Synthesis and Structural Studies of a New Potassium Uranyl Selenate K(H 5 O 2 )[(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] with Strongly Deformed Layers

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1 ISSN , Radiochemistry, 2012, Vol. 54, No. 1, pp Pleiades Publishing, Inc., Original Russian Text V.V. Gurzhiy, O.S. Tyumentseva, S.V. Krivovichev, I.G. Tananaev, B.F. Myasoedov, 2012, published in Radiokhimiya, 2012, Vol. 54, No. 1, pp Synthesis and Structural Studies of a New Potassium Uranyl Selenate K(H 5 O 2 )[(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] with Strongly Deformed Layers V. V. Gurzhiy* a,b, O. S. Tyumentseva c, S. V. Krivovichev а, I. G. Tananaev c, and B. F. Myasoedov c а Chair of Crystallography, St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, Russia; * vladgeo17@mail.ru b Chemical Faculty, St. Petersburg State University, St. Petersburg, Russia c Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russia Received October 18, 2011 Abstract Single crystals of a new uranyl selenate, K(H 5 O 2 )[(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] (I), were prepared by isothermal evaporation at room temperature. The crystal structure of I was solved by the direct method (space group P2 1 /c; a = (2), b = (1), c = (2) Å; β = (4), V = (4) Å 3 ; Z = 4) and refined to R 1 = (wr 2 = ) for 3375 reflections with F o 4σ F. The structure of I is based on layers of the composition [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] 2. The charge of the inorganic layer is compensated by potassium and oxonium ions located in the interlayer space. Each potassium ion is coordinated by seven oxygen atoms belonging to uranyl selenate layers, including uranyl oxygen atoms, which leads to bending of uranyl selenate structural elements. Keywords: potassium uranyl selenates, uranium, selenates, single crystal X-ray diffraction DOI: /S By now, more than 15 uranyl selenates with alkali metal cations (Na, K, Rb, Cs) are known [1 11]. The most interesting of them are the K-containing systems, because specifically in these systems uranyl selenate nanotubulenes of the composition [(UO 2 ) 3 (SeO 4 ) 5 ] 4 were obtained [12 14]. It was suggested in [15 17] that potassium atoms interact with uranyl selenate complexes in a specific manner, which leads to bending of these complexes up to formation of a tubular structure. At the same time, recent results of structural studies of two potassium uranyl selenates [18] showed no curvature of layered uranyl selenate complexes in structures with a high degree of hydration, which is due to additional coordination of potassium ions with water molecules. Here we report on the synthesis and structural study of a new potassium uranyl selenate, K(H 5 O 2 )[(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] (I), in which the interaction of K + cations with uranyl selenate layers leads to strong deformation of these layers. SYNTHESIS Single crystals of I were prepared by isothermal evaporation at room temperature. The crystals formed from 2 ml of an aqueous solution containing 0.05 g of UO 2 (NO 3 ) 2 6H 2 O, 0.2 ml of H 2 SeO 4, and g of KOH. After mixing and homogenization, portions of the solution were placed in a fume hood, where yellow-green platelike crystals of X-ray quality formed on the crystallizer bottoms in 4 days. X-RAY DIFFRACTION EXPERIMENT X-ray diffraction experiment was performed with a Stoe IPDS II diffractometer equipped with an X-ray sensitive plate with optical memory (Image Plate). The unit cell parameters of I (Table 1) were determined and refined using least-squares method on the basis of reflections with 2θ in the range The systematic absences and reflection distribution statistics determined space group P2 1 /с. The absorption correction was introduced using X-RED program by numerical integration taking into account the experimentally determined and optimized crystal shape by X-SHAPE algorithm [19]. The structure was solved by the direct methods and refined to R 1 = (wr 2 = ) for 3375 reflections with F o 4σ F using SHELXL-97 program [20]. The final model included the coordinates and anisotropic thermal pa- 43

2 44 GURZHIY et al. Table 1. Crystallographic data and structure refinement parameters for K(H 5 O 2 )[(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] Parameter Value a, Å (2) b, Å (1) c, Å (2) α, deg 90 β, deg (4) γ, deg 90 V, Å (4) Space group P2 1 /с μ, mm Z 4 D calc, g cm Crystal size, mm Radiation MoK α Total number of reflections Number of unique reflections θ measurement range, deg Number of reflections with F o 4σ F 3375 R int R σ R 1 ( F o 4σ F ) wr 2 ( F o 4σ F ) R 1 (all data) wr 2 (all data) S ρ min, ρ max, e/å , Note: R 1 = F o F c / F o ; wr 2 = { [w(f o F 2 c ) 2 ]/ [w(f 2 o ) 2 ]} 1/2 ; w = 1/[σ 2 (F 2 o ) + (ap) 2 + bp], where P = (F 2 o + 2F 2 c )/3; s = { [w(f 2 o F 2 c )]/(n p)} 1/2 (n is the number of reflections, and p, number of refined parameters). rameters of all the atoms (Table 2). We failed to determine the positions of H atoms. The interatomic distances are given in Table 3. Additional crystallographic data for this study can be found in ICSD These data can be retrieved free of charge from the inorganic crystal structure database, STRUCTURE DESCRIPTION In the crystal structure of K(H 5 O 2 )[(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] (Fig. 1), there are two crystallographically independent U atoms, each forming uranyl cation UO 2 2+ with two short bonds U 6+ O [1.761(9) 1.774(9) and 1.759(9) 1.766(9) Å for U(1) and U(2), respectively]. The uranyl ion is surrounded in the equatorial plane by five ligand atoms to form a pentagonal bipyramid. The U(1)O 2+ 2 cation is coordinated by five O atoms belonging to selenate groups [U O 2.380(9) 2.417(10) Å], whereas the U(2)O 2+ 2 cation shares only four O atoms Table 2. Coordinates and thermal parameters (Å 2 ) of atoms forming the structure of K(H 5 O 2 )[(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] Atom x y z U eq U(1) (4) (4) (3) (11) U(2) (4) (4) (3) (11) Se(1) (10) (12) (8) (2) Se(2) (11) (12) (10) (3) Se(3) (10) (12) (8) (2) O(1) (8) (9) (6) (19) O(2) (7) (10) (6) 0.029(2) O(3) (8) (10) (8) 0.041(3) O(4) (9) (10) (8) 0.038(2) O(5) (8) (10) (7) 0.031(2) O(6) (8) (9) (7) 0.030(2) O(7) (8) (10) (6) 0.030(2) O(8) (8) (9) (6) 0.028(2) O(9) (7) (9) (7) 0.028(2) O(10) (8) (10) (6) 0.031(2) O(11) (8) (10) (6) 0.031(2) O(12) (9) (11) (8) 0.042(3) O(13) (8) (9) (6) 0.028(2) O(14) (9) (9) (6) 0.031(2) O(15) (8) (9) (6) 0.028(2) O(16) (8) (9) (6) 0.030(2) O(17) (10) (10) (7) 0.038(2) O(18) (10) (12) (8) 0.048(3) O(19) (13) (14) (10) 0.070(4) K (3) (3) (2) (7) with the adjacent selenate polyhedra [U O 2.340(8) 2.397(9) Å] and is also coordinated by one water molecule [U(2) H 2 O(17) 2.472(10) Å]. Three crystallographically independent Se atoms have tetrahedral surrounding of O atoms. The selenate tetrahedra SeO 4 are tridentate-bridging owing to the participation of three O atoms in Se O U bonding. Forming bonds with the polyhedra of U atoms via three vertices, the selenate tetrahedra lie in the plane of the inorganic layer with the free vertices oriented upwards and downwards in the alternating fashion. The bond lengths with the bridging atoms are within 1.639(8) 1.648(9), 1.616(10) 1.650(9), and 1.629(9) 1.636(9) Å for Se(1), Se(2), and Se(3), respectively. With the terminal atoms, the bonds are shorter: 1.604(9), 1.633(11), and 1.625(9) Å for Se(1), Se(2), and Se(3), respectively. The potassium atoms and the protonated and neu-

3 SYNTHESIS AND STRUCTURAL STUDIES OF A NEW POTASSIUM URANYL SELENATE 45 tral water molecules are located in the interlayer space of I (see below). The IR spectrum of I (Fig. 2), measured in the range cm 1, is well consistent with the results of X-ray diffraction analysis. A strong band in the region of 950 cm 1 should be assigned to stretching vibrations of UO 2+ 2 cations, and a still stronger split band in the region of 850 cm 1, to stretching vibrations of SeO 2 4 anions [21, 22]. A broad band of irregular shape with a maximum in the region of 3400 cm 1 and the absorption in the region of 1600 cm 1 should be assigned to stretching and bending vibrations, respectively, of water molecules and oxonium ion. Bands with the frequencies below 500 cm 1 can belong to bending vibrations of selenate ions and stretching vibrations of equatorial U O bonds in the uranyl complex and K O bonds. The structure of I is based on layers of the composition [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] 2 formed by the coordination polyhedra of the U and Se atoms, linked via common O atoms (Fig. 3). The layers are parallel to the (001) plane and strongly bent. The bending vector is oriented along [010] and equal to the parameter b [10.231(5) Å]; the bending amplitude is about 6 Å. Analysis of the topology of the uranyl selenate layers using the graph theory [23, 24] showed that the topology of two-dimensional complexes in the structure of I belongs to type l2/3d (Fig. 3a). Such layer topology was already observed previously in uranyl selenates, e.g., in [C 4 H 14 N 2 ][(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] (H 2 O) 2 and [C 4 H 12 N] 2 [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] [25]. The structural feature of this type of layers is the presence of dense four-member rings U Se U Se (Fig. 3b) and of large hollow six-membered rings forming chains oriented along [010] by sharing common edges. The K atoms are located in the interlayer space, being associated with large hollow rings. The charge of the inorganic layer [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] 2 is compensated by potassium and oxonium ions located in the interlayer space. The oxonium ions are protonated water complexes (H 5 O 2 ) + binding uranyl selenate layers with each other by hydrogen bonds. Oxonium complexes can be identified by short O O distances between the water molecules and terminal O atoms of the polyhedra of the inorganic layer. The (H 5 O 2 ) + group is formed by the O(18) and O(19) atoms [O(18) O(19) 2.458(19) Å]. The O(18) atoms form two short bonds with the terminal O atoms of the selenate tetrahedra [O(18) O(12) 2.539(15), O(18) O(14) Table 3. Selected interatomic distances (d) and angles (ω) in the structure of K(H 5 O 2 )[(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] Bond d, Å Bond d, Å U(1) O(1) 1.761(9) Se(1) O(16) 1.604(9) U(1) O(5) 1.774(9) Se(1) O(2) 1.639(8) U(1) O(8) 2.380(9) Se(1) O(9) 1.644(9) U(1) O(11) 2.385(9) Se(1) O(8) 1.648(9) U(1) O(9) 2.394(9) Se O(av.) U(1) O(3) 2.400(10) Se(2) O(3) 1.616(10) U(1) O(4) 2.417(10) Se(2) O(4) 1.625(10) U(1) O Ur (av.) Se(2) O(12) 1.633(11) U(1) O eq (av.) Se(2) O(6) 1.650(9) U(2) O(15) 1.759(9) Se O(av.) U(2) O(10) 1.766(9) Se(3) O(14) 1.625(9) U(2) O(2) 2.340(8) Se(3) O(11) 1.629(9) U(2) O(7) 2.365(9) Se(3) O(7) 1.634(9) U(2) O(13) 2.383(9) Se(3) O(13) 1.636(9) U(2) O(6) 2.397(9) Se O(av.) U(2) O(17) 2.472(10) U(2) O Ur (av.) U(2) O eq (av.) Angle ω, deg Angle ω, deg U(1) O(8) Se(1) 130.5(5) U(2) O(2) Se(1) 142.5(5) U(1) O(9) Se(1) 130.4(5) U(2) O(6) Se(2) 137.0(5) U(1) O(4) Se(2) 134.9(6) U(2) O(7) Se(3) 135.3(5) U(1) O(3) Se(2) 154.8(7) U(2) O(13) Se(3) 136.0(5) U(1) O(11) Se(3) 134.4(5) c b Fig. 1. Crystal structure of I: projection onto (100) plane. The uranyl bipyramids and selenate tetrahedra are shown light gray and gray, respectively. The K atoms are shown gray. The O atoms of oxonium complexes are shown dark gray and cross-hatched. Dashed lines denote hydrogen bonds.

4 46 GURZHIY et al. K Fig. 2. IR spectrum of K(H 5 O 2 )[(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)]. (a) (b) Se(3) U(1) U(1) U(2) U(2) Se(3) Se(1) Se(1) Se(2) Se(2) Fig. 3. (a) Structure of the selenatouranylate layer in I and (b) graph of this layer. Fig. 4. Coordination of K atoms in the structure of I (15) Å], whereas the O(19) atoms form short bonds only with one O atom of selenate groups [O(19) O(14) 2.869(17) Å], with the second short bond formed with the uranyl oxygen atom [O(19) O(15) 2.905(16) Å]. The most interesting aspect of the structure of the compounds studied is the coordination of potassium ions (Fig. 4). The crystallographically independent K atom in the structure of I occupies the position between the polyanionic layers and is coordinated by seven O atoms with the K O distances of ~3 Å. In one layer, the K atoms are bonded with three O atoms of uranyl cations [K O(1) 2.767(10), K O(5) 2.865(10), and K O(10) 2.972(10) Å] and one terminal O atom of the selenate tetrahedron [K O(16) 2.910(10) Å]. In the second layer, the K atoms are coordinated by two terminal O atoms of the selenate tetrahedra [K O(16) 2.763(10) and K O(12) 3.020(12) Å] and one bridging O atom [K O(8) 2.888(9) Å]. The structure of I, in contrast to the structures of the two recently synthesized potassium uranyl selenates K 2 (H 5 O 2 )(H 3 O)[(UO 2 ) 2 (SeO 4 ) 4 (H 2 O) 2 ](H 2 O) 4 and K 3 (H 3 O)[(UO 2 ) 2 (SeO 4 ) 4 (H 2 O) 2 ](H 2 O) 5 [18], is based on strongly deformed bent layered complexes. The structure of I differs from those studied previously in that it contains no water molecules in the interlayer space, whereas oxonium complexes are present in all the three structures. Apparently, the presence of a large amount of water molecules in the interlayer space re-

5 SYNTHESIS AND STRUCTURAL STUDIES OF A NEW POTASSIUM URANYL SELENATE 47 duces the capability of the K atoms to form bonds with uranyl ions, which results in inhibition of the curvature of the uranyl selenate layers. For example, for I the K/(H 2 O + H 3 O + H 5 O 2 ) ratio in the interlayer space is 1/1, whereas for the compounds studied in [18] it is 1/3 and 1/2, respectively. It follows from these data that the formation of uranyl selenate nanotubulenes as final elements of layer rolling-up is controlled not only by ph of the solution (presence of protonated water complexes), but also by filling of the interlayer space and by the ratio of potassium atoms and water molecules in it. ACKNOWLEDGMENTS The study was supported by Basic Research Program no. 21 of the Presidium of the Russian Academy of Sciences Foundations of Basic Research in the Field of Nanotechnologies and Materials, by a grant from the internal budget of the St. Petersburg State University (project code ), and within the framework of implementation of the Personnel Federal Target Program (measure 1.4). REFERENCES 1. Kuchumova, N.V., Shtokova, I.P., Serezhkina, L.B., and Serezhkin, V.N., Zh. Neorg. Khim., 1989, vol. 34, no. 4, pp Mikhailov, Yu.N., Gorbunova, Yu.E., Serezhkina, L.B., et al., Zh. Neorg. Khim., 2001, vol. 46, pp Mikhailov, Yu.N., Gorbunova, Yu.E., Baeva, E.E., et al., Zh. Neorg. Khim., 2001, vol. 46, no. 12, pp Shishkina, O.V., Mikhailov, Yu.N., Gorbunova, Yu.E., et al., Dokl. Ross. Akad. Nauk, 2001, vol. 376, no. 3, pp Krivovichev, S.V. and Kahlenberg, V., Z. Anorg. Allg. Chem., 2005, vol. 631, pp Baeva, E.E., Virovets, A.V., Peresypkina, E.V., and Serezhkina, L.B., Zh. Neorg. Khim., 2006, vol. 51, pp Baeva, E.E., Virovets, A.V., Peresypkina, E.V., and Serezhkina, L.B., Zh. Neorg. Khim., 2006, vol. 51, pp Gurzhiy, V.V., Bessonov, A.A., Krivovichev, S.V., et al., Zap. Ross. Mineral. O va., 2009, vol. 138, no. 1, pp Serezhkina, L.B., Peresypkina, E.V., Virovets, A.V., et al., Kristallografiya, 2009, vol. 54, no. 1, pp Serezhkin, V.N., Verevkin, A.G., Smirnov, O.P., and Plakhtii, V.P., Zh. Neorg. Khim., 2010, vol. 55, no. 10, pp Serezhkina, L.B., Peresypkina, E.V., Virovets, A.V., et al., Kristallografiya, 2010, vol. 55, no. 3, pp Krivovichev, S.V., Kahlenberg, V., Kaindl, R., et al., Angew. Chem. Int. Ed., 2005, vol. 44, pp Krivovichev, S.V., Tananaev, I.G., Kahlenberg, V., et al., Radiokhimiya, 2005, vol. 47, no. 6, pp Alekseev, E.V., Krivovichev, S.V., and Depmeier, W., Angew. Chem. Int. Ed., 2008, vol. 47, pp Krivovichev, S.V., Eur. J. Inorg. Chem., 2010, vol. 2010, pp Krivovichev, S.V., Gurzhiy, V.V., Tananaev, I.G., and Myasoedov, B.F., Zap. Ross. Mineral. O va., special issue: Kristallogen. Mineral., 2007, pp Krivovichev, S.V., Gurzhiy, V.V., Tananaev, I.G., and Myasoedov, B.F., Actinide Nanoparticle Research, Kalmykov, S.N. and Denecke, M., Eds., Springer, Gurzhiy, V.V., Tyumentseva, O.S., Krivovichev, S.V., et al., Radiokhimiya, 2011, vol. 53, no. 6, pp Stoe & Cie, Darmstadt (Germany): Stoe & Cie GmbH, Sheldrick, G.M., Acta Crystallogr., Sect. A, 2008, vol. 64, pp Volod ko, L.V., Komyak, A.I., and Umreiko, D.S., Uranilovye soedineniya: spektry, stroenie (Uranyl Compounds: Spectra, Structure), Minsk: Bel. Gos. Univ., 1981, vol Nakamoto, K., Infrared and Raman Spectra of Inorganic and Coordination Compounds, New York: Wiley, Krivovichev, S.V., Crystallogr. Rev., 2004, vol. 10, pp Krivovichev, S.V., Structural Crystallography of Inorganic Oxysalts, Oxford: Oxford Univ. Press, Krivovichev, S.V., Gurzhiy, V.V., Tananaev, I.G., and Myasoedov, B.F., Dokl. Ross. Akad. Nauk, 2006, vol. 409, pp