A unique uranyl framework containing uranyl pentamers as secondary building units: synthesis, structure, and spectroscopic properties

Two three-dimensional uranyl framework compounds consisting of 1,2,4-benzenetricarboxylic ligands and uranyl units have been synthesized under mild solvothermal conditions. Compound 1 adopts an open framework structure built from uranyl pentamers, which is a rare topology for uranyl structures. Compound 2 is constructed from UO8 and UO7 bipyramids that are connected by the ligand to form a three-dimensional framework. As a consequence, compound 1 exhibits an unusual photoluminescence spectrum of one broad peak at 545 nm with a significant red shift compared to the typical uranyl emissive peaks as shown in the spectra of uranyl nitrate and compound 2. In addition, since compound 1 crystallizes in the noncentrosymmetric space group Cc, its secondary-harmonic generation property was measured under 1064 nm laser radiation, showing a moderate SHG signal response of 0.91 × KDP.