Redetermination of the crystal structure of NaTcO4 at 100 and 296 K based on single-crystal X-ray data

German, K.E.; Grigoriev, M.S.; Garashchenko, B.L.; Kopytina, A.V.; Tyupina, E.A.

Авторы: German Konstantin E., Grigoriev Mikhail S., Garashchenko Bogdan L., Kopytina Alexander V., Tyupina Ekaterina A.
Журнал: Acta Crystallographica Section E Crystallographic Communications
Том: 73
Год издания: 2017
Издательство: International Union of Crystallography
Местоположение издательства: United Kingdom
Первая страница: 1037
Последняя страница: 1040
DOI: 10.1107/S2056989017008362
Аннотация: The redetermination of the title compound, sodium pertechnate, from single crystal CCD data recorded both at 296 and 100 K confirms previous studies based on X-ray powder diffraction film data [Schwochau (1962). Z. Naturforsch. Teil A, 17, 630; Keller & Kanellakopulos (1963). Radiochim. Acta, 1, 107–108] and neutron powder diffraction data using the Rietveld method [Weaver et al. (2017). Inorg. Chem. 12, 677–681], but reveals a considerable improvement in precision. The standard uncertainties of the room-temperature structure determination are about seven times lower than those of the neutron diffraction structure determination and about 13 times lower at 100 K, due to the decrease in the amplitude of librations. The crystal expansion could be approximated linearly with a thermal volumic expansion coefficient of 1.19 (12) 104 K1. NaTcO4 adopts the scheelite (CaWO4) structure type in space group type I41/a with Na and Tc atoms (both with site symmetry 4) replacing Ca and W atoms, respectively.The greatest distortion of the TcO4 anion from an ideal tetrahedral configuration reported by Weaver et al. (2017) is confirmed by our analysis of the O—Tc—O angles in the NaTcO4 structure, but the difference is not as high as in the model from the neutron diffraction experiment (Weaver et al., 2017). The maximum deviation values are 3.12 at 100 K and 3.08 at 296 K for the sodium salt and are larger in comparison with the potassium and rubidium salts, because the sodium cation has the smallest ionic radius compared to K+ and Rb+and hence has the highest polarizing ability. This distortion is insensitive to the temperature change from 100 K to 296 K. The packing of Na+ cations and TcO4 anions in the crystal is presented in Fig. 2. Each Na+ cation is coordinated by eightoxygen atoms that are belonging to four TcO4 anions. The resulting coordination polyhedron can be described as a distorted dodecahedron (Fig. 3). The two dihedral angles between pairs of two triangular faces sharing an edge that connects two five-edged vertices of the dodecahedron are equal to 21.2 and 30.3, respectively. The corresponding faces should form an angle of 29.5 for a dodecahedron and 0 for a square anti-prism according to the Aslanov–Porai-Koshits criterion (Porai-Koshits & Aslanov, 1972). Hence the coordination polyhedron of the sodium cation is closer to a dodecahedron than to a square anti-prism. Each of the four oxygen atoms of an individual TcO4 anion is in contact with two sodium cations, so that each TcO4 anion is directly contacted with eight sodium cations
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Redetermination of the crystal structure of NaTcO4 at 100 and 296 K based on single-crystal X-ray dataстатья

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