Synthese,Kristallstruktur und thermische Entwässerung von CsMnF4 · 2H2O

Synthesis, crystal structure and thermal dehydration of CsMnF₄ · 2H₂O The preparation of a new fluoromanganate (III)-complex CsMnF₄ · 2H₂O is reported. It crystallizes in the monoclinic space group C2 with a = 11.891(2) Å, b = 6.589(1) Å, c = 10.558(1) Å, β = 131.46(1)° and Z = 4. The crystal structure has been solved from diffractometer data by heavy-atom methods and refined to a conventional R-value of 1.8% (including the contributions of three hydrogen atoms in measured and one in calculated positions). The structure is characterized by isolated, tetragonally distorted MnF₄(OH₂)₂]-octahedra with Mn-F-distances from 1.801(8) Å to 1.870(7) Å and Mn-O-distances of 2.146(6) Å and 2.268(6) Å. Cesium exhibits an irregular 10-coordination by 8 F-atoms and 2 O-atoms (mean values for the two independent cesium ions: Cs-F = 3.17 Å and 3.21 Å, Cs-O = 3.32 Å and 3.29 Å). The MnF₄(OH₂)₂]-octahedra are connected to six neighbouring octahedra by hydrogen bonding. The dehydration of the complex has been studied by thermoanalytical methods and power x-ray-diffractometry. The unit cell of the dehydrated compound, CsMnF₄, is tetragonal with a = 7.936(1) Å and c = 6.341(1) Å. A close relationship to the structure of CsFeF₄, which is a superstructure variant of the T1A1F₄-type6], is indicated by the similarity of the corresponding unit cells and preliminary structure factor calculations. A proposition for the crystal structure of CsMnF₄ is developed on the basis of (2 + 2 + 2)-orthorhombic distorted MnF₆-octahedra.