Metal‐Carboxyl Helical Chain Secondary Units Supported Ion‐Exchangeable Anionic Uranyl–Organic Framework

Abstract

As al ess explored avenue, actinide-based metal-organic frameworks (MOFs) are worth studying for the particularity of actiniden odes in coordination behaviour and assembly modes.I nt his work, an azobenzenetetracarboxylate-based anionic MOF supported by uranylcarboxyl helical chain units was synthesized,i ncorporating linear uranyl as the metal centre. This kindo fh elical chain-type building unit is reported for the first time in uranyl-based MOFs. Structurala nalysis reveals that the formation of helical chain secondary units can be attributed to restricted equatorial coordination of rigid flat azobenzene ligand to uranyl centres. Meanwhile, this newly-synthesized anionic material has been used to remove Eu 3 + ions, as an on-radioactive surrogate of Am 3 + ion, through an ion-exchange process with [(CH 3 ) 2 NH 2 ] + ions in its open channels, as evidenced by ac ombinationo f 1 HN MR spectroscopy,E DS and PXRD.As emerging porous materialsf eaturing well-defined reticular architectures, high porosity,a nd good designability in topological structures and pores, [1] metal-organic frameworks (MOFs) have aroused vast amounts of attention from chemists and materials specialists.T his typeo fv ersatile inorganic-organic hybrid materials hows promising applications in aw ide range of fields such as gas storagea nd separation, [2] catalysis, [3] drug delivery, [4] chemical sensors, [5] and other aspects. [6] Compared to the abundance and massive diversity of MOFs based on transition metalsa nd lanthanides, [7] actinide-based MOFs that utilize actinide ions or clusters as buildingn odes are still less studied.As the heaviest natural element, the actinide element uranium exhibits rich coordinationc hemistry relevant to its intriguing 5f orbital electronic structure andf ascinating bondinga bility. [8] Uranium possesses various oxidation states from + 2t o + 6, among which hexavalent uranium in al inear uranyl (UO 2 2 + )f ormi si ts most commons pecies. The occupationo f relativelyi nert axial oxygen atoms forces foreign ligands to coordinate on the equatorial plane of the uranylc entre, thus resultingi nt etragonal, pentagonal, and hexagonal-bipyramidal geometries through binding four,f ive and six coordinative atoms. [9] Because of the characteristic equatorially-directed coordination sphereo ft he linear uranyl cation, uranyl-basedc oordination polymers have at endency to form architectures in one dimensional (1D) chains or two dimensional (2D) networks, whereas the amount of three-dimensional (3D) uranyl-organic frameworks (UOFs) is relativelyl ess, although al arge variety of UOFs have been reported based on organic linkersf unctionalized with different groups such as carboxylic acids, [10] phosphonic acids, [11] cucurbituril-based pseudorotaxanes, [12] etc.The rational choice of ligands is of great significance for the design and synthesis of UOFs,e specially for those with specific properties. [13] For example, one effective approacht ob uild uranylf rameworks is by endowing organic linkersw ith multide...

Modular Assembly of Isostructural Mixed-Ligand Uranyl Coordination Polymers Based on a Patterning Strategy

“…As mentioned above, there are a large number of [(CH 3 ) 2 NH 2 ] + ions formed by in situ heating decomposition of solvent DMF in the interlayer space of 1–5 , which can also be proven by 1 H NMR spectra of digested solutions of 1 and 2 (Figure S5). These [(CH 3 ) 2 NH 2 ] + ions are fixed by typical N–H···O and C–H···O hydrogen bond interactions between them and the host skeleton (Figures S6–S10 and Tables S3–S7). The [(CH 3 ) 2 NH 2 ] + ion that shows weak interactions with the host cationic framework gives these uranyl coordination polymers the ability to exchange with other metal ions such as several heavy metal ions or radioactive ions by ion exchange.…”

Double-Layer Nitrogen-Rich Two-Dimensional Anionic Uranyl–Organic Framework for Cation Dye Capture and Catalytic Fixation of Carbon Dioxide

“…1 H NMR spectroscopy can confirm the presence of [(CH 3 ) 2 NH 2 ] + counterions in the crystal lattice (Figure S3). It is worth mentioning that the anionic uranyl framework exhibits the ability to remove Eu 3+ (as a nonradioactive surrogate to Am 3+ ) . In Eu 3+ aqueous solutions at concentrations of 5 and 10 ppm, Eu 3+ removal rates can reach 96% and 77% at pH 6, respectively (Figure S4).…”

Counterion-Controlled Formation of Layered Honeycomb and Polythreading Uranyl Networks and the Highly Sensitive and Selective Detection of Fe3+ in Aqueous Media

“…Therefore, H 3 tci has been widely used in constructing transition/lanthanide metal organic complexes, − which is not commonly found for actinides. As far as we know, only two uranium complexes and one thorium complex have been crystallographically characterized in our previous work. , Recently, more studies are focusing on the exploration of the influence of additional 3d metal ions and N-donating chelation, which either demonstrated coordinated − or acted as a neutral guest − or played as a counterion. ,− …”