Synthesis, luminescence and magnetic properties of dinuclear complexes based on a “pincer” Schiff base and different β-diketonate ligands

Abstract

Twelve new dinuclear rare earth complexes in three series were successfully synthesized with a “pincer” Schiff base H2L and different β-diketonate ligands: Ln2(acac)2(L)2·2C2H5OH (Ln = Eu (1), Tb (2), Dy (3), Er (4)), Ln2(dbm)2(L)2·2C3H7NO (Ln = Eu (5), Tb (6), Dy (7), Er (8), Yb (9)), Ln2(TTA)2(L)2·2H2O (Ln = Eu (10), Tb (11), Dy(12)). (H2L = 3-aminopyrazine-2-carboxylic acid [(2-hydroxybenzylidene)] hydrazide; Hacac = acetylacetone; Hdbm = dibenzoylmethane; HTTA = 2-thiophene trifluoroacetone). These complexes are centrosymmetric dinuclear structures and RE3+ ions are bridged by oxygen atoms in carbonyl of Schiff base to form the core unit of Ln2O2. The characteristic emission peaks of Er3+ and Yb3+ in 4, 8 and 9 can be observed in Near-infrared luminescence spectra, that is confirmed the central ions were sensitized effectively via ligands. Moreover, 1, 5, 6 and 10 were sensitized in various degrees. The dynamic magnetization curves indicate that 3, 7 and 12 are typical SMMs with slow magnetic relaxation behaviors. Their effective energy barriers are 48.20 K (3) and 42.30 K (12) under 3000 Oe dc field and 81.89 K (7) under zero dc field. The pre-exponential factors (τ0) are 1.35 × 10−6 s (3), 1.38 × 10−10 s (7) and 4.93 × 10−6 s (12), respectively. It is confirmed that the magnetic properties of SMMs can be regulated by different β-diketonate ligands.