Die Kristallstrukturen der Tetrafluoromanganate(III) AMnF4 (A = K, Rb, Cs) / The Crystal Structures of the Tetrafluoromanganates(III) AMnF4 (A = K, Rb, Cs)

Abstract

The crystal structures of AMnF4 compounds (A = K, Rb, Cs) were determined by X-ray diffraction on twinned single crystals: The K and Rb compound are isostructural: space group P21/a, Z = 4; KMnF4: lattice constants a = 769.9(2), b = 764.4(2), c = 576.9(1) pm, β = 90.54(3)°; R/wR = 0.029/0.025 for 481 reflections; pseudomerohedral (100) twin. RbMnF4: lattice constants a = 782.2(5), b = 777.7(3), c = 605.0(2) pm, β = 90.83(4)°; R/wR = 0.0665/0.0513 for 471 reflections. The structure of CsMnF4 has been refined anew in the space group P4/n (Z = 4) as a merohedral (110) twin (lattice constants a = 794.40(6), c = 633.76(9) pm; R/wR = 0.051/0.044 for 820 reflections). All three structures derive from the T1A1F4 type and show puckered [MnF4]- layers with an antiferrodistortive order of strongly Jahn-Teller distorted [MnF6] octahedra. The elongated axes (Mn-F for KMnF4: 215.8, RbMnF4 215.2, CsMnF4216.8 pm) alternate with shorter ones (188.1,188.3,185.4 pm) within the layer planes. The terminal Mn-F bonds are very short (180.3, 180.6,181.7 pm). The Mn-F-Mn bridging angles are 140.6° and 146.4° for the K, 148.3° and 152.1° for the Rb, and 161.9° for the Cs compound. The magnetostructural relations and the three puckering types are discussed for all the AMnF4 layered structures.