Series of Mixed Uranyl–Lanthanide (Ce, Nd) Organic Coordination Polymers with Aromatic Polycarboxylates Linkers

Enhanced water stability and catalytic activity of Fe-based metal-organic frameworks with co-ligands for 2,4-dichlorophenol degradation

Fe-based metal-organic frameworks (MOFs) have good photocatalytic performance, environmental friendliness, low cost, and abundance. However, their applications are limited by low water stability, particularly in the presence of light irradiation and oxidizing agents. In this study, we present a MIL-53(Fe)-based MOF using 1,4-naphthalene dicarboxylic (1,4-NDC) and 1,4-benzenedicarboxylic (H2BDC) acid co-ligands, denoted MIL-53(Fe)-Nx, where Nx represents the ratio of 1,4-NDC. This MOF exhibits high water stability and good photocatalytic activity because of the hydrophobicity of naphthalene. The removal and mineralization rates for 100 mg/L 2,4-dichlorophenol reached 100% and 22%, respectively, within 60 min. After three cycles of use, the Fe leached into the solution from the catalysts was significantly lower than the maximum permissible limit indicated in the European Union standard. Of note, 1,4-NDC can be used to make a rigid MOF, thereby improving the crystallinity, porosity, and hydrophobicity of the resultant materials. It also significantly reduced the bandgap energy and improved the charge separation efficiency of the catalysts. This study provides a route to enhance the water stability of Fe-based MOFs via a mixed-ligand strategy to expand their applications in pollutant control.

Varied role of organic carboxylate dizwitterions and anionic donors in mixed-ligand uranyl ion coordination polymers

Two organic dizwitterions were combined with various anionic donors to generate a series of five uranyl ion complexes crystallizing as mono- or diperiodic coordination polymers, with separation into two distinct networks in one case.

Hydrothermal Syntheses of Uranium Oxide Hydrate Materials with Sm(III) Ions: pH-Driven Diversities in Structures and Morphologies and Sm-Doped Porous Uranium Oxides Derived from Their Thermal Decompositions

We report the hydrothermal syntheses of three uranyl oxide hydroxy-hydrate (UOH) materials containing Sm(III) ions (UOH-Sm) by controlling the solution pH and a new way to make Sm-doped porous uranium oxides with different U-to-Sm atomic ratios via their thermal decompositions. While layer-structured UOH-Sm phases with U-to-Sm atomic ratios of 1 (UOH-Sm1) and 4 (UOH-Sm2) were obtained from the reaction of schoepite and samarium nitrate with final solution pH values of over 4, similar reactions without pH adjustment with final solution pH values of less than 4 led to the formation of a uranyl oxide framework (UOF-Sm) with a U-to-Sm atomic ratio of 5.5. The crystal structure of compound UOF-Sm was revealed with synchrotron single-crystal X-ray diffraction and confirmed with transmission electron microscopy. The two-dimensional uranyl oxide hydroxide layers, similar to that for β-U₃O₈, are linked by double pentagonal uranyl polyhedra to form a three-dimensional framework with Sm(III) ions in the channels. Scanning electron microscopy characterization revealed nanoplate crystal morphologies for the two UOH-Sm phases, in contrast to the needle morphology for UOF-Sm. Subsequent thermal treatments led to the formation of Sm-doped uranium oxides, maintaining the original crystal shapes and U-to-Sm ratios but with nanopores. This work demonstrated that the hydrothermal synthesis conditions, especially fine-tuning of the solution pH, have a significant impact on the uranium hydrolysis, thus leading to well-defined products. This will facilitate the targeted syntheses of UOH phases with lanthanide (Ln) ions and explore the subsequent applications of these materials and Ln-doped porous uranium oxides as potential nuclear or functional materials.

Expanding uranyl dicyanoaurate coordination polymers into the second and third dimensions

The solvothermal synthesis and characterization of a three-dimensional, interpenetrated uranyl dicyanoaurate coordination polymer, K2(UO2)2(UO2)2(Au(CN)2)2(O)2(NO3)4, from UO2(NO3)2·6H2O and KAu(CN)2 is described. The structure contains a three-dimensional (3D) lattice of planar tetranuclear uranyl–oxo–nitrate clusters connected by dicyanoaurate linkers, with the rotation of the clusters providing the increased dimensionality. The material undergoes a reversible single-crystal to single-crystal transformation on exposure to water vapour, which is taken up in the channels of the 3D system. A second uranyl dicyanoaurate coordination polymer of the form [UO2(DMSO)3(H2O)(Au(CN)2)][Au(CN)2] was structurally characterized as a linear chain of dicyanoaurate units connected by gold–gold bonds with pendant uranyl–water–DMSO adducts that are hydrogen bonded into a two-dimensional sheet. Both materials exhibit emission arising from both the uranyl moiety and the gold(I) centre and represent the first multidimensional uranyl–dicyanoaurate coordination polymers.

Full-Range Ratiometric Detection of D2O in H2O by a Heterobimetallic Uranyl/Lanthanide Framework with 4f/5f Bimodal Emission

A uranyl-europium heterobimetallic compound, (TEA)₃[(UO₂)₆Eu(H₂O)₄(PPA)₆] (H₃PPA = phosphonoacetic acid, TEA = tetraethylammonium cation), was synthesized under mild hydrothermal conditions. The emission spectrum contains characteristic electronic transition features of both Eu³⁺ and UO₂²⁺, while the peak intensity of Eu³⁺ is notably higher than that of UO₂²⁺. This is primarily attributed to the energy transfer from uranyl to europium in the structure. Significantly, a positive correlation between the Eu³⁺ peak intensity at 621 nm and the D₂O content can be established in the aqueous system, while the uranyl peak intensity is almost unchanged, allowing for the full-range ratiometric detection of D₂O in H₂O.

Formation of uranyl phthalate coordination polymers with unusual 2D net topologies in the presence of organic cations

Inclusion of heterocyclic cations into a uranyl-phthalate system allowed the formation of 2D coordination polymers whose topological analysis revealed that the underlying nets had unusual topologies.

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·2HCl) in deionized water containing drops of H₂SO₄ resulted in the formation of a novel two-dimensional uranyl coordination polymer, namely poly[tetraoxido{μ₂-1,1'-[1,4-phenylenebis(methylene)]bis(pyridin-1-ium-4-carboxylate)}di-μ₃-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.

Nine isomorphous lanthanide–uranyl f–f bimetallic materials with 2-thiophenecarboxylic acid and terpyridine: structure and concomitant luminescent properties

Concomitant and semi-selective uranyl and lanthanide luminescence observed within a series of f–f bimetallic molecular materials (UO₂²⁺/Ln = Pr–Er).

Coordination Polymers and Cage-Containing Frameworks in Uranyl Ion Complexes with rac- and (1R,2R)-trans-1,2-Cyclohexanedicarboxylates: Consequences of Chirality

Racemic and enantiopure (1R,2R) forms of trans-1,2-cyclohexanedicarboxylic acid (H₂chdc and R-H₂chdc, respectively) have been used in the synthesis of a series of 13 uranyl ion complexes, all obtained under solvo-hydrothermal conditions and in the presence of additional metal cations and/or N-donor ligands. While the homometallic complex [UO₂(R-chdc)] (1) was only obtained with the enantiopure ligand, complexes [UO₂(chdc)(THF)] (2), [UO₂(chdc)(DMF)] (3), and [UO₂(chdc)(NMP)] (4), with a coordinated solvent molecule, were obtained from the racemic form only; all crystallize as two-dimensional (2D) assemblies. The two complexes [UO₂(chdc)(bipy)](5) and [UO₂(R-chdc)(bipy)] (6), where bipy is 2,2'-bipyridine, are isomorphous since 5 crystallizes as a racemic conglomerate; they are both one-dimensional (1D) homochiral, helical polymers. The heterometallic complexes [UO₂Cu(chdc)₂(bipy)(H₂O)]·H₂O (7) and [UO₂Cu(R-chdc)₂(bipy)]·3H₂O (8) crystallize as a 1D or a 2D species, respectively, while [UO₂Cd(R-chdc)₂(H₂O)₂]·H₂O (9) displays a 2D arrangement with the unusual Cairo pentagonal tiling topology. The four complexes [(UO₂)₂Na₂(chdc)₃(H₂O)₂] (10), [(UO₂)₂Ag₂(chdc)₃(H₂O)₂] (11), [(UO₂)₂Na₂(R-chdc)₃(H₂O)₂] (12), and [(UO₂)₂Pb(R-chdc)₃(H₂O)₄] (13) are closely related, all of them containing tetranuclear, pseudotetrahedral [(UO₂)₄(chdc/R-chdc)₆]^4- cage motifs, that are assembled into a three-dimensional (3D) framework by bridging counterions (Na⁺, Ag⁺, or Pb²⁺). These cages define a new pathway to assembly of such species based on the unique coordination geometry of uranyl ion, differing from the widely exploited use of octahedral metal ions.

Two uranyl heterocyclic carboxyl compounds with fluorescent properties as high sensitivity and selectivity optical detectors for nitroaromatics

Uranyl skeleton compounds showed high sensitivity and selectivity for the detection of nitroaromatics.

Recent advances in structural studies of heterometallic uranyl-containing coordination polymers and polynuclear closed species

A survey is given of recent original structural results on heterometallic species incorporating uranyl ions, particularly with carboxylate ligands.

Solvent effects in solvo-hydrothermal synthesis of uranyl ion complexes with 1,3-adamantanediacetate

Uranyl ion complexes with 1,3-adamantanediacetate display different topologies arising from variations in coordination mode and the presence of additional ligands.

A family of 3D UO22+–5-X-1,3-dicarboxylate (X = –H, –NO2, –NH2, –OH) hybrid materials: structural relevance with variation of substituent groups and photochemical properties

A family of 3D uranyl hybrid materials based on 5-X-1,3-dicarboxylate have been synthesized, in which two types of 1D chains assembled by the same uranyl dimer motif [(UO₂)₂L₂] exist.

Poly[di-ammonium [di-aqua-(μ7-benzene-1,2,3,4,5,6-hexa-carboxyl-ato)tetra-oxido-diuranium(VI)]]

Uranyl-carboxyl-ate hybrid materials dominate the catalog of uranyl compounds owing in part to the affinity between COO(-) functional groups and UO2 (2+). Polycarboxyl-ate organic ligands may present a degree of steric hindrance and could thus influence the resulting uranyl topology. Single crystals of the title compound, {(NH4)2[(UO2)2(C12O12)(H2O)2]} n , were synthesized hydro-thermally as a result of reacting uranyl nitrate with benzene-1,2,3,4,5,6-hexa-carb-oxy-lic acid (mellitic acid). The structure is comprised of a single unique monomeric uranyl cation adopting a penta-gonal bipyramidal geometry. The uranyl coordination sphere is composed of four O atoms originating from one half of a fully deprotonated mellitic acid ligand and a single water mol-ecule. The observed axial U-O bonds display an average distance of 1.765 (8) Å, whereas equatorial O atoms are found at an average distance of 2.40 (5) Å. All uranium-oxygen bond lengths are in good agreement with literature values. Furthermore, the coordin-ation between the uranyl penta-gonal bipyramids and the mellitic acid anion constructs a three-dimensional anionic framework which is charge-balanced with ammonium cations. Additional stabilization of the structure is provided by O-H⋯O and N-H⋯O hydrogen bonding inter-actions between the components.