Reactions of Some Ammonium Fluorometalates with XeF2
Jože Slivnik+*, Branko Družina, and Boris Žemva
Jozef Stefan Institute and+Faculty for Natural Sciences and Technology,
Edvard Kardelj University, Ljubljana, Yugoslavia
Dedicated to Prof. Dr. Drs. h. c. Oskar Glemser on the occasion of his 70th birthday
Z. Naturforsch. 36b, 1457-1460 (1981); received May 7, 1981
Xenon Difluoride Reactions, Ammonium Fluorometalates, Hydrazinium Fluorometalates
The reactions between (NH^TiFe, (NH^ZrFe, (NfL^HfFe, (NELtfeVFe, (NH4)3CrF6,
NH4MnF3, (NH4)3FeFe and excess xenon difluoride were investigated. The listed ammonium fluorometalates react with xenon difluoride to form corresponding xenon(II)
fluorometalates, monoammoniumfluorometalateswith metal in the same oxidation state,
and ammoniumfluorometalateswith metal in higher oxidation state, respectively.
The reactions between binary fluorides and xenon
difluoride or xenon hexafluoride, respectively, yield
a series of xenon(II) or xenon(VI) fluorometalates.
We have investigated these reactions in detail
succeeded to isolate and identify seven xenon(II)
and thirteen xenon(VI) fluorometalates [1].
Since in some cases the reaction between binary
fluoride and xenon hexafluoride did not proceed at
all under the applied reaction conditions, we
supposed that the binary fluoride is not reactive
enough and that the reaction might proceed if the
binary fluoride would be available in a more
reactive form. Highly reactive, pure binary fluorides
were prepared in this laboratory earlier by reacting
hydrazinium fluorometalates with elemental fluorine [2].
It was expected, therefore, that the metal fluoride
which is formed in situ during the reaction between
hydrazinium fluorometalates and xenon hexafluoride should be in a highly reactive form and
should consequently react immediately with excess
xenon hexafluoride to form xenon(VI) fluorometalates. We checked our speculation in the reaction between N 2 HeFeF5 and xenon hexafluoride.
Indeed XeFö • FeF 3 was isolated [3], a compound
which could not be obtained by other, more conventional ways. This result encouraged us to initiate a
systematic study of the reactions between xenon
difluoride or xenon hexafluoride on one side and
hydrazinium(l - f )
fluorometalates,
hydrazinium( 2 - f ) fluorometalates and metal fluoride adducts
with hydrazine on the other side [4-10]. So far the
following new compounds, not accessible by other
conventional methods, were isolated and characterized: X e F e • FeF 3 [3], X e F 6 • ZrF 4 , X e F 6 • H f F 4
[11], X e F 6 • 2 AlFs and X e F 6 • GaF 3 [12]. This study
is still being continued.
Following the same basic approach we extended
the investigations recently onto reactions between
xenon difluoride or xenon hexafluoride and ammonium fluorometalates.
Experimental
Materials
Fluorine was prepared and purified in this laboratory as described elsewhere [13]. Its purity was
99 ± 0.5 v o l % . Additional purification, mainly from
oxygen, was performed b y irradiation of liquefied
fluorine with the near UV light at 77 K [14]. The
purity of so obtained fluorine was above 99.9 v o l % .
X e n o n was supplied b y l'Air Liquide (Paris,
France) in 99.5% purity (the balance was krypton).
X e n o n difluoride was prepared by photosynthesis
using near U V lamp [15]. The purity of xenon
difluoride was checked b y I R spectrum of the
vapours and by the determination of its triple point.
(NH 4 ) 2 MF 6 (M = Ti, Zr, H f ) were prepared b y
crystallization from the water solutions of corresponding fluorometallic acid and ammonium
fluoride [16-18].
(NH 4 ) 3 MF 6 (M = V, Cr, Fe) were prepared b y
crystallization of solutions obtained by dissolving of
corresponding metal trifluoride trihydrate in water
solution of ammonium fluoride [19-21].
NH 4 MnF 3 was prepared by reaction between
Mn(N0 3 ) 2 • 4 H 2 0 and ammonium fluoride in water
solution [22].
General procedure
Reactions were carried out in argon arc welded
nickel or copper pressure and weighing vessels
equipped with Teflon packed nickel valves. The
volume of the reaction vessel was about 100 ml.
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Chemical analysis of the products:
Compound
Calcd [ % ]
NH4ZrF5
NH 4 HfF 5
(NH4)3VF8
NH4CrF4
NH4MnF4
NEUFeF4
Zr
Hf
V
Cr
Mn
Fe
44.67
61.23
19.82
35.62
36.89
37.27
Found [ % ]
F
F
F
F
F
F
46.52
32.59
59.16
52.05
51.03
50.72
NIL* 8.81
XH 4 6.18
NH 4 21.02
NH4 12.33
NH4 12.08
NH4 12.01
They were tested hydrostatically up to 200 atm
and were designed also for manipulating solid
materials. All transfers of materials were carried out
either in the atmosphere of a dry box or by distillation under vacuum in a well dried apparatus.
In a typical run 3 to 6 mmoles of ammonium
fluorometalate was weighed into reaction vessel and
dried by pumping upon in a dynamic vacuum for
12 h. Then a corresponding amount of xenon difluoride was added by sublimation. The vessel was
then thermostated at predetermined temperature
for several hours. After the reaction was completed,
the reaction products were separated by fractional
sublimation, isolated and identified. Volatiles at
77 K , 193 K , 233 K and at room temperature were
characterized by mass spectrometry and infrared
spectroscopy. Solids were identified by chemical
analysis, X - r a y powder diffraction patterns, infrared and Raman spectroscopy and magnetic susceptibility measurements. The stoichiometry of the
reactions was followed throughout of experiment b y
weighing of all reactants and products to ± 5 mg.
General apparatus and techniques
Raman spectra were recorded using a Spex 1401
double monochromator. As exciting radiation, the
515.5 nm line of an Ar+ laser or 647.1 nm of a Kr+
laser (Coherent Radiation) were used. Powdered
samples were loaded into quartz cappilaries in a dry
box temporarily plugged with Kel-F grease and
sealed off b y a small flame outside the dry box.
Raman spectrum of (NH 4 ) 3 VF 8 : 612(100), 596(83),
490(9), 342(96), 310(57), 270(76), 216(11), 188(9)
cm-1.
I R spectra were recorded using Perkin Elmer 521
and Zeiss UR-20 spectrometers over the range 400
to 4000 c m - 1 . The sample was finely powdered and
dusted onto silver chloride plates sandwiched in a
leak tight brass holder.
X-ray powder photographs were obtained b y the
Debye Scherrer method on E N R A F (Delft, Holland)
using graphite monochromatized CuK<* radiation.
In the case of known compounds X-ray powder
photographs were compared with the data from
ASTM tables. Finely powdered samples were sealed
in 0.5 mm thin walled quartz capillaries as described
under Raman spectra.
Zr
Hf
V
Cr
Mn
Fe
43.9
61.7
19.6
34.4
35.7
37.1
F
F
F
F
F
F
46.0
31.9
55.4
50.2
50.5
50.5
NH4
NH 4
NH 4
NHi
NH 4
NHj
8.5
5.9
20.3
10.2
11.8
11.3
Mass spectra were recorded on a Nier type mass
spectrometer with an inlet system for the analysis
of gases.
Results and Discussion
The reactions between (NH 4 )2TiF 6 , (NH 4 ) 2 ZrF 6 ,
(NH 4 ) 2 HfF 6 , (NH 4 ) 3 VF 6 , (NH 4 ) 3 CrF 6 , NH 4 MnF 4 ,
(NH 4 ) 3 FeFe and excessive xenon difluoride were
investigated. The listed ammonium fluorometalates
react with xenon difluoride in a three different
modes as follows:
1. Ammonium fluorometalate is completely fluorinated by xenon difluoride to corresponding
binary fluoride which reacts further with excess
of xenon difluoride to form correspondings xenon(II) fluorometalate.
2. Tri- or di-ammonium fluorometalate is only
partially fluorinated by xenon difluoride to form
monoammonium fluorometalate with the metal
in the same oxidation state.
3. Only metal in ammonium fluorometalate is
oxidized while the rest of the compound does not
change.
The reaction between (NH 4 ) 2 TiF6 and xenon
difluoride belongs to the first group:
(NH 4 ) 2 TiF 6 + nXeFa
453 K
several hours
X e F 2 • TiF 4 + *N 2 + 2 ( 1 — x ) N F 3 +
8 HF + 3 ( 2 — x ) X e + n-(7—3z)XeF2
n > 10, a: > 0 . 7 .
The reaction between (NH 4 ) 2 TiFe and xenon difluoride starts somewhere around 413 K but is very
slow. Even at 433 K with periodic pumping away
of all volatile reaction products it takes several days,
before the reaction is completed. Normally the
reaction was carried out at 453 K . Obviously the
related hydrazinium(2+) compound N 2 HeTiF6 is
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much more reactive. It reacts with xenon difluoride
already at 393 K forming XeF 2 • TiF4.
Interestingly enough, also some nitrogen trifluoride was obtained during the reaction. This is,
as far as we know, the first chemical reaction where
nitrogen trifluoride was prepared by the reaction
with xenon difluoride.
The reactions in the analogous systems
(NH 4 ) 2 ZrF 6 /XeF 2 and (NH 4 ) 2 HfF 6 /XeF 2 belong to
the second group:
(NH 4 ) 2 MF 6 + nXe F 2
423 K
36 h
•
NEUMFs + 0.5 N 2 + 4 HF + 1.5 X e +
(n— 1.5)XeF 2
n > 6 , M = Zr, Hf.
Also in this case the reaction proceeds at the temperature around 423 K but only to NH 4 ZrF 5 [22]
and NELiHfFs [23], respectively. Both formed compounds are very stable and do not react further
with excess of xenon difluoride even at 473 K .
The most interesting reaction in the investigated
series of ammonium fluorometalates is the reaction
between ( N H ) V F E and xenon difluoride:
4
3
(NH 4 ) 3 VF 6 + wXe F 2
343 K
several days
•
(NH 4 ) 3 VF 8 + X e + ( n — l ) X e F 2
n >8.
The volatiles which were pumped away after reaction, were only pure xenon and excess of xenon
difluoride as shown by mass spectrometry and
infrared spectroscopy. Neither nitrogen, nor nitrogen
trifluoride or any other nitrogen fluoride were found
in volatiles. The amount of evolved xenon was
equivalent to the oxidation of V 3 + to V5+ by xenon
difluoride. As shown by the magnetic susceptibility
measurements (NH 4 ) 3 VFs is diamagnetic what is
also the evidence that vanadium was oxidized to
the 5 + oxidation state.
The formation of VFs 3 - anion should be very
unlikely but some of the experimental results
collected so far indicate vanadium atom has coordination of fluoride ions above six. Xenon difluoride is electrophylic agent, therefore we would
expect its attack on the anion rather than on a
cation.
The symmetrical (V-F) stretching mode in Raman
spectrum of NH 4 VFe, which contains isolated octa-
hedra of VF 6 -, appears at 660 cm- 1 [25]. The
corresponding band in the Raman spectrum of our
compound is at 612 cm - 1 indicating higher coordination number of fluorine around vanadium than six.
The compound decomposes in X-ray beam and it
turns very quickly from a white colour with a pink
cast to a green colour. This behaviour also rules out
the potential possibility of having a mixture of
ammonium fluoride and NHiVFe as the reaction
product. Both components are white and very
stable in X-ray beams. Quite interesting is also
the comparison with the analogous reaction of
(N2H5)3VF6 and xenon difluoride. In this case
NH 4 VFe [25] was obtained besides of nitrogen,
hydrogen fluoride, xenon and excess of xenon difluoride. It should be mentioned here that in this
case ammonium hexafluorovanadate(III) and hydrazinium hexafluorovanadate(III) appear to be
approximately equally stable. The reason for this is
that vanadium is in 3 + oxidation state what is not
the stable oxidation state of vanadium in xenon(II)
fluorovanadates consequently the oxidation of the
metal takes place. At higher temperatures (about
400 K or higher) the reaction between (N2H5)3VF6
or (NH 4 ) 3 VF 6 and xenon difluoride proceeds in both
cases to XeF 2 • VF 5 .
Reactions between N H 4 M n F 3 , ( N H 4 ) 3 C r F 6 and
( N H 4 ) 3 F e F 6 and xenon difluoride yield corresponding N I L I M F 4 compounds. All three compounds are
isomorphous as shown by X-ray diffraction patterns.
NH4MnF3 + wXe F 2
333 K
several hours
NH4MnF4 [26] + 0.5 Xe + (n — 0.5)XeF 2
n >6
(NH4)3CrF6 + nXeF2
393 K
several hours
NH4CrF4 [27] + N 2 + 8 HF + 3 Xe +
(n—3)XeF 2
n>7
(NH 4 ) 3 FeF 6 + wXeF2
393 K
several hours
NH 4 FeF 4 [28] + N 2 + 8 HF - f 3 Xe +
(n—3)XeF 2
n>7
It is somewhat surprising that NHiMnF 3 is
oxidized to NH4MnF4. The product formed at
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analogous reaction between (N 2 Hs) 2 MnF 4 and xenon
difluoride would namely suggest formation of
NH 4 MnF5 [25] specially so since Mn 4+ is the only
known oxidation state in the xenon(II) and
xenon(VI) fluorometalates. Interestingly enough,
the reaction between NH4MnF 3 and xenon hexafluoride proceeds to the formation of
NH 4 + XeF 5 +MnF 6 2 - [29].
Ammonium hexafluorochromate(III) and -ferrate(III) reacted with xenon difluoride according to our
expectation. NH 4 CrF4 was obtained also by the
reaction of hydrazinium fluorochromate(III) with
xenon difluoride, while in a similar reaction
N2H 6 FeF 5 yielded iron trifluoride.
As expected, ammonium fluorometalates react
with xenon difluoride less readily than the corresponding hydrazinium fluorometalates. This is
specially true if the oxidation state of a metal in the
[1] J. Slivnik and coauthors in the Noble Gas Compounds, A Bibliography 1962-1976 (compiled by
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IFI/Plenum, New York-Washington-London
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starting compound is the same or higher than the
usual oxidation state of a metal in corresponding
xenon(II) fluorometalates {e.g. Ti4+, Zr 4 *, Cr4*, V5+
etc.). If the oxidation state of a metal in the starting
compound is lower than already mentioned {e.g.
Mn 2 + , V 3 + ) than the reactivity of such an ammonium
fluorometalate is comparable with the reactivity of
the corresponding hydrazinium fluorometalate. This
system offers a convenient way for the syntheses of
ammonium fluorometalates with a metal in higher
oxidation state.
This work was financed through the Research
Community of Slovenia. The authors are indebted
to Mrs. A. Rahten for preparation of numerous
ammonium fluorometalates, Miss B. Sedej did the
analytical work and Dr. H. Leskoväek recorded
mass spectra.
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375 (1981).
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