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

A series of three-dimensional (3-D) lanthanide-organic frameworks (LnOFs), with the general formula [Ln2(H-L)3(H2O)][infinity] (H-L = N-protonated 2,6-dihydroxypyridine-4-carboxylate; Lniii = Laiii for 1, Priii for 2, Ndiii for 3, and Smiii 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 [small mu ]4- and [small mu ]5-bridging fashions. Remarkably, thermogravimetric analysis of the crystalline materials shows their exceptionally high thermal stability (up to 530 [degree]C), which should originate from the dense nature of the packing lattices and the unusual network structures.