Tuning N-donor coordination and assembly structures in uranyl compounds of carboxylate ligands with divergent vinyl pyridine groups

Abstract

As N-donors exhibit weaker bonding with uranyl ions than O-donors, the coordination ability of a single N-donor in hetero-donor ligands to a uranyl ion is rarely explored without the aid of ortho-carboxyl groups. In this work, two hetero-donor ligands with divergent pyridine and carboxylate groups linked via a vinyl unit as the spacer and one N-methylated derivate were used to coordinate hydrothermally with uranyl ions, and six uranyl compounds (1–6) were synthesized. The molecular structures and physico-chemical properties of these compounds were investigated using single crystal X-ray diffraction and theoretical calculations, together with infrared (IR) spectroscopy, UV-vis absorption spectroscopy, and fluorescence spectroscopy. Results showed that the pyridinyl N-donor in these compounds possessed the ability to participate in uranyl coordination, and its coordination behaviour could be regulated via structural modification or by employing a secondary organic carboxylic acid as a competing ligand. Furthermore, 1 and 2 were assessed for their gas-phase iodine sorption capability; their maximum iodine sorption capacities were determined to be 122 mg g⁻¹ and 100 mg g⁻¹, respectively. X-ray photoelectron spectroscopy and Raman analysis confirmed iodine sorption mainly as triiodide (I₃⁻), indicating electron transfer between the guest iodine molecules and electron-rich framework of 1 or 2. These results demonstrate the ability of single N-donors to coordinate with uranyl ions and also highlight the potential of uranyl-based hybrid materials for environmental remediation applications, such as iodine capture.