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 [Ln(2)(H-L)(3)(H2O)](infinity) (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 mu(4)- and mu(5)-bridging fashions. Remarkably, thermogravimetric analysis of the crystalline materials shows their exceptionally high thermal stability (up to 530 degrees C), which should originate from the dense nature of the packing lattices and the unusual network structures.