Thermochemical and structural investigations on alkali metal chlorides-iron(III)-chloride systems

The pseudobinary systems ACl?FeCl₃ (A=Na, K, Rb, Cs) were reinvestigated by means of differential thermal analysis and X-ray powder diffraction. The existence of the compounds AFeCl₄ (A=Na?Cs) and Cs₃Fe₂Cl₉ could be confirmed; Cs₃Fe₂Cl₉ is a stable compound which decomposes to CsCl and CsFeCl₄ above 270°C. Additionally, two Rb-compounds—Rb₃FeCl₆ and Rb₃Fe₂Cl₉—were found, which decompose, when heated, in the solid state. Rb₃Fe₂Cl₉ is isotypic with the analogous Cs-compound; Rb₃FeCl₆ has the Cs₃BiCl₆ structure. Cs₃FeCl₆ is isotypic with Cs₃CrCl₆, a recently found orthorhombic variant of the elpasolite type.