Several (4,4)- and (5,6,8)-connected lanthanide–organic frameworks: structures, luminescence and magnetic properties

Abstract

A series of lanthanide-based organic frameworks with formulas of {[PrL(H₂O)₂]·2H₂O}_n (1) and {[Ln₃L₃(H₂O)₂]·2H₂O}_n (Ln = Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7); H₃L = 4-(carboxymethoxy)isophthalic acid), were hydrothermally synthesized and structurally characterized. It is the first time that 4-(carboxymethoxy)isophthalic acid is employed in producing lanthanide compounds. The seven compounds exhibit two types of structures with the decreasing radius of the lanthanide ions, representing the lanthanide contraction effect. Compound 1 with the large Pr³⁺ ion displays a 2D layered structure with a binodal (4,4)-connected topology with the Schläfli symbol of (3³6³)₂, whereas compounds 2–7 with small Ln³⁺ ions feature a 3D framework constructed from carboxyl groups with a (5,6,8)-connected topology with the Schläfli symbol of (3²4⁴5⁴)·(3⁴4⁴5⁴6³)·(3⁴4⁸5⁶6⁹8). The luminescence and magnetic properties were investigated, and the results indicate that the H₃L ligand can sensitize the lanthanide luminescence in compounds 2, 4 and 5 and makes a contribution to the antiferromagnetic interactions in compound 3 or the uncertain magnetic interactions in compounds 4–7. Additionally, the thermal analyses suggest the high thermal stability of compounds 1–7.