A New Series of Three-Dimensional Metal-Organic Framework, $[M_2(H_2O)][C_5N_1H_3(COO)_2]_3\cdot 2H_2O, M = La, Pr,$ and Nd: Synthesis, Structure, and Properties

Abstract

A new series of lanthanide pyridine dicarboxylates of the general formula, $[M_2(H_2O)][C_5N_1H_3(COO)_2]_3\cdot 2H_2O$, 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 $MO_8N$ and $MO_7N_2$ (M= lanthanide) polyhedra connected to the dicarboxylate anions forming the three-dimensional structure with onedimensional channels. A striking feature of this structure is the presence of an unusual Z-shaped tetramer of the formula $M_4O_{24}N_6$. 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