Reactivity of Ammonium Halides: Action of Ammonium Chloride and Bromide on Iron and Iron(III) Chloride and Bromide

Abstract Ammonium chloride and bromide, (NH 4 )Cl and (NH 4 )Br, act on elemental iron producing divalent iron in [Fe(NH 3 ) 2 ]Cl 2 and [Fe(NH 3 ) 2 ]Br 2 , respectively, as single crystals at temperatures around 450 °C. Iron(III) chloride and bromide, FeCl 3 and FeBr 3 , react with (NH 4 )Cl and (NH 4 )Br producing the erythrosiderites (NH 4 ) 2 [Fe(NH 3 )Cl 5 ] and (NH 4 ) 2 [Fe(NH 3 )Br 5 ], respectively, at fairly low temperatures (350 °C). At higher temperatures, 400 °C, iron(III) in (NH 4 ) 2 [Fe(NH 3 )Cl 5 ] is reduced to iron(II) forming (NH 4 )FeCl 3 and, further, [Fe(NH 3 ) 2 ]Cl 2 in an ammonia atmosphere. The reaction (NH 4 )Br + Fe (4:1) leads at 500 °C to the unexpected hitherto unknown [Fe(NH 3 ) 6 ] 3 [Fe 8 Br 14 ], a mixed‐valent Fe II /Fe I compound. Thermal analysis under ammonia and the conditions of DTA/TG and powder X‐ray diffractometry shows that, for example, FeCl 2 reacts with ammonia yielding in a strongly exothermic reaction [Fe(NH 3 ) 6 ]Cl 2 that at higher temperatures produces [Fe(NH 3 )]Cl 2 , FeCl 2 and, finally, Fe 3 N.