The Fluoroperovskite TlMnF₃

TlMnF₃ was obtained from the reduction of Tl₃MnF₆ under liquid ammonia, in which Mn^III 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) ų 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) ų. 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 T_N = 82 K and a Weiss temperature θ of –151.2(2) K.