Hydrothermal synthesis, crystal structure and properties of a two-dimensional uranyl coordination polymer based on a flexible zwitterionic ligand

The interaction between the uranyl cation, (UO2)(2+), and organic species is of interest due to the potential applications of the resulting compounds with regard to nuclear waste disposal and nuclear fuel reprocessing. The hydrothermal reaction of various uranyl compounds with flexible zwitterionic 1,1'-[1,4-phenylenebis(methylene)]bis(pyridin-1-ium-4-carboxylate) dihydrochloride (Bpmb center dot 2HCl) in deionized water containing drops of H2SO4 resulted in the formation of a novel two-dimensional uranyl coordination polymer, namely poly[tetraoxido{mu(2)-1,1'-[1,4-phenylenebis(methylene)] bis(pyridin-1-ium-4-carboxylate)}di-mu(3)-sulfato-diuranium(VI)], [(UO2)(2)(SO4)(2)(C20H16N2O4)](n), (1). Single-crystal X-ray diffraction reveals that this coordination polymer exhibits a layered arrangement and the (UO2)(2+) centre is coordinated by five equatorial O atoms. The structure was further characterized by FT-IR spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). The polymer shows high thermal stability up to 696 K. Furthermore, the photoluminescence properties of (1) has also been studied, showing it to exhibit a typical uranyl fluorescence.