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Four new uranyl arsenates, Cs2[(UO2)(As2O7)] (1), α-Cs[(UO2)(HAs2O7)] (2), β-Cs[(UO2)(HAs2O7)] (3), Cs[(UO2)(HAs2O7)]·0.17H2O (4), were synthesized by high-temperature/high pressure (HT/HP) reactions at 900 °C and 3 GPa. These phases were subsequently characterised structurally as well as chemically. We demonstrated that compound 1 can also be obtained at ambient pressure. Compounds 1, 2, and 4 are based on two-dimensional (2D) anionic layers with two different topological types. The layers possess a similar composition, [(UO2)(As2O7)]2− in 1 and [(UO2)(HAs2O7)]− in 2 and 4. However, the presence of hydrogen in 2 and 4 leads to a change in coordination modes of the pyroarsenate groups. There are additional 0.17 H2O molecules per formula unit in 4, which cause slight distortions of the layers in 4. All these layers can be simplified to a common net, which is typical of autunite-like layered compounds. Compound 3 is a polymorph of compound 2, but the structural arrangements in these two are significantly different. The structure of 3 is based upon a three-dimensional (3D) framework, in which UO7 is coordinated by arsenate groups in order to form uranyl anion sheets, and UO6 is located within the interlayers. Bond valance analysis proved the presence of OH− groups in compounds 2, 3, and 4, respectively, and water molecules in 4. The Raman analyses enabled the study of the local environments of the arsenate and the uranyl groups within the investigated phases, respectively. It turned out that the applied HT/HP synthesis method strongly affects the crystal chemistry as well as the observed structural features of all obtained compounds. [ABSTRACT FROM AUTHOR]

While extensive success has been gained in the structural chemistry of the U-Se system, the synthesis and characterization of Th-based Se structures are widely unexplored. Here, four new Th-Se compounds, α-Th(SeO3)2, β-Th(SeO3)2, Th(Se2O5)2, and Th3O2(OH)2(SeO4)3, have been obtained from mild hydrothermal or low-temperature (180-220 °C) flux conditions and were subsequently structurally and spectroscopically characterized. The crystal structures of α-Th(SeO3)2 and β-Th(SeO3)2 are based on ThO8 and SeO3 polyhedra, respectively, featuring a three-dimensional (3D) network with selenite anions filling in the Th channels along the a axis. Th(Se2O5)2 is a 3D framework composed of isolated ThO8 polyhedra interconnected by [Se2O5]2- dimers. Th3O2(OH)2(SeO4)3 is also a 3D framework constructed by octahedral hexathorium clusters [Th6(µ3-O)4(μ3-OH)4]12+, which are interlinked by selenate groups SeO42-. The positions of the vibrational modes associated with both SeIVO32- and SeVIO42- units, respectively, were determined for four compounds, and the Raman spectra of α- and β-Th(SeO3)2 are compared and discussed in detail. [ABSTRACT FROM AUTHOR]

Herein, the novel uranyl selenate and selenite compounds Rb2[(UO2)2(SeO4)3], Rb2[(UO2)3(SeO3)2O2], Rb2[UO2(SeO4)2(H2O)]·2H2O, and (UO2)2(HSeO3)2(H2SeO3)2Se2O5 have been synthesized using either slow evaporation or hydrothermal methods under acidic conditions and their structures were refined using single crystal X-ray diffraction. Rb2[(UO2)2(SeO4)3] synthesized hydrothermally adopts a layered 2D tetragonal structure in space group P42/ncm with a = 9.8312(4) Å, c = 15.4924(9) Å, and V = 1497.38(15) Å, where it consists of UO7 polyhedra coordinated via SeO4 units to create units UO2(SeO4)58− moieties which interlink to create layers in which Rb+ cations reside in the interspace. Rb2[(UO2)3(SeO3)2O2] synthesized hydrothermally adopts a layered 2D triclinic structure in space group P 1 ¯ with a = 7.0116(6) Å, b = 7.0646(6) Å, c = 8.1793(7) Å, α = 103.318(7)°, β = 105.968(7)°, γ = 100.642(7)° and V = 365.48(6) Å3, where it consists of edge sharing UO7, UO8 and SeO3 polyhedra that form [(UO2)3(SeO3)2O2] layers in which Rb+ cations are found in the interlayer space. Rb2[UO2(SeO4)2(H2O)]·2H2O synthesized hydrothermally adopts a chain 1D orthorhombic structure in space group Pmn21 with a = 13.041(3) Å, b = 8.579(2) Å, c = 11.583(2) Å, and V = 1295.9(5) Å3, consisting of UO7 polyhedra that corner share with one H2O and four SeO42− ligands, creating infinite chains. (UO2)2(HSeO3)2(H2SeO3)2Se2O5 synthesized under slow evaporation conditions adopts a 0D orthorhombic structure in space group Cmc21 with a = 28.4752(12) Å, b = 6.3410(3) Å, c = 10.8575(6) Å, and V = 1960.45(16) Å3, consisting of discrete rings of [(UO2)2(HSeO3)2(H2SeO3)2Se2O5]2. (UO2)2(HSeO3)2(H2SeO3)2Se2O5 is apparently only the second example of a uranyl diselenite compound to be reported. A combination of single crystal X-ray diffraction and bond valance sums calculations are used to characterise all samples obtained in this investigation. The structures uncovered in this investigation are discussed together with the broader family of uranyl selenates and selenites, particularly in the context of the role acidity plays during synthesis in coercing specific structure, functional group, and topology formations. [ABSTRACT FROM AUTHOR]

Pentavalent uranium compounds are key components of uranium‘s redox chemistry and play important roles in environmental transport. Despite this, well‐characterized U(V) compounds are scarce primarily because of their instability with respect to disproportionation to U(IV) and U(VI). In this work, we provide an alternate route to incorporation of U(V) into a crystalline lattice where different oxidation states of uranium can be stabilized through the incorporation of secondary cations with different sizes and charges. We show that iriginite‐based crystalline layers allow for systematically replacing U(VI) with U(V) through aliovalent substitution of 2+ alkaline‐earth or 3+ rare‐earth cations as dopant ions under high‐temperature conditions, specifically Ca(UVIO2)W4O14 and Ln(UVO2)W4O14 (Ln=Nd, Sm, Eu, Gd, Yb). Evidence for the existence of U(V) and U(VI) is supported by single‐crystal X‐ray diffraction, high energy resolution X‐ray absorption near edge structure, X‐ray photoelectron spectroscopy, and optical absorption spectroscopy. In contrast with other reported U(V) materials, the U(V) single crystals obtained using this route are relatively large (several centimeters) and easily reproducible, and thus provide a substantial improvement in the facile synthesis and stabilization of U(V). [ABSTRACT FROM AUTHOR]

Single crystals of α-Th(SeO3)2 (I) and β-Th(SeO3)2 (II) are grown under hydrothermal conditions using Th(NO3)4, SeO2, and NaNO3 (for intentional Na-containing compounds) in molar ratios of 1:3:5 and 1:1:3, resp. [ABSTRACT FROM AUTHOR]

The study of phase formation in the U-Te-O systems with mono and divalent cations under high-temperature high-pressure (HT/HP) conditions has resulted in four new inorganic compounds: K 2 [(UO 2 ) (Te 2 O 7 )], Mg [(UO 2 ) (TeO 3 ) 2 ], Sr [(UO 2 ) (TeO 3 ) 2 ] and Sr [(UO 2 ) (TeO 5 )]. Tellurium occurs as Te IV , Te V , and Te VI in these phases which demonstrate the high chemical flexibility of the system. Uranium VI) adopts a variety of coordinations, namely, UO 6 in K 2 [(UO 2 ) (Te 2 O 7 ), UO 7 in Mg [(UO 2 ) (TeO 3 ) 2 ] and Sr [(UO 2 ) (TeO 3 ) 2 ], and UO 8 in Sr [(UO 2 ) (TeO 5 )]. The structure of K 2 [(UO 2 ) (Te 2 O 7 )] is featured with one dimensional (1D) [Te 2 O 7 ] 4- chains along the c -axis. The Te 2 O 7 chains are further linked by UO 6 polyhedra, forming the 3D [(UO 2 ) (Te 2 O 7 )] 2- anionic frameworks. In Mg [(UO 2 ) (TeO 3 ) 2 ], TeO 4 disphenoids share common corners with each other resulting in infinite 1D chains of [(TeO 3 ) 2 ] 4- propagating along the a -axis. These chains link the uranyl bipyramids by edge sharing along two edges of the disphenoids, resulting in the 2D layered structure of [(UO 2 ) (Te 2 O 6 )] 2- . The structure of Sr [(UO 2 ) (TeO 3 ) 2 ] is based on 1D chains of [(UO 2 ) (TeO 3 ) 2 ] ∞ 2- propagating into the c -axis. These chains are formed by edge-sharing uranyl bipyramids which are additionally fused together by two TeO 4 disphenoids, which also share two edges. The 3D framework structure of Sr [(UO 2 ) (TeO 5 )] is composed of 1D [TeO 5 ] 4- chains sharing edges with UO 7 bipyramids. Three tunnels based on 6-Membered rings (MRs) are propagating along [001] [010] and [100] directions. The HT/HP synthetic conditions for the preparation of single crystalline samples and their structural aspects are discussed in this work., Competing Interests: Authors EL, BX and PK were employed by Institute of Energy and Climate Research (IEK-6), Forschungszentrum Jülich GmbH. Authors R-AE and EA were employed by Institute of Energy and Climate Research (IEK-9), Forschungszentrum Jülich GmbH. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Hao, Langer, Xiao, Kegler, Cao, Hu, Eichel, Wang and Alekseev.)

Applying physical pressure in the uranyl-sulfate system has resulted in the formation of the first purely inorganic uranyl oxo-salt phase with a considerable uranyl bend: Na 4 [(UO 2 )(SO 4 ) 3 ]. In addition to a strong bend of the typically almost linear O═U═O, the typically equatorial plane is broken up by two out-of-plane oxygen positions. Computational investigations show the origin of the bending to lie in the applied physical pressure and not in the electronic influence or steric hindrance. The increase in pressure onto the system has been shown to increase uranyl bending. Furthermore, the phase formation is compared with a reference phase of a similar structure without uranyl bending, and a transition pressure of 2.5 GPa is predicted, which is well in agreement with the experimental results.

A systematic investigation is presented which examines the structural chemistry of anhydrous and hydrous ternary hexavalent uranium and neptunium dinitrato, trinitrato, and tetranitrato complexes. Using slow evaporation methods under acidic conditions the uranium and neptunium nitrate complexes γ-K[UO 2 (NO 3 ) 3 ], K 2 [UO 2 - cis -(NO 3 ) 4 ], [NpO 2 (NO 3 ) 2 (H 2 O) 2 ]·4H 2 O, and Cs[NpO 2 (NO 3 ) 3 ] have been synthesized and their structures refined using single-crystal X-ray diffraction data. γ-K[UO 2 (NO 3 ) 3 ] adopts an orthorhombic structure in space group Pbca consisting of antiparallel aligned [UO 2 (NO 3 ) 3 ] - moieties. K 2 [UO 2 - cis -(NO 3 ) 4 ] adopts a monoclinic structure in space group P 2 1 / c consisting of [UO 2 (NO 3 ) 4 ] 2- moieties with two monodentate and two bidentate nitrate ligands that are arranged in a cis configuration about the uranyl, UO 2 2+ , center. Previous investigations have only identified trans variants of this monoclinic structure, and this is the first report of the cis form and also the occurrence of geometric isomerism in uranyl nitrates. [NpO 2 (NO 3 ) 2 (H 2 O) 2 ]·4H 2 O adopts an orthorhombic structure in space group Cmc 2 1 consisting of parallel aligned [NpO 2 (NO 3 ) 2 (H 2 O) 2 ] moieties that are in a trans configuration with respect to the bidentate nitrate ligands. Cs[NpO 2 (NO 3 ) 3 ] adopts a hexagonal structure in space group R 3 c consisting of parallel aligned [NpO 2 (NO 3 ) 3 ] - moieties. It was found that despite using a Np(V) nitrate solution as the starting reagent, Np(VI) nitrate structures were consistently recovered under acidic conditions. These observations are discussed and rationalized with respect to standard reduction potentials, particularly how redox conditions and acidity affect the oxidation state of Np and subsequent structure formation. The structures uncovered in this investigation are discussed comparatively and systematically in detail with other reported anhydrous and hydrous ternary hexavalent uranium and neptunium dinitrato, trinitrato, and tetranitrato complexes, particularly with respect to how synthesis conditions, including pH and geometric isomerism, affect the structural chemistry.

Four new uranyl arsenates, Cs2[(UO2)(As2O7)] (1), α-Cs[(UO2)(HAs2O7)] (2), β-Cs[(UO2)(HAs2O7)] (3), Cs[(UO2)(HAs2O7)]·0.17H2O (4), were synthesized by high-temperature/high pressure (HT/HP) reactions at 900 °C and 3 GPa. These phases were subsequently characterised structurally as well as chemically. We demonstrated that compound 1 can also be obtained at ambient pressure. Compounds 1, 2, and 4 are based on two-dimensional (2D) anionic layers with two different topological types. The layers possess a similar composition, [(UO2)(As2O7)](2-) in 1 and [(UO2)(HAs2O7)](-) in 2 and 4. However, the presence of hydrogen in 2 and 4 leads to a change in coordination modes of the pyroarsenate groups. There are additional 0.17 H2O molecules per formula unit in 4, which cause slight distortions of the layers in 4. All these layers can be simplified to a common net, which is typical of autunite-like layered compounds. Compound 3 is a polymorph of compound 2, but the structural arrangements in these two are significantly different. The structure of 3 is based upon a three-dimensional (3D) framework, in which UO7 is coordinated by arsenate groups in order to form uranyl anion sheets, and UO6 is located within the interlayers. Bond valance analysis proved the presence of OH(-) groups in compounds 2, 3, and 4, respectively, and water molecules in 4. The Raman analyses enabled the study of the local environments of the arsenate and the uranyl groups within the investigated phases, respectively. It turned out that the applied HT/HP synthesis method strongly affects the crystal chemistry as well as the observed structural features of all obtained compounds.

While extensive success has been gained in the structural chemistry of the U-Se system, the synthesis and characterization of Th-based Se structures are widely unexplored. Here, four new Th-Se compounds, α-Th(SeO3)2, β-Th(SeO3)2, Th(Se2O5)2, and Th3O2(OH)2(SeO4)3, have been obtained from mild hydrothermal or low-temperature (180-220 °C) flux conditions and were subsequently structurally and spectroscopically characterized. The crystal structures of α-Th(SeO3)2 and β-Th(SeO3)2 are based on ThO8 and SeO3 polyhedra, respectively, featuring a three-dimensional (3D) network with selenite anions filling in the Th channels along the a axis. Th(Se2O5)2 is a 3D framework composed of isolated ThO8 polyhedra interconnected by [Se2O5](2-) dimers. Th3O2(OH)2(SeO4)3 is also a 3D framework constructed by octahedral hexathorium clusters [Th6(μ3-O)4(μ3-OH)4](12+), which are interlinked by selenate groups SeO4(2-). The positions of the vibrational modes associated with both Se(IV)O3(2-) and Se(VI)O4(2-) units, respectively, were determined for four compounds, and the Raman spectra of α- and β-Th(SeO3)2 are compared and discussed in detail.