Regulating the Porosity of Uranyl Phosphonate Frameworks with Quaternary Ammonium: Structure, Characterization, and Fluorescent Temperature Sensors

Abstract

Regulating the porosity of metal phosphonate frameworks is still challenging, even though this is not an issue for carboxylate-based metal−organic frameworks (MOFs). Quaternary ammonium cations are common template reagents widely used for structure control. However, it is not successful for uranyl phosphonate frameworks (UPFs) because the large volume sizes of templates make it challenging to enter the channels constructed by phosphonate ligands with small pore sizes and low dimensions. In this work, three new porous three-dimensional UPFs were synthesized using the phosphonate ligand and template reagents with the same geometry, namely, (TEA) 2 (UO 2 ) 3 (TppmH 4 ) 2 • 2H 2 O (UPF-106), (TPA) 2 (UO 2 ) 3 (TppmH 4 ) 2 (UPF-107), and (TBA) 2 (UO 2 ) 5 (TppmH 2 ) 2 (H 2 O) 2 •4H 2 O (UPF-108). The porosity of the UPFs in this work showed a positive relation with the sizes of the template ammonium cations. Thermogravimetric analysis and infrared and ultraviolet spectroscopy were performed. The variable-temperature fluorescence spectra of the three compounds showed that the fluorescence intensity has an excellent relation to temperature with a potential application as fluorescence temperature sensors.

Reticular chemistry of uranyl phosphonates: synthesis, design, and beyond

“…2D SBUs are found in UPF-104, UPF-108, and UPF-109, respectively. 19–21 It is worth noting that the dimers of UO 7 units are found in the wave-like layers of uranyl phosphonates, which play a critical role in extending the topology link, similar to other reported 2D structures of uranyl phosphonates (Fig. 2 and S3†).…”

“…S2 † and 2). 19,20 The final structures are obtained by the connection of the 1D chain SBUs and the ligands, which provide more space for design.…”

“…22 The porosity can be regulated by the template reagent in UPFs. 20 Therefore, the SHPL strategy can also put designability into practice by modifying the rigid carbon backbone, achieving the concept of reticular chemistry in the uranyl phosphonate system. It is successfully in constructing 3D porous metal phosphonates not only for uranyl but also for transition, lanthanide, and actinide metal ions.…”

Photochromic Uranyl-Based Coordination Polymer for Quantitative and On-Site Detection of UV Radiation Dose

“…The asymmetric unit contains one crystallographically independent UO 2 2+ ion, one PBPCA 2– ligand, one coordinate DMF molecule, and one dissociative DMF molecule (Figure S2). The uranium­(VI) center adopts a typical pentagonal bipyramidal coordination geometry with bonds to the two axial oxo atoms [1.758(4) and 1.747(5) Å]; four oxygen atoms come from three PBPCA 2– [2.322(3), 2.329(4), 2.427(4), and 2.444(4) Å] and one oxygen atom from DMF [2.402(4) Å] . Two UO 2 2+ ions are bridged by two independent PBPCA 2+ ligands, forming a dimer; then, two dimers are bridged by two ligands and extend into infinite charge-balanced uranyl-PBPCA chains, with coordinating DMF located on both sides of the chain (Figure a).…”

“…The uranium(VI) center adopts a typical pentagonal bipyramidal coordination geometry with bonds to the two axial oxo atoms [1.758(4) and 1.747(5) Å]; four oxygen atoms come from three PBPCA 2− [2.322(3), 2.329(4), 2.427(4), and 2.444( 4) Å] and one oxygen atom from DMF [2.402(4) Å]. 57 Two UO 2 2+ ions are bridged by two independent PBPCA 2+ ligands, forming a dimer; then, two dimers are bridged by two ligands and extend into infinite charge-balanced uranyl-PBPCA chains, with coordinating DMF located on both sides of the chain (Figure 1a). The distance between two PBPCA 2− ligands on adjacent chains is 3.592 Å, indicating the presence of significant parallel πstacking between the aromatic ring and pyridine ring of PBPCA 2− ligands (Figure 1c,d).…”