Redetermination of the crystal structure of NaTcO4at 100 and 296 K based on single-crystal X-ray data

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 [Weaveret 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) × 10⁻⁴K⁻¹. NaTcO₄adopts the scheelite (CaWO₄) structure type in space group typeI4₁/awith Na and Tc atoms (both with site symmetry -4) replacing Ca and W atoms, respectively.