Reactivity of ammonium halides: Action of ammonium chloride and bromide on iron and iron(III) chloride and bromide

Ammonium chloride and bromide, (NH4)Cl and (NH4)Br, act on elemental iron producing divalent iron in [Fe(NH3)(2)]Cl-2 and [Fe(NH3)(2)]Br, respectively, as single crystals at temperatures around 450 degreesC. Iron(III) chloride and bromide, FeCl3 and FeBr3, react with (NH4)Cl and (NH4)Br producing the erythrosiderites (NH4)(2)[Fe(NH3)Cl-5] and (NH4)(2)[Fe(NH3)Br-5], respectively, at fairly low temperatures (350 degreesC). At higher temperatures, 400 degreesC, iron(III) in (NH4)(2)[Fe(NH3)Cl-5] is reduced to iron(II) forming (NH4)FeCl3 and, further, [Fe(NH3)(2)]Cl-2 in an ammonia atmosphere. The reaction (NH4)Br + Fe (4:1) leads at 500 degreesC to the unexpected hitherto unknown [Fe(NH3)(6)](3)[Fe8Br14], 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, FeCl2 reacts with ammonia yielding in a strongly exothermic reaction [Fe(NH3)(6)]Cl-2 that at higher temperatures produces [Fe(NH3)(2)]Cl-2, FeCl2 and, finally, Fe3N.