 5 ), Yb ( 8 )) and [RE 2 (acac) 2 L 2 (CH 3 OH) 2 ] (RE = Dy ( 9 ), Er ( 10 ), Yb ( 11 )) (H 2 L = 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 H 2 L 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 (−Δ S 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 Dy 2 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.