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

Article abstract of DOI:10.1002/zaac.200300142

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 (NH ₄)Cl and (NH₄)Br producing the erythrosiderites (NH ₄)₂[Fe(NH₃)Cl₅] and (NH ₄)₂[Fe(NH₃)Br₅], respectively, at fairly low temperatures (350°C). At higher temperatures, 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 + Fe (4:1) leads at 500°C to the unexpected hitherto unknown [Fe(NH₃)₆]₃[Fe ₈Br₁₄], 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]Cl₂ that at higher temperatures produces [Fe(NH ₃)]Cl₂, FeCl₂ and, finally, Fe₃N.

Full text of DOI:10.1002/zaac.200300142

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

S. Bremm, G. Meyer
6 (NH4)2[Fe(NH3)Cl5] Ǟ 6 (NH4)FeCl3 ϩ N2 ϩ 10 (NH4)Cl ϩ 2 HCl.
At 450 °C, (NH4)FeCl3 reacts with ammonia produced by
the decomposition of (NH4)Cl to yield [Fe(NH3)2]Cl2, viz.
(NH4)FeCl3 ϩ NH3 Ǟ [Fe(NH3)2]Cl2 ϩ HCl
Under ammonia, Fe(NH3)2Cl2 is reduced further yielding
Fe3N with iron in the ϩ1 state.
1
3 [Fe(NH3)2]Cl2 Ǟ Fe3N ϩ /2 N2 ϩ 4 (NH4)Cl ϩ 2 HCl
As HCl is often one of the reaction products, these reac-
tions proceed under higher partial pressures of ammonia
and at higher temperatures.
Scheme 1 Reactions in the systems (NH4)Cl/Fe and (NH4)Cl/FeCl3:
molar ratios, temperatures and products
Bromides. In close analogy to the Fe/(NH4)Cl system,
(NH4)Br acts on elemental iron at 350 °C irrespective of the
molar ratio of 1:1 or 1:2 (Fe : (NH4)Br) to yield
(NH4)2[Fe(NH3)Br5] with iron in the ϩ3 state. At higher
temperatures (450 °C), [Fe(NH3)2]Br2 is produced.
(NH4)FeBr3 could not be detected which does not mean
that it would not play a role in the reaction pathways. At
even higher temperatures, 500 °C, and with a higher content
of (NH4)Br in the reaction mixture (Fe : (NH4)Br ϭ 1:4),
a
novel, hitherto unknown mixed-valent compound,
[Fe(NH3)6]3[Fe8Br14], appears with divalent iron in the
hexammine complex and monovalent (!) iron in the octa-
meric anion [Fe8Br14]6Ϫ. Its formation may be formulated
as follows:
18 (NH4)Br ϩ 11 Fe Ǟ [Fe(NH3)6]3[Fe8Br14] ϩ 4 HBr ϩ 7 H2
Scheme 2 Reactions in the system (NH4)Br/Fe: molar ratios, tem-
peratures and products
Another possibility would be that [Fe(NH3)2]Br2 formed at
450 °C undergoes an “internal” redox reaction such as:
was investigated by thermogravimetry and difference ther-
mal analysis (TG, DTA) and by time- and temperature-re-
solved X-ray powder diffractometry. Schemes 1 and 2 in-
form on reaction mixtures and temperatures and the prod-
ucts obtained.
33 [Fe(NH3)2]Br2 Ǟ 3 [Fe(NH3)6]3[Fe8Br14] ϩ 4 N2 ϩ 4 (NH4)Br
ϩ 20 HBr.
This would, in conclusion, mean that (NH4)2[Fe(NH3)Br5]
first produced from iron and ammonium bromide at 350 °C
undergoes an internal redox reaction at 450 °C yielding
[Fe(NH3)2]Br2, which reacts further, at 500 °C, yielding
[Fe(NH3)6]3[Fe8Br14]. Under ammonia, [Fe(NH3)2]Br2 is
stable up to 375 °C after which further reduction takes
place forming Fe3N with all iron monovalent as is the case
in the analogous system [Fe(NH3)2]Cl2 Ǟ Fe3N.
Chlorides. Elemental iron reacts with ammonium chlo-
ride in a sealed Monel container at a temperature as high as
450 °C to yield iron(II) diammine dichloride, Fe(NH3)2Cl2.
2 (NH4)Cl ϩ Fe Ǟ [Fe(NH3)2]Cl2 ϩ H2
This appears to be a key product as it is also obtained from
previously produced iron(II) chloride, FeCl2, with gaseous
ammonia. Here at ambient temperature, an exothermic re-
action takes place yielding the hexa-ammoniate,
[Fe(NH3)6]Cl2, which decomposes under an ammonia
pressure of 1 bar to [Fe(NH3)2]Cl2 at 115 °C according to
thermal analysis data. Furthermore, iron(III) chloride,
FeCl3, reacts with ammonium chloride at about 350 °C to
produce (NH4)2[Fe(NH3)Cl5], still with iron in the ϩ3 state.
At about 400 °C, iron(III) is reduced yielding (NH4)FeCl3,
probably via an “internal” redox reaction such as:
Crystal Structures
At the obviously lowest possible reaction temperatures
(350 °C), the erythrosiderites (NH4)2[Fe(NH3)Cl5] and
(NH4)2[Fe(NH3)Br5] are obtained, the first one as single
crystals. This structure, first determined for the mineral er-
ythrosiderite, K2[Fe(H2O)Cl5] [5], may be derived from the
basic K2[PtCl6] type of stucture, all well known from text-
books [6]. Tables 1 and 2 contain the crystallographic de-
tails for (NH4)2[Fe(NH3)Cl5]; Fe3ϩ-ClϪ distances are be-
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Reactivity of Ammonium Halides
Table 1 Crystallographic data and their determination for [Fe(NH3)2]Cl2, [Fe(NH3)2]Br2, NH4FeCl3, [Fe(NH3)6]3[Fe8Br14], and
(NH4)2[Fe(NH3)Cl5]
[Fe(NH3)2]Cl2
[Fe(NH3)2]Br2
(NH4)FeCl3
[Fe(NH3)6]3[Fe8Br14
]
(NH4)2[Fe(NH3)Cl5]
Lattice constants / pm
a ϭ 804.2(4)
b ϭ 799.8(5)
c ϭ 373.8(2)
240.45·106
2
a ϭ 1187.2(4)
b ϭ 592.1(1)
c ϭ 399.11(8)
280.53·106
2
a ϭ 698.4(2)
cϭ 599.6(2)
a ϭ 1069.4(1)
c ϭ 2133.5(5)
a ϭ 1372.7(2)
b ϭ 993.4(2)
c ϭ 706.1(1)
962.8·106
Cell volume / pm3
Z
253.22
2
2440.01·106
2
4
Space group
Diffractometer
Radiation
Monochromator
Temperature
Scan mode
Cmmm (Nr.65)
Stoe IPDS II
Pbam (Nr. 55)
Stoe IPDS I
P63/mmc (Nr.194)
Stoe IPDS I
MoKa. λ ϭ 71.07 pm
Graphite
20 °C
2° steps, 125 frames
I 4/mmm (Nr. 139)
Stoe IPDS I
Pnma (Nr.62)
Stoe IPDS
ϕ ϭ 0°, ω: 2° steps,
90 frames
ϕ ϭ 90°, ω: 2° steps,
87 frames
3.8 < 2θ < 70.6
160.0
2°, steps, 125 frames
2° steps, 100 frames
2° steps, 100 frames
Measured range / °
F(000)
3.8 < 2θ < 56.3
219.9
3.8 < 2θ < 56.3
176.0
3.8 < 2θ < 56.3
1911.4
3.8 < 2θ < 56.3
571.9
Absorption correction
numerical
3.90
numerical
16.77
numerical
4.19
numerical
14.34
numerical
2.89
µ/ mmϪ1
Measured reflections
Unique reflections
Rint
Structure solution and
refinement
3405
154
0.1699
3156
374
0.1661
2236
127
0.0555
11618
744
0.1209
8606
1242
0.1216
SHELXS-97 and SHELXL-97 [7]
Scattering factors
Parameters
R1
International Tables for Crystallography, Vol. C
12
17
9
41
49
0.0497 for 124
Fo > 4σ(Fo);
0.0581 for all data
0.1629
1.038
412907
0.590 for 281
Fo > 4σ(Fo);
0.0298 for 111
Fo > 4σ(Fo)
0.0459 for 457
Fo > 4σ(Fo)
0.085 for all data
0.1252
0.0449 for 644
Fo > 4σ(Fo)
0.1131 for all data
0.0970
1.009
412905
0.591 0.0795 for all data 0.0371 for all data
wR2 (all data)
Goodness of fit
CSD
0.1543
0.987
412906
0.1025
1.033
0.984
412904
412650
Table 2 Atomic positions and equivalent temperature factors in
pm2 for (NH4)2[Fe(NH3)Cl5]
Atom
Site
x
y
z
Ueq
Fe
4c
4c
8d
4c
4c
4c
8d
0.38389(9)
0.2522(2)
0.3951(1)
0.4939(2)
0.2769(2)
0.5033(5)
0.1420(3)
0.25
0.25
0.0108(1)
0.25
0.25
0.1895(2)
0.3983(3)
0.1763(2)
0.4531(3)
0.9280(3)
0.999(10)
0.1588(7)
228(3)
272(5)
317(4)
337(5)
349(6)
220(10)
350(10)
Cl1
Cl2
Cl3
Cl4
N1
N2
0.25
0.5007(5)
tween 233 and 240 pm, the Fe3ϩ-N(H3) distance is 212 pm.
The [Fe(NH3)Cl5]2- octahedra are all equal and, of course,
distorted but with ClϪ-Fe3ϩ-ClϪ angles close to 90° and the
ClϪ-Fe3ϩ-N(H3) angle almost 180°. Fig. 1 gives an im-
pression of the crystal structure of (NH4)2[Fe(NH3)Cl5].
(NH4)FeCl3 crystallizes with the hexagonal CsNiCl3/
BaNiO3 type of structure (Tables 1 and 3). Previously space
group P63mc was addressed to (NH4)FeCl3 [8]; we find no
reason for a deviation from space group P63/mmc. In the
crystal structure of (NH4)FeCl3, [FeCl6] octahedra share
common faces forming columns that run parallel to [001].
Fe2ϩ-ClϪ distances are all equal, 244.8(1) pm, Cl-Fe-Cl
angles are 86.42(4) and 93.58(4)°, respectively.
Fig.
1
Perspective view of the crystal structure of
(NH4)2[Fe(NH3)X5] (X ϭ Cl,Br), the erythrosiderite type of struc-
ture
Table 3 Atomic positions and equivalent temperature factors in
pm2 for (NH4)FeCl3
atom
site
x
y
z
Ueq
Fe
Cl
N
2a
6h
2c
0
0
0
0.25
0.75
228(6)
336(6)
470(31)
0.8400(1)
0.667
0.1600(1)
0.333
Fe(NH3)2Cl2 crystallizes with the Cd(NH3)2Cl2 type of
structure [9] with [Fe-trans-(NH3)2Cl4] octahedra sharing
opposite edges forming infinite chains that run parallel
to [001] which is in accord with the formulation
[Fe(NH3)2/1Cl4/2]. Therefore, Fe2ϩ-Fe2ϩ distances of
373.8(2) pm occur. Fe2ϩ-ClϪ distances are 254.0(2) pm and
Z. Anorg. Allg. Chem. 2003, 629, 1875Ϫ1880
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S. Bremm, G. Meyer
Table 6 Atomic positions and equivalent temperature factors in
pm2 for[Fe(NH3)6]3[Fe8Br14]
atom
site
x
y
z
Ueq
Fe1
Fe2
Fe3
Br1
Br2
Br3
N1
N2
N3
N4
16m
4d
2b
4e
8i
16m
8g
8j
4e
16n
0.1411(1)
0
0.5
0
0.2739(2)
0.26903(8)
0
0.5
0.5
0
0.1411(1)
0.5
0.5
0
0.0702(1)
0.25
0
0.1364(1)
0
0.13465(6)
0.1476(7)
0
578(7)
226(7)
219(10)
404(7)
414(5)
422(4)
473(40)
483(42)
472(58)
437(27)
0
0.26903(8)
0.5
0.704(1)
0.5
0.899(1)
0.2474(5)
0.297(1)
Fig. 2 A representation of the chain of edge-sharing [Fe(NH3)2-
Hal4/2] octahedra and perspective views of the crystal structures of
[Fe(NH3)2]Cl2 (left) and [Fe(NH3)2]Br2 (right), representatives of
the structure types of [Cd(NH3)2]Cl2 and [Mg(NH3)2]Br2
Table 4 Atomic positions and equivalent temperature factors in
pm2 for [Fe(NH3)2]Cl2
atom
site
x
y
z
Ueq
Fe
Cl
N
2b
4j
4g
0.5
0.5
0.242(1)
0
0
0.5
0
286(9)
320(10)
333(21)
0.2151(2)
0
Fig.
3
Perspective view of the crystal structure of
[Fe(NH3)6]3[Fe8Br14] and of the octameric anion [Fe8Br14]6Ϫ
therein
Table 5 Atomic positions and equivalent temperature factors in
pm2 for [Fe(NH3)2]Br2
219 pm and Fe1ϩ in tetrahedral surrounding with Fe1ϩ-BrϪ
distances of 237.4(2) and 255.7(2) (2x) and 255.8(3) pm.
Eight of these tetrahedra are connected such that an octa-
nuclear anion [Fe8Br14]6Ϫ occurs were the Fe1ϩ ions occupy
the corners of an almost undistorted cube, six bromide ions
reside as µ4 ligands above the faces of the cube and eight
additional bromide ions are terminal, in accord with the
formulation [Fe8(µ4-Br6)(µ1-Br8)]6Ϫ. These anions (Fig. 3)
are isolated from each other as are the cations
[Fe(NH3)6]2ϩ. A tetragonal body-centered crystal structure
occurs with the anions residing at the corners and in the
center of the unit cell and with the cations centering the
(001) faces and residing on the (011) faces and on the [001]
edge, as is illustrated in Fig. 3. The octameric anion is also
known from (Et4N)2[Fe8S6I8](CH2Cl2)2 [12].
atom
site
x
y
z
Ueq
Fe
Br
N
2c
4h
4g
0
0.5
0.2791(2)
0.243(2)
0
0.5
0
312(8)
317(5)
330(26)
0.1129(1)
0.8736(9)
Fe2ϩ-N(H3) distances are 207.6(9) pm. For crystallographic
details see Tables 1 and 4, for a representation of the crystal
structure Fig. 2. This compound has been well investigated
previously, see ref. [10].
Fe(NH3)2Br2 crystallizes with the [Mg(NH3)2]Br2 type of
structure [11], equally with edge-sharing [Fe-trans-
(NH3)2Br4] octahedra (Tables 1 and 5). Fe2ϩ-BrϪ and Fe2ϩ
-
NH3 distances are, of course, longer than in the chloride
analogue, 273.7(1) and 214 pm, respectively. The Fe2ϩ-Fe2ϩ
distances are also longer, 399.11(8) pm. The difference be-
tween both structures lies in the arrangement of the chains
relative to each other. These are arranged in the fashion of
a tetragonal packing of rods in [Fe(NH3)2]Cl2 and like a
hexagonal packing of rods in [Fe(NH3)2]Br2, see Fig. 2.
[Fe(NH3)6]3[Fe8Br14] exhibits a crystal structure hitherto
unobserved (Tables 1 and 6). This compound is mixed-val-
ent and contains Fe2ϩ in an octahedral surrounding of NH3
ligands with Fe2ϩ-N(H3) distances ranging from 215 to
Thermal Behaviour
The reaction of the iron(II) and iron(III) chlorides and bro-
mides, respectively, with ammonia was investigated by pow-
der temperature/time resolved X-ray diffractometry and by
simultaneous DTA/TG analysis.
Fig. 4 gives, for example, the DTA and TG curves of the
reaction of FeCl2 with ammonia. At room temperature, a
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Reactivity of Ammonium Halides
cause the successive reactions [Fe(NH3)2]Cl2 Ǟ FeCl2 Ǟ
Fe3N are too fast to be observed in the slow equilibrium
controlled X-ray experiment.
Similar reactions take place when iron(III) chloride is re-
acted with ammonia: First [Fe(NH3)6]Cl3 is produced spon-
taneously. At about 325 °C [Fe(NH3)2]Cl2 is observed,
formed by reduction of iron(III) to iron(II) and release of
ammonia. Of course, the so produced [Fe(NH3)2]Cl2 reacts
at 350 °C yielding Fe3N.
Iron(II) bromide, FeBr2, also reacts with ammonia for-
ming [Fe(NH3)6]Br2 which decomposes to Fe(NH3)2Br2 at
225 °C in the X-ray diffraction experiment under ammonia.
This first crystallizes with the [Cd(NH3)2]Cl2 type of struc-
ture and transforms to the [Mg(NH3)2]Br2 type at 375 °C.
Note that the latter structure was observed from single crys-
tals that were obtained by the action of (NH4)Br on elemen-
tal iron. [Fe(NH3)2]Br2 is finally transformed to Fe3N at
400 °C.
Fig. 4 Thermogravimetry (TG) and difference thermal analysis
(DTA) diagrams of the reaction of iron(II) chloride with ammonia
Experimental Details
spontaneous exothermic reaction takes place with the for-
mation of [Fe(NH3)6]Cl2. With increasing temperature und
an atmosphere of about 1 bar of NH3, this is gradually de-
composed to [Fe(NH3)2]Cl2 at 115 °C which loses further
ammonia at 290 °C with the binary FeCl2 formed at 360 °C
(there is one further step at about 350 °C which could be
attributed to “FeCl2(NH3)” which could not be charac-
terized further). Iron(II) chloride then reacts with ammonia
yielding the nitride Fe3N.
The same experiment, FeCl2 ϩ NH3(gas), was carried out
in the X-ray powder diffractometer (Fig. 5). There
[Fe(NH3)6]Cl2 is also produced spontaneously and crystal-
line at ambient temperature. Interestingly, Fe(NH3)2Cl2 is
only formed at 225 °C, at a much higher temperature than
in the DTA/TG experiment which may be due to a some-
what higher ammonia pressure. At about 350 °C, Fe3N is
produced. FeCl2 can not be observed, most certainly be-
Iron and ammonium chloride, (NH4)Cl, were purchased from
Merck (reinst), (NH4)Br as p.a., sublimed quality from Acros Or-
ganics, New Jersey, USA. Ammonia was 6.0 grade from Linde
(Hannover). All other chemicals used were of the highest possible
purity.
Iron trichloride, FeCl3, was produced from the elements. Reduction
with hydrogen gas at 320-340 °C yields iron dichloride, FeCl2. For
anhydrous FeBr2, iron was dissolved in conc. hydrobromic acid
solution under anaerobic conditions (argon stream) and the solvent
was removed at 100 °C under vaccum.
Ampoules made of tubing of the Monel alloy (Cu32Ni68, DIN
2.4360) were used as reaction containers. The educt mixtures were
filled within an argon dry box (M. Braun, Garching) in ampoules
that had been sealed at one end using an helium arc welder. These
were then crimped, transferred to the arc welder and sealed at the
second end. The Monel ampoules were then jacketed with silica
ampoules under a slight vacuum. They were then heated in tubular
Fig. 5 The same reaction as recorded in Fig. 4 now in the Bühler chamber of a X-ray powder diffractometer with θ-θ geometry
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 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1879

S. Bremm, G. Meyer
furnaces at chosen temperatures or featuring temperature programs
and, after cooling, opened in the argon dry box.
References
Single crystals were selected under a microspcope equipped with
polarisator/analysator in an argon dry box, and mounted in thin-
walled glass capillaries. The crystals were checked for their quality
on an image plate diffractometer IPDS (I and II, Stoe & Cie.,
Darmstadt), and intensity data sets were collected afterwards using
the same diffractometer. For details see Table 1. Further details
may be obtained from the Fachinformationszentrum Karlsruhe,
76344 Eggenstein-Leopoldshafen (FAX: (ϩ49)7247-808-666, email:
crysdata@fiz-karlsruhe.de) referring to the CSD number, the au-
thors and the journal citation.
[1] G. Meyer, T. Staffel, S. Dötsch, Th. Schleid, Inorg. Chem.
1985, 24, 3504; G. Meyer, Inorg. Synth. 1989, 25, 146.
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[3] G. Meyer, Adv. Synth. React. Solids 1994, 2, 1.
[4] S. Bremm, Dissertation, Univ. zu Köln, 2002.
[5] A. Bellanca, Ric. Sci. Ricost. 1947, 17, 1360.
[6] U. Müller, Anorganische Strukturchemie, B.G. Teubner,
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[7] G. M. Sheldrick, Programs for the solution and refinement of
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[8] M. Amit, A. Zodkevitz, J. Makovsky, Israel J. Chem. 1970,
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[9] C. H. MacGillavry, J. M. Bijvoet, Z. Kristallogr. 1936, 94, 231.
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The reaction products were also checked for their purity and their
phase content making use of a Huber Guinier diffracometer; small
powder samples were therefore filled in thin-walled glass capillaries
in the argon dry box immediately after opening the reaction con-
tainers. For reactions under ammonia the Stoe θ-θ diffracometer
equipped with a so-called Bühler camera (HDK 2.4) was used.
Thermal analysis (thermogravimetry, TG, and difference thermal
analysis, DTA) was carried out with a Mettler TA 1 where reactions
under an ammonia gas flow at a pressure of approximately 1 bar
of ammonia were possible.
Acknowledgements. This work was supported by the Deutsche For-
schungsgemeinschaft (DFG), Bonn, within the frame of the special
programme “Reaktivität von Festkörpern” (Reactivity of Solids).
We are equally grateful to the State of Nordrhein-Westfalen and
the Universität zu Köln for excellent equipment and conditions for
our research.
[12] S. Pohl, W. Saak, Angew. Chem. 1984, 96, 886; Angew. Chem.
Int. Edit. Engl. 1984, 23, 907.
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 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
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Z. Anorg. Allg. Chem. 2003, 629, 1875Ϫ1880