mer-Triammine trifluorido iron(III), mer-[FeF3(NH 3)3]

Article abstract of DOI:10.1515/znb-2011-0814

Metal fluorides are scarcely soluble in liquid ammonia, and their ammine complexes are rare. The synthesis and crystal structure of the first ammine complex of an iron fluoride, the mer-triammine trifluorido iron(III), mer-[FeF₃(NH₃)₃], is presented. The compound crystallizes in the form of colorless, needle-shaped single crystals in the monoclinic space group P2₁/n with Z = 4. The molecules are interconnected by strong N-H?F hydrogen bonds.

Full text of DOI:10.1515/znb-2011-0814

Note
865
Table 1. Selected bond lengths and angles of the mer-[FeF -
3
mer-Triammine Trifluorido Iron(III),
mer-[FeF (NH ) ]
(
NH ) ] molecule.
3 3
3
3 3
˚
Atoms
Distance (A)
Atoms
Angle (deg)
179.33(8)
89.87(7)
Fe(1)-F(1)
Fe(1)-F(2)
Fe(1)-F(3)
Fe(1)-N(1)
Fe(1)-N(2)
Fe(1)-N(3)
1.8981(15)
1.9088(16)
1.8988(15)
2.139(3)
F(1)-Fe(1)-F(3)
F(1)-Fe(1)-F(2)
F(3)-Fe(1)-F(2)
N(3)-Fe(1)-N(1)
N(2)-Fe(1)-N(1)
N(3)-Fe(1)-N(2)
Florian Kraus and Sebastian A. Baer
89.46(7)
AG Fluorchemie, Department Chemie,
174.95(11)
88.70(11)
87.01(10)
Technische Universit a¨ t M u¨ nchen, Lichtenbergstraße 4,
2.122(2)
2.118(3)
85747 Garching, Germany
Reprint requests to PD Dr. Florian Kraus.
Fax: +49-89-289-13762. E-mail: fluorchemie@mytum.de
Z. Naturforsch. 2011, 66b, 865 – 867;
received June 24, 2011
Metal fluorides are scarcely soluble in liquid ammonia,
and their ammine complexes are rare. The synthesis and crys-
tal structure of the first ammine complex of an iron fluoride,
the mer-triammine trifluorido iron(III), mer-[FeF (NH ) ],
3
3 3
is presented. The compound crystallizes in the form of col-
orless, needle-shaped single crystals in the monoclinic space
group P2 /n with Z = 4. The molecules are interconnected
1
by strong N–H···F hydrogen bonds.
Fig. 1. The structure of the mer-[FeF (NH ) ] molecule
3
3 3
at 150 K. Displacement ellipsoids are shown at the
0 % probability level, hydrogen atoms with arbitrary radii.
Key words: Iron, Fluoride, Ammine, Crystal Structure,
7
Liquid Ammonia
on the common 4e Wyckoff position. The iron atom
is coordinated by three symmetry-inequivalentfluoride
ions and three inequivalent nitrogen atoms of ammonia
molecules. The ligands are arranged in an octahedron-
like manner to give the meridional isomer shown in
Fig. 1. Explainable by VSEPR theory, the mer-isomer
is more stable than the fac-isomer. The Fe-F distances
Introduction
The chemistry of inorganic fluorides in liquid am-
monia is scarcely explored due to their low solubil-
ity [1]. Biltz and coworkers found a way to avoid the
solubility problem by using hydrates of fluorides and
extracting them with liquid ammonia to obtain am-
moniates [2]. The compositions of these ammoniates
were analyzed using tensieudiometric, that is, volume-
pressure measurements [3]. To our knowledge, the re-
˚
are approximately 1.9 A, the Fe-N distances are found
˚
around 2.1 A. These bond lengths agree well with stan-
dard literature data [4]. The bond angles differ only
◦
little from the ideal 90 and 180 , with the largest de-
◦
viation at 5 for the N(1)-Fe-N(3) angle. The N–H dis-
tances are found in a range from 0.78(3) to 0.89(3) A,
with H–N-H bond angles from 101(2) to 118(3) . For
˚
action of FeF with liquid ammonia has not been in-
◦
3
vestigated and we present here the first structural evi-
dence for the existence of ammine complexes of iron
fluorides.
individual bond lengths and angles see Table 1.
All hydrogen atoms are involved in N–H···F hydro-
gen bonds (Fig. 2) to nine symmetryequivalent [FeF -
3
(
NH ) ] molecules, where each fluorine atom is an ac-
3 3
Results and Discussion
ceptor of three hydrogen bonds. For details of the hy-
If moisture is completely excluded from the reaction drogen bonding see Table 2. To discuss the strength of
of FeF with liquid ammonia no reaction is observed. the encountered hydrogen bonds, a plot is used where
3
However, if the reaction vessel is not dried properly, the shortening percentage of the distance of the hydro-
FeF reacts with liquid ammonia forming the title com- gen atoms to the fluorine atoms as compared to the sum
3
pound in quantitative yield. mer-[FeF (NH ) ] crystal- of their van der Waals radii is plotted versus the devia-
3
3 3
◦
lizes in the monoclinic space group P2 /n with crystal- tion of the N–H···F angle from 180 . Strong hydrogen
1
lographic details as shown in Table 3. All atoms reside bonds with a large shortening percentage and a small
0
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866
Note
˚
Table 2. Hydrogen bond details of the title compound (A, Table 3. Crystal data and structure determination details for
a
deg) .
mer-[Fe(NH ) F ].
3 3 3
D–H
H···A
D···A
∠DHA
Formula
Mr
Crystal system
Size, mm
Fe(NH3)3F3
163.95
monoclinic
0.2×0.01×0.01
P21/n
7.3559(8)
9.5447(9)
7.7722(7)
92.009(9)
545.35(9)
4
2.00
0.71073
150
2.7
0.0596 / 0.0963
1869 / 101 / 0
0.0355 / 0.0871
0.0606 / 0.0669
0.797
N(1)-H(1A)···F(3c)
N(1)-H(1B)···F(1f)
N(1)-H(1C)···F(1h)
N(2)-H(2A)···F(2d)
N(2)-H(2B)···F(2h)
N(2)-H(2C)···F(3g)
N(3)-H(3A)···F(3d)
N(3)-H(3B)···F(1b)
N(3)-H(3C)···F(2e)
a
0.78(3) 2.34(3) 3.122(3) 175(3)
0.86(4) 2.08(4) 2.929(3) 170(3)
0.86(4) 2.28(4) 3.119(3) 163(3)
0.89(3) 2.11(3) 2.984(3) 169(3)
0.88(3) 2.01(3) 2.892(3) 175(3)
0.87(3) 2.00(3) 2.836(3) 161(3)
0.84(3) 2.09(3) 2.906(3) 165(3)
0.86(3) 2.13(3) 2.976(3) 168(3)
0.84(4) 2.07(4) 2.893(3) 168(3)
3
Space group
˚
a, A
˚
b, A
˚
c, A
β, deg
˚
3
V, A
Z
Symmetry operations as in Fig. 2.
3
ρcalc, g/cm
˚
λ, A
T, K
−
1
µ(MoKα ), mm
Rint / Rσ
Data / parameters / restraints
a
R(F) [I ≥ 2σ(I)] / all data
2
a
wR(F ) [I ≥ 2σ(I)] / all data
2
b
GoF (F , all data)
˚
−3
∆
ρmax/min, e A
0.64 / −0.58
0.0036(9)
2
Extinction
a
wR(F2)
R1(F)
=
2 1/2
ꢀFo| − |Fcꢀ/Σ|Fo|,
=
Σw(Fo
−
2
2
2
2
2
Fc ) /Σw(Fo ) ]
(
b
,
for the compound: w = [σ (Fo ) +
2
−1
2
2
0.0261P) + 0.000P]
GoF = [Σw(Fo −Fc ) /(nobs −nparam)]
,
where P = (Max(Fo ,0) + 2Fc )/3;
2
2
2
1/2
.
Fig. 2. The N–H···F hydrogen bonds (dashed) of the am-
mine ligands to adjacent, symmetry-equivalent fluoride ions
of nine other [FeF (NH ) ] molecules are projected. Dis-
3
3 3
placement ellipsoids are shown at the 70 % probability level,
hydrogen atoms with arbitrary radii. Symmetry transforma-
tions for the generation of equivalent atoms: a = 1/2 − x,
1
3
2
/2+y, 1/2−z; b = −1/2+x, 3/2−y, 1/2+z; c = 1/2+x,
/2−y, −1/2+z; d = −1/2+x, 3/2−y, −1/2+z; e = −x,
−y, 1−z; f = 1/2+x, 3/2−y, 1/2+z; g = −x 1, −y, 1−z;
h = 1/2−x, −1/2+y, 1/2−z.
◦
deviation from 180 generally appear in the upper left,
weak hydrogen bonds in the lower right corner of the
plot (Fig. 3).
Fig. 3. Plot of the shortening percentage of the H···F dis-
All hydrogen bonds of the compound show de-
◦
◦
tance as compared to the van der Waals radii of H and F,
viations from 180 of only 5 to 19 . This is a quite
narrow range, and because in reference compounds
◦
plotted versus the deviation of the N–H···F angle from 180 .
◦
The margins of error are typically within 0.7 % and 3 , re-
shortening percentages between 19 to 33% are found, spectively.
rather strong hydrogen bonds must be assumed. In
other ammine complexes of fluorides, like [BeF2- acidify the protons of the ammine ligands making
(
(
(
[
NH ) ], [Ag(NH ) ]F·2NH , [M(NH ) F ]·NH
the nitrogen atoms better H-donors. The N–H···F
3
2
=
3 2
3
3 4
4
3
M
Zr, Hf), (N H )F, (NH ) (N H )[UF - hydrogen bonding in crystals of the title compound
2 7 4 2 2 7 7
NH )],
[UF (NH ) ]·NH ,
[BF (NH )]·3NH , leads to a complex three-dimensional network of
3
4
3 4
3
3
3
3
SiF (NH ) ]·2NH , [Cs F (NH ) ], and [NH CsF ], [FeF3(NH3)3] molecules. A projection of the unit cell
4
3 2
3
3
3
3 4
4
2
a diagonal trend from the upper left to the lower right of mer-[FeF3(NH3)3] is shown in Fig. 4.
◦
is observed [5 – 10], and deviations from 180 extend
The compound mer-[FeF (NH ) ] offers the first
3 3 3
◦
well beyond 40 . These data confirm that the N–H···F structural evidence of ammine complexes of iron flu-
hydrogen bonds of the title compound are really rather orides. The strong and extensive N–H···F hydrogen
3
+
strong. This is not unexpected, as Fe must strongly bonding in the crystals lends this compound sufficient
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Note
867
Experimental Part
All work was carried out under argon (4.8, Westfalen
AG) using standard Schlenk techniques. Liquid ammonia
(
3.8, Westfalen AG) was dried and stored over sodium
◦
metal at −78 C. FeF was prepared from the reaction of
3
◦
FeCl ·6H O with 100 % F gas at 300 C. A reaction ves-
3
2
2
sel was charged with 130 mg (1.15 mmol) of FeF and, af-
3
ter evacuation, with approximately 10 mL of liquid ammo-
◦
nia at −40 C. Colorless, needle-shaped crystals suitable for
the X-ray diffraction experiment were obtained. The crys-
tals are temperature-sensitive and decrepitate at temperatures
◦
above −20 C losing ammonia. All crystals were handled
in a perfluorinated ether under nitrogen atmosphere at tem-
◦
peratures below −50 C, and mounted on the diffractometer
using the MiTeGen MicroLoop system. The structure was
solved using Direct Methods and refined on F [11, 12].
All non-hydrogen atoms were localized by Fourier cycling
methods and refined anisotropically. The hydrogen atoms
were localized by Fourier cycling methods and refined iso-
tropically.
Fig. 4. The unit cell of the title compound at 150 K. Dis-
placement ellipsoids are shown at the 70 % probability level,
hydrogen atoms with arbitrary radii.
2
stability at low temperature, but decomposition occurs
on warming.
Further details of the crystal structure investigation
are available from the FachinformationszentrumKarls-
ruhe, D-76344 Eggenstein-Leopoldshafen (Germany),
Acknowledgements
F. K. would like to thank the Fonds der Chemischen Indus-
http://www.fiz-karlsruhe.de/icsd.html, on quoting the trie for his stipend and Solvay Fluor for a continuous supply
of elemental fluorine. Deutsche Forschungsgemeinschaft is
depository number CSD 423231 for the compound, the
names of the authors, and the citation of the paper.
acknowledged for financial support.
[
[
[
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