Vibrational spectra of AuF5 complexes with nitrogen fluorides and oxofluorides

Article abstract of DOI:10.1007/s11172-012-0073-y

Vibrational spectra and structural features of AuF₅ complexes with nitrogen fluorides (NF₃, N₂F₄) and oxofluorides (FNO, NF₃O) are investigated. Vibrational frequency assignment in the solid phase and

Full text of DOI:10.1007/s11172-012-0073-y

Russian Chemical Bulletin, International Edition, Vol. 61, No. 3, pp. 497—505, March, 2012
497
Full Articles
Vibrational spectra of AuF complexes with nitrogen fluorides and oxofluorides
5
Sh. Sh. Nabiev, V. B. Sokolov, and B. B. Chaivanov
National Research Centre Kurchatov Institute,
1
pl. Kurchatova, 123182 Moscow, Russian Federation.
Fax: +7 (499) 194 1994. Eꢀmail: nabiev@imp.kiae.ru
Vibrational spectra and structural features of AuF complexes with nitrogen fluorides (NF ,
5
3
N F ) and oxofluorides (FNO, NF O) are investigated. Vibrational frequency assignment in
2
4
3
the solid phase and in solution of anhydrous HF was made. Distinctive features of vibrational
+
ꢀ
+
+
+
+
spectra of X AuF6 (X = NF4 , N2F3 , NO , NOF2 ) related to structural transformations of
cations and hexafluoroaurate anion due to the influence of the crystal field and cation—anion
interactions are discussed.
Key words: nitrogen fluorides and oxofluorides, Lewis acid, cation—anion interactions,
hexafluoroaurate anion.
Particular interest in nitrogen fluorides and oxofluorꢀ
ides (NF , N F , N F , FNO, FNO , NF O) and their
Polynitrogen compounds may seem to be promising
explosives because extraordinary ability of these environꢀ
mentally safe molecules to release large amounts of energy
compared to the most powerful energetic materials, nameꢀ
ly, hexanitrohexaazaisowurtzitane (CLꢀ20) and octaꢀ
nitrocubane (ONC), gave an impetus to research on
the determination of the possibility for other promising
polynitrogen compounds to exist.9
3
2
4
2
2
2
3
complexes with Lewis acids is due to the fact that these
systems are energetic compounds and can be used as strong
fluoro oxidants in inorganic synthesis of fluorineꢀcontaining
1
—3
compounds and for solving various applied problems.
Such compounds are used in nanotechnologies when conꢀ
ducting controlled reactions (including cryoreactions) of
atoms, molecules, clusters, and nanoparticles on various
Recently, important key blocks were established for
4
5
the complexes with Nk+ (k  5) and N O cations proꢀ
+
surfaces, in technologies for nuclear fuel processing, and
7
6
chemistry of molten salts. They can also be used for the
duced in the reactions of nitrogen fluorides and oxofluoꢀ
1
0,11
synthesis of homoleptic polynitrogen compounds whose
existence was predicted in many quantum chemical studies.7
According to various estimates, the properties and perforꢀ
mance of polynitrogen compounds as monopropellants can
improve the corresponding properties of hydrazine and
appear to be superior to those of composite propellants.8
rides with Lewis acids (BF , SbF , PF , etc.).
The use
3
5
5
+
of NF4+, N2F3+, N F , and NOF cations as comꢀ
+
2
2
ponents of the complexes with AuF (abnormally strong
5
Lewis acid) in such blocks can make feasible the syntheꢀ
sis of novel energetic materials based on polynitrogen
compounds.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 497—505, March, 2012.
066ꢀ5285/12/6103ꢀ497 © 2012 Springer Science+Business Media, Inc.
1

498
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 3, March, 2012
Nabiev et al.
Earlier,12 we have studied the IR and Raman spectra
After completion of the reaction recognized by ceasing fluorine
consumption, the reactor was slowly defrosted, the unreacted
krypton was condensed into a collector, and the reactor temperꢀ
ature was raised to ambient temperature. Crypton difluoride was
condensed into a collector cooled with liquid nitrogen or solid
carbon dioxide.
of AuF complexes with chlorine fluorides and oxofluoꢀ
5
rides. It was shown that vibrational spectroscopy, which
combines high sensitivity and the possibility of detailed
1
3
investigations of various spectroscopic effects, makes it
possible to obtain reliable information on the structural
features and on the nature of chemical bonds in gold pentaꢀ
fluoride complexes which are highly reactive similarly to
AuF5.1
IR absorption spectra of solid samples (finely disperse powꢀ
ders placed in a hermetically sealed Teflon protecting casing
between AgCl plates) were studied with a Perkin—Elmerꢀ325
4
–1
spectrophotometer in the 400—3000 cm range. The spectral
slit width was 2.5—3.0 cm–
1
.
In this work, we report the results of our studies of the
+
–
Raman spectra were recorded with a Dilor RTIꢀ30 Raman
spectrometer using a conventional 90 illumination geometry.
vibrational spectra and structural features of NF AuF6
,
4
+
–
+
–
+
–
N2F3 AuF6 , NO AuF and NOF2 AuF6 complexes
in which NF4 , N F , NO , and NOF2 cations are
6
+
+
+
+
The spectral slit width was maintained constant at 3.7 and
2
3
–1
2
.0 cm for solid samples and their solutions in anhydrous HF,
stabilized by AuF6– octahedral anion.
respectively. The excitation sources were a 500ꢀmW LGNꢀ503
+
Ar laser (excitation line at  = 488 nm) and a 50ꢀmW LGNꢀ104
Experimental
He—Ne laser (excitation line at  = 632.8 nm). In carrying out
polarization measurements, a polaroid analyzer was mounted
between the condenser (F = 50 mm, d : r = 1 : 1.8) and the input
slit of the spectrometer. The direction of polarization of excitaꢀ
tion laser light was changed by the polarizer (a /2 plate). This
procedure for observation of the Raman spectra made it possible
Hexafluoroaurates NF AuF , NOAuF , N F AuF , and
4
6
6
2
3
6
NOF AuF were synthesized in solutions in anhydrous hydrogen
2
6
fluoride by fluorination of metallic gold (foil with Au content
99.99 mass %) with krypton difluoride (purity >99.5 mass %) at
>
T < 293 K in the presence of corresponding gaseous reactant
following a known procedure.1 Owing to high solubility of AuF5,
complexation in HF solutions proceeds rapidly and quantitaꢀ
19
to exclude the instrumental polarization correction. The Raꢀ
5
man spectrometer was calibrated in  units using the spectral
lines of electric discharge in a Ne lamp ( = 493—520 nm) and
some lines in the Raman spectrum of liquid indene.
tively and transformation of gold in the presence of NF , NOF,
3
N F , and NOF gives corresponding stable salts.
2
4
3
As in the case of AuF complexes with chlorine fluorides and
5
All operations related to the synthesis of the starting reacꢀ
oxofluorides,12 the samples under study were placed in transparꢀ
tants and products were carried out on a tailorꢀmade vacuum
bench with metallic supply lines and bleed traps cooled with
liquid nitrogen. Complexes were synthesized in minireactors
made of transparent fluoroplastic 4ꢀMB.
ent fluoroplastic 4ꢀMB tubes, the temperature of the samples
was maintained at 292±2 K with a water thermostat. The conꢀ
centrations of AuF5 complexes in HF were determined to an
accuracy of 5—10%. Hydrogen fluoride was thoroughly dried.
All operations related to the synthesis of samples were carried
out in a box in dry argon atmosphere.
Commercially available nitrogen trifluoride (TU 6ꢀ02ꢀ2ꢀ
8
52ꢀ85, purity 99.2 vol.%) was used. Tetrafluorohydrazine was
obtained by the reaction of NF3 with copper flakes in a flow
reactor made of stainless steel, and nitrosyl fluoride was preꢀ
The spectra were processed using appropriate software. The
accuracy of determination of spectral line maxima in the IR and
pared by the reaction of anhydrous NOBF and NaF ("chemiꢀ
–1
4
Raman spectra was 1.5 and 1.0 cm , respectively.
1
6
cally pure" grade) in a nickel flow reactor at 450 K. Nitrogen
oxotrifluoride was synthesized following a procedure for the synꢀ
Results and Discussion
thesis of KrF by the action of fluorine atom beams on nitrosyl
2
fluoride in a cylindrical aluminum thermocatalytic reactor at
7
7 K (see below).
Thermally and thermodynamically unstable krypton difluorꢀ
To date, the physicochemical properties, as well as
vibrational, microwave, and NMR spectra, structural
features, and the character of bonds in almost all known
nitrogen fluorides and oxofluorides have been studꢀ
ide was synthesized under conditions of thermocatalytic dissociꢀ
ation of molecular fluorine and subsequent reaction of fluorine
atoms with solid krypton on the reactor wall cooled with liquid
nitrogen (77 K) to stabilize the compound. Spatial separation of
the zones of the generation of fluorine atoms and the synthesis of
krypton difluoride was ensured by creating a high temperature
gradient (500—1000 K cm–1) between the zones and using
a catalyst for heterogeneous reaction of molecular fluorine dissoꢀ
ciation. Fluorine atoms were generated by the surface of nickel
catalyst (nickel coil) heated to 900—1000 K and positioned coꢀ
axially with the aluminum cylindrical reactor. Catalytic dissoꢀ
ciation of molecular fluorine and generation of fluorine atoms
1
,2,11,20
ied.
A feature of some molecules consists in the
existence of isomers that have the same symmetry, being
structurally different.
This, in particular, concerns FNO molecules that can
exist in two isomeric forms, F—N=O and F—O=N, both
having a C symmetry and different structures. According to
s
21
microwave spectroscopy data, the geometric parameters
of F—O=N are as follows: R(O—N) = 1.336±0.003 Å,
R(N—F) = 1.512±0.005 Å, the F—O—N angle is 119.9,
whereas for F—N=O one has R(O—N) = 1.27 Å,
1
7,18
have been studied in detail earlier.
Gaseous krypton was preliminarily condensed on the reactor
wall at 77 K. Then, molecular fluorine (30—40 Torr) was supꢀ
plied to the reactor in the presence of catalyst heated to 1000 K
2
2
R(N—F) = 1.55 Å, and the F—N—O angle is 113.0.
Molecules N F also exist as two isomers, cisꢀN F
2 2
2
2
at a rate equal to the consumption rate of F in order to maintain
the fluorine pressure at a constant level during the synthesis.
(C2v symmetry) and transꢀN2F2 (C2h symmetry), their ratio
in the mixture being 9 : 1.
2
2
3

Vibrational spectra of AuF complexes
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 3, March, 2012
499
5
Depending on the angle of internal rotation, N2F4
the IR active vibrations.42 The Raman spectra of some
molecules can exist as three isomers, viz., transꢀN2F4
AuF complexes with nitrogen fluorides and oxofluorides
5
(
C2h symmetry), gaucheꢀN F (C2 symmetry), and
are shown in Fig. 1.
2
4
cisꢀN F (C symmetry).2 Deviation of the N—NF fragꢀ
4
Compound NF4+AuF6–. The synthesis and some physꢀ
2
4
2v
2
+
ment from planarity is due to the presence of the lone
electron pair at nitrogen atom. Therefore, N F exists as
a transꢀ or gaucheꢀisomer, or as their mixture.
icochemical properties of complex salts containing NF
cation were for the first time reported in 1967.43 At present,
4
2
2
4
4
+
there is a large number of complexes comprising NF
4
–
–
The N—F, N—N, and N—O bond lengths, as well as
the corresponding bond angles and vibrational frequencies
of nitrogen fluorides and oxofluorides determined by
microwave spectroscopy and gasꢀphase electron diffracꢀ
tion are summarized in Table 1. For some molecules,
shown are the results of quantum chemical calculations.
Also, for all values from Table 1 listed are methods of
investigation and corresponding references. As can be seen,
cation and XF (X = B, Al, Br), YF5 (Y = Ge, Ti, Sn) and
4
–
ZF6 (Z = P, As, Sb, Bi, Cr, Pt) anions (see Refs 44—47
and references cited therein). The vibrational and
1
9
45—49
F NMR spectra,
as well as the stability conditions
and the mechanisms of formation and decomposition of
some salts containing NF4+ cation were determined.
According to spectroscopic data,
ion has a tetrahedral structure with T symmetry. Transꢀ
50
4
4,46—49
the NF4+ catꢀ
d
+
the N—O bond length in the FNO and NF O molecules
formation of NF molecule to NF cation is accomꢀ
3
3
4
varies insignificantly, whereas the N—F bond lengths
change considerably on going from nitrogen fluorides to
oxofluorides.
panied by an increase in the force constant of the N—F
bond in NF4+, and by strengthening of the N—F bond
–
1
(fr = 4.3 mdyn Å and R(N—F) = 1.365 Å for NF vs.
3
As mentioned earlier,12 AuF complexes were studied
f = 6.15 mdyn Å and R(N—F) = 1.310 Å for NF4 ).
–1
–1
+ 48
5
r
by Raman spectroscopy. Wide use of this method is due to
the fact that for high symmetry of the structures of the
compounds under study (O , T , etc.), the number of the
The NF4+ cation with T symmetry is characterized by
d
four normal vibrations with the symmetry types vib
=
= A (Raman) + E (Raman) + 2 F (IR, Raman). All four
h
d
1
2
Raman active vibrations is 1.5—2 times larger than that of
vibrations are Raman active, whereas only two triply deꢀ
Table 1. N—X bond lengths (R), X—N—F (X = O, N, F) bond angles, and corresponding frequencies () of N—X vibrations in
molecules comprised of N, F, and O atoms
Molecule
X—N—F
Angle/deg
N—F
N—O (N—N)
X
R/Å
/cm–1
R/Å
/cm–1
2
1
21
21
NOF
O
110.08±0.15 (MWS)
1.512±0.005 (MWS)
765.8
(see Ref. 25)
836
(1.136±0.003 (MWS)
1843.5
(see Ref. 25)
1691
1
12.5 (C)2
6
1.516 (C)
1.434 (GED)
1.445 (C)
26
(1.13155(23) (MWS)
27
2
2
8
8
28
28
NOF3
O
F
O
F
117.1 (GED)
100.8 (GED)
117.38 (C)31
(1.159 (GED)
31
31
(see Refs 29, 30) (1.154 (C)
(see Refs 29, 30)
3
2
32
NF3
102.37±0.3 (MWS)
01.84 (MWS)33
114.44±1.0 (GED)
1.365±0.002 (MWS)
1032.0
(see Ref. 33)
33
1
1.3676 (MWS)
3
4
34
(1.214±0.012) (GED)34
cisꢀN2F2
N
1.410±0.008 (GED)
896
(1525)
(
see Refs 35, 36)
(see Refs 35, 36)
9
52
(
see Ref. 35)
1010
transꢀN2F2
N
105.50±0.7 (GED)34
1.396±0.008 (GED)34
(1.232±0.01) (GED)34
(1522)
(
(
see Refs 36, 37)
90
see Refs 36, 37)
1009
(see Refs 36, 37)
9
gaucheꢀN F
F
N
F
105.1±1.0 (GED)38
1.375±0.004 (GED)
1.372±0.002 (GED)
38
(1.489±0.007) (GED)38
(590)
(see Refs 39, 40)
2
4
3
4
4
8
1
1
41
41
100.1±1.0 (GED)
103.1±0.6 (GED)
101.6±0.4 (GED)
(see Refs 39, 40) (1.492±0.007) (GED)
N
F
3
8
1.372±0.002 (GED)41
(1.492±0.007) (GED)41
transꢀN2F4
102.9±0.75 (GED)
1036
(600)
(see Refs 39, 40)
3
4
4
8
N
F
N
100.6±0.6 (GED)
103.1±0.6 (GED)
101.6±0.4 (GED)
(see Refs 39, 40)
1
1
Note. Notations of methods are as follows: MWS is microwave spectroscopy, GED is gasꢀphase electron diffraction, and C denotes
quantum chemical calculations.

500
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 3, March, 2012
Nabiev et al.
Frequency assignment for AuF6– anion in all comꢀ
plexes of gold pentafluoride with nitrogen fluorides and
oxofluorides was made under assumption of undistorted
I (rel. units)
a
(AuF –
1
)
6
1
0
.0
.5
0
octahedral (O ) structure based on the results of the asꢀ
h
1
2,15
signment
taking account of polarization measurements
–)
5(AuF
6
in the Raman spectra of their solutions in anhydrous HF.
As can be seen, in accordance with the selection rules
for the XY structures with T symmetry, the Raman specꢀ
4
(NF4+)
2
(AuF –
)
6
4
d
+
trum of NF4 cation exhibits vibrational bands  (A ),
(E), and  (F ) at 848, 611, and 442 cm , respectively,
(NF4+)
2(NF4+)
1
1
1
–
1
2
4 2
and its IR spectrum shows a  (F ) band and a band of the
4
2
–
1
stretching antisymmetrical vibration  (F ) at 1160 cm
.
3
2
8
00
600
400
200 /cm–1
For both spectra, one has 3 > 1 and 4 >  ; this
2
is characteristic of almost all tetrahalides with T symꢀ
metry.
d
I (rel. units)
.0
b
42,51
1
(AuF –
)
6
1
0
The data of Table 2 also indicate a number of anomaꢀ
+
–
lies in the spectra of NF AuF6 . For instance, the Raꢀ
4
man spectrum of NF4+ cation shows no line of antisymꢀ
metrical stretching vibration,  (F ), allowed by the selecꢀ
tion rules. Vice versa, the IR spectrum of NF4 demonꢀ
3
2
+
5(FNO2+)
.5
0
+)
3(FNO
2
strates the  (E) band of symmetrical deformation vibraꢀ
2
5
(AuF6–)
tion forbidden by the selection rules. Also, the Raman
spectrum of NF4+ cation in solid NF4+AuF6 shows no
splitting of the  (F ) band of the triply degenerate vibraꢀ
(FNO2+)
1
–
2
(AuF –
)
6
3
2
4
5—49
tion observed in some studies.
positional symmetry5 and characteristic of XF (T ) molꢀ
This splitting is due to
1
1
000
800
600
400
200 /cm–1
4
d
ecules in the solid state. An additional analysis of the
+
–
Raman spectra of the salt NF4 AuF revealed very
I (rel. units)
.0
6
c
–
1
(AuF –
)
6
weak lines at 490, 502, and 1074 cm . Low intensities of
these lines are not surprising because, unlike the NF XF
1
+
–
1
0
4 6
salts, the intensity ratio of the strongest Raman lines
+
–
is  (NF ) :  (AuF )  0.15, whereas the ratios
1
4
1
6
+
–
48,49
1
0.6—0.8.
These facts suggest noticeable cation—anion interacꢀ
(NF4 ) :  (XF6 ) (X = As, Sb, etc.)
lie in the range
1
.5
0
(AuF –
)
6
5
+
–
tions in NF4 AuF6 , characteristic of gold pentafluoride

(NO2+)
6–)
2(AuF
12
complexes. These interactions affect the lengths of some
N—F bonds in the tetrahedral cation (according to our
estimates, their variation can amount to 0.1 Å). In addiꢀ
2
300 2200
600
400
/cm–1
+
tion, transformation of NF molecule to NF cation can
3
4
Fig. 1. Raman spectra of crystalline NF4+AuF6– (a),
NOF2 AuF6 (b), and NO AuF6 (c).
be accompanied by some change in the hybridization of
valence orbitals at nitrogen atom and by strengthening of
+
–
+
–
one or two N—F bonds. As a result, the T ꢀstructure of
d
+
NF4 cation can be distorted to give C ꢀ or C ꢀstructures
3v
2v
generate vibrations with the symmetry type F ( ,  ) are
with nonequivalent fluorine atoms in axial and equatorial
positions (Fig. 2).
2
3
4
IR active.
The vibrational frequencies of NF4+AuF6– in the solid
state and in solution in HF are listed in Table 2.
A possible distortion of the tetrahedral structure of
NF4+ cation was also suggested in studies
52,53
of the
Frequency assignment in the spectra of NF4+ cation was
crystal structure and vibrational spectrum of crystalline
salt NF4+BF4 . The unit cell of NF4+BF4 contains two
–
–
carried out assuming an undistorted tetrahedral (T ) structure
d
+
based on the results of polarization measurements in the
Raman spectrum of NF4+AuF6 solutions in anhydrous
HF taking into account the published frequency assignꢀ
crystallographically independent cations N(1)F and
N(2)F4+ (space groups 4 and mm, respectively).
4
–
–
52,53
The
bond lengths in these cations are noticeably different:
R(N(1)—F(1)) = 1.301(6) Å, R(N(2)—F(2)) = 1.265(9),
and R(N(2)—F(3)) = 1.321(10) Å; the F(1)—N(1)—F(1)
4
5,47,49,50
ment data.
Also, the interpretation of the vibraꢀ
4
2
tional spectrum of the isoelectronic analog CF was used.
4

Vibrational spectra of AuF complexes
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 3, March, 2012
501
5
Table 2. Experimental frequencies (cm–1) in vibrational spectra of NF4+AuF – and their assignment
6
Raman spectrum
IR spectrum
Frequency assignment and types of vibrations
(
crystalline
sample)
Crystalline Solution in HF
sample
AuF6–(Oh)
NF4+(Td)
2
4
4
5
5
5
6
6
6
8
1
27 (43)
42 (8)
90 (<1)?
02 (<1)?
27 (6)
96 (95)
00 (100)
11 (14)
49 (1)
48 (12)
074 (<1)?
221 (34) р
437 (5) р
—
—
 (F ),  (F—Au—F)
—
5
2g
s
450 (vw)
—
—
—
 (E),  (F—N—F)
2
s
—
—
—
—
—
—
—
522 (4) р
 (E ),  (Au—F)
2 g s
599 (100) р
608 (sh) dp
—
 (A ),  (Au—F)
—
1
1g
s
610 (m)
648 (vs)
—
—
 (F ),  (F—N—F)
4 2 аs
—
3(F1u),  (Au—F)
—
as
843 (9) р
—
—
—
—
—
 (A ),  (N—F)
1
1
s
—
—
—
—
—
—
—
—
—
1160 (s)
1219 (w)
1460 (w)
 (F ),  (N—F)
3 2 аs
2 (A + E + F )
4
1
2
 +  (F )
1
4
2
Note. Notations used here and in Tables 3—5 are as follows:  is stretching,  is deformation, s is
symmetrical, as is antisymmetrical vibration; vs is very strong, s is strong, m is medium, w is weak,
vw is very weak band; p is polarized and dp is depolarized line. For the Raman frequencies, listed
are the corresponding line intensities in relative units.
+
angle is 108.5(3) and 111.5(5), the F(2)—N(2)—F(2) anꢀ
(BF ). Therefore, the NF cation can have a T ꢀstrucꢀ
3
4
d
gle is 109.9(4), and the F(3)—N(2)—F(3) angle is
ture. At the same time, cation—anion interactions in the
1
07.4(9).
A
complex salts with AuF (abnormally strong Lewis acid)
5
1
9F MAS NMR study54 of the structure of NF4+BF4–
+
may cause structural distortions in NF as in the case of
4
+
–
+
–
12,55
revealed that crystalline salt NF4 BF4 contains only tetꢀ
ClF2 MF6 (M = Nb, Ta, Au) salts.
rahedral NF4+ cations and that the conclusion
52,53
about
Thus, the observed features of the vibrational spectrum
distortion of the tetrahedral structure of NF4+ was erroneꢀ
ous owing to incorrect interpretation of the results obꢀ
of NF + cation as component of NF4+AuF6 salt (the
–
4
presence of "extra" lines in the Raman spectrum, the abꢀ
tained. However, since information about nonequivalence
sence of vibrational bands for the T ꢀstructure allowed by
d
of NF4+ cations was obtained
52,53
by Xꢀray analysis which
the selection rules or, vice versa, the presence of correꢀ
sponding bands forbidden by the selection rules, possible
occurrence of noticeable cation—anion interactions afꢀ
gives the bond lengths and bond angles directly rather
1
9
than indirectly, as F MAS NMR spectroscopy, the conꢀ
5
4
+
+
–
clusions about the presence of only tetrahedral NF in
fecting the N—F bond lengths in the NF4 AuF6 cation)
4
the crystalline salt NF4+BF4 are doubtful.
–
leave the problem of the structure of NF as constituent
+
4
of NF4+AuF6 in the solid phase unsolved. We believe
–
We believe that no cation—anion interactions can occur
in the NF +BF4 complex with a rather weak Lewis acid
–
that detailed quantum chemical calculations of the geomꢀ
4
F
F
F
F
N
N
F
N
F
F
F
F
F
F
F
Fig. 2. Structural transformations T  C3v or T  C upon distortion of tetrahedral NF4+ cation.
d
d
2v

502
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 3, March, 2012
Nabiev et al.
etry of NF + cation, as well as studies on solidꢀstate
Indeed, the N2F3+ cation can be represented by two
resonance structures (I and II) with different types of bonds
between nitrogen atoms.
4
molecular geometry using new spectroscopic methods of
investigation are on demand. These will allow one to study
the formation of lines in the spectrum of this cation
+
–
as a component of crystalline salt NF4 AuF6 and its
structure.
As to the AuF6– anion, the observed splitting of the
1
(A ) line can be due to slight tetragonal distortions of
1g
–
the O ꢀstructure of AuF in the anion lattice field, which
h
6
lead to reduction of the anion symmetry owing to strucꢀ
According to calculations,50,61 the resonance structure I
is energetically more favorable than structure II. Therefore,
tural transformations O  D , O  C etc. characterisꢀ
h
4h
h
4v
5
6
+
tic of some hexafluoro complexes. This is also favored by
the assignment of vibrational frequencies of N F cation
2
3
as constituent of the N2F3+AuF6 salt was carried out for
–
the appearance of a  (F ) line of the vibration forbidden
3
1u
–
1
42
by the selection rules at about 650 cm in the Raman
spectrum. In addition, splitting of the  line (AuF6 ) in
the planar C ꢀstructure similar to that of C F molecule.
s
2 4
–
+
Planar cation N2F3 (C ) is characterized by nine IR
1
s
the Raman spectra can be a consequence of manifestaꢀ
tions of internal asymmetry of AuF6 owing to perturbaꢀ
tive effect of excited electronic states with lower symmetry
and Raman active normal modes with the symmetry types
vib = 6 A´ (IR, Raman) + 3 A (IR, Raman). The modes
belonging to the symmetry type A have higher depolarꢀ
ization ratios.
–
5
1,56
on the groundꢀstate O symmetry.
.
h
Compound N2F3+AuF6 . Unlike NF4 cation, data on
the vibrational spectra of N F cation first synthesized in
965 are scarce. There are only a few studies on the
vibrational and NMR spectra of N F cation as constituent
–
+
The vibrational frequencies of N F3+AuF6– and
2
+
N2F3+AuF6 in the solid state and in solution in HF are
–
2
3
5
7
1
listed in Table 3. Frequency assignment in the spectra of
+
+
N2F3 cation was based on the results of polarization meaꢀ
2
3
+
–
+
–
+
–
of salts, namely, N F XF6 (X = As, Sb), N F SnF5
,
surements in the Raman spectrum of N2F3 AuF6 soluꢀ
tions in anhydrous HF and taking into account the pubꢀ
lished data6 which seem to be quire reliable.
2
3
2 3
and N2F3+(SbF ) (n = 2, 3).
–
58—60
According to the availꢀ
able spectroscopic data, planar (C ) and nonplanar (C )
6 n
0
s
1
+
structures of N F cation are equiprobable; therefore,
Eight vibrational bands are observed in the spectra of
N2F3+ (see Table 3). Bands in the region 300—700 cm
were assigned to the inꢀplane and outꢀofꢀplane deformaꢀ
2
3
–1
the assignment of the observed vibrational frequencies of
+
59,60
N F was the subject of a special discussion.
2
3
Table 3. Experimental frequencies (cm–1) in vibrational spectra of N2F3+AuF – and their assignment
6
Raman spectrum
IR spectrum
Frequency assignment and types of vibrations
(
crystalline
sample)
Crystalline
sample
Solution in HF
AuF6–(Oh)
N F3+(Cs)
2
2
2
3
4
5
5
5
6
6
6
9
9
1
1
—
—
1
—
—
—
27 (43)
34 (sh)
11 (6)
99 (1)
21 (10)
42 (5)
92 (66)
02 (100)
59 (2)
73 (8)
26 (21)
98 (2)
125 (8)
309 (3)
231 (35) p
—
 (F )
—
5
2g
311 (4) p
496 (1) dp
518 (8) p
539 (4) p
597 (100) p
—
—
—
—
 (А´), (FNNF ) inꢀplane
6 2
495 (m)
515 (m)
—
 (А´),  (FNNF ) outꢀofꢀplane
8 s 2
 (А´),  (NF ) inꢀplane
5
s
2
 (E )
—
—
2
g
—
 (A )
1
1g
—
670 (5) dp
923 (20) р
992 (1) р
1122 (5) р
1305 (2) р
—
650 (vs)
669 (sh)
922 (m)
995 (w)
1129 (s)
1312 (s)
1342 (w)
1439 (vw)
1523 (m)
1643 (w)
1976 (w)
2231 (vw)
 (F )
3 1u
—
—
—
—
—
 (А),  (FNNF ) outꢀofꢀplane
7 as 2
 (А´),  (NF )
4
s
2
2 (А´)
8
 (А´),  (NF )
3 s 2
 (А´),  (NF )
2
as
2
—
—
—
—
—
—
2 (А´)
7
—
 +  (А´)
3 6
519 (4)
1517 (2) р
—
1(А´), (N=N)
 +  (А´)
3
5
—
—
 +  (А´´)
2 7
 +  (А´)
2 4

Vibrational spectra of AuF complexes
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 3, March, 2012
503
5
+
–
+
– 59,63,64
tion vibrations of FNNF and NF fragment ( ,  ,  ,
NF O XF (X = As, Sb), and NF O Sb F
2 11
,
2
2
5
6
7
2
6
2
6
5
8
). The bands corresponding to symmetrical ( ,  ) and
and on the crystal structure of some of these salts. It was
shown that the NF O cation has a C ꢀstructure with
3
4
+
antisymmetrical ( ) stretching vibrations and to the N=N
2
2
2v
stretching vibration ( ) appear at higher frequencies,
R(N—O) = 1.114 Å, R(N—F) = 1.284 Å, the F—N—F is
1
–
1
66
namely, at 900—1500 cm
A characteristic feature of the spectra of N F as conꢀ
stituent of the N2F3+AuF6 salt is the lack of the IR band
.
107.9, and the O—N—F angle is 126.0.
+
The NOF2+ cation (C2v symmetry) is characterized by
six IR and Raman active normal vibrations with the symꢀ
metry types vib = 3 A (IR, Raman) + 2 B (IR, Raman) +
2
3
–
corresponding to the  (A´) vibration allowed by the selecꢀ
6
1
1
tion rules and the appearance of IR bands assigned to
+ B (IR, Raman).
2
+
The vibrational frequencies of NOF2+AuF – in the solꢀ
compound vibrations and overtones of N F . Also, no band
2
3
6
–
1
of the  (A) torsional vibration near 350 cm was detectꢀ
id state and in solution in HF are listed in Table 4. Freꢀ
quency assignment in the spectra of NOF2+ cation was
carried out based on the results of polarization measureꢀ
ments in the Raman spectrum of NOF2+AuF6 solutions
in anhydrous HF taking into account the interpretation of
the vibrational spectrum of the isoelectronic analog COF2
(see Ref. 42) and the assignment proposed in Ref. 64.
9
6
0
ed in our study, although it was observed in the spectra
of N2F3+ as constituent of N2F3+XF6 (X = As, Sb) salts.
These features can be due to spectroscopic manifestaꢀ
tions of structural nonrigidity by the mechanisms considꢀ
–
–
1
2,62
ered earlier,
in particular, by the mechanism of fast
intramolecular exchange of Fꢀligands. In addition, they
can be related to the formation of intermediate C ꢀstrucꢀ
The vibrational spectrum of crystalline NOF2+AuF –
s
6
ture F(1)NNF(2) with nonequivalent fluorine atoms; this
structure is different from the resonance structures I and II.
Such intermediate structures are formed in the course of
(see Fig. 1) and its solution in HF exhibits all lines allowed
2
by the selection rules for structures with the C (NOF2+
)
2v
–
and O (AuF6 ) point symmetries.
h
2
3
A feature of the Raman spectrum of NOF2+AuF – is
trans—cisꢀisomerization of N F molecules.
2
2
6
–
The spectra of AuF6 anion exhibit splitting of the
(A ) and  (F ) lines and a line at 650 cm correꢀ
that, unlike the AuF complexes considered above, the
5
–
1
–
1
splitting of the  (A ) line for AuF anion and the  (F )
1g
5
2g
1
1g
6
3
1u
sponding to the  (F ) vibration forbidden by the selecꢀ
line forbidden by the selection rules are not observed,
3
1u
+
–
tion rules. As in the case of NF4 AuF6 , this can be
a consequence of (i) slight tetragonal distortions of the
whereas the line  (F ) corresponding to a deformation
5
2g
vibration is split into three components. This may indicate
–
+
–
O ꢀstructure of AuF anion in the crystal field and
weakening of cation—anion interactions in NOF AuF6
,
h
6
2
+
–
–
(
ii) manifestations of internal asymmetry of N2F3 AuF6
.
so that distortion of the O ꢀstructure of AuF can mainly
h
6
1
2,67
Taken altogether, these factors lead to symmetry reducꢀ
tion of AuF6– anion.
be due to the effect of the crystal field.
+
–
Compound NO AuF6 . A number of studies describe
Compound NOF2+AuF6–. There are some studies on
the vibrational spectra of NO cation as constituent of
+
+
+
–
+
–
the vibrational and NMR spectra of NF O cation as
NO XY (X = P, As, Sb; Y = F, Cl), NO UF ,
2
6
7
+
–
+
–
(NO)2+UF8 , NO BrF O , NO ZOF (Z = Mo, W,
2–
+
–
+
–
constituent of compounds NF O BF , NF O B F
,
2
4
2
2
7
4 5
Table 4. Experimental frequencies (cm–1) in vibrational spectra of NOF2+AuF – and their assignment
6
Raman spectrum
IR spectrum
Frequency assignment and types of vibrations
AuF6–(Oh) NOF2+(C2v)
(
crystalline
sample)
Crystalline
sample
Solution in HF
2
2
2
5
5
6
6
24 (23)
32 (sh)
39 (sh)
37 (6)
76 (7)
00 (100)
32 (12)
221 (17) p
—
 (F )
—
5
2g
532 (4) p
572 (4) p
596 (100) p
627 (sh) dp
—
710 (1) dp
895 (13) p
—
—
581 (s)
—
 (E )
2 g
—
—
 (A ),  (F—N=O) inꢀplane
3
1
s
 (A )
—
1
1g
633 (sh)
652 (vs)
725 (m)
903 (s)
1148 (w)
1237 (vw)
1792 (w)
—
—
 (B ),  (F—N=O) inꢀplane
5
1
as
—
 (F )
—
3
1u
7
8
1
—
—
14 (2)
97 (15)
163 (1)
—
 (B ), (F—N=O) outꢀofꢀplane
6 2
—
—
—
—
—
—
 (A ),  (F—N)
2 1 s
 (B ),  (F—N)
4 1 as
—
—
2 (B )
5 1
2 (A )
1 1
1
1
844 (1)
858 (1)
1848 (1) p
—
 (A ), (N=O)
1
1
1869 (w)
—

504
Russ.Chem.Bull., Int.Ed., Vol. 61, No. 3, March, 2012
Nabiev et al.
Table 5. Experimental frequencies (cm–1) in vibrational spectra of NO AuF and their assignment
+
–
6
Raman spectrum
IR spectrum Frequency assignment and types of vibrations
(
crystalline
sample)
AuF6–(Oh)
NO (Cv)
+
Crystalline
оsample
Solution in HF
2
2
5
5
6
29 (19)
37 (sh)
29 (5)
91 (sh)
01 (100)
225 (17)
—
 (F )
—
5
2g
525 (4)
596 (100)
—
—
 (E )
—
—
2
g
 (A )
1 1g
—
—
649 (s)
2324 (m)
1329 (sh)
 (F )
—
—
3
1u
1
+
2
2
322 (sh)
329 (18)
2329 (13)
(  ), (NO)
Cr), and (NO) +ZOF62– (Z = Mo, W) salts
59,68—71
as
fluorides. These features should be taken into account when
using such compounds to solve fundamental and applied
problems, in particular, in the synthesis of novel energetic
materials.
2
6
9,71,72
well as their NMR spectra and crystal structures.
7
3
The synthesis of a NOF•AuF adduct was reported;
however, no vibrational frequency assignment was made.
5
+
Transformation of NOF molecule to NO cation owꢀ
ing to a change in the atomic charge of oxygen having
a higher electronegativity compared to nitrogen is accomꢀ
panied by an increase in the nitrogen—oxygen bond order
and in the (N—O) vibrational frequency. The effect of
the change in charge (loss of an electron) on (N—O) is
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2
3
+
–
2– 42
clearly seen in the series NO > NO > NO > NO
.
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v
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+ 59,72
term  ).
+
–
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6
7
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–
+
–
1
2, 405.
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–
1
shifted by 10—15 cm toward the longꢀwavelength reꢀ
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–
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6
2
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1
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+
+
–
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6
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5
6,57
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6
1
1g
1
6. Handbuch der Präparativen Anorganischen Chemie, Vol. 1,
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3
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1u
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5
2g
1
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–
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1
977].
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