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By applying high temperature (1270 K) and high pressure (3.5 GPa), significant changes occur in the structural volume and crystal topology of ThMo2O8, allowing the formation of an unexpected new ThMo2O8 polymorph (high-temperature/high-pressure (HT/HP) orthorhombic ThMo2O8). Compared with the other three ThMo2O8 polymorphs prepared at the ambient pressure (monoclinic, orthorhombic, and hexagonal phases), the molar volume for the quenched HT/HP-orthorhombic ThMo2O8 is decreased by almost 20 %. As a result of such a dramatic structural transformation, a permanent high-pressure quenchable state is able to be sustained when the pressure is released. The crystal structures of the three ambient ThMo2O8 phases are based on three-dimensional (3D) frameworks constructed from corner-sharing ThO x ( x=6, 8, or 9) polyhedra and MoO4 tetrahedra. The HT/HP-orthorhombic ThMo2O8, however, crystallizes in a novel structural topology, exhibiting very dense arrangements of ThO11 and MoO4+1 polyhedra connecting along the crystallographic c axis. The phase transitions among all four of these ThMo2O8 polymorphs are unveiled and fully characterized with regard to the structural transformation, thermal stability, and vibrational properties. The complementary first principles calculations of Gibbs free energies reveal the underlying energetics of the phase transition, which support the experimental findings. [ABSTRACT FROM AUTHOR]

Four novel thorium molybdates containing alkaline-earth or rare-earth metals were isolated from high-temperature solid-state synthesis. The incorporation of divalent and trivalent cations into the thorium molybdate system results in complex structural topologies. A2MgTh3(MoO4)8 (A = K, Rb) which crystallizes in the space group C2/c is the first instance among the thorium molybdate family that incorporates alkaline-earth metals. Its crystal structure is based on complex channels composed of ThO8 square antiprisms and MoO4 tetrahedra arranged in a corner-sharing manner. K2SrTh2(MoO4)6, as the first thorium polymolybdate compound, is constructed from ThO8 square antiprisms and Mo4O16 tetramers. The Mo4O16 tetramers, lying in the (001) plane, are built from four edge-sharing MoO6 octahedra. Nd2Th3(MoO4)9 is the first thorium molybdate containing rare-earth cations. The resemblance of Nd2Th3(MoO4)9 with hexagonal-ThMo2O8 reveals its potential as a host for different trivalent transuranium elements. Raman spectra analysis shows that the different Mo polyhedral geometries (MoO4 tetrahedra and MoO6 octahedra) have significant effects on the vibrational bands of these compounds. The thermal behavior and stability of the newly obtained materials have been studied. [ABSTRACT FROM AUTHOR]

A tetragonal modification of uranium polymetaphosphate U(PO3)4, a mixed U4+/Nd3+ polymetaphosphate '(U0.62Nd0.38)(PO3)4', and two new tetraphosphates, Th(P4O12) and U(P4O12), were synthesized. The structures of the obtained materials were characterized by X-ray diffraction and Raman spectroscopy. The presence of Nd in (U0.62Nd0.38)(PO3)4 was proven by energy-dispersive X-ray spectroscopy (EDX), and the measured degree of substitution for U agrees well with the X-ray crystallography results; however, the mechanism of the necessary charge compensation could not be identified. The cation arrangements in the crystal structures of thorium and uranium polymetaphosphates have been studied in terms of Voronoi-Dirichlet polyhedra. Different conformations of the tetraphosphate polyanions were observed in the crystal structures of Th(P4O12) and U(P4O12). The Raman spectrum of a single crystal of Th(P4O12) was recorded, and the bands were assigned. [ABSTRACT FROM AUTHOR]

Invited for the cover of this issue are the groups of Evgeny V. Alekseev at the Forchungszentrum Jülich and Thorstem M. Gesing at the University of Bremen. The image depicts the complex thorium tungstate polyanions, having a six-leafed lily cross-section, containing a rare confacial [W2O9]6− bioctahedral core. Read the full text of the article at . [ABSTRACT FROM AUTHOR]

The exploration of phase formation in the Th-Mo/W-Te systems has resulted in four mixed oxo-anion compounds from high-temperature solid-state reactions: ThWTe2O9, Th(WO4)(TeO3), ThMoTe2O9, and Th2(MoO4)(TeO3)3. All four compounds contain edge-sharing thorium polyhedra linked by MoO4/WO6 and different tellurium oxo-groups to form three-dimensional frameworks. In ThWTe2O9, each helical Th based chain is connected by four tungstotellurite clusters resulting in a building fragment which has a cross-section of four-leafed clovers. The structure of Th(WO4)(TeO3) exhibits a multilayer-sandwich framework composed of thorium tellurite layers with tungsten chains in between. In the case of the molybdate family, ThMoTe2O9 and Th2(MoO4)(TeO3)3 are built from puckered Th-Te sheets which are further interconnected by MoO4 tetrahedral linkers. The DSC-TG technique was performed to gain insight into the thermal behavior of the synthesized compounds. Raman spectra of as-prepared phases were obtained and analyzed for signature peaks. [ABSTRACT FROM AUTHOR]

By applying high temperature (1270 K) and high pressure (3.5 GPa), significant changes occur in the structural volume and crystal topology of ThMo2O8, allowing the formation of an unexpected new ThMo2O8 polymorph (high-temperature/high-pressure (HT/HP) orthorhombic ThMo2O8). Compared with the other three ThMo2O8 polymorphs prepared at the ambient pressure (monoclinic, orthorhombic, and hexagonal phases), the molar volume for the quenched HT/HP-orthorhombic ThMo2O8 is decreased by almost 20 %. As a result of such a dramatic structural transformation, a permanent high-pressure quenchable state is able to be sustained when the pressure is released. The crystal structures of the three ambient ThMo2O8 phases are based on three-dimensional (3D) frameworks constructed from corner-sharing ThO x ( x=6, 8, or 9) polyhedra and MoO4 tetrahedra. The HT/HP-orthorhombic ThMo2O8, however, crystallizes in a novel structural topology, exhibiting very dense arrangements of ThO11 and MoO4+1 polyhedra connecting along the crystallographic c axis. The phase transitions among all four of these ThMo2O8 polymorphs are unveiled and fully characterized with regard to the structural transformation, thermal stability, and vibrational properties. The complementary first principles calculations of Gibbs free energies reveal the underlying energetics of the phase transition, which support the experimental findings. [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]

A new alkaline thorium arsenate family was obtained and systematically investigated. The structures of A2Th(AsO4)2 (A = Li, Na, K, Rb, Cs) were determined from single crystal X-ray diffraction data. Li2Th(AsO4)2 and either isostructural K2Th(AsO4)2 and Rb2Th(AsO4)2 crystallize in the monoclinic crystal system. Na2Th(AsO4)2 and Cs2Th(AsO4)2 crystallize in the orthorhombic and tetragonal crystal systems, respectively. Li2Th(AsO4)2 consists of [Th(AsO4)2]2- layers with Li atoms in the interlayer space. The rest of the compounds are based on 3D frameworks. Differences in local environments of ThO8 coordination polyhedra are described in relation to the symmetry. Despite different local environments of ThO8 coordination polyhedra and different structural symmetry, underlying nets of A2Th(AsO4)2 (A = Na, K, Rb, Cs) were shown to be the same. Single-crystal and powder Raman spectra were measured, and bands are assigned. DSC measurements showed phase transitions in K2Th(AsO4)2 and Rb2Th(AsO4)2, which were studied using high-temperature powder X-ray diffraction (HT-PXRD). The data of HT-PXRD demonstrates two high-temperature polymorphic modification of K2Th(AsO4)2 and only one for the isotypic Rb2Th(AsO4)2. The phase transitions in both K and Rb phases are reversible. [ABSTRACT FROM AUTHOR]

Threecesium thorium molybdates [Cs2Th(MoO4)3, Cs2Th3(MoO4)7, andCs4Th(MoO4)4] weresynthesized via the high-temperature solid-state method. Cs2Th(MoO4)3crystallizes in orthorhombic spacegroup Pnnm, containing [Th(MoO4)3]2–chains extending along the [100] direction.Cs2Th3(MoO4)7is basedon an open framework with channels occupied by Cs+ionsand running parallel through the [100] direction. It is the firstcase in which thorium atoms coordinate simultaneously in three distinctenvironments, namely, 7-coordinated pentagonal bipyramid, 8-coordinatedsquare antiprism, and 9-coordinated tricapped trigonal prism. Cs4Th(MoO4)4is monoclinic, built from[Th(MoO4)4]4–sheets formedby vertex sharing of MoO4tetrahedra and ThO8antiprisms. The Raman and infrared spectra were recorded, and thevibrations related to internal and external Mo–O bonds in theMoO42–coordination geometry were discussed. [ABSTRACT FROM AUTHOR]

A high-temperature/high-pressure method was employed to investigate phase formation in the Th(NO3)4⋅5H2O-As2O3-CsNO3 system. It was observed that an excess of arsenic(III) in starting system leads to the formation of Th(AsIII4AsV4O18), which is representative of a rare class of mixed-valent arsenic(III)/arsenic(V) compounds. This compound was studied with X-ray diffraction, energy-dispersive X-ray, and Raman spectroscopy methods. Crystallographic data show that Th(AsIII4AsV4O18) is built from (AsIII4AsV4O18)4- layers connected through Th atoms. The arsenic layers are found to be isoreticular to those in previously reported As2O3 and As3O5(OH), and the geometric differences between them are discussed. Bands in the Raman spectrum are assigned with respect to the presence of AsO3 and AsO4 groups. [ABSTRACT FROM AUTHOR]

Single crystals of monoclinic ThMo2O8 are prepared by solid state reaction of Th(NO3)4 and MoO3 (1273 K, 6 h). [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]

Crystals of Th(As8O18) are obtained along with an amorphous phase and CsAs3O8 by high-temperature/high-pressure reaction of Th(NO3)4·5H2O, As2O3, and CsNO3 in a ratio of 1:8:2 (Pt capsule, 3 GPa, 1200 °C; 0.2 °C/min cooling rate). [ABSTRACT FROM AUTHOR]

Rb8Th(MoO4)6 (I), Rb2Th(MoO4)3 (II), Rb4Th(MoO4)4 (III), and Rb4Th5(MoO4)12 (IV) are prepared by solid state reaction of Th(NO3)4, RbNO3, and MoO3 in molar ratios of 1:2:2 for (I), 1:3:4 for (II), 1:2:4 for (III), and 1:1:1 for (IV), resp. [ABSTRACT FROM AUTHOR]