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Single crystals of four novel uranyl selenate and selenite-selenate oxysalts with protonated ethylamine molecules, (C 2 H 8 N) 2 [(UO 2 )(SeO 4 ) 2 (H 2 O)](H 2 O) ( I ), (C 2 H 8 N) 3 [(UO 2 )(SeO 4 ) 2 (HSeO 4 )] ( II ), (C 2 H 8 N)[(UO 2 )(SeO 4 )(HSeO 3 )] ( III ), and (C 2 H 8 N)(H 3 O)[(UO 2 )(SeO 4 ) 2 (H 2 O)] ( IV ) have been prepared by isothermal evaporation from aqueous solutions. Uranyl-containing 1D and 2D units have been investigated using topological approach and information-based complexity measurements that demonstrate the evolution of structural units and the increase of topological complexity with the decrease of H 2 O content. [ABSTRACT FROM AUTHOR]

Abstract: Single crystals of the new compounds Li6[(UO2)12(PO4)8(P4O13)] (1), Li5[(UO2)13(AsO4)9(As2O7)] (2), Li[(UO2)4(AsO4)3] (3) and Li3[(UO2)7(AsO4)5O)] (4) have been prepared using high-temperature solid state reactions. The crystal structures have been solved by direct methods: 1—monoclinic, C2/m, a=26.963(3)Å, b=7.063(1)Å, c=19.639(1)Å, β=126.890(4)°, V=2991.2(6)Å3, Z=2, R 1=0.0357 for 3248 unique reflections with |F 0|≥4σF ; 2—triclinic, , a=7.1410(8)Å, b=13.959(1)Å, c=31.925(1)Å, α=82.850(2)°, β=88.691(2)°, γ=79.774(3)°, V=3107.4(4)Å3, Z=2, R 1=0.0722 for 9161 unique reflections with |F 0|≥4σF ; 3—tetragonal, I 41/amd, a=7.160(3)Å, c=33.775(9)Å, V=1732(1)Å3, Z=4, R 1=0.0356 for 318 unique reflections with |F 0|≥4σF ; 4—tetragonal, , a=7.2160(5)Å, c=14.6540(7)Å, V=763.04(8)Å3, Z=1, R 1=0.0423 for 1600 unique reflections with |F 0|≥4σF . Structures of all the phases under consideration are based on complex 3D frameworks consisting of different types of uranium polyhedra (UO6 and UO7) and different types of tetrahedral T O4 anions ( T =P or As): PO4 and P4O13 in 1, AsO4 and As2O7 in 2, and single AsO4 tetrahedra in 3 and 4. In the structures of 1 and 2, UO7 pentagonal bipyramids share edges to form (UO5)∞ chains extended along the b axis in 1 and along the a axis in 2. The chains are linked via single T O4 tetrahedra into tubular units with external diameters of 11Å in 1 and 11.5Å in 2, and internal diameters of 4.1Å in 1 and 4.5Å in 2. The channels accommodate Li+ cations. The tubular units are linked into 3D frameworks by intertubular complexes. Structures of 3 and 4 are based on 3D frameworks composed on layers united by (UO5)∞ infinite chains. Cation–cation interactions are observed in 2, 3, and 4. In 2, the structure contains a trimeric unit with composition [OU(1)O]–U(13)–[OU(2)O]. In the structures of 3 and 4, T-shaped dimers are observed. In all the structures, Li+ cations are located in different types of cages and channels and compensate negative charges of anionic 3D frameworks. [Copyright &y& Elsevier]

Abstract: The three new framework Rb uranyl phosphates and arsenates with anionic parts based on different type of polymeric anions have been prepared by high-temperature solid-state reactions: Rb4[(UO2)6(P2O7)4(H2O)] (1), Rb2[(UO2)3(P2O7)(P4O12)] (2), Rb[(UO2)2(As3O10)] (3). The crystal structures of the synthesized compounds have been solved by direct methods: 1—monoclinic P21/c, a=9.672(1)Å, b=12.951(1)Å, c=32.231(3)Å, β=90.116(4)°, V=4037.3(6)Å3, Z=4, R 1=0.0926 for 6351 unique reflections with ; 2—monoclinic, P21/c, a=6.791(1)Å, b=16.155(3)Å, c=19.856(4)Å, β=97.48(5)°, V=2159.8(7)Å3, Z=4, R 1=0.0286 for 3617 unique reflections with ; 3—orthorhombic, Pbcn, a=10.558(1)Å, b=11.037(1)Å, c=11.464(1)Å, V=1335.9(2)Å3, Z=4, R 1=0.0489 for 1384 unique reflections with . The structures of title are compounds based on 3D negatively charged frameworks with chemical compositions [(UO2)6(P2O7)4(H2O)]4− in 1, [(UO2)3(P2O7)(P4O12)]2− in 2 and [(UO2)2(As3O10)]− in 3. These negative charges are compensated by rubidium cations which are in the channels of 1 and closed cages in structures of 2 and 3. The channels in 1 are directed along the a direction and have minimum dimensions ∼5Å×6Å. This is the first example of porosity generation through solid state synthesis in uranyl compounds. For the first time in uranium chemistry polymeric anionic groups P4O12 and As3O10 were observed in structure of 2 and 3. [Copyright &y& Elsevier]

Abstract: Four new Li uranyl phosphates and arsenates have been prepared by high-temperature solid-state reactions: α-Li[(UO2)(PO4)] (1), α-Li[(UO2)(AsO4)] (2), β-Li[(UO2)(AsO4)] (3) and Li2[(UO2)3(P2O7)2] (4). The structures of the compounds have been solved by direct methods: 1—triclinic, , a=5.0271(1)Å, b=9.8799(2)Å, c=10.8920(2)Å, α=108.282(9)°, β=102.993(8)°, γ=104.13(1)°, V=470.69(2)Å3, Z=4, R 1=0.0415 for 2786 unique reflections with |F 0|⩾4σF ; 2—triclinic, , a=5.129(2)Å, b=10.105(3)Å, c=11.080(3)Å, α=107.70(2)°, β=102.53(3)°, γ=104.74(3)°, V=501.4(3)Å3, Z=4, R 1=0.055 for 1431 unique reflections with |F 0|⩾4σ F; 3—triclinic, , a=5.051(1)Å, b=5.303(1)Å, c=10.101(1)Å, α=90.31(1)°, β=97.49(1)°, γ=105.08(1)°, V=258.80(8)Å3, Z=2, R 1=0.0339 for 2055 unique reflections with |F 0|⩾4σ F; 4—triclinic, , a=5.312(1)Å, b=6.696(1)Å, c=12.542(1)Å, α=94.532(9)°, β=99.059(8)°, γ=110.189(7)°, V=409.17(10)Å3, Z=2, R 1=0.0565 for 1355 unique reflections with |F 0|⩾4σ F. The structures of all four compounds are based upon 3-D frameworks of U and T polyhedra (T=P, As). Phases 1 and 2 are isostructural and consist of U2O12 dimers and UO6 square bipyramids linked by single TO4 tetrahedra. The structure of 3 consists of 3-D framework of corner-sharing UO6 bipyramids and AsO4 tetrahedra. In the structure of 4, the framework is composed of U2O12 dimers, UO6 bipyramids and P2O7 dimers. In all the compounds, Li+ cations reside in framework cavities. The topologies of the 3-D frameworks can be described as derivatives of the PtS (cooperite) network. [Copyright &y& Elsevier]

Abstract: Three new uranyl tungstates, A 8[(UO2)4(WO4)4(WO5)2] (A=Rb (1), Cs (2)), and Rb6[(UO2)2O(WO4)4] (3), were prepared by high-temperature solid-state reactions and their structures were solved by direct methods on twinned crystals, refined to , 0.042, and 0.052 for 1, 2, and 3, respectively. Compounds 1 and 2 are isostructural, monoclinic P21/n, (1): , , , , , and (2): , , , , , . There are four symmetrically independent U6+ sites that form linear uranyl [O=U=O]2+ cations with rather distorted coordination in their equatorial planes. There are six W positions: W(1) and W(2) have square-pyramidal coordination (WO5), whereas W(3), W(4), W(5), and W(6) are tetrahedrally coordinated. The structures are based upon a novel type of one-dimensional (1D) [(UO2)4(WO4)4(WO5)2]4− chains, consisting of WU4O25 pentamers linked by WO4 tetrahedra and WO5 square pyramids. The chains run parallel to the a-axis and are arranged in modulated pseudo-2D-layers parallel to (010). The A+ cations are in the interlayer space between adjacent pseudo-layers and provide a 3D integrity of the structures. Compounds 1 and 2 are the first uranyl tungstates with 2/3 of W atoms in tetrahedral coordination. Such a high concentration of low-coordinated W6+ cations is probably responsible for the 1D character of the uranyl tungstate units. The compound 3 is triclinic, P1¯, , , , , , , . There are four U positions in the structure with a typical coordination of a pentagonal bipyramid that contain uranyl ions, UO2 2+, as apical axes. Among eight W sites, the W(1), W(2), W(3), W(4), W(5), and W(6) atoms are tetrahedrally coordinated, whereas the W(7) and W(8) cations have distorted fivefold coordination. The structure contains chains of composition [(UO2)2O(WO4)4]6− composed of UO7 pentagonal bipyramids and W polyhedra. The chains involve dimers of UO7 pentagonal bipyramids that share common O atoms. The dimers are linked into chains by sharing corners with WO4 tetrahedra. The chains are parallel to [−101] and are arranged in layers that are parallel to (111). The Rb+ cations provide linkage of the chains into a 3D structure. The compound 1 has many structural and chemical similarities to its molybdate analog, Rb6[(UO2)2O(MoO4)4]. However, the compounds are not isostructural. Due to the tendency of the W6+ cations to have higher-than-fourfold coordination, part of the W sites adopt distorted fivefold coordination, whereas all Mo atoms in the Mo compound are tetrahedrally coordinated. Distribution of the WO5 configurations along the chain extension does not conform to its ‘typical’ periodicity. As a result, both the chain identity period and the unit-cell volume are doubled in comparison to the Mo analog, which leads to a new structure type. [Copyright &y& Elsevier]

Two new mixed organic–inorganic uranyl molybdates, (C6H14N2)3[(UO2)5(MoO4)8](H2O)4 (1) and (C2H10N2)[(UO2)(MoO4)2] (2), have been obtained by hydrothermal methods. The structure of 1 [triclinic, P1¯, Z=1, a=11.8557(9), b=11.8702(9), c=12.6746(9) A˚, α=96.734(2)°, β=91.107(2)°, γ=110.193(2)°, V=1659.1(2) A˚] has been solved by direct methods and refined on the basis of F2 for all unique reflections to R1=0.058, which was calculated for the 5642 unique observed reflections (|Fo|⩾4σF). The structure contains topologically novel sheets of uranyl square bipyramids, uranyl pentagonal bipyramids, and MoO4 tetrahedra, with composition [(UO2)5(MoO4)8]6−, that are parallel to (−101). H2O groups and 1,4-diazabicyclo [2.2.2]-octane (DABCO) molecules are located in the interlayer, where they provide linkage of the sheets. The structure of 2 [triclinic, P1¯, Z=2, a=8.4004(4), b=11.2600(5), c=13.1239(6) A˚, α=86.112(1)°, β=86.434(1)°, γ=76.544(1)°, V=1203.14(10) A˚] has been solved by direct methods and refined on the basis of F2 for all unique reflections to R1=0.043, which was calculated for 5491 unique observed reflections (|Fo|⩾4σF). The structure contains topologically novel sheets of uranyl pentagonal bipyramids and MoO4 tetrahedra, with composition [(UO2)(MoO4)2]2−, that are parallel to (110). Ethylenediamine molecules are located in the interlayer, where they provide linkage of the sheets. All known topologies of uranyl molybdate sheets of corner-sharing U and Mo polyhedra can be described by their nodal representations (representations as graphs in which U and Mo polyhedra are given as black and white vertices, respectively). Each topology can be derived from a simple black-and-white graph of six-connected black vertices and three-connected white vertices by deleting some of its segments and white vertices. [Copyright &y& Elsevier]

Five Rb uranyl molybdates have been prepared by solid-state reactions and hydrothermal syntheses. The structure of each compound has been investigated using single-crystal X-ray diffraction data collected using MoKα radiation and a Charge-Coupled-device-based area detector. The structure of Rb6[(UO2)(MoO4)4] (monoclinic, C2/c, Z=4,a=17.312(1) A˚, b=11.5285(8) A˚, c=13.916(1) A˚, β=127.634(1)°, V=2199.4(3) A˚3, R1=0.029) is based on finite clusters of composition [(UO2)(MoO4)4]6− composed of a UrO4 (Ur: UO22+ uranyl ion) tetragonal bipyramid that shares each equatorial vertex with an adjacent MoO4 tetrahedron. The structure of Rb6[(UO2)2O(MoO4)4] (triclinic, P-1, Z=2, a=10.1567(5) A˚, b=10.1816(5) A˚, c=13.1129(6) A˚, α=76.921(1)°, β=76.553(1)°, γ=65.243(1)°, V=1184.8(1) A˚3, R1=0.047) is based upon chains of composition [(UO2)2O(MoO4)4]6− containing UrO5 pentagonal bipyramids and MoO4 tetrahedra. The structure of Rb2[(UO2)(MoO4)2] (monoclinic, P21/c, Z=8, a=12.302(1) A˚, b=13.638(1) A˚, c=13.508(1) A˚, β=94.975(2)°, V=2257.8(4) A˚3, R1=0.059) contains sheets of composition [(UO2)(MoO4)2]2− involving corner-sharing UrO5 pentagonal bipyramids and MoO4 tetrahedra. The structure of Rb2[(UO2)2(MoO4)3] (orthorhombic, Pna21, Z=4, a=20.214(1) A˚, b=8.3744(4) A˚, c=9.7464(5) A˚, V=1649.9(1) A˚3, R1=0.027) consists of a framework with composition [(UO2)2(MoO4)3]2− that involves corner-sharing UrO5 pentagonal bipyramids and MoO4 tetrahedra. The structure of Rb2[(UO2)6 (MoO4)7 (H2O)2] (orthorhombic, Pbcm, Z=4, a=13.961(2) A˚, b=10.7515(16) A˚, c=25.579(4) A˚, V=3839(1) A˚3, R1=0.037) consists of a framework of corner-sharing UrO5 pentagonal bipyramids, UrO4(H2O) pentagonal bipyramids and MoO4 tetrahedra. These structures are compared to those of other uranyl molybdates. The structural diversity and variability of uranyl molybdates is related to the high degree of flexibility of the U–O–Mo linkages. [Copyright &y& Elsevier]

The compound Na 2 CaPO 4 F has at least three polymorphic modifications: monoclinic α (also known as the natural mineral nacaphite), orthorhombic β and rhombohedral γ. All three polymorphs have antiperovskite-type structures belonging to either 2 H (α and β) or 15 R (γ) polytypes. The β-phase was synthesized using CaF 2 , NaF and Na 3 PO 4 as initial reagents at 800 ​°C. Its crystal structure is orthorhombic (Pnma, a ​= ​5.3542(1), b ​= ​7.0878(2), c ​= ​12.2560(3) Å, V ​= ​465.11(3) Å3, Z ​= ​4) and based upon the chains of fluorine-centered face-sharing octahedra running along [100]. Upon heating, the β form is stable up to 640 ​°C, when it melts and, in the temperature range of 640–800 ​°C, the γ form crystallizes. Its crystal structure (rhombohedral, R 3 ¯ m , a ​= ​7.0272(3), c ​= ​40.609(2) Å, V ​= ​1736.66(18) Å3, Z ​= ​15) consists of framework based upon pentamers of face-sharing [F(Na,Ca) 6 ] octahedra connected to each other through common Na vertices. The strongest thermal expansion for both modifications is parallel to the modules of face-sharing anion-centered octahedra, whereas it is almost isotropic within the plane perpendicular to the modules. The information-theoretic structural complexity analysis points out to the possible metastable character of the β-polymorph. The proposed stability row of the Na 2 CaPO 4 F phases under ambient conditions corresponds to the following sequence: α ​> ​γ ​> ​β. This agrees well with the relations among their structural complexities, degrees of order, physical and information densities. The sequence of phase transitions α → β → γ proceeds via transitional metastable β-phase. The α → β transition is reversible and of the order-disorder type with the conservation of structural topology, whereas the β → γ transition is reconstructive and irreversible. The latter transition is associated with the transformation of the antiperovskite 2 H polytype into the 15 R polytype. The β-Na 2 CaPO 4 F transforms into γ-Na 2 CaPO 4 F in the temperature range 640–720 ​°C. The transition is not direct and involves melting of the initial phase and its re-crystallization. The crystal structure of γ-Na 2 CaPO 4 F is based on pentamers of face-sharing octahedra connected with each other through common Na1 vertices (instead of chains observed in other polymorphs). [Display omitted] • The possible metastable character of the β-polymorph is discussed on the base of the information-theoretic structural complexity analysis. • The α → β transition is reversible and has the order-disorder type, the β → γ transition is reconstructive and irreversible; • Thermal expansion of all three Na 2 CaPO 4 F polymorphs is anisotropic and has the same general features. [ABSTRACT FROM AUTHOR]

Phase formation in the mixed sulfate-selenate aqueous system of uranyl nitrate and cesium nitrate has been investigated. Two types of crystalline compounds have been obtained and characterized using a number of experimental (single crystal XRD, FTIR, SEM) and theoretical (information-based complexity calculations, topological analysis) techniques. No miscibility gaps have been observed for Cs 2 [(UO 2 ) 2 ( T O 4 ) 3 ] ( T = S, Se), which crystallizes in tetragonal system, P -42 1 m , a =9.616(1)–9.856(2), c =8.105(1)–8.159(1) Å, V =749.6(2)–792.5(3) Å 3 . Nine phases with variable amount of S and Se have been structurally characterized. The structures of the Cs 2 [(UO 2 ) 2 ( T O 4 ) 3 ] ( T = S, Se) compounds are based upon the [(UO 2 ) 2 ( T O 4 ) 3 ] 2- layers of corner-sharing uranyl pentagonal bipyramids and T O 4 tetrahedra. The layers contain two types of tetrahedral sites: T 1 (3-connected, i.e. having three O atoms shared by adjacent uranyl polyhedra) and T 2 (4-connected). The Se-for-S substitution in tetrahedral sites is highly selective with smaller S 6+ cation showing a strong preference for the more tightly bonded T 2 site. Crystallization in the pure Se system starts with the formation of Cs 2 [(UO 2 )(SeO 4 ) 2 (H 2 O)](H 2 O) crystals, its subsequent dissolution and formation of Cs 2 [(UO 2 ) 2 (SeO 4 ) 3 ]. The information-based structural complexity calculations for these two phases support the rule that more topologically complex structures form at the latest stages of crystallization. [ABSTRACT FROM AUTHOR]

Thermal expansion of Ba silicates with tetrahedrally coordinated Si atoms in the temperature range of 25–1100 °C had been studied by high-temperature X-ray powder diffraction. The volume thermal expansion coefficients (TECs) are in the range 41–50×10 −6 °C −1 with an average value of 〈 α V 〉 = 45 × 10 − 6 ° C − 1 . In the structures with chain and layered silicate anions, thermal expansion is anisotropic: the direction of maximal TEC is parallel to the extension of the zweier chains of silicate tetrahedra, which are strained owing to the interactions with Ba 2+ . The strain is released during thermal expansion due to the increasing effective size of Ba 2+ induced by thermal vibrations. Information-theoretic analysis of the structural and topological complexities of Ba silicates indicates that their structural complexity is a function of the topological complexity of their silicate anions. The latter displays a non-linear behaviour with increasing SiO 2 content (=the increasing degree of polymerization and increasing dimensionality): it starts from simple topologies, reaches a maximum at topologies of intermediate complexity, and ends up at simple topologies again. The specificity of the interactions of Ba 2+ with the silicate anions results in higher complexity of high-temperature α -BaSi 2 O 5 compared to that of low-temperature β -BaSi 2 O 5 . This uncommon behaviour may be explained by the vibrational advantages provided by flatter and more complex silicate layers in the α -phase, which overcome negative differences in configurational entropies of the two modifications apparent in the differences of their structural Shannon information. [ABSTRACT FROM AUTHOR]

High-temperature phase transition of synthetic kogarkoite, Na 3 SO 4 F, has been studied by high-temperature X-ray powder and single-crystal diffraction. The temperature of the phase transition can be estimated as 112.5±12.5 °C. The low-temperature phase, α-Na 3 SO 4 F, at 293 K, is monoclinic, P 2 1 / m , a= 18.065(3), b= 6.958(1), c= 11.446(1) Å , β= 107.711(1)°, Z =12. The structure contains thirteen symmetrically independent Na sites with coordination numbers varying from 6 to 8, and six independent S sites. The high-temperature β-phase at 423 K is rhombohedral, R- 3 m , a= 6.94(1), c= 24.58(4) Å, Z =9. The crystal structure of both polymorphs of Na 3 SO 4 F can be described as a 9 R antiperovskite polytype based upon triplets of face-sharing [FNa 6 ] octahedra linked into a three-dimensional framework by sharing corners. In the α-modification, the SO 4 tetrahedra are completely ordered and located in the framework cavities. In the β-modification, there are only two symmetrically independent Na atoms in the structure. The main difference between the structures of the α- and β-phases is the degree of ordering of the SO 4 tetrahedra: in the α-modification, they are completely ordered, whereas, in the β-modification, the complete disorder is observed, which is manifested in a number of low-occupied O sites around fully occupied S sites. The phase transition is therefore has an order–disorder character and is associated with the decrease of structural complexity measured as an information content per unit cell [577.528 bits for the low- (α) and 154.830 bits for the high- (β) temperature modifications]. [ABSTRACT FROM AUTHOR]

Abstract: Single crystals of Cs2(UO2)(CrO4)2 and Rb2(UO2)(CrO4)2 were prepared by solid state reactions. The structures are based upon the [(UO2)(CrO4)2]2− chains. Within the chains, UrO5 pentagonal bipyramids (Ur=uranyl) form Ur 2O8 dimers, which are linked via CrO4 tetrahedra into one-dimensional chains. The CrO4 tetrahedra coordinate uranyl ions in both mono- and bidentate fashion, which is unusual for uranyl chromates. The bidentate coordination has a strong influence upon geometrical parameters of both U and Cr coordination polyhedra. The conformation of the chains in 1 and 2 is different due to the different size of the Cs+ and Rb+ cations. [Copyright &y& Elsevier]

Abstract: Crystal growth experiments yielded single crystals of Sr4Ga2O7. The title compound is monoclinic, space group P1c1, , , , , , ( for 7155 observed reflections and 660 parameters). The crystals showed twinning by pseudo-merohedry. Furthermore, the diffraction data exhibited the typical features of a superstructure. Sr4Ga2O7 can be classified as a mixed anion gallate comprising insular [GaO4]-groups and [Ga3O10]-trimers. Both anion groups are located in layers perpendicular to [100]. 32 symmetrically independent Sr-cations crosslink between the tetrahedral anion groups. Alternatively, the compound can be described as a 3×4×4 superstructure of ABO3 perovskite, with 22.2% vacancies in the oxygen sublattice. The relationship with perovskite can be expressed in the following crystal chemical formula: Sr(Ga2/3Sr1/3)(O7/9□2/9)3. A discussion of the structure in the context with other similar defect perovskites in presented. [Copyright &y& Elsevier]

Single crystals of seven novel uranyl oxysalts of selenium with protonated methylamine molecules, [C 2 H 8 N] 2 [(UO 2 )(SeO 4 ) 2 (H 2 O)] ( I ), [C 2 H 8 N] 2 [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] ( II ), [C 4 H 15 N 3 ][H 3 O] 0.5 [(UO 2 ) 2 (SeO 4 ) 2.93 (SeO 3 ) 0.07 (H 2 O)](NO 3 ) 0.5 ( III ), [C 2 H 8 N] 3 [H 5 O 2 ][(UO 2 ) 2 (SeO 4 ) 3 (H 2 O) 2 ] 2 (H 2 O) 5 ( IV ), [C 2 H 8 N] 2 [H 3 O][(UO 2 ) 3 (SeO 4 ) 4 (HSeO 3 )(H 2 O)](H 2 SeO 3 ) 0.2 ( V ), [C 4 H 12 N] 3 [H 3 O][(UO 2 ) 3 (SeO 4 ) 5 (H 2 O)] ( VI ), and [C 2 H 8 N] 3 (C 2 H 7 N)[(UO 2 ) 3 (SeO 4 ) 4 (HSeO 3 )(H 2 O)] ( VII ) have been prepared by isothermal evaporation from aqueous solutions. Their crystal structures have been solved by direct methods and their uranyl selenate and selenite–selenate units investigated using black-and-white graphs from the viewpoints of topology of interpolyhedral linkages and isomeric variations. The crystal structure of IV is based upon complex layers with unique topology, which has not been observed previously in uranyl selenates. Investigations of the statistics and local distribution of the U–O br –Se bond angles demonstrates that shorter angles associate with undulations, whereas larger angles correspond to planar areas of the uranyl selenite layers. [ABSTRACT FROM AUTHOR]

Borophosphates of transition 3d metals are based on the mixed heteropolyhedral MTT - or MTTTr -type frameworks formed by M Ø 6 octahedra, two types of T Ø tetrahedra (PO 4 and BO 4 tetrahedra), and, more rarely, Tr O 3 triangles (BO 3 triangles). Family of compounds with the general formula A 1 − x + B x 2 + { M x 2 + M 1 − x 3 + [BP 2 O 8 (OH)]} (where A + ​= ​K, Rb, Cs, NH 4 , B 2+ = Ba, Pb, M 2+ ​= ​Fe, Co, Zn, and M 3+ ​= ​Al, Ga, V3+, Fe3+, Sc, In; x ​= ​0, 1) includes monoclinic (space group P 2 1 / c) and triclinic (space group P 1 ¯) borophosphates. Single crystals of Rb{V[BP 2 O 8 (OH)]} were synthesized by a hydrothermal method. The crystal structure was studied by single-crystal X-ray diffraction analysis: space group P 2 1 / c (No. 15), a ​= ​9.3699(8), b ​= ​8.3162(7), c ​= ​9.6707(8) Å, β ​= ​102.073(9); V ​= ​736.89(11) Å3. The crystal structure of Rb{V[BP 2 O 8 (OH)]} was refined to the final R ​= ​4.52%. A topological description of both structure types of the A 1 − x + B x 2 + { M x 2 + M 1 − x 3 + [BP 2 O 8 (OH)]} compounds and related vanadium-containing phases is given. Because these compounds are characterized by the microporous crystal structures, the possible migration paths for different alkaline ions have been calculated. Family of compounds with the general formula A 1 − x + B x 2 + { M x 2 + M 1 − x 3 + [BP 2 O 8 (OH)]} includes monoclinic (space group P 2 1 / c) and triclinic (space group P 1 ¯) borophosphates.A topological description of both structure types and related vanadium-containing phases is given.The possible migration paths for different alkaline ions have been calculated. [Display omitted] • A topological description of both structure types of the A 1 − x + B x 2 + { M x 2 + M 1 − x 3 + [BP 2 O 8 (OH)]} compounds and related vanadium-containing phases is given. • The possible migration paths for different alkaline ions have been calculated. [ABSTRACT FROM AUTHOR]

K[AsW2O9], prepared by high-temperature solid-state reaction, is the first member of the arsenate–tungsten bronze family. The structure of K[AsW2O9] is based on a 3-dimensional (3D) oxotungstate–arsenate framework with the non-centrosymmetric P212121 space group, a=4.9747(3)Å, b=9.1780(8) Å, c=16.681(2) Å. The material was characterized using X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Raman and infrared (IR) spectroscopic techniques. The results of DSC demonstrate that this phase is stable up to 1076K. Second harmonic generation (SHG) measurements performed on a powder sample demonstrate noticeable (0.1 of LiIO3) non-linear optical (NLO) activity. [ABSTRACT FROM AUTHOR]

Abstract: Two new bismuth phosphate halides [Bi8O8][BiO2](PO4)2Cl and [Bi8O8][BiO2](PO4)2Br, high-temperature phases have been obtained by the solid-state reaction method. Oa–Bi bonds (Oa—additional oxygen atoms not bonded to P) are the shortest and therefore the strongest in the studied structures, which makes it reasonable to consider the Bi–O substructure consisting of OBi4 tetrahedra and OBi3 triangles as an independent structural unit interacting with X atoms and PO4 tetrahedra through relatively weak Bi–X and Bi–O bonds. The topology of this oxocentered Bi–O structural unit is two-dimensional and obviously related to the [O2Bi2]2+ layer typical for the Aurivillius type compounds. The formula of the oxocentered block is ([O8Bi8][O2Bi])7+ with the first part in square brackets designating the moiety formed by the OBi4 tetrahedra, whereas the second part shows 3-coordinated O atoms and the Bi atoms not participating in the OBi4 tetrahedra. The interlayer in between the oxocentered 2D blocks is occupied by the phosphate groups and halogen atoms which are organized in alternating stripes. In the case of studied bismuth oxyphosphate halides as well as in other previously reported compounds, ‘additional’ oxygen atoms can be considered as segregation centers for Bi3+ cations. This viewpoint may appear to be useful for design of new schemes and synthetic routes to the bismuth oxysalt compounds with different structural architectures and possible useful applications. The comparison with the similar stairs-like layers in bismuth oxysalt structures is also given. [Copyright &y& Elsevier]

Cs 2 [(An O 2) 2 (T O 4) 3 ] (where An ​= ​U, Np; T ​= ​S, Se, Cr, Mo) is a remarkable family of actinide-bearing compounds due to the surprising persistence of its structure type despite the substitutions in actinide and oxyanion sites. Cesium uranyl sulfate and selenate compounds have been analysed using high-temperature powder X-ray diffraction, Raman and luminescence spectroscopy techniques; in addition, high-temperature oxide-melt calorimetry studies had been carried out to derive the enthalpies of formation of both compounds. The crystal structures of all six known isotypic compounds have been compared to reveal specific geometric parameters, which results in differences of thermal behavior and spectra. Chemical alteration in the An and T sites results in changes of the Cs+ coordination environment, which in turn leads to an increase of its influence on the layered structural units and the stability of the structure itself. These substitution mechanisms may be regarded as an example of the chemical composition selectivity for the preparation of compounds with the desired properties. The crystal chemistry review and properties of probably the most outstanding family of actinyl-bearing isotypic compounds Cs 2 [(An O 2) 2 (T O 4) 3 ] (where An ​= ​U, Np and T ​= ​S, Se, Cr, Mo), which is the only known to date example of structural type preservation with such a large diversity in chemical composition. Image 1 • Thermal behaviour of Cs uranyl sulfate and selenate was analysed. • Enthalpy of formation and luminescence properties of Cs uranyl sulfate and selenate were determined. • Crystal-chemical review of a family of Cs 2 [(An O 2) 2 (T O 4) 3 ] (An ​= ​U, Np; T ​= ​S, Se, Cr, Mo) compounds was prepared. [ABSTRACT FROM AUTHOR]