Reactivity of Ammonium Halides:
Action of Ammonium Chloride and Bromide on Iron and Iron(III) Chloride and
Bromide
Stephan Bremm and Gerd Meyer*
Köln, Institut für Anorganische Chemie der Universität
Received December 15th, 2002.
Abstract. Ammonium chloride and bromide, (NH4)Cl and
(NH4)Br, act on elemental iron producing divalent iron in
[Fe(NH3)2]Cl2 and [Fe(NH3)2]Br2, respectively, as single crystals at
temperatures around 450 °C. Iron(III) chloride and bromide, FeCl3
and FeBr3, react with (NH4)Cl and (NH4)Br producing the
erythrosiderites (NH4)2[Fe(NH3)Cl5] and (NH4)2[Fe(NH3)Br5],
respectively, at fairly low temperatures (350 °C). At higher tempera-
tures, 400 °C, iron(III) in (NH4)2[Fe(NH3)Cl5] is reduced to iron(II)
forming (NH4)FeCl3 and, further, [Fe(NH3)2]Cl2 in an ammonia
atmosphere. The reaction (NH4)Br ϩ Fe (4:1) leads at 500 °C to
the unexpected hitherto unknown [Fe(NH3)6]3[Fe8Br14], a mixed-
valent FeII/FeI 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]Cl2 that at higher temperatures pro-
duces [Fe(NH3)]Cl2, FeCl2 and, finally, Fe3N.
Keywords: Iron; Halides; Ammonium halides; Reactivity
Reaktivität von Ammoniumhalogeniden.
Einwirkung von Ammoniumchlorid und -bromid auf Eisen und Eisen(III)-chlorid
bzw. -bromid
Inhaltsübersicht. Ammoniumchlorid und -bromid, (NH4)Cl und
(NH4)Br, wirken auf elementares Eisen unter der Bildung von zwei-
wertigem Eisen in [Fe(NH3)2]Cl2 bzw. [Fe(NH3)2]Br2 ein, die in
Form von Einkristallen bei etwa 450 °C gebildet werden. Eisen-
(III)-chlorid und -bromid, FeCl3 und FeBr3, reagieren mit (NH4)Cl
zu [Fe(NH3)2]Cl2 umgesetzt. Bei der Reaktion (NH4)Br ϩ Fe (4:1)
entsteht bei 500 °C völlig unerwartet das bislang unbekannte
[Fe(NH3)6]3[Fe8Br14], eine gemischtvalente FeII/FeI-Verbindung.
Thermische Analysen unter Ammoniak unter den Bedingungen der
DTA/TG bzw. der Pulver-Röntgen-Diffraktometrie zeigen, daß bei-
spielsweise FeCl2 zunächst mit Ammoniak in einer stark exother-
men Reaktion zu [Fe(NH3)6]Cl2 umgesetzt wird, das dann bei hö-
heren Temperaturen nacheinander [Fe(NH3)]Cl2, FeCl2 und
schließlich Fe3N bildet.
and
(NH4)Br
unter
Bildung
der
Erythrosiderite
(NH4)2[Fe(NH3)Cl5] bzw. (NH4)2[Fe(NH3)Br5] bei niedrigeren
Temperaturen (350 °C). Bei höheren Temperaturen, 400 °C, wird
Eisen(III) in (NH4)2[Fe(NH3)Cl5] in Ammoniak-Atmosphäre zu
Eisen(II) reduziert unter der Bildung von (NH4)FeCl3 und weiter
Introduction
with ammonia (NH3), together with in situ recording of
weight gain or loss and enthalpic effects (i.e., thermogravi-
metry and thermal analysis) and powder diffraction pat-
terns dependent upon temperature and/or time, respectively.
As part of our ongoing efforts [3], we have now investi-
gated the action of ammonium chloride and bromide,
(NH4)Cl and (NH4)Br, on elemental iron (Fe) and on the
iron chlorides and bromides with iron in the highest pos-
sible oxidation state ϩ3, FeCl3 and FeBr3 [4].
Ammonium halides, (NH4)X, may transform oxides or
non-noble metals to halides, for example yttria (Y2O3) or
yttrium into yttrium trichloride (YCl3) [1]. As intermedi-
ates, compounds such as (NH4)3[YCl6], (NH4)2[Sc(NH3)I5],
[Zn(NH3)2]Cl2, [Ga(NH3)(NH2)]F2 oder (NH4)6[Ta5-
(NH)4]Cl17 [2] are observed. Their isolation and charac-
terization may give important information on the reaction
pathways leading to their formation.
Further information on these systems may be obtained
through their reaction with reactive gases, most importantly
Results and Discussion
The action of ammonium chloride and bromide, (NH4)Cl
and (NH4)Br, respectively, on elemental iron and on
iron(III) chloride, FeCl3, and bromide, FeBr3, respectively,
has been investigated by preparative means in Monel am-
poules at temperatures between 350 and 500 °C. The reac-
tion products were analyzed by single crystal and powder
X-ray diffraction. Their thermal behaviour under ammonia
* Prof. Dr. G. Meyer
Institut für Anorganische Chemie
Universität zu Köln
Greinstraße 6
D-50939 Köln
Fax: 0221 470 5083
E-Mail: gerd.meyer@uni-koeln.de
Z. Anorg. Allg. Chem. 2003, 629, 1875Ϫ1880
DOI: 10.1002/zaac.200300142
2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1875