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Crystalline coordination complexes of actinides, especially in atypical oxidation states, are not only fundamentally important for expanding the notably limited knowledge on the bonding nature of a...

99 Tc contamination at legacy nuclear sites is a serious and unsolved environmental issue. The selective remediation of 99 TcO4 - in the presence of a large excess of NO3 - and SO4 2- from natural waste systems represents a significant scientific and technical challenge, since anions with a higher charge density are often preferentially sorbed by traditional anion-exchange materials. We present a solution to this challenge based on a stable cationic metal-organic framework, SCU-102 (Ni2 (tipm)3 (NO3 )4 ), which exhibits fast sorption kinetics, a large capacity (291 mg g-1 ), a high distribution coefficient, and, most importantly, a record-high TcO4 - uptake selectivity. This material can almost quantitatively remove TcO4 - in the presence of a large excess of NO3 - and SO4 2- . Decontamination experiments confirm that SCU-102 represents the optimal Tc scavenger with the highest reported clean-up efficiency, while first-principle simulations reveal that the origin of the selectivity is the recognition of TcO4 - by the hydrophobic pockets of the structure.

f-element-bearing iodate compounds are a large family mostly synthesized by hydrothermal reactions starting with actinide/lanthanide ions and iodic acid or iodate salt. In this work, we introduce melting periodic acid flux as a new reaction medium and provide a safe way for single-crystal growth of a series of new f-element iodate compounds including UO2(IO3)2·H2O (1), UO2(IO3)2(H2O)·HIO3 (2), α-Th(IO3)2(NO3)(OH) (3), β-Th(IO3)2(NO3)(OH) (4), and (H3O)9Nd9(IO3)36·3HIO3 (5). The structures of these compounds deviate from those afforded from hydrothermal reactions. Specifically, compounds 1 and 2 exhibit pillared structures consisting of uranyl pentagonal bipyramids and iodate trigonal pyramids. Compounds 3 and 4 represent two new thorium iodate compounds that are constructed from subunits of thorium dimers. Compound 5 exhibits a flower-shaped trivalent lanthanide iodate structure with HIO3 molecules and H3O+ cations filled in the channels. The aliovalent replacement of f elements in 5 is available from a h...

We report one of the most efficient scavenger materials, a cationic crystalline coordination polymer SBN for trapping ReO4–, a surrogate for 99TcO4–, as an anionic radioactive contaminant of great concern. The uptake capacity for ReO4– reaches 786 mg/g, a value noticeably higher than the state of art anion-exchange resins and other inorganic or hybrid anion sorbents. Once being captured, ReO4– is greatly immobilized, as almost no ReO4– can be eluted using large excess of nitrate, carbonate, and phosphate anions. The processes are featured by a complete and irreversible single-crystal to single-crystal structural transformation from SBN to the ReO4–-incorporated phase (SBR). The coordination environments of NO3– and ReO4– probed by single-crystal structures clearly unravel the underlying mechanism, where each ReO4– in SBR binds to multiple Ag+ sites forming strong Ag–O–Re bonds, and to 4,4′-bipyridine through a dense hydrogen bond network. These structural insights lead to a significant difference in solub...

Searching for new host materials tailored for the high proton conductivity is highly desirable for the new generation of fuel cell system. We report here an anion-exchangeable cationic metal organic framework with the formula of [Ce(Ccbp)2]Br0.25Cl0.75·6H2O·2DMF (compound 1), which is constructed through the self-assembly of zwitterionic-based ligands H2CcbpBr (H2CcbpBr = 4-carboxy-1-(4-carboxybenzyl)pyridinium bromide) and (NH4)2Ce(NO3)6. During the investigation of humidity-dependent proton conduction behavior, we observed a rare case of rapid water-induced single-crystal-to-single-crystal phase transformation from compound 1 to a neutral chain [Ce(Ccbp)3(H2O)3]·8H2O (compound 2). This structural transformation originates from the coordination of water to Ce(III) metal centers, distortion of ligands, and the soft nature of the cationic framework 1, as probed and confirmed by a variety of investigations including color change, water vapor adsorption measurement, powder X-ray diffraction, single-crystal X...

As the crucial soluble species of long-lived radionuclides 129I and 79Se, iodate and selenite anions commonly share similar geometry of the trigonal pyramid XO3 (X = I, Se) but in different valence states. Although large amounts of investigations have been performed aiming at understanding the environmental behavior of these two anions individually, studies on cases when they coexist are extremely scarce. Structurally well-characterized natural/synthetic crystalline solids simultaneously incorporating these two anions as potential solubility-limiting products at the nuclear waste geological depository remain elusive. We report here a crystalline solid Th(IO3)2(SeO3) representing the first example of aliovalent substitution between IO3– and SeO32– sharing the same structural site, as demonstrated by single crystal X-ray diffraction, laser-ablation inductively coupled plasma mass spectrometry analysis, and spectroscopic techniques including infrared, Raman, and X-ray absorption spectroscopies. Sequentially,...

The example of phase transformation from a centrosymmetric space group at low temperature (LT) to a chiral space group at high temperature (HT) is reported, which was clearly resolved in a single-crystal-to-single-crystal manner in a 3D uranyl(vi) phosphonate compound [TMA][(UO2)2(1,3-pbpH)(1,3-pbpH2)] () (TMA(+) = tetramethylammonium cation; 1,3-pbpH4 = 1,3-phenylenebis(phosphonic acid)).

The limited long-term hydrolytic stability of rapidly emerging 3D-extended framework materials (MOFs, COFs, MOPs, etc.) is still one of major barriers for their practical applications as new solid-state electrolytes in fuel cells. To obtain hydrolytically stable materials, two H2 PO4 (-) -exchanged 3D inorganic cationic extended frameworks (CEFs) were successfully prepared by a facile anion-exchange method. Both anion-exchanged CEFs (YbO(OH)P and NDTBP) show significantly enhanced proton conductivity when compared with the original materials (YbO(OH)Cl and NDTB) with an increase of up to four orders-of-magnitude, reaching 2.36×10(-3) and 1.96×10(-2) S cm(-1) at 98 % RH and 85 °C for YbO(OH)P and NDTBP, respectively. These values are comparable to the most efficient proton-conducting MOFs. In addition, these two anion-exchanged materials are stable in boiling water, which originates from the strong electrostatic interaction between the H2 PO4 (-) anion and the cationic host framework, showing a clear advance over all the acid-impregnated materials (H2 SO4 @MIL-101, H3 PO4 @MIL-101, and H3 PO4 @Tp-Azo) as practical solid-state fuel-cell electrolytes. This work offers a new general and efficient approach to functionalize 3D-extended frameworks through an anion-exchange process and achieves water-stability with ultra-high proton conductivity above 10(-2) S cm(-1) .

The preparation of proton-conducting materials that are functional and stable at intermediate temperatures (393-573 K) is a focal point of fuel cell development. The purely inorganic material, HNd(IO3)4, which possesses a dense 3D framework structure, can reach a maximum of 4.6 × 10(-4) S·cm(-1) at 353 K and 95% relative humidity and exhibit a high conductivity of 8.0 × 10(-5) S·cm(-1) from 373 to 553 K under the flow of wet N2. HNd(IO3)4 exhibits a variety of improvements including high thermal stability, low solubility in water, and resistance to reducing atmosphere. The proton conductivity in such a wide temperature range originates from the intrinsic liberated protons in the structure and the resulting 1D hydrogen-bonding network confirmed by bond valence sum calculation and solid-state NMR analysis. Moreover, two different activation energies are observed in different temperature regions (0.23 eV below 373 K and 0.026 eV from 373 to 553 K), indicating that two types of proton motion are responsible for proton diffusion, as further domenstrated by temperature-dependent open-circuit voltage hysteresis in a tested fuel cell assembly as well as variable-temperature and double quantum filtered solid-state NMR measurements.

Two new uranyl vanadates have been prepared from hydrothermal reactions and structurally characterized by single-crystal X-ray diffraction. The structure of (H3O)UO2VO4 (UVO-1) consists of anionic layers containing UO2(2+) pentagonal bipyramids coordinated by edge-sharing VO5 square pyramids, with the charge balanced by interlaminar H3O(+) cations. Vanadium in (UO2)3(VO4)2(H2O)3 (UVO-2) exists as monomeric VO4 tetrahedra coordinating to UO2(2+) pentagonal bipyramids, forming a 3D uranyl(VI) vanadate framework. Similar reactions with the addition of Ln(NO3)3 (Ln = Nd, Eu) afford the three heterobimetallic lanthanide uranyl vanadate frameworks Nd(UO2)3(VO4)3(H2O)11 (NdUVO-1), Eu(UO2)3(VO4)3(H2O)10 (EuUVO-1), and Eu2(UO2)12(VO4)10(H2O)24 (EuUVO-2). In NdUVO-1 and EuUVO-1, Ln(3+) cations are inserted into the interlayer space of UVO-1 substituting for H3O(+) and further bridging adjacent layers into 3D frameworks. Similarly, EuUVO-2 adopts the same sheet topology as UVO-2, with Eu(3+) ions replacing some of the interlayer uranyl ions in UVO-2. Our work has demonstrated that uranyl vanadate extended structures are excellent hosts for further incorporation of trivalent lanthanide/actinide cations and has provided a new way to create new heterobimetallic 4f-5f and 5f-5f compounds.

Searching for new chemically durable and radiation-resistant absorbent materials for actinides and their fission products generated in the nuclear fuel cycle remain highly desirable, for both waste management and contamination remediation. Here we present a rare case of 3D uranyl organic framework material built through polycatenating of three sets of graphene-like layers, which exhibits significant umbellate distortions in the uranyl equatorial planes studied thoroughly by linear transit calculations. This unique structural arrangement leads to high β and γ radiation-resistance and chemical stability in aqueous solutions within a wide pH range from 3 to 12. Being equipped with the highest surface area among all actinide compounds known to date and completely exchangeable [(CH3)2NH2](+) cations in the structure, this material is able to selectively remove cesium from aqueous solutions while retaining the polycatenated framework structure.

By controlling the extent of hydrolysis during the self-assembly process of a zwitterionic-based ligand with uranyl cations, we observed a structural evolution from the neutral uranyl-organic framework [(UO2)2(TTTPC)(OH)O(COOH)]·1.5DMF·7H2O (SCU-6) to the first cationic uranyl-organic framework with the formula of [(UO2)(HTTTPC)(OH)]Br·1.5DMF·4H2O (SCU-7). The crystal structures of SCU-6 and SCU-7 are layers built with tetranuclear and dinuclear uranyl clusters, respectively. Exchangeable halide anions are present in the interlaminar spaces balancing the positive charge of layers in SCU-7. Therefore, SCU-7 is able to effectively remove perrhenate anions from aqueous solution. Meanwhile, the H2PO4(-)-exchanged SCU-7 material exhibits a moderate proton conductivity of 8.70 × 10(-5) S cm(-1) at 50 °C and 90% relative humidity, representing nearly 80 times enhancement compared to the original material.

The first thorium framework compound with mixed-valent phosphorus-based (phosphite and pyrophosphate) ligands, [BMMim]2[Th3(PO3)4(H2P2O7)3] (ThP-1), was synthesized by ionothermal reactions concurrent with the partial oxidation of phosphoric acid. The overall structural topology of ThP-1 highly resembles that of MOF-5, containing only one type of three-dimensional channels with a window size of 11.32 Å × 11.32 Å. ThP-1 has a free void volume of 50.8%, making it one of the most porous purely inorganic actinide-based framework materials. More importantly, ThP-1 is highly stable in aqueous solutions over an extremely wide pH range from 1 to 14 and thus may find potential applications in selective ion exchange and catalysis.

The solvothermal reaction of thorium nitrate and tris-(4-carboxylphenyl)phosphine oxide in DMF affords a centrosymmetric porous thorium organic framework compound [Th(TPO)(OH)(H2O)]·8H2O (1). In contrast, the ionothermal reaction of the same reagents in the ionic liquid 1-butyl-2,3-dimethylimidazolium chloride results in the formation of a rare example of a chiral and porous thorium organic framework compound, [C9H17N2][Th(TPO)Cl2]·18H2O (2), which is derived solely from achiral starting materials. The geometries of the Th(iv) centers in compounds 1 and 2 are both atypical for low valent actinides, which can be best described as a ten-coordinate spherical sphenocorona and an irregular muffin, respectively. A large cavity of 17.5 Å (max. face to face) × 8 Å (min. face to face) with a BET surface area of 623 m(2) g(-1) in compound 2 is observed. The poor stability indicated by thermal gravimetric analysis and the water-resistance test for compound 2 may be due to the unique anisotropic coordination geometry for thorium. Temperature-dependent luminescence studies for both compounds indicate that the trends in the intensity vary as the Th-Th distance and the coordination environments of Th(iv) centers change.

Selenium is of great concern owing to its acutely toxic characteristic at elevated dosage and the long-term radiotoxicity of 79Se. The contents of selenium in industrial wastewater, agricultural runoff, and drinking water have to be constrained to a value of 50 μg/L as the maximum concentration limit. We reported here the selenium uptake using a structurally well-defined cationic layered rare earth hydroxide, Y2(OH)5Cl·1.5H2O. The sorption kinetics, isotherms, selectivity, and desorption of selenite and selenate on Y2(OH)5Cl·1.5H2O at pH 7 and 8.5 were systematically investigated using a batch method. The maximum sorption capacities of selenite and selenate are 207 and 124 mg/g, respectively, both representing the new records among those of inorganic sorbents. In the low concentration region, Y2(OH)5Cl·1.5H2O is able to almost completely remove selenium from aqueous solution even in the presence of competitive anions such as NO3–, Cl–, CO32–, SO42–, and HPO42–. The resulting concentration of selenium is b...

The limited long-term hydrolytic stability of rapidly emerging 3D-extended framework materials (MOFs, COFs, MOPs, etc.) is still one of major barriers for their practical applications as new solid-state electrolytes in fuel cells. To obtain hydrolytically stable materials, two H2 PO4 (-) -exchanged 3D inorganic cationic extended frameworks (CEFs) were successfully prepared by a facile anion-exchange method. Both anion-exchanged CEFs (YbO(OH)P and NDTBP) show significantly enhanced proton conductivity when compared with the original materials (YbO(OH)Cl and NDTB) with an increase of up to four orders-of-magnitude, reaching 2.36×10(-3) and 1.96×10(-2) S cm(-1) at 98 % RH and 85 °C for YbO(OH)P and NDTBP, respectively. These values are comparable to the most efficient proton-conducting MOFs. In addition, these two anion-exchanged materials are stable in boiling water, which originates from the strong electrostatic interaction between the H2 PO4 (-) anion and the cationic host framework, showing a clear advance over all the acid-impregnated materials (H2 SO4 @MIL-101, H3 PO4 @MIL-101, and H3 PO4 @Tp-Azo) as practical solid-state fuel-cell electrolytes. This work offers a new general and efficient approach to functionalize 3D-extended frameworks through an anion-exchange process and achieves water-stability with ultra-high proton conductivity above 10(-2) S cm(-1) .

Straight boron nitride nanotubes (BNNTs) with pure hexagonal phase were conveniently prepared by heating the mixture of Mg(BO 2 ) 2 · H 2 O, NH 4 Cl, NaN 3 and Mg powder in an autoclave at 600 °C for 20–60 h. These BNNTs had diameters mainly ranging 30–300 nm and lengths up to ∼5 μm, and a majority of them had at least one closed end. Besides the traditional end tips, additional cone-like tips were frequently found to be attached on the BNNTs. The effects of temperature, reactants and the possible mechanism of the catalytic formation of the BNNTs are discussed.

Systematic control of the reactions between U(VI) and 1,4-phenylenebis(methylene))bis(phosphonic acid) (pmbH4) allows for alterations in the bonding between these constituents and affords three uranyl phosphonate compounds with chiral one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) structures, namely, [TPA][UO2(pmbH3)(pmbH2)H2O]·2H2O (1), [NH4]2[UO2(pmb)] (2), UO2(pmbH2) (3), and the first uranyl mixed phosphite/phosphonate compound [TMA]2[(UO2)2(pmb)(HPO3)] (4) (TPA = NPr4+, TMA = NMe4+). These compounds crystallize in the space groups P212121, P1̅, P21/c, and Cmcm, respectively. Further investigation of the local uranyl coordination environment reveals that in 1 only oxygen atoms from P=O moieties ligate the uranium centers; whereas in 2 only P-O(-) oxygen atoms are involved in bonding and yield a layered topology. Compound 3 differs sharply from the first two in that conjugated P=O and P-O(-) oxygen atoms chelate the uranium centers resulting in a 3D framework. In compound 4, a phosphonate group bridges three uranyl centers further coordinated with a phosphite ligand HPO32–, which is a product of pmbH4 decomposing, forming a 2D layered structure. Compounds 3 and 4 also contain a different coordination environment for U(VI) than that found in 1 or 2. In this case, tetragonal bipyramidal UO6 units occur instead of the far more common UO7 pentagonal bipyramids found in 1 and 2. Interestingly, 1 converts to 3 at elevated reaction temperatures, indicating that the formation of 1 is likely under kinetic control. This is supported by thermal analysis, which reveals that 3 has higher thermal stability than 1 or 2. UV-vis-near-IR absorption and fluorescence spectroscopy show that the absorption and photoluminescence intensity increases from 1 to 4. Density functional theory electronic structure calculations provide insight into the nature of the interactions between U(VI) and the phosphonate ligands.