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

Konstantin E German,Alexander V Kopytin,Mikhail S Grigoriev,Bogdan L Garashchenko,Ekaterina A Tyupina

doi:10.1107/s2056989017008362

Abstract

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) × 10-4 K-1. 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.

Highlights

The redetermination of the title compound, sodium pertechnate, from singlecrystal CCD data recorded both at 296 and 100 K confirms previous studies based on X-ray powder diffraction film data [Schwochau (1962)
For sodium (German et al, 1987b, 1993), potassium (German et al, 1993; Gafurov & Aliev, 2005) and caesium (Tarasov et al, 1991, 1992) tetraoxidotechnates, the existence of phase transitions was noted at high temperatures, while for the rhenium analogue, caesium tetraoxidorhenate, the ability of laserexcited second harmonic generation has been observed (Stefanovich et al, 1991)
For 99Tc into stable scheelite matrices of different compositions. Another aspect for obtaining more precise structure data on pertechnates is to clarify if pseudo-Jahn–Teller distortions of d0-tetraoxide anions really take place when compared with previous determinations (German et al, 1987a; Spitsyn et al, 1987; Tarasov et al, 1983, 1991). In this context we have reinvestigated the crystal structure of NaTcO4 that is known from powder diffraction data only, namely by inspection of its X-ray powder diffraction pattern (Schwochau, 1962; Keller & Kanellakopulos, 1963) and Rietveld refinement of neutron powder diffraction data (Weaver et al, 2017)

Summary

Introduction

The redetermination of the title compound, sodium pertechnate, from singlecrystal CCD data recorded both at 296 and 100 K confirms previous studies based on X-ray powder diffraction film data [Schwochau (1962). Vienna University of Keywords: Technetium; sodium; redetermination; crystal structure; low temperature; high precision. 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.

Results

Conclusion