The Fluoroperovskite TlMnF₃

Abstract

TlMnF3 was obtained from the reduction of Tl3MnF6 under liquid ammonia, in which MnIII is obviously not redox‐stable under the applied conditions. The crystal structure of TlMnF3 was determined on a single crystal using X‐ray diffraction. The previously reported structure model was deduced from powder X‐ray diffraction data only and therefore a much higher precision has been reached now. The compound crystallizes in the shape of colorless cubes with lattice parameters a = 4.2370(4) Å, V = 76.06(2) Å3 with Z = 1 at T = 140 K in the perovskite structure type (Pm3m, no. 221). At room temperature (T = 293 K), the lattice parameter of the slightly pink, almost colorless powderous compound is a = 4.2535(2) Å, V = 76.953(4) Å3. As the displacement parameter of the Tl atom was observed being rather large in comparison to the other atoms, the CAIT technique was used to demonstrate the mobility of the Tl cations. Additionally, quantum chemical calculations were carried out to further investigate the behavior of the Tl atoms. We calculate that most of the Tl atoms vibrate already at 75 K. Magnetic measurements showed that TlMnF3 is an antiferromagnet with TN = 82 K and a Weiss temperature θ of –151.2(2) K.

Structures and Ionic Transport Properties of Perovskite-Related BIAIIX3 and BIA2IIX5 Halides

“…A better way to do so is using structure field diagrams in which the stability of perovskites and related structures are mapped according to their ionic radii quotients. This was already done by Beck et al and Schilling and Meyer, who gave a comprehensive overview of several ABX 3 − and A I B 2 II X 5 / B I A 2 II X 5 ,,,,− halides and showed the correlation of the different structure types with the ratio of the ionic radii quotients r ( A )/ r ( X ) and r ( B )/ r ( X ), as depicte...…”

“…In this structure type, the A I -cations show a CN of 9 and form tricapped trigonal prisms as coordination polyhedra. A minor decrease of the r ( A )/ r ( X ) ratio already leads to the filled PuBr 3 type ( Cmcm ), which is shown in Figure e, and where the A I -cations exhibit bicapped trigonal prisms with a further reduced CN of 8. − …”