Structural Diversity of Bipyridinium-Based Uranyl Coordination Polymers: Synthesis, Characterization, and Ion-Exchange Application

Abstract

As well-known functional groups with excellent electro/photochromic and ion-exchange properties, bipyridinium motifs have been used in functionalized metal-organic coordination polymers, but they are still rarely applied to construct actinide coordination polymers. In this work, we utilized a bipyridinium-based carboxylic acid, 1,1'-bis(4-carboxyphenyl)-4,4'-bipyridinium bis(chloride) ([H₂bcbp]Cl₂), as the organic ligand to assemble with uranyl cations. By the introduction of different kinds of auxiliary ligands and adjustment of the pH, five novel uranyl coordination compounds, <b>1</b>-<b>5</b>, have been synthesized through hydrothermal reactions. Starting from uranyl ions and terephthalic acid (H₂TP) and H₂bcbp ligands, [(UO₂)₂(bcbp)(TP)₂]·3H₂O (<b>1</b>) has a wave-shaped two-dimensional (2D) structure consisting of dinuclear units connected by terephthalate linkers and further supported by the longer H₂bcbp ligands. [(UO₂)₂(bcbp)(PA)₂]·4H₂O (<b>2</b>) has a zigzag chain of dimeric uranium units, and [(UO₂)₂(bcbp)(bpdc)₂]·5H₂O (<b>3</b>) forms a one-dimensional ribbonlike structure. The 2D structures of [(UO₂)(bcbp)(OH)(H₂O)]·Cl (<b>4</b>) and [(UO₂)(bcbp)Cl]·Cl (<b>5</b>) are similar, both of which are constructed from dinuclear uranyl units and bcbp^2- ligands. Furthermore, the performance for perrhenate removal of compound <b>4</b> with a cationic framework is assessed, and we found that compound <b>4</b> can efficiently remove ReO₄^- from an aqueous solution in a wide range of pH values. This work extends the library of viologen derivative-based uranyl coordination polymers, provides to some extent broader insights into actinide coordination chemistry of functionalized ligands, and may facilitate the ion-exchange applications of related coordination polymers.