Highly-thermostable lanthanide–organic coordination frameworks with N-protonated 2,6-dihydroxypyridine-4-carboxylate exhibiting unusual 3-D mixed-connected network topology

Abstract

A series of three-dimensional (3-D) lanthanide–organic frameworks (LnOFs), with the general formula [Ln₂(H–L)₃(H₂O)]_∞ (H–L = N-protonated 2,6-dihydroxypyridine-4-carboxylate; Ln^III = La^III for 1, Pr^III for 2, Nd^III for 3, and Sm^III for 4), have been synthesized under hydrothermal conditions. X-Ray diffraction and energy dispersive X-ray spectroscopy (EDS) analyses reveal that complexes 1–4 are isostructural and exhibit the unique 3-D coordination framework with (4,5,7)-connected network topology, in which the H–L ligands adopt the μ₄- and μ₅-bridging fashions. Remarkably, thermogravimetric analysis of the crystalline materials shows their exceptionally high thermal stability (up to 530 °C), which should originate from the dense nature of the packing lattices and the unusual network structures.