A new series of three-dimensional metal-organic framework, [M2(H2O)][C5N1H3(COO)2]3•2H2O, M = La, Pr, and Nd:: Synthesis, structure, and properties

A new series of lanthanide pyridine dicarboxylates of the general formula, [M-2(H2O)][C5N1H3(COO)(2)](3)center dot 2H(2)O, M = La (1), Pr (2), and Nd (3), has been prepared by the reaction of trivalent lanthanide salts and pyridine dicarboxylic acids employing a mild condition hydrothermal reaction. The structures are built up from MO8N and MO7N2 (M = lanthanide) polyhedra connected to the dicarboxylate anions forming the three-dimensional structure with one-dimensional channels. A striking feature of this structure is the presence of an unusual Z-shaped tetramer of the formula M4O24N6. Extraframework water molecules, located within the open channels, are reversibly adsorbed. Detailed in situ and ex situ investigations using FTIR and PXRD studies clearly show that the removal of the water molecules is reversible and accompanied by changes in the size of the channel. Partial substitution at the La sites by Eu gives rise to characteristic red-pink luminescence, indicating a ligand-sensitized metal-centered emission.