The reactions of silver, zirconium, and hafnium fluorides with liquid ammonia: Syntheses and crystal structures of Ag(NH3) 2F·2NH3, [M(NH3)4F 4]·NH3 (M = Zr, Hf), and (N2</s

Article abstract of DOI:10.1002/ejic.200800980

By reaction of the tetrafluorides MF₄ or the ternary silver fluorides Ag₃M₂F₁₄ (M = Zr, Hf) with dry liquid ammonia at -40°C, the pentaammoniates [M(NH₃)₄F ₄]·NH₃ (1,

Full text of DOI:10.1002/ejic.200800980

FULL PAPER
DOI: 10.1002/ejic.200800980
The Reactions of Silver, Zirconium, and Hafnium Fluorides with Liquid
Ammonia: Syntheses and Crystal Structures of Ag(NH ) F·2NH ,
3
2
3
[
M(NH ) F ]·NH (M = Zr, Hf), and (N H )F
3
4 4
3
2
7
[a]
[a]
[a]
Florian Kraus,* Sebastian A. Baer, and Matthias B. Fichtl
Keywords: Fluorides / Ammonia / Hafnium / Zirconium / Silver
By reaction of the tetrafluorides MF
fluorides Ag 14 (M = Zr, Hf) with dry liquid ammonia at
40 °C, the pentaammoniates [M(NH ]·NH (1, M = Zr; 2,
M = Hf) were obtained, and these compounds represent hith-
erto unknown molecular inorganic Zr and Hf compounds that
simultaneously bear nitrogen and fluorine ligands. The com-
pounds crystallize isotypically in the shape of colorless need-
les in the tetragonal space group P4/ncc. As a further product
4
or the ternary silver
2
thesized either from AgF or AgF in liquid ammonia. The
3
M
2
F
compound crystallizes merohedrally twinned in the ortho-
rhombic space group Pnna and represents the first crystallo-
graphically characterized diamine silver(I) halide complex.
In the latter two structures, free fluoride anions are encoun-
tered. The ammoniates are highly temperature-sensitive and
decompose at temperatures above –30 °C due to their ammo-
nia pressure.
–
3
)
4
F
4
3
[
NH
4
(NH
3
)]F (3) was isolated in the form of colorless cubes
. It is the first ammoni-
F·2NH (4) can be syn-
in the orthorhombic space group Pca2
ate of ammonium fluoride. Ag(NH
1
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
3
)
2
3
Introduction
also found [NH
of ammonia.
(NH )]F as a byproduct of the oxidation
4 3
Solid fluorides in general show the highest lattice ener-
gies and hence lowest solubilities. Their solution chemistry
is quite well known in aqueous solutions, hydrofluoric acid,
Results and Discussion
[
1–5]
or anhydrous HF.
We set out to explore the reactions of
In the redox reaction of blue-violet Ag M F with liquid
ammonia, colorless crystals of [Ag(NH ) (µ-NH )Ag-
fluorides with liquid ammonia, which could yield sub-
stances like fluoride ammoniates, amine fluorides and
3
2 14
3 3
3
amide- or imide fluorides,[
6–9]
(NH ) ]MF (M = Zr, Hf) were obtained that feature Ag–
or even nitride fluorides and
3 4 6
[
6]
[10]
Ag interactions. The formal equation for this reaction can
be written as:
nitrides as the final products of these reactions. With the
exception of the nitrides, all these classes of compounds are
only scarcely known and could feature interesting proper- 2Ag M F + 32NH Ǟ
3
2
14
3
ties depending on the metal ion.
3Ag
2
MF
6
·8NH
3
+ N
2
+ 6NH
4
F + MF
4
(M = Zr, Hf)
Recently, we reported the reaction of blue-violet
Ag MF ·8NH {[Ag(NH ) (µ-NH )Ag(NH ) ]MF } was
2
6
3
3 3
3
3 4
6
Ag M F (M = Zr, Hf)[
11,12]
with liquid ammonia and es-
3
2 14
identified by single-crystal structure analysis at low tem-
tablished one product to be [Ag(NH ) (µ-NH )Ag(NH ) ]-
[6]
3
3
3
3 4
perature, the evolution of nitrogen was observed during
[6]
MF (M = Zr, Hf) featuring Ag–Ag interactions. Now we
6
the reaction, and NH F was detected by X-ray powder dif-
4
were able to identify the other products of this complex
fraction after pumping off the liquid ammonia at room
reaction by X-ray diffraction methods as M(NH ) F ·NH
3
4
4
3
temperature. However, MF could not be detected in the
4
(
1
1, M = Zr; 2, M = Hf) and [NH (NH )]F (3). Compounds
4 3
powder diffraction patterns of the reaction products; it is
and 2 can also be obtained from neat MF (M = Zr, Hf)
4
supposed that MF is produced either as an amorphous
4
in liquid NH . Mixtures of AgF or AgF /MF (M = Zr,
3
2
4
material or that ammoniates are formed. After prolonged
storage of the reaction vessel containing Ag M F and li-
Hf) in liquid ammonia gave the known product [Ag(NH ) -
3
3
3
2 14
[6]
(
µ-NH )Ag(NH ) ]MF (M = Zr, Hf), the pentaammoni-
3 3 4 6
quid NH , we isolated crystals of the pentaammoniates of
3
atesM(NH ) F ·NH (1, M=Zr;2,M=Hf)andAg(NH ) F·
3
4
4
3
3 2
MF , that is, M(NH ) F ·NH (1, M = Zr; 2, M = Hf).
4
3 4
4
3
2
NH (4). When AgF was used as the silver source we
3 2
Compounds 1 and 2 are also formed in the reaction of neat
MF with liquid ammonia within weeks.
4
[
a] Department Chemie, Technische Universität München,
Lichtenbergstr. 4, 85747 Garching
Fax: +49-89-289-13186
In the crystal structures of 1 and 2, the zirconium and
hafnium atoms occupy the Wyckoff position 4a of the space
group P4/ncc. The metal atoms show a coordination
E-mail: florian.kraus@lrz.tum.de
Eur. J. Inorg. Chem. 2009, 441–447
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
441

F. Kraus, S. A. Baer, M. B. Fichtl
FULL PAPER
number of eight in total. They are bisphenoidally coordi- Thus, the [M(NH ) F ] moieties are interconnected along
3
4 4
nated by four symmetry-equivalent fluorine atoms F(1) the ab plane diagonals (Figure 2b). The second type of hy-
(Wyckoff position 16g) and four molecules of ammonia, drogen bonds are of the N–H···N type: The solvated ammo-
with the symmetry equivalent nitrogen N(1) atoms also in nia molecule with the nitrogen N(2) atom in the 4c position
position 16g in a bisphenoidal way. The Zr–F and Hf–F acts as an acceptor of four hydrogen bonds from symmetry-
distances of 2.036(2) and 2.043(5) Å and the Zr–N and Hf– equivalent NH molecules. This interconnection leads to a
3
2
N distances of 2.397(3) and 2.383(8) Å are in accord with
[M(NH ) F ·NH ] layer parallel to the ab plane, which, in
ϱ
3 4 4 3
distances known from the literature.[ The coordination contrast to the above 2 [M(NH ) F ] layer, expands along
13]
ϱ
3 4 4
sphere of Zr and Hf is similar to a distorted square anti- the a and b axes (Figure 2c). Thus, all hydrogen atoms of
prism, whose corners are occupied by alternating ammonia the metal-bound ammonia molecules are involved in hydro-
molecules and fluorine atoms, resulting in discrete M(NH ) - gen bonding. From the N(2)···F distances of 2.994(2) Å in
3
4
F units (M = Zr, Hf; Figure 1). An additional NH mole- 1 and 2.997(6) Å in 2, N–H···F hydrogen bonding must be
4
3
3
cule with the nitrogen N(2) atom is present in the 4c posi- inferred, which leads to [N(2)···F M(NH ) ] layers parallel
ϱ
4
3 4
tion. It is 4.476(1) or 4.483(3) Å away from the Zr or Hf to the ab plane.
atom, respectively, and may thus be regarded as a solvated The overall arrangement of the components in the crys-
NH molecule. Because of the fourfold symmetry of this tals of 1 and 2 is shown in Figure 3, and the hydrogen bond
3
position, we were not able to localize the hydrogen atoms.
lengths and angles are available in the caption of Figure 2.
The M(NH ) F units are interconnected by hydrogen
bonds in two formally different ways: First, a ϱ[M- tained from mixtures of MF (M = Zr, Hf) with AgF in
The previously reported Ag MF ·8NH can also be ob-
3
4
4
2
6
3
3
4
(
NH ) F ] network is generated through N(1)–H···F hydro- liquid ammonia, but they are always formed together with
3 4 4
gen bonds. The shortest and hence strongest N–H···F hy- 1, 2, and 4. The latter, [Ag(NH ) ]F·2NH (4), can be pre-
3
2
3
1
drogen bond forms [M(NH ) F ] strands running along pared either from AgF in liquid ammonia or by a redox
ϱ
3 4 4
the c axis (Figure 2a), and the second N–H···F hydrogen reaction of AgF , which also generates 3:
2
2
bond leads to [M(NH ) F ] layers parallel to the ab plane.
ϱ
3 4 4
6
2 3
AgF + 38NH Ǟ
3 2 3 2 4 3
6[Ag(NH ) ]F·2NH (4) + N + 6[NH (NH )]F (3)
The silver(I) cation in Ag(NH ) F·2NH (4) in the Wyck-
3
2
3
off position 4a carries two symmetry-equivalent molecules
of ammonia with the nitrogen N(1) atom in position 8e of
+
space group Pnna leading to the well-known [Ag(NH ) ]
3
2
cation, which is linear by symmetry. The Ag–N distance of
.095(2) Å is reasonably shorter than the Ag–N distances
2
in [Ag(NH ) (µ-NH )Ag(NH ) ]MF (M = Zr, Hf) with
3
3
3
3 4
6
Ag–N bond lengths between 2.207(2) and 2.422(3) Å,[ as
6]
3 4 4
Figure 1. Projection of the M(NH ) F (M = Zr, Hf) unit present
in 1 and 2. Thermal ellipsoids are shown at the 70% probability
level.
a consequence of the decrease in the coordination number
+
from four to two. Other [Ag(NH ) ] complexes show sim-
3
2
Figure 2. Hydrogen bonding motifs present in 1 and 2. (a) and (b) N–H···F hydrogen bonds (dashed); (c) N–H···N hydrogen bonds. D–
H, H···A, and D···A hydrogen bond lengths [Å] and DHA angles [°] (D = Donor, A = Acceptor) for M = Zr: N(1)–H(1A)···F(1)#4 0.91,
2
.25, 3.112(4), 158.0; N(1)–H(1B)···N(2)#5 0.91, 2.46, 3.300(5), 153.0; N(1)–H(1C)···F(1)#6 0.91, 2.06, 2.955(3), 166.1. For M = Hf:
N(1)–H(1A)···F(1)#4 0.91, 2.26, 3.121(9), 157.3; N(1)–H(1B)···N(2)#5 0.91, 2.48, 3.317(11), 153.2; N(1)–H(1C)···F(1)#6 0.91, 2.07,
.959(8), 166.6. Symmetry transformations for the generation of equivalent atoms: #4 –y + 0.5, x – 1, z; #5 –x + 1, y – 0.5, –z + 0.5; #6
y + 0.5, –x + 1, –z.
2
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Reactions of Silver, Zirconium and Hafnium Fluorides with Liquid NH
3
Figure 4. The diamine silver(I) ion and its hydrogen bonding to
adjacent ammonia molecules and fluoride anions. Thermal ellip-
soids are shown at the 70% probability level. Hydrogen bonds are
shown as dashed lines. D–H, H···A, and D···A hydrogen bond
lengths [Å] and DHA angles [°] (D = Donor, A = Acceptor): N(1)–
H(1A)···F(1)#4 0.93(3), 2.00(4), 2.908(4), 166(3); N(1)–H(1B)···
N(2) 0.78(3), 2.28(3), 3.040(4), 168(4); N(1)–H(1C)···F(1)#5
.82(4), 2.12(4), 2.927(4), 168(4). N(2)–H(2A)···F(1) 0.75(5),
.40(4), 3.121(4), 162(4); N(2)–H(2B)···F(1)#6 0.90(4), 2.17(4),
Figure 3. A projection of the unit cell of 1 and 2. Thermal ellipsoids
are shown at the 70% probability level.
0
2
ilar Ag–N distances of 2.10–2.16 Å, but the Ag cation in 3.063(4), 170(3). Symmetry transformations for the generation of
equivalent atoms: #1 –x, –y, –z; #4 x – 0.5, y, –z; #5 x – 1, y, z;
these complexes is always coordinated to the anion. It is
#6 x – 0.5, y, –z + 1; #7 0.5 – x, –y, z; #8 1 – x, –y, –z.
I
notable that the Ag cation in 4 is not directly coordinated
–
to the F anion, as the nearest Ag–F distance is Ͼ4 Å and
the free ammonia molecule with the nitrogen N(2) atom is
also more than 4 Å away. All other diamine silver(I) com-
plexes found in the literature show silver···anion distances
in the range of 2.9–3.3 Å. The closest intermolecular con-
tact is between neighboring silver cations at a distance of
3.4126 Å (0.5a), which leads to silver columns along the
a axis. The Ag···Ag distance is too long for argentophilic
interactions, which are in the range of 2.9–3.2 Å, and is
close to the van der Waals distance of 3.44 Å. Compound 4
is, to the best of our knowledge, the first ammoniate of
the binary silver halides AgHal. The diaminesilver(I) cation
forms N–H···N and N–H···F hydrogen bonds to two adja-
cent ammonia molecules and to four fluoride ions with the Figure 5. Projection of the unit cell of 4 on the ab plane where the
1
+
shorter and stronger ones being of the N–H···F type (for
detailed information see the caption of Figure 4). There is
no clear distinction in the strength of the hydrogen bond
formed with the N(1) atom of the metal-bound ammonia
ϱ
[Ag(NH
3 2
) ] strands run parallel to the a axis and the eightfold
coordination of the fluoride ion by hydrogen bonding leads to
2
–
ϱ
3 8
[F(NH ) ] layers parallel to the ac plane.
molecule or the N(2) atom of the solvated ammonia mole- space group Pca2 . The nitrogen and fluorine atoms were
1
cule.
easily distinguishable by their thermal displacement param-
The fluoride ion in Wyckoff position 4d acts as an ac- eters. The N(1) atom was assignable to the nitrogen atom
ceptor of eight hydrogen bonds from four solvate ammonia of the ammonium ion and the N(2) atom to the nitrogen
+
molecules and four [Ag(NH ) ] molecules. The coordina- atom of ammonia, as the hydrogen atoms were found by
3
2
tion sphere can be best described as square-antiprismatic. difference Fourier synthesis and included into the refine-
The solvated ammonia molecule with the nitrogen N(2) ment cycles with restraints. This assignment is supported by
atom bridges two fluoride ions through hydrogen bonds the N–F distances. The N(1)–F(1) distance is 2.716(3) Å;
2
(
(
Figure 4). This hydrogen bonding formally leads to [F- whereas the N(2)–F(1) distance is 3.066(3) Å. All hydrogen
ϱ
–
1
+
NH ) ] layers parallel to the ac plane and [Ag(NH ) ]
atoms are involved in hydrogen bonding. The ammonium
3
8
ϱ
3 2
strands parallel to the a axis, as shown in Figure 5.
ion is donor of three N–H···F and one N–H···N hydrogen
A byproduct of the redox reactions of AgII with liquid bonds. The latter shows a short N(1)···N(2) distance of only
ammonia is [NH (NH )]F (3), which can also be obtained 2.890(3) Å, and the hydrogen bond is almost linear with
4
3
from finely dispersed NH F in NH after prolonged storage 172(2)°. Thus, this entity is better described as a
4
3
+
at –38 °C. NH F was said to be insoluble in liquid ammo- diaminehydrogen(1+) ion N H known from the litera-
nia. However, we obtained some single crystals immersed ture,
in a white crystalline powder (unreacted NH F), indicating 2.864(3) Å in [N H ][Li(NH ) ][P(NH )S ] and 2.69(5) Å in
4
2
7
[
14]
[15–18]
where the N···N distance is found to be
4
2
7
3 4
2
3
that NH F is sparingly soluble in ammonia. The asymmet- the cubic and 2.76(5) Å in the orthorhombic low-tempera-
4
ric unit of 3 contains two nitrogen atoms, N(1) and N(2), ture phase of [N H ]I. The H···F distances of the hydrogen
2
7
and one fluorine anion, all on the Wyckoff position 4a of bonds in 3 are about 0.2 Å shorter than the H···N distance
Eur. J. Inorg. Chem. 2009, 441–447
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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443

F. Kraus, S. A. Baer, M. B. Fichtl
FULL PAPER
with 1.97(2) Å. Detailed hydrogen bond lengths and angles
are summarized in the caption of Figure 6. The ammonia
molecule displays three N–H···F hydrogen bonds with H···F
distances in the range of 2.07 to 2.20 Å. These are 0.3 Å
longer than the H···F distances of the ammonium ion pre-
sumably due to its Coulombic interaction with the fluoride
anion.
Figure 6. (a) Hydrogen bonds of the ammonium ion. (b) Hydrogen
bonds of the solvated ammonia molecule in 3. Thermal displace-
ment parameters are shown at the 70% probability level. Hydrogen
bonds are shown as dashed lines. D–H, H···A, and D···A hydrogen
bond lengths [Å] and DHA angles [°] (D = Donor, A = Acceptor):
N(1)–H(1A)···N(2)#1 0.92(2), 1.97(2), 2.890(3), 172(2); N(1)–
H(1B)···F(1)#2 1.04(2), 1.68(2), 2.716(3), 176(3); N(1)–H(1C)···
F(1) 0.93(3), 1.79(3), 2.716(3), 173(2); N(1)–H(1D)···F(1)#3
1
3
1
.04(2), 1.66(2), 2.700(3), 174(3). N(2)–H(2A)···F(1) 1.02(3) 2.07(3)
.066(3) 165(2); N(2)–H(2B)···F(1)#4 0.97(3), 2.13(3), 3.075(3),
65(3); N(2)–H(2C)···F(1)#5 0.90(2), 2.20(2), 3.067(3), 160.6(17).
Figure 8. (a) The interconnection of fluoride and ammonium ions.
(
b) The interconnection of fluoride ions and ammonia molecules.
Symmetry transformations for the generation of equivalent atoms:
1 –x + 0.5, y + 1, z + 0.5; #2 –x + 0.5, y, z + 0.5; #3 –x, –y + 2,
#
z + 0.5; #4 –x + 0.5, y, z – 0.5, #5 –x, –y + 1, z – 0.5.
The fluoride ion, acting as an acceptor of six hydrogen
bonds, shows an almost octahedral coordination sphere
(Figure 7) with F···N distances of approximately 2.7 and
3.0 Å.
2 7
Figure 9. Projection of the unit cell of [N H ]F onto the ac plane.
Figure 7. The coordination of the fluoride ion by three ammonium
and three ammonia molecules in 3.
A comparison of the hydrogen bonds of compounds 1–
is shown in Figure 10. The H···A distance is compared
4
2
The fluoride ions form a corrugated [NH F] layer with with the sum of the van der Waals radii of the hydrogen
ϱ
4
2
–
six-membered annulated rings at z ≈ 0 and a [NH F] layer and acceptor atoms, and the percent shortening of the
ϱ
3
at z ≈ 0.5, both parallel to the ac plane (Figure 8). In total, H···A distance is calculated. This shortening is plotted
3
[19]
a [N H F] network is obtained. The unit cell of [N H ]F against the deviation of the D–H···A angle from 180°.
ϱ
2
7
2
7
is shown in Figure 9.
The strongest hydrogen bonds should show distinct short-
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Reactions of Silver, Zirconium and Hafnium Fluorides with Liquid NH
3
ening and no or little deviation from 180°. It is obvious companied by an increase in the interatomic distances. As
from the upper left plot that the strongest hydrogen bonds can be seen from Figure 10, this trend is not very clear.
are the N–H···F hydrogen bonds of the ammonium ion to First, the ammonium ion is bound stronger than the ammo-
the fluoride anion of 3, which is accountable to Coulombic nia molecule, so the distances decrease. Second, the
interaction. The other N–H···F hydrogen bonds of the ammonia···fluoride distances in 3 and 4 are not clearly dis-
+
[
NH (NH )] ion (from NH ) are weaker but are found in tinct. One N···F distance in 4 is larger than the N···F dis-
4
3
3
+
the region of metal-bound ammonia like in [Ag(NH ) ] in tances in 3, but another N···F distance in 4 is almost in the
3
2
4
or the strongest hydrogen bonds in 1 and 2. These data same range as that in 3. More data on such fluorides need
reveal that N–H···F hydrogen bonds are stronger than N– to be collected for a better evaluation.
H···N hydrogen bonds within the same compound. This
also holds true for [N H ]F, where the N–H···N hydrogen
2
7
bond is shorter than usual for this type of interaction.
Metal-bound fluorine atoms are expected to be weaker hy-
drogen-bond acceptors. This is confirmed here and is also
Conclusions
The solid-state fluorides ZrF and HfF crystallize iso-
4
4
found in [Ag(NH ) (µ-NH )Ag(NH ) ]MF (M = Zr, typically in the UF structure with the monoclinic space
3
3
3
3 4
6
4
[
6]
Hf), where the hydrogen bonds do not seem to reach group C2/c, where eight fluorine atoms coordinate to the
shortenings above 35%. A comparison of the N–H···N hy- central metal atom in a square-antiprismatic fashion. The
drogen bonds shows them to span the region from 25 to square antiprisms are interconnected by sharing all corners.
1
0% shortening and an angle range of 12 to 45° with the These fluorides are soluble in liquid ammonia and form the
+
exception of the N H ion, which shows stronger N–H···N pentaammoniates [M(NH ) F ]·NH (1, M = Zr; 2, M =
2
7
3 4
4
3
hydrogen bonding. By comparison with results on the am- Hf). Such ammoniates should also be obtainable for the
[
19–22]
monium–ammonia system obtained by Korber et al.,
other isotypic tetrafluorides CeF , ThF , NpF , PuF ,
4 4 4 4
it becomes obvious that none of the N–H···N hydrogen CmF , and UF , which are already under investigation. The
4
4
bonds shows a shortening of more than 35%. Thus, this square-antiprismatic coordination sphere is also observed
region might be exclusive for ammonium···fluoride interac- in the products M(NH ) F . Ammonia as a softer Lewis
3
4 4
tions.
base than fluoride seems to be strong enough to substitute
4+
the hard fluoride ions on the presumably hard Zr and
4+
Hf ions, and the large excess of liquid ammonia shifts the
equilibrium of the reaction
MF + 5NH h [M(NH ) F ]·NH
4
3
3 4
4
3
to the product side. This may offer the chance for the syn-
thesis of compounds like amide fluorides like [M(NH3)4–x
NH ) F4–x] (x = 1, 2, or 3) imide fluorides, nitride fluo-
-
(
2
x
rides, and finally nitrides. Compounds 1 and 2 are the first
molecular inorganic molecules where Zr and Hf are simul-
taneously coordinated by nitrogen and fluorine ligands.
AgF dissolves easily in liquid ammonia, and its ammoni-
ate [Ag(NH ) ]F·2NH (4) is obtained. It is interesting to
3
2
3
note that only the diaminesilver(I) cation and not higher
amine complexes as in [Ag(NH ) (µ-NH )Ag(NH ) ]MF
3
3
3
3 4
6
are obtained. This finding might be due to the size of the
anion, as larger anions favor the assembly of larger cations
and vice versa. With a silver···fluoride distance of Ͼ4 Å,
Figure 10. A plot of hydrogen bond strength in compounds 1–4. the silver cation is not coordinated by the anion, which is
N–H···N hydrogen bonds are shown in black, N–H···F hydrogen the case in several other diaminesilver(I) complexes with
bonds in grey. Hydrogen bonds of 1 are represented by triangles,
nitrate or sulfate counterions, where the silver···anion dis-
those of 2 by circles, those of 3 by diamonds, and those of 4 by
tance is in the range of 2.9–3.3 Å. To the best of our knowl-
squares. The margins of error are typically within 0.7% and 3°.
edge, compound 4 represents the first ammoniate of a silver
A comparison of the coordination numbers and spheres halide characterized by single-crystal X-ray analysis.
of the encountered not metal-bound fluoride ions shows
NH F seems to be sparingly soluble in liquid ammonia,
4
that they can be an acceptor of eight hydrogen bonds form- as the ammoniate [NH (NH )]F (3) is obtained after reac-
4
3
ing a square antiprism as in 4 or of six hydrogen bonds tion times of several weeks. It is also available through the
II
forming an octahedron as in 3. Free, that is, not directly reactive fluoride route by using Ag as an oxidizing agent,
metal-bound fluoride ions, are found in (NH ) SiF ·NH F but in this case, it is obtained together with compound 4.
4
2
6
4
and other compounds,[
23–25]
where the fluoride ion is octa- Of the other halides, only the ammoniates (NH )X·3NH3
4
hedrally coordinated by potassium ions in a distance range (X = Cl, Br, I), [NH (NH )]I, and NH I·4NH are
4
3
4
3
[
16–18,26,27]
of 2.7 to 2.9 Å similar to the fluoride···ammonium distances known,
of 3. An increase in the coordination number is usually ac- niate of NH F.
and thus, compound 3 is the first ammo-
4
Eur. J. Inorg. Chem. 2009, 441–447
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
445

F. Kraus, S. A. Baer, M. B. Fichtl
FULL PAPER
Table 1. Summary of crystallographic data.
1
2
3
4
Empirical formula
H
15
F
4
N
5
Zr
H
15
F
4
N
5
Hf
H
7
FN
2
H12AgFN
4
colorless needle
195.01
Color and appearance–
colorless needle
252.39
colorless needle
339.66
colorless cube
54.08
1
Molecular mass [gmol ]
Crystal system
Space group
a [Å]
tetragonal
P4/ncc (130)
8.7745(1)
8.7745(1)
10.6618(4)
820.87(3)
4
tetragonal
P4/ncc (130)
8.7875(7)
8.7875(7)
10.6766(9)
824.45(12)
4
orthorhombic
Pca2 (29)
1
8.1065(6)
5.7346(5)
7.3988(6)
343.95(5)
4
orthorhombic
Pnna (52)
6.8252(2)
13.5405(6)
6.8252(2)
630.76(4)
4
b [Å]
c [Å]3
V [Å ]
Z
–3
ρcalcd. [mgm ]
2.042
2.736
1.044
2.053
λ [Å]
T [K]
µ(Mo-K
0.71073
150(2)
1.356
0.71073
150(2)
12.669
0.71073
123(2)
0.111
0.71073
150(2)
3.106
–
1
α
) [mm ]
θ
max [°]
32.80
32.70
32.84
32.72
3
Size [mm ]
R
R(F) [IϾ2σ(I), all data]
wR(F ) [IϾ2σ(I), all data]
0.02ϫ0.02ϫ0.01
0.067, 0.034
0.041, 0.067
0.129, 0.135
1.18
0.1ϫ0.07ϫ0.07
0.090, 0.036
0.053, 0.084
0.089, 0.095
1.10
0.04ϫ0.04ϫ0.04
0.099, 0.188
0.039, 0.122
0.058, 0.066
0.705
0.2ϫ0.08ϫ0.08
0.036, 0.027
0.016, 0.039
0.033, 0.035
0.83
int, Rσ
2
S (all data)
Data, parameter, restraints
∆ρmax, ∆ρmin [eÅ ]
Ratio of twin volumes
Extinction coefficient
750, 25, 0
0.834, –0.724
–
735, 25, 0
2.260, –1.415
–
654, 56, 3
0.169, –0.140
–
1196, 56, 0
0.46, –0.53
0.451(1)
–3
–
–
–
0.0048(4)
tem. Cell determination routines gave a pseudo-I-centered tetrago-
nal unit cell but refinements in the tetragonal space groups were
unsuccessful. The real symmetry orthorhombic (Pnna) and the
Experimental Section
General: All work was carried out with the exclusion of moisture
and air under an atmosphere of dried and purified argon
structure was refined as a merohedral twin by using the matrix
(Westfalen AG) or fluorine (Solvay Fluor) by using high-vacuum
[28]
(
2
0 0 1) (0 –1 0) (1 0 0). When AgF was used as the silver source,
glass lines, monel lines, or a glove box (MBraun, Garching). Liquid
ammonia (Air Liquide) was dried and stored over sodium in a spe-
cial high-vacuum glass line. The solubilities of compounds 1–4
3
was obtained as a byproduct of the reaction.
The structures were solved by using direct methods[ and refined
on F . All non-hydrogen atoms were localized by Fourier cycling
29]
1
9
2 [30]
seem to be very low, as we could not obtain any signals by
NMR spectroscopy.
F
methods and refined anisotropically; hydrogen atoms were treated
isotropically in a riding model or freely where applicable. To check
the selection of the space groups, searches for additional symmetry
M(NH
reaction of elemental fluorine with MO
was mixed with dried and distilled liquid ammonia (10 mL) at
78 °C. The Schlenk tubes were stored at –38 °C and sporadically
3
)
4
F
4
·NH
3
(1, M = Zr; 2, M = Hf): MF
4
was synthesized by
2
at 450 °C. MF
4
(100 mg)
were performed by using PLATON[ and KPlot,
28]
[31]
which in all
cases stated the correctness of the assignments. All crystals are not
stable above –30 °C due to their high ammonia vapor pressure.
Further details of the crystal-structure investigations may be ob-
tained from the Fachinformationszentrum Karlsruhe, 76344 Egg-
enstein-Leopoldshafen, Germany, on quoting the depository
numbers CSD-419917 (for 1), -419919 (for 2), -419918 (for 3), and
–
shaken. After 3 weeks colorless needle-shaped crystals of 1 and 2
had formed quantitatively, which were subjected to low-tempera-
ture X-ray diffraction analysis (Table 1) with an Oxford Xcalibur3
system. Alternatively, 1 and 2 can be synthesized as products of the
3 2
M F
14 (M = Zr, Hf) with liquid ammonia.[6]
reaction of Ag
NH (NH )]F (3): The monoammoniate of ammonium fluoride was
obtained in two ways: By reaction of NH F (1 g) in liquid ammonia
-
419924 (for 4).
[
4
3
4
(
10 mL) or by the oxidation of liquid ammonia with silver(II) com- Acknowledgments
[6]
pounds. After several weeks of storage at –38 °C, colorless cube-
shaped crystals of 3 were obtained and subjected to low-tempera-
ture X-ray diffraction analysis (Table 1) with an Oxford Xcalibur3
system. With fluorine being the heaviest element present, the abso-
lute structure could not be determined unambiguously, so Friedel
pairs were merged.
S. A. B. and F. K. thank the Fonds der Chemischen Industrie for a
fellowship. The authors would like to thank B. Wahl for hints to-
ward the structure solution of the silver compound, Prof. Dr. R.
Hoppe and Prof. Dr. B. G. Müller, both Giessen, for generous do-
nation of chemicals and equipment, Solvay Fluor for the donation
of fluorine, and Prof. Dr. T. F. Fässler for his continuous support.
Ag(NH
3 2 3 2
) F·2NH (4): AgF and AgF were obtained by literature
procedures with hydrofluoric acid or elemental fluorine and
[
1]
Ag
2
CO
3
or Ag
2
O. Dried and distilled liquid ammonia (15 mL,
(100 mg) in
Schlenk tubes at –78 °C. The Schlenk tubes were stored at –38 °C
and sporadically shaken. After 3 weeks colorless needle-shaped
crystals of 4 had formed, which were subjected to low-temperature
X-ray diffraction analysis (Table 1) with an Oxford Xcalibur3 sys-
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446
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 441–447

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Received: October 6, 2008
Published Online: December 9, 2008
1
Eur. J. Inorg. Chem. 2009, 441–447
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
447