Novel type of molecular connectivity in one-dimensional uranyl compounds: [K@(18-crown-6)(H 2 O)][(UO 2 )(SeO 4 )(NO 3 )], a new potassium uranyl selenate with 18-crown-6 ether Vladislav V. Gurzhiy a, ⁎, Olga S. Tyumentseva a , Sergey V. Krivovichev a , Ivan G. Tananaev b a Department of Crystallography, Geological Faculty, St. Petersburg State University, University Emb. 7/9, St. Petersburg 199034, Russian Federation b Frumkin Institute of Physical Chemistry and Electrochemistry RAS, Leninsky Pr. 31, Block 4, Moscow 119991, Russian Federation abstract article info Article history: Received 18 March 2014 Accepted 11 April 2014 Available online 22 April 2014 Keywords: Uranyl selenates Potassium Crown ether Crystal structure Topology Single-crystal X-ray diffraction New hybrid organic–inorganic uranyl selenate, [K(C 12 H 24 O 6 )(H 2 O)][(UO 2 )(SeO 4 )(NO 3 )] (I), has been prepared by a room-temperature evaporation from the aqueous solutions of uranyl nitrate, selenic acid, potassium nitrate and 18- crown-6 ether. The crystal structure of I [monoclinic, P2 1 /c, a = 7.2404(2), b = 21.2024(7), c = 15.7322(5) Å, β = 91.5810(10)°, V = 2414.19(13) Å 3 , Z = 4, R 1 = 0.023] is based upon the [(UO 2 )(SeO 4 )(NO 3 )] - one-dimensional uranyl nitrate–selenate chains consisting of UO 7 pentagonal bipyramids, SeO 4 tetrahedra and nitrate groups. The chains are linked to the [K@(18-crown-6)(H 2 O)] + complexes via the K + \O bonds to form a “multi-axis transporter” {[K@(18-crown-6)(H 2 O)][(UO 2 )(SeO 4 )(NO 3 )]} bands that are linked together via weak hydrogen bonds only. The infrared spectroscopy data support the structural data. © 2014 Elsevier B.V. All rights reserved. Uranyl selenate compounds display extraordinary structural and chemical diversity with more than 120 novel structures reported re- cently [1–3], most part of which are hybrid organic–inorganic compos- ites. Organic substructure is usually represented by protonated amine molecules with the wide range of shape and size of their hydrocarbon parts. Uranyl selenates templated with crown ether molecules occupy a particular place in this group due to their unique structural features that, in some case, leads to the formation of microporous frameworks and nanotubular topologies [4]. The structures of crown-ether- containing uranyl oxysalts are controlled by the relatively large size of the crown ether molecules, on one hand, and their electroneutrality, on the other. In highly acidic uranyl-selenate solutions, crown-ether molecules form [(H 3 O)@(n-crown-m-ether)] + complexes that act as large cations to compensate for the negative charge of the uranyl selenate polymeric units [4,5]. In this case, interactions between inor- ganic and organic parts of the structure are provided by hydrogen bonds that involve hydronium ions, H 3 O + . The presence of K + cations in the solution promotes formation of modulated (curved) or tubular topologies due to the fine tuning between the size of the K + ions and the ability of planar uranyl selenate units to fold around them [4,6–8]. Herein, we report on the synthesis, crystal structure and IR- spectroscopic investigations of new potassium uranyl selenate with 18-crown-6 ether molecules. Compound I was synthesized by isothermal evaporation from 5 ml of an aqueous solution of uranyl nitrate hexahydrate, selenic acid, potas- sium nitrate and 18-crown-6 ether at room-temperature conditions [9]. The crystals of I formed from the mixture after 3 days. The structure of I was analyzed by single-crystal X-ray diffraction [10] and IR spectrosco- py (Fig. 3) [11]. The band assignment shows that the vibrational spectroscopic data are in a good agreement with the composition and single-crystal X-ray diffraction results. Single-crystal X-ray diffraction analysis reveals that I crystallizes in the monoclinic P2 1 /c space group. The unit cell of I contains one sym- metrically independent U atoms with two short U 6+ _O 2 - bonds (1.760(2) and 1.763(2) Å) forming an approximately linear UO 2 2+ uranyl ion (Ur). The U(1)O 2 2+ cation is coordinated by three oxygen atoms (U1\O eq = 2.324(2)–2.343(2) Å) that belong to the selenate tetrahedra and two oxygen atoms of the nitrate groups (2.500(2) and 2.501(2) Å) that are arranged in the equatorial plane of the Ur(1)O 5 pentagonal bipyramid. One symmetrically non-equivalent Se 6+ atom is tetrahedrally coordinated by four O 2- atoms (b Se(1)\O N = 1.632 Å). The [Se(1)O 4 ] 2 - groups are tridentate, sharing three vertices with the adjacent uranium polyhedra. Non-shared vertices of the selenate tetrahedra are oriented either up or down relative to the planes of the chains. The structure of I is based upon the [(UO 2 )(SeO 4 )(NO 3 )] - uranyl selenate chains formed by linkage of the U and Se coordination polyhedra via common O atoms and arranged according to a hexagonal packing of rods along the a axis (Fig. 1a). The negative charge of the 1D uranyl Inorganic Chemistry Communications 45 (2014) 93–96 ⁎ Corresponding author. Tel.: +7 812 350 66 88; fax: +7 812 328 44 18. E-mail address: vladgeo17@mail.ru (V.V. Gurzhiy). http://dx.doi.org/10.1016/j.inoche.2014.04.012 1387-7003/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche