Hydrothermal synthesis of uranyl–organic frameworks with pyrazine-2,3-dicarboxylate linkers

Abstract

The reaction of uranyl nitrate with pyrazine-2,3-dicarboxylic acid (H₂PZDC) under hydrothermal conditions and in the presence of different bases gave three novel polymeric assemblages. The complexes [UO₂(PZDC)(H₂O)₂] (1) and [UO₂(PZDC)(H₂O)] (2), obtained with NMe₄OH and pyridine as base, respectively, differ by the coordination mode of the ligand, with O,N-chelation and one monodentate carboxylate group in 1 and both O,N- and O,O-chelation (the latter involving both carboxylate groups) in 2. In both cases, one-dimensional coordination polymers are formed, which are further assembled into three-dimensional networks by hydrogen bonding. In the presence of CsOH as a base, the heterometallic complex [(UO₂)₂Cs(PZDC)₂(OH)(H₂O)] (3) was isolated, which is a compact, three-dimensional framework. One uranyl ion is bis-O,N-chelated and the other is bound to three monodentate ligands, whereas each cesium cation is bound to three uranyl oxo groups, one nitrogen and five carboxylate oxygen atoms. The metal atoms are further bridged by μ₂-hydroxide and μ₂-aqua ligands. One of the PZDC²⁻ ligands in 3 assembles five metal atoms and the other four, thus demonstrating the potential of this molecule for the building of three-dimensional uranyl–organic frameworks.