Syntheses, structures, photoluminescence and magnetic properties of four-connected lanthanide–tricarboxylate coordination polymers

Abstract

Ten novel lanthanide-based coordination polymers {[LnL(H₂O)₂]·H₂O}_n (Ln = Pr (1), Nd (2), Eu (3), Gd (4), Tb (5), Dy (6), Ho (7), Er (8), Yb (9), and Lu (10), H₃L = 2-(carboxylmethoxy)terephthalic acid), have been successfully synthesized through hydrothermal reactions of corresponding Ln(OH)₃ with semirigid tricarboxylate H₃L ligands. Compounds 1 and 2 are isostructural, containing a 3D porous framework built of carboxylate-bridged layers with 6⁶-topology, while 3–10 display the same 2D double-layer structure based on binuclear Ln₂O₂ units with 4³·6³-topology. The PXRD and TGA prove their phase purity and high thermal stability, respectively. Photoluminescent studies indicate the efficient energy transfer from L³⁻ ligand to Ln³⁺ ions, exhibiting the typical intense emissions of corresponding Ln³⁺ ions in the visible region. The magnetic exchange interactions also are studied in compounds 4–7 for their short O bridges between Ln³⁺ ions, and the results show that there may be ferromagnetic interactions in 4–6, while in 7 the interactions cannot be distinctly deduced from the curves due to the nature of the Ho³⁺ ions. Furthermore, compound 6 displays slow magnetization relaxation, exhibiting single-molecule magnetic behavior.