Modulation of the properties of dinuclear lanthanide complexes through utilizing different β-diketonate co-ligands: near-infrared luminescence and magnetization dynamics

Abstract

A family of new dinuclear lanthanide complexes as the simplest entities showing intramolecular magnetic interactions, [Ln₂(dbm)₂(L)₂(CH₃OH)₂] (Ln = Tb (1), Dy (2), Ho (3), Er (4), Yb (5), Lu (6)), [Ln₂(acac)₂(L)₂(EtOH)₂] (Ln = Dy (7), Er (8)), [Dy₂(TTA)₂(L)₂(CH₃OH)₂]·2CH₂Cl₂ (9) and [Dy₂(tfa)₂(L)₂(CH₃OH)₂] (10) (H₂L = N′-(2-hydroxy-5-methylphenyl)-pyrazine-2-carbohydrazide, Hdbm = 1,3-diphenyl-1,3-propanedione, Hacac = acetylacetone, HTTA = 2-thenoyltrifluoroacetone, Htfa = trifluoroacetylacetone), were constructed successfully by the reaction of a Schiff base ligand H₂L and four different β-diketonate salts. As for complexes 4, 5 and 8, all exhibit the characteristic emission peaks of the corresponding Er³⁺, Yb³⁺ and Er³⁺ ions, respectively. Meanwhile, the excitation wavelength (510 nm) of 5 is located in the visible region, confirming its significant potential application value. Magnetic studies indicate that complexes 9 and 10 exhibit characteristic slow relaxation of magnetization with the energy barriers (U_eff) of 102 K for 9 and 140 K for 10 under a zero dc field. Under the optimized dc fields, slow magnetic relaxations are present in 2 and 7, and the U_eff values of 9 and 10 have been improved. This proves that the β-diketonate co-ligands deserve an important role in regulating Dy-SMMs influenced by the diverse perturbations of the axial crystal field originating from minor changes in the coordination environment.