ISSN 1066-3622, Radiochemistry, 2018, Vol. 60, No. 5, pp. 498–506. © Pleiades Publishing, Inc., 2018. Original Russian Text © E.V. Nazarchuk, D.O. Charkin, O.I. Siidra, V.V. Gurzhiy, 2018, published in Radiokhimiya, 2018, Vol. 60, No. 5, pp. 429–435.
Synthesis and Crystal Structures of New Layered Uranyl Compounds Containing Dimers [(UO2)2O8] of Edge-Linked Pentagonal Bipyramids E. V. Nazarchuk*а, D. O. Charkinb, O. I. Siidraа, and V. V. Gurzhiyа а
Institute of Earth Sciences, St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034 Russia b Chemical Faculty, Moscow State University, Moscow, Russia *e-mail:
[email protected] Received July 27, 2017
Abstract—Two new U(VI) compounds, [((CH3)2CHNH3)(CH3NH3)][(UO2)2(CrO4)3] (1) and [CH3NH3][(UO2)· (SO4)(OH)] (2), were prepared by combining hydrothermal synthesis with isothermal evaporation. Compound 1 crystallizes in the monoclinic system, space group Р21, a = 9.3335(19), b = 10.641(2), c = 9.436(2) Å, β = 94.040(4)°. Compound 2 crystallizes in the rhombic system, space group Рbca, a = 11.5951(8), b = 9.2848(6), c = 14.5565(9) Å. The structures of the compounds were solved by the direct methods and refined to R1 = 0.041 [for 5565 reflections with Fo > 4σ(Fo)] and 0.033 [for 1792 reflections with Fo > 4σ(Fo)] for 1 and 2, respectively. Single crystal measurements were performed at 296 and 100 K for 1 and 2, respectively. The crystal structure of 1 is based on [(UO2)2(CrO4)3]2– layers, and that of 2, on [(UO2)(SO4)(OH)]– layers. Both kinds of layers are constructed in accordance with a common principle and are topologically similar. Protonated isopropylamine and methylamine molecules are arranged between the layers in 1, and protonated methylamine molecules, in 2. Compound 1 is the second known example of a U(VI) compound templated with two different organic molecules simultaneously. Keywords: uranyl compounds, crystal structure DOI: 10.1134/S1066362218050041
Interest in studying U(VI) compounds is due both to a set of problems related to reprocessing and disposal of spent nuclear fuel (SNF) and to the development of new functional materials based on depleted uranium [1]. This system is being actively studied owing to the topological diversity of U(VI) compounds and simplicity of their syntheses. A series of uranyl selenates, sulfates, molybdates, chromatres, and phosphates have been prepared and characterized; the diversity of their topologies is due, along with other factors, to the effect of the additional cations [2]. As demonstrated by the example of the uranyl chromate system [3–8], the ability of chromate complexes to polymerize significantly contributes to the topological diversity of the structures of uranium compounds. These processes are particularly pronounced in uranium compounds templated with organic molecules. The majority of the known uranium compounds with organic molecules are hybrid materials in which
organic molecules directly coordinate the uranyl ion (UO2)2+. However, there are also compounds (templated phases) in which the inorganic and organic groups are linked by weak hydrogen bonds having an important function and determining the structure of the inorganic uranium-containing complex. In these compounds, the amine molecules owing to protonation of nitrogen atoms acquire additional positive charge compensating the negative charge of inorganic structures. Layers of the general composition [(UO2)2(TO4)3· (H2O)n] (n = 0–1, T = S, Se, Cr, Mo) are a brilliant illustration of the topological diversity arising when the uranium polyhedra and TO4 tetrahedra are combined. The topology of such structures was studied using the apparatus of the graph theory [2, 9–11] and the method of anionic topologies [12, 13]. Seven topologically different types of such layers have been described by now. Five types correspond to the [(UO2)2(TO4)3· (H2O)] layer, and two types, to the [(UO2)2(TO4)3] 498
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layer. The [(UO2)2(TO4)3(H2O)] layers and one of the [(UO2)2(TO4)3] layers are formed when the uranium polyhedra and TO4 tetrahedra (T = S, Se, Cr, Mo) are combined via common vertices. The compounds based on such layers, namely, uranyl selenates [14– 16], sulfates [17–20], and chromates [21, 22], have been comprehensively studied. It is interesting that only one of the seven layers of the [(UO2)2(ТO4)3] type is built of the [(UO2)2(TO4)8]12– dimers; it was found for the first time in the structure of johannite mineral in 1982 [23]. In such layer, each dimer is built of two edge-linked uranium polyhedra incrusted by TO4 tetrahedra [24]. Here we report the synthesis and crystal structure of two new U(VI) compounds: [((CH3)2CHNH3)(CH3 · NH3)][(UO2)2(CrO4)3] (1) and [CH3NH3][(UO2)(SO4)· (OH)] (2). Both compounds are based on topologically related layers derived from [(UO2)2(CrO4)3]. Compound 1 is a second example of a U(VI) compound with complexes of TO4 tetrahedra, templated by two different organic molecules. The first compound, (C3N6H7)(CN3H6)2[(UO2)(CrO4)4]·4H2O [25], was obtained by Serezhkina et al. in 2009. In this study, the syntheis procedure was aimed at preparing a compound with two different amines, whereas in [25] the formation of two organic cations (guanidine and melamine) in the crystallization medium occurred in the course of transformation of the starting cyanoguanidine. EXPERIMENTAL Synthesis of [((CH3)2CHNH3)(CH3NH3)][(UO2)2· (CrO4)3] (1). Crystals of 1 were prepared by combination of the hydrothermal method with isothermal evaporation [26]. A Teflon capsule was charged with a mixture of 0.08 g of CrO3 (Vekton, 99.5%), 0.1 g of (UO2)(NO3)2·6H2O (Vekton, 99.7%), 0.01 mL of isopropylamine (Aldrich, 99.5%), and 5 mL of distilled water. The capsule was placed in a steel autoclave, which was heated to 90°C, kept at this temperature for 24 h, and cooled to room temperature over a period of 48 h. As a result, we obtained a yellow transparent solution. To the solution placed on a watch glass, 0.01 mL of methylamine (Aldrich, 99.5%) was added. The resulting liquid was left on the watch glass for evaporation. Green tabular crystals of 1 were formed in 3 days. Synthesis of [CH3NH3][(UO2)(SO4)(OH)] (2). Crystals of 2 were prepared by isothermal evaporation. RADIOCHEMISTRY Vol. 60 No. 5 2018
Table 1. Crystallographic parameters of [((CH3)2CHNH3)· (CH3NH3)][(UO2)2(CrO4)3] (1) and [CH3NH3][(UO2)(SO4)· (OH)] (2) Parameter Crystal system, space group a, Å b, Å c, Å β, deg V, Å3 Dx, g cm–3 Irradiation, λ, Å Crystal size, mm Diffractometer θmax, deg Range of h, k, l Number of measured/ unique reflections Rint Rsigma wR1 R1 S CCDC code
1 2 Monoclinic, P21 Rhombic, Pbca 9.3335(19) 11.5951(8) 10.641(2) 9.2848(6) 9.436(2) 14.5565(9) 94.040(4), 90 934.8(3) 1567.13(18) 3.482 3.519 MoKα, 0.71073 0.12 × 0.10 × 0.07 0.10 × 0.11 × 0.06 Bruker Kappa Apex II Duo 36.17 36.40 –13 ≤ h ≤ 15, –15 ≤ h ≤ 14, –17 ≤ k ≤17, –9 ≤ k ≤ 12, –15 ≤ l ≤ 15 –15 ≤ l ≤ 18 8394/5665 1792/1645 0.071 0.139 0.066 0.041 0.776 1 561 730
0.042 0.027 0.083 0.033 1.180 1 561 732
A mixture of 0.2 mL of 98% sulfuric acid (Aldrich, 99%), 0.05 g of uranyl nitrate [(UO2)(NO3)2·6H2O, Vekton, 99.7%], and 0.004 g of methylamine [(CH3NH2), Aldrich, 98%] was dissolved in 2 mL of distilled water. The solution was placed on a watch glass and left for evaporation at room temperature. Green plates of 2 were formed in 5 days. X-ray diffraction experiment. Single crystals of 1 and 2 selected for X-ray diffraction analysis were glued onto glass fiber and arranged in a Bruker Kappa Apex II Duo diffractometer with microfocal X-ray tube. Single crystal measurements were performed at 296 and 100 K for 1 and 2, respectively. The unit cell parameters were calculated by the least-squares method. The data were corrected for the background, Lorentz effect, and polarization effect using an empirical spherical model in Bruker APEX2 and XPREP programs [27]. The structures were solved by direct methods using the SHELX program complex [28]. The parameters of the X-ray diffraction experiment and structure refinement are given in Table 1. The final models of the compounds include the coordinates and anisotropic thermal parameters for all the atoms. The hydro-
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Table 2. Bond lengths d in the structure of 1 Bond U(1)–O(7) U(1)–O(15) Ur(1)–Oav U(1)–O(9) U(1)–O(12) U(1)–O(5) U(1)–O(6) U(1)–O(4) U(1)–Oav Cr(1)–O(11) Cr(1)–O(8) Cr(1)–O(12) Cr(1)–O(9) Cr(1)–Oav Cr(3)–O(16) Cr(3)–O(14) Cr(3)–O(6) Cr(3)–O(4) Cr(3)–Oav
d, Å 1.738(6) 1.754(7) 1.746 2.315(7) 2.351(6) 2.386(6) 2.422(6) 2.455(6) 2.350 1.595(6) 1.651(6) 1.661(7) 1.671(6) 1.644 1.587(7) 1.647(6) 1.652(7) 1.751(6) 1.659
Bond U(2)–O(10) U(2)–O(1) Ur(2)–Oav U(2)–O(2) U(2)–O(8) U(2)–O(14) U(2)–O(4) U(2)–O(5) U(2)–Oav Cr(2)–O(13) Cr(2)–O(3) Cr(2)–O(2) Cr(2)–O(5) Cr(2)–Oav
d, Å 1.745(6) 1.749(6) 1.747 2.330(6) 2.359(6) 2.397(6) 2.426(6) 2.456(6) 2.394 1.580(7) 1.582(7) 1.691(6) 1.735(6) 1.647
Table 3. Bond lengths in the structure of 2 Bond U(1)–O(1) U(1)–O(3) Ur(1)–Oav U(1)–O(2) U(1)–O(2) U(1)–O(4) U(1)–O(5) U(1)–O(6) U(1)–Oav
d, Å 1.769(6) 1.775(5) 1.772 2.355(5) 2.355(5) 2.388(5) 2.407(5) 2.392(5) 2.379
Bond S(1)–O(4)t S(1)–O(5) S(1)–O(6) S(1)–O(7) S(1)–Oav
d, Å 1.434(6) 1.492(5) 1.479(5) 1.446(5) 1.463
gen atoms are localized in the mathematically calculated positions. The structural data are filed at the СCDС database (nos. 1 561 730 and 1 561 732 for 1 and 2, respectively). The interatomic distances are given in Tables 2 and 3. RESULTS Coordination of cations. In the crystal structure of 1, there are two symmetrically independent U atoms, each of which is coordinated by two O atoms with the formation of uranyl ion (Ur) (U–Oav = 1.746 Å) (Table 2). In the equatorial plane, the U(1) and U(2) atoms are bonded with five O atoms each to form pentagonal bipyramids UrO5 [U–Oav = 2.350 and 2.394 Å for U(1) and U(2), respectively]. Three symmetrically independent Cr atoms are tetrahedrally coordinated
with four O atoms to form the CrO42– anion [Cr–Oav = 1.644, 1.647, and 1.659 Å for Cr(1), Cr(2), and Cr(3), respectively]. In the crystal structure of 2, there is one symmetrically independent U atom coordinated by two O atoms with the formation of uranyl ion (U–Oav = 1.772 Å) (Table 3). In the equatorial plane, the U atom is bonded with three O atoms and two OH groups to form a pentagonal bipyramid UrO3(OH2) (U–Oav = 2.366, U–OHav = 2.399 Å). One symmetrically independent S atom has a tetrahedral coordination (S–Oav = 1.463 Å). The local valence balance was calculated using parameters from [29] for U6+ and from [30] for Cr6+ and S6+. The valence sums are equal to 6.13 and 6.09 v.u. for U(1) and U(2) in 1 and to 5.98 v.u. for U(1) in 2. For Cr(1), Cr(2), and Cr(3) in 1, the valence sums are 6.00, 6.04, and 5.81 v.u., respectively, and for S(1) in 2, 6.20 v.u. Structure description. In the crystal structure of 1, two pentagonal bipyramids UrO5 sharing a common edge form a dimer (Ur2O8) (Fig. 1b). In the plane of the dimer, there are eight vertices to which chromate tetrahedra are bonded. As a result, the complexes [(UO2)2(CrO4)8]12– are formed. In [(UO2)2(CrO4)3]2– layers, the [(UO2)2(CrO4)8]12– groups are linked via common chromate ions. Protonated isopropylamine and methylamine molecules are arranged between the layers (Fig. 1a). The organic molecules and inorganic layers are linked with each other via a system of hydrogen bonds (Fig. 2a). In the structure of 1, protonated isopropylamine and methylamine molecules are arranged between the layers in the staggered fashion. The isopropylamine molecules link the layers into a three-dimensional structure via hydrogen bonds (Fig. 2a), and the methylamine molecules are linked to the edges of the CrO4 tetrahedra and to the O atoms of uranyl groups. The hydrophilic moiety of the isopropylamine molecule forms three bonds with the free vertices of the CrO4 tetrahedra in the uranyl chromate layers. The N(1)–H···O distances are 2.826–3.081 Å. The methylamine molecules are linked via hydrogen bonds to two free vertices of the chromate tetrahedra [N(2)–H···O = 2.848 and 3.150 Å] and two O atoms of uranyl groups [N(2)–H···O = 2.944 and 3.005 Å]. In the structure of 2, a pair of UrO3(OH2) polyhedra are combined in a dimer Ur2O6(OH)2 by sharing a common OH–OH edge (Fig. 1d). The dimers Ur2O6· (OH)2 are incrusted with six SO4 tetrahedra in such a RADIOCHEMISTRY Vol. 60 No. 5 2018
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Fig. 1. Projections of the crystal structures of (a) [((CH3)2CHNH3)(CH3NH3)][(UO2)2(CrO4)3] onto bc plane and (c) [CH3NH3]· [(UO2)(SO4)(OH)] onto ac plane; dimers in the structures of (b) 1 and (d) 2. The U polyhedra are black, and the Cr and S polyhedra are white. The U atoms are shown as large black balls; S and Cr atoms, as large white balls; O atoms, as light gray balls; N atoms, as medium-size black balls; and H atoms, as small black balls; the same for Fig. 2.
fashion that the vertices of the uranium polyhedra that are occupied by OH groups remain unshared with the sulfate tetrahedra. The resulting complexes are linked via common sulfate ions to form [(UO2)(SO4)(OH)]– layers (Fig. 3b). Protonated methylamine molecules are arranged between the layers (Fig. 2c). In the (110) plane, the amine molecules are arranged in the staggered fashion. The hydrophilic moiety of the molecule forms four hydrogen bonds with the uranyl sulfate layer (Fig. 2b): two bonds with the free vertices of the sulfate tetrahedra [N(1)–H···O(7)t = 3.031 Å], one bond with the uranyl oxygen atom [N(1)–H···O(3)Ur = 2.861 Å], and one bond with the OH group [N(1)– H···OH(2) = 2.872 Å]. The structural role of methylRADIOCHEMISTRY Vol. 60 No. 5 2018
amine molecules in 1 and 2 is different. In 1, they only incrust one of the layers of the cell, whereas in 2 they link the [(UO2)(SO4)(OH)]– layers in a threedimensional structure. DISCUSSION The layers built of dimers incrusted with TO4 tetrahedra in structures of uranium compounds are well known [31]. A total of 18 uranium compounds based on such layers have been studied (Table 4). There are three topological types of such layers (Fig. 3), corresponding to the anionic topologies 61524232, 544132-1, and 524432. Types L(1) and L(2), though corresponding
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Fig. 2. Systems of hydrogen bonds (black dashed lines) in the structures of (a) 1 and (b) 2.
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Fig. 3. Four types of layers formed by combination of the dimers via common vertices of TO4 tetrahedra. Compounds for which each type of layers is described are given in Table 4. The U polyhedra are black, and the Cr and S polyhedra are white. The anionic topology is shown for each type of layers.
to the same anionic topology 61524232, differ by one TO4 tetrahedron. In different topological types, the vertices linking the uranium polyhedra are occupied by different anions. In johannite mineral, as in the structure of 2, these sites are occupied by OH– anions [23], and in Rb(UO2)F(HPO4), by F– anions [31]. In Li2[(UO2)2(CrO4)3](H2O)7 and Zn[(UO2)2(CrO4)3]· (H2O)3 [24], as in 1, these sites are occupied by O atoms. The layers in the three latter compounds have the same anionic topology, 524432. As noted in [24], the system of hydrogen bonds between the layers and water molecules coordinating the interlayer cations
Li(H2O)+6 и Zn(H2O)62+ plays in important role in formation of such layer topology. The differences between the topological types of layers are manifested in the position of the dimers in the layer plane and in the degree of distortion of their geometry. In layers of L(1) and L(4) types, the dimers are arranged in the staggered fashion parallel to each other, and in layers of L(2) and L(3) types, at a certain angle to each other. To study the geometry of the dimer, we have measured the O(1)–O(5)–O(15) angle [Q(1)] and the angle between the equatorial planes of the uranyl polyhedra in the dimer [Q(2)] (Fig. 5). AnRADIOCHEMISTRY Vol. 60 No. 5 2018
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Table 4. Parameters of compounds with layer topologies, containing dimers Ur2O8 Formula Mg(H2O)6[(UO2)2(CrO4)2(OH)2](H2O)3 [C6N2H16][(UO2)(SO4)F]2 Rb[(UO2)(HPO4)F] Sr[(UO2)(CrO4)(OH)2](H2O)8 Cu[(UO2)2(SO4)2(OH)2](H2O)8 [CN3H6][(UO2)(MoO4)(OH)] (NH4)2[(UO2)2(CrO4)2(OH)2](H2O)3 Rb2[(UO2)2(CrO4)2(OH)2](H2O)3 Cs[(UO2)(CrO4)(OH)]H2O Rb[(UO2)(CrO4)(OH)]H2O K2[(UO2)2(CrO4)2(OH)2](H2O)3 Cs[(UO2)(HPO4)F](H2O)0.5 [CH3NH3][(UO2)(SO4)(OH)] Li2[(UO2)2(CrO4)3](H2O)7 Zn[(UO2)2(CrO4)3](H2O)9 [((CH3)2CHNH3)(CH3NH3)][(UO2)2(CrO4)3] Co(H2O)4(Co(H2O)6)2[(UO2)4(CrO4)6(OH)2](H2O)4
Symmetry Layer type Angle Q1 Cmcm L(1) 89.59 Pmmn L(1) 72.97 Cmc21 L(1) 77.30 P1¯ L(1) 81.55 P1¯ L(1) 81.70 P21/c L(1) 87.84 P21/c L(2) 72.95 P21/c L(2) 72.92 P21/c L(2) 83.14 P21/c L(2) 83.64 P21/c L(2) 73.63 Pca21 L(2) 66.81 Pbca L(2) 81.59 P21/c L(3) 57.54 P212121 L(3) 58.01 P21 L(3) 57.72 P21/n L(4) 61.54
gle Q(1) reflects the extent to which two uranium polyhedra are inclined relative to each other, and angle Q(2) reflects the extent to which the dimer plane deviates from the horizontal. Angles Q(1) and Q(2) are given in Table 4. In dimers characteristic of L(1) and L(2) layer topologies, angles Q(1) vary within 70°– 90°. The lowest values are characteristic of compounds in which the uranium coordination sphere contains fluorine, and also for a series of uranyl chromates of the general formula A2[(UO2)2(CrO4)2(OH)2](H2O)3 (A = Rb, K, NH4). For the other compounds, angles Q(1) vary in the range 80°–90°; i.e., uranyl ions are oriented virtually perpendicularly to the layer plane. This is confirmed by the scatter of angles Q(2) for these compounds (173°–180°). In the L(4) topology, compared to the L(1) and L(2) topologies, one additional tetrahedron, and in the L(3) topology, two additional tetrahedra appear. These additional tetrahedra
Angle Q2 169.86 165.18 155.86 179.87 180.00 173.09 165.53 166.43 180.00 180.00 166.41 155.01 180.00 147.75 143.18 146.68 150.96
References [24] [44] [40] [43] [21] [41] [24] [24] [24] [24] [40] [40] This work [24] [24] This work [24]
distort the geometry of the dimers. Angles Q(1) are 57°–58° and 61°, and angles Q(2), 143°–148° and 151° for L(3) and L(4) topologies, respectively. Strong distortion of the dimers in L(4) type layers is also due to the fact that the two uranium polyhedra are combined by sharing an O–OH edge. Thus, the dimers “adapt” to an increase in the number of TO4 tetrahedra by changing their geometry. Combination of the uranium polyhedra and TO4 tetrahedra via bridging О atom leads to the formation of a flexible U–O–T hinge. A study of the flexibility of the hinges on bridging O atoms shows that the polyhedral structures can compensate the external action by changing the U–O–T angle [2, 32]. Such compensation is expressed, in particular, in a broad range of U–O–T angles at the bridging O atom. In 1, the U–O–Cr angle varies within 106.8°–154.3°, and in 2, from 140.6° to
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Fig. 4. Angles measured in dimers Ur2O8: (a) Q(1), O(1)–O(5)–O(15) angle, and (b) Q(2), angle between the equatorial planes of the bipyramids. RADIOCHEMISTRY Vol. 60 No. 5 2018
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Fig. 5. Projection of layers and interlayer cations in the structures of (a) [((CH3)2CHNH3)(CH3NH3)][(UO2)2(CrO4)3], (b) Zn[(UO2)2· (CrO4)3](H2O)9, and (c) Li2[(UO2)2(CrO4)3](H2O)7 with the indicated symmetry elements.
143.7°. The methylamine molecules in 1, due to hydrogen bonds, elevate the tetrahedra over the layer plane owing to the hinge flexibility. Thus, the structural role of the two amines is different. Ten U(VI) compounds with complexes of TO4 tetrahedra, templated with isopropylamine [15, 21, 33, 34], and 11 compounds with the complexes templated
with methylamine [35–37] have been described in the literature. In the crystals of these compounds, there is a wide spectrum of topologies of the inorganic structures, from chains to complex nanostructured layers [38] and frameworks. The role of amines in the structures of these compounds can be described in terms of hydrophilic-hydrophobic interaction [15, 39]. It is interesting that selenates, sulfates, and arsenates temRADIOCHEMISTRY Vol. 60 No. 5 2018
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plated with methylamine have been reported, but no U(VI) chromates templated with methylamine are known by now. In addition, uranyl selenates contain, along with protonated methylamine, also oxonium ions [35]. Three compounds, Li2[(UO2)2(CrO4)3](H2O)7, Zn[(UO2)2(CrO4)3](H2O)9, and [(C3H10N)(CH6N)]· [(UO2)2(CrO4)3], belong to topological type L(3). The lithium uranyl chromate crystallizes in centrosymmetrical space group P21/c; the zinc compound, in space group P212121; and compound 1, in space group P21. The projections of three uranyl chromate layers onto the ab plane with the indicated symmetry elements of the space groups are shown in Fig. 5. The geometry of the arrangement of the uranyl chromate layer elements in all the three cases allows the presence of the inversion center. In lithium uranyl chromate, the inversion center is also preserved for the arrangement of the interlayer cations (Fig. 5c), in contrast to the zinc phase (Fig. 5b). In the structure of 1, isopropylamine and methylamine molecules are located between the uranyl chromate layers (Fig. 5a). Each kind of molecules forms its own centrosymmetrical system in ab plane, but superposition of these two systems leads to the loss of the inversion center. ACKNOWLEDGMENTS The study was financially supported by Russian Science Foundation (project 16-17-10 085) and Russian Federation President’s grant no. MK-6209.2016.5 (for V.V.G.) and was technically supported by the Resource Center of the St. Petersburg State University for X-ray Diffraction Methods of Investigation. REFERENCES 1. The Chemistry of the Actinide and Transactinide Elements, Morss, L.R., Edelstein, N.M., and Fuger, J., Eds., Netherlands: Springer, 2006, 3rd ed., p. 3474. 2. Structural Chemistry of Inorganic Actinide Compounds, Krivovichev, S.V., Burns, P.C., and Tananaev, I.G., Eds., Amsterdam: Elsevier, 2007, p. 494. 3. Nazarchuk, E.V., Siidra, O.I., and Kayukov, R.A., Radiochemistry, 2016, vol. 58, no. 6, pp. 571–577. 4. Siidra, O.I., Nazarchuk, E.V., Agakhanov, A.A., and Zadoy, A.I., Inorg. Chem. Commun., 2015, vol. 62, pp. 15–18. 5. Siidra, O.I., Nazarchuk, E.V., and Krivovichev, S.V., Z. Kristallogr., 2012, vol. 227, pp. 530–535. RADIOCHEMISTRY Vol. 60 No. 5 2018
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