Spontaneous resolution and magnetic properties of lanthanide metal organic frameworks based on oxydiacetate

Chiral lanthanide metal organic frameworks (Ln-MOFs) have become a kind of promising platform for developing various chiral functional materials. However, their members are still scarce up to now, especially those obtained from spontaneous resolution. In this work, two pairs of enantiomers of chiral Ln-MOFs, namely, [Ln2(oda)3(H2O)4]·2H2O [Ln = Dy (Λ-1 and Δ-1), Gd (Λ-2 and Δ-2); oda = oxydiacetate], have been prepared from an achiral H2oda ligand by spontaneous resolution. They display homochiral Λ- or Δ-configurational 2D grid-like frameworks in the absence of any chiral source, where four carboxylate groups of oda2− ligands within each [LnIII(oda)3]3− module link to adjacent four Ln ions either in a left- or right-handed fashions. Their homochirality was further confirmed by solid-state circular dichroism (CD) spectrum. Magnetic measurements revealed that Λ-1 exhibits field-induced dual-relaxation behavior of single-molecule magnet (SMM). The effective energy barrier (Ueff) and relaxation time (τ0) of slow relaxation (SR) process are 92.63 K and 1.49 × 10−12 s, respectively. Furthermore, Λ-2 was found to show magnetocaloric effect (MCE), with the maximum magnetic entropy change (−ΔSm) of 10.02 J kg−1 K−1 at 7.0 T and 2.0 K.