Tetrakis(methylammonium) hexachloroferrate(III) chloride

The compound has the form of hygroscopic orange crystals.[2] The hexachloroferrate(III) anion is a coordination complex centred on an iron atom in the +3 oxidation state that is covalently bound to six chloride atoms arranged octahedrally around it. Interstitial chloride anions are each surrounded by four methylammonium cations, with hydrogen bond-like links between the ammonium cations and the ligands of the hexachloroferrate(III) moieties.[1] Each [(CH₃NH₃)₄Cl]³⁺ unit balances a [FeCl₆]^3–, analogous to how hexachloroferrate(III) forms stable compounds with various large triply-cationic atoms[1] and other triply-cationic complexes.[2]

The compound is synthesised by reacting methylammonium chloride, CH₃NH₃Cl, with anhydrous iron(III) chloride and adding hydrochloric acid with heating. Crystals of the product, which precipitate as the solvent evaporates, are collected and dried using vacuum desiccation.[2]

There is a series of bands from 3129 to 2830 cm⁻¹ that represent stretching modes of the nitrogen–hydrogen bonds. In addition, a distinct peak is found at 2517 cm⁻¹, whereas the corresponding signal for methylammonium chloride is at 2476 cm⁻¹.[1][3] The 31 cm⁻¹ shift is due to the coordination of an ammonium hydrogen with the hexachloroferrate(III).