Interaction of copper with dinitrogen tetroxide in 1-butyl-3-methylimidazolium-based ionic liquids

Article abstract of DOI:10.1039/c6dt04526j

Ionic liquids that are stable toward oxidation and nitration and are based on the 1-n-butyl-3-methylimidazolium cation (BMIm⁺) can be used as solvents and reaction media for copper dissolution in liquid dinitrogen tetraoxide N₂O₄. The ionic liquid not only favors the dissociation of N₂O₄ into NO⁺ and NO₃^?, but also takes part in the formation of different crystalline products. Thus, NO[BF₄], NO[Cu(NO₃)₃] and (BMIm)₂[Cu₂(CF₃COO)₆] were prepared using (BMIm)A, A^? = [BF₄]^?, (CF₃SO₂)₂N^?, CF₃COO^?, respectively. The formation of a certain product is determined by the nature of the anion A^? and the relative solubility of the reaction products in the ionic liquid. Crystals of NO[BF₄] were also prepared directly from a mixture of N₂O₄ and BMImBF₄. According to XRD single-crystal structure analysis, the structure of NO[BF₄] consists of tetrahedral [BF₄]^? anions and nitrosonium NO⁺ cations; the formation of these ions prove the heterolytic dissociation of N₂O₄ dissolved in the ionic liquid. The crystal structure of the earlier unknown binuclear copper trifluoroacetate (BMIm)₂[Cu₂(CF₃COO)₆] were determined by X-ray diffraction. The peculiarity of this dimer compared to the majority of known dimeric copper(ii) carboxylates is the unusually long Cu?Cu distance (3.15 ?), with Cu(ii) ions demonstrating an atypical coordination of a distorted trigonal bipyramid formed by five O atoms of five trifluoroacetate groups.

Full text of DOI:10.1039/c6dt04526j

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DOI: 10.1039/C6DT04526J
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ARTICLE
Interaction of Copper with Dinitrogen Tetroxide in 1-Butyl-3-
methylimidazolium-based Ionic Liquids
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
I. V. Morozova, E. B. Deevaa, T. Yu. Glazunovaa, S. I. Troyanova, F. I. Guseinova,b, and L. M. Kustova,b,*
www.rsc.org/
It was demonstrated that ionic liquids that are stable toward oxidation and nitration and are based on 1-n-butyl-3-
methylimidazloium cation (BMIm+) can be used as solvents and reaction media for copper dissolution in liquid dinitrogen
-
tetraoxide N2O4. The ionic liquid not only favors dissociation of N2O4 into NO+ and NO3 , but also takes part in the formation
of different crystalline products. Thus NO[BF4], NO[Cu(NO3)3] and (BMIm)2[Cu2(CF3COO)6] were prepared using (BMIm)A, A-
= [BF4]-, (CF3SO2)2N-, CF3COO-, respectively. The formation of a certain product is determined by the nature of the anion A-
and the relative solubility of reaction products in the ionic liquid. Crystals of NO[BF4] were also prepared directly from a
mixture of N2O4 and BMImBF4. According to the data of XRD single-crystal structure analysis, the structure of NO[BF4]
consists from tetrahedral [BF4]- anions and nitrosonium NO+ cations, the formation of these ions proving the heterolytic
dissociation of N2O4 dissolved in the ionic liquid. The crystal structure of the earlier unknown binuclear copper
trifluoroacetate (BMIm)2[Cu2(CF3COO)6] was also studied by XRD structure analysis. The peculiarity of this dimer compared
to the majority of the known dimeric copper(II) carboxylates is the unusually long Cu···Cu distance (3.15Å), with Cu(II) ions
demonstrating an atypical coordination of a distorted trigonal bipyramid formed by five O atoms of five trifluoroacetate
groups.
Introduction
the formation of nitrosonium cations. The latter serve as an oxidant
acting to transform a metal into the dissolved state:
Since early 1990s the interest to ionic liquids and to their unique
properties is steadily growing. This can be explained by the variability
of the reactivity of many chemical compounds being dissolved in
ionic liquids. As a result, the synthesis of known products can be
simplified in many cases, whereas new, previously unknown
products can be synthesized in ionic liquids, including inorganic
compounds.1 In this concern, the use of ionic liquids as a reaction
medium for the reactions between metals and liquid dinitrogen
tetroxide (N2O4) is of special interest.
-
N2O4 + Solv = NO+solv + NO3 solv
M + n NO+  Mn+ + n NO
Nitrosonium nitratometallate can be precipitated from this solution
by adding an excess of N2O4, whereas in the case of an insufficient
amount of N2O4, solvent molecules enter the coordination sphere of
the complexing metal atom.2
Taking into account the polar nature of ionic liquids, we assumed that
they will facilitate the dissociation of N2O4 and will cause the
dissolution of metals. In such a case, not only nitrates, but also some
other products containing a cation and/or an anion of the ionic liquid
can be obtained. Noteworthy that non-aqueous solutions containing
cations of d- and f-elements can find application as catalysts in
organic synthesis.3 The objective of this work was to check the above
Dissolution of metals in liquid N2O4 serves as a general method of
synthesis of nitrosonium nitratometallates NOm[M(NO3)n+m]..2 This
method was developed in 1950s and the main reaction can be
presented as:
M + (n+m)N2O4  NOm[M(NO3)n+m] + nNO
In most cases, the reaction requires the addition of a polar N- or O- assumption on the use of ionic liquids as reaction media for the
containing organic solvent to liquid N2O4, which results in an increase reactions of metals with liquid N2O4 by taking copper as an example
of the extent of heterolytic dissociation of dinitrogen tetraoxide with of the metal. The ionic liquids that are rather stable toward oxidation
and nitration were chosen, namely, those based on 1-n-butyl-3-
methylimidazolium cation (BMIm)A with the following anions A-=
[BF4]-, (CF3SO2)2N-, and CF3COO-.
a.Lomonosov Moscow State University, Department of Chemistry, Leninskie Gory,
1-3, Moscow 119991, Russia
b.National University of Science and Technology MISiS, Leninsky prosp. 4, Moscow,
Russia, lmk@ioc.ac.ru.
†
Corresponding author: Prof. Leonid M. Kustov, National University of Science and
Results and discussion
Technology MISiS, Leninsky prosp. 4, Moscow, Russia, phone/fax: +7499 137 2935,
e-mail: lmk@ioc.ac.ru
Electronic Supplementary Information (ESI) available: See DOI:
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The occurrence of this reaction is confirmed by the results of
DOI: 10.1039/C6DT04526J
XRD study of the precipitate formed. The X-ray diffraction pattern
Interaction of ionic liquids with liquid N2O4, synthesis and crystal
structure of NO[BF4]
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of the polycrystalline sample demonstrates the good agreement with
the theoretical diffraction pattern derived from the single-crystal
structure data and also with XRD data for NO[BF4] reported in 7. The
presence of several peaks due to admixtures, with the overall
intensity below 1-2% of the intensity of the main reflections, can be
explained by the partial decomposition of the sample in the course
The first stage of the study was focused on the elaboration of the
effect of the ratio between the ionic liquid (IL) and dinitrogen
tetraoxide. A mixture of equal volumes of liquid N2O4 and IL under
some cooling (to 5-10оС) was stirred in sealed ampules and was left
at room temperature for one week. In the case of BMIm[BF4] as IL,
tiny crystals precipitated from a pale-brown solution almost
immediately after mixing the components. When the tiny crystals of the X-ray experiment. The parameters of the unit cell of sample
were kept for 45 days at 40оС, the average size of the crystals
increased, so that single-crystal XRD structure analysis could be
performed. This analysis showed that the precipitate represented
nitrosonium tetrafluoroborate NO[BF4] (I) (Table 1). When the
starting mixture was cooled to 0oC, the yield of the precipitate
increased noticeably.
I somewhat increased compared to the parameters determined
by X-ray structure analysis due to the difference in the
temperatures of the measurements in X-ray structure analysis
(150 K) and powder XRD (298 K) (see the Supplementary
Information).
Colorless crystals of I are prompt to fast decomposition in humid air
due to the action of water vapors. The crystals are dissolved in water
with evolution of gaseous nitrogen oxides, NO and NO2, which is
characteristic for nitrosonium salts.
Table 1. Crystallographic data and some details of data
collection and refinement
Formula
(BMIm)2
NO[BF4]
[Cu2(CF3COO)6]
CCDC 1520782
monoclinic
P21/n
16.466(3)
15.871(3)
17.043(3)
90.00
In the case of dissolution of N2O4 in other ionic liquids BMImA used
in this work, no precipitate formation was found. The experiments
showed a rather high chemical stability of the BMIm+ cation with
respect to the interaction with nitrogen (IV) dioxide, which is a strong
oxidizing as well as nitrating agent. During the storage of the mixture
of BMIm[BF4] with N2O4 in a sealed ampoule at 40оС for 45 days, no
noticeable changes and no formation of side products were
observed.4
ICSD number
Crystal system
Space group
a, Å
CSD 432338
orthorhombic
Pnma
8.856(2)
b, Å
5.6314(14)
6.8410(16)
90.00
c, Å
α, o
β, o
90.00
90.00
341.17(14)
4
117.32(3)
90.00
3957.1(14)
8
The structure analysis data for the products of the syntheses are
presented in Table 1. The ionic structure of (NO)[BF4] (I) includes
nitrosonium cations and tetrafluoroborate anions, with the
environment of a boron atom being a weakly distorted
tetrahedron formed by four fluorine atoms (Fig. 1). Two B-F
distances (1.385(1), 1.386(1) Å) are somewhat shorter than the
γ, o
V, Å3
Z
d cal, g cm-3
λ (MoK), Å
Crystal dimensions, mm
Temperature, K
2.274
0.71073
1.819
0.71073
0.5

0.5

0.2
0.600.110.08
two others (21.406(1) Å), and the F-B-F angles are varying
between 108.43(9)o and 111.25(9)o.
150(2)
28.48
100(2)
29.18
10646

(max), o
The N-O bond length in a disordered NO+ cation is equal to
1.017(2) Å, which, according to the literature data, corresponds
to a typical bond length in a nitrosonium cation.5 The positions
of N and O atoms are linked by crystallographic mirror plane and
are, therefore, indistinguishable. Each NO+ cation forms
contacts with fluorine atoms of seven surrounding [BF4]
tetrahedra at distances N(O)···F ranging within 2.62–2.92 Å.
It should be noted that the structure I is isotypical of alkaline
metal tetrafluoroborates A[BF4] (A=K, Rb, Cs).6 All these
isostructural compounds, similar to I, are crystallized in an
orthorhombic space group Pnma and adopt the same packing
motif with the only difference that the diatomic NO+ cation is
replaced for a monoatomic cation A+ located on a mirror plane.
The sizes of the unit cells increase with increasing size of the
cation in the row K < NO < Rb < Cs.
Reflections.
unique
number 458
Reflections. number with 417
F2>2 (F2)
6311

Parameters in refinement 37
657
0.077
wR2 (F2)
0.054
R1
0.021
0.939
0.042
1.032
Goodness of fit
Dissolution of copper in a ionic liquid/N2O4 mixture. Synthesis
and crystal structure of (BMIm)2[Cu2(CF3COO)6]
The next step was the study of the interaction of copper with
liquid N2O4 in the presence of different ionic liquids. The
reaction was carried out at 0-5 oC under conditions excluding
the contact of the reaction mixture with air moisture. After
dissolution of the metal, the reaction glass ampules were sealed
and were kept for crystallization. When the ionic liquid
BMIm(CF3SO2)2N was used, blue-green crystals of NO[Cu(NO3)3]
were formed after seven days according to X-ray powder
Dissolution of N2O4 in the ionic liquid BMIm[BF4] with the
formation of crystals of I is the direct evidence that ionic liquids
promote heterolytic dissociation of dinitrogen tetraoxide:
BMIm[BF4] + N2O4 → BMIm[NO3] + NO[BF4]
2 | J. Name., 2012, 00, 1-3
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analysis.8 In the experiment with BMIm[BF4], a precipitate of
NO[BF4] was formed.7 In the case of BMIm(CF3COO), a highly Table 2. Selected bond lengths (Å) and angles ( ) in the trigonal
hygroscopic precipitate as blue needles was observed. The bipyramidal coordination environment of copper atoms in
needles were grown for a month to reach the size sufficient for crystal structure (BMIm)2[Cu2(CF3COO)6] (II).
X-ray diffraction study resulting in the structure determination
of (BMIm)2[Cu2(CF3COO)6] (II) (Table 1). The similarity of the
powder diffraction pattern to the theoretical one confirmed
the phase purity of this sample.
ARTICLE
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DOI: 10.1039/C6DT04526J
o
Neighbors of atom Cu1
Neighbors of atom Cu2
Axial apex Cu1O7
Cu1O3
Equatorial Cu1O1
1.925(2)
1.937(2)
2.072(2)
1.976(6)
2.154(2)
2.19(3)
Cu2O5
Cu2O2
Cu2O11
Cu2O4
Cu2O8
1.934(2)
1.939(2)
2.000(2)
2.019(2)
2.254(2)
(a)
apex
Cu1O9
Cu1O6
Cu1O9A
Cu1O10A
2.41(3)
Axial axis O7Cu1O3
Axial axis – O7Cu1O1
equatorial O7Cu1O6
176.75(8) O5Cu2O2 175.16(9)
89.74(9)
88.24(8)
92.3(3)
O2Cu2O4 88.99(8)
O2Cu2O8 89.62(8)
O2Cu2O11 92.07(9)
plane
O7Cu1O9
O1Cu1O6
O9Cu1O6
O9Cu1O1
O1Cu1O9A
O6Cu1O9A
134.71(8) O4Cu2O8 133.70(7)
Angles in
equatorial
plane
89.5(3)
135.8(3)
82.7(3)
142.4(3)
O11Cu2O8 86.42(8)
O11Cu2O4 139.88(9)
Cu1···Cu2 3.150(3)
(b)
The terminal CF3COO group in the neighborhood of the Cu(1)
atom is disordered over two orientations. In the main
orientation (occupancy 0.653), this carboxylate group is
monodentate (the Cu1-O9 bond length is equal to 1.976(6) Å
while distance Cu1···O10 is 2.791(7) Å), and according to Fig. 2
and Table 2, in this case coordination of Cu1 corresponds to the
trigonal bipyramid polyhedra very similar like polyhedra of Cu2
atom. In the second orientation (occupancies of O9A and O10A
are both 0.347), the carboxylate group exhibits a character of
an asymmetric bidentate group (the distances to O9A and O10A
atoms are 2.19(3) and 2.41(3) Å, respectively). As a result, for
Fig. 1. Crystal structure of (NO)[BF4]: (а) projection along the a
axis with a part of BF4 anions shown as tetrahedra; (b) View
-
the minor coordination of Cu1,
a distorted tetragonal
bipyramidal coordination of Cu1 takes place. However, the
geometry of the Cu1 polyhedron for the main and minor
orientation is about the same without taking into account the
additional Cu-O10A bond (Table 2).
along the b axis with some displacement..
According to X-ray structure analysis, crystals of sample II
contain
methylimidazolium trifluoroacetocuprate. It consists of 1-butyl-
3-methylimidazolium cations and dimeric
(BMIm+)
a new binuclear copper(II) complex, 1-butyl-3-
The trigonal bipyramid polyhedra of the Cu1 and Cu2 atoms are
very much alike. One can see that the axial Cu-O bonds are
shorter than the equatorial bonds. Furthermore, one of the
three angles in the equatorial plane (89.5 and 86.4о at the Cu1
and Cu2 atoms, respectively) is significantly smaller than the
other two angles (133.7, 135.7о and 133.7, 139.9о, respectively).
It should be noted that similar geometrical features (a shorter
axial and differences in the angles and bond lengths in the
equatorial plane) that can be explained by the Jahn-Teller effect
are observed for the known cases of the trigonal bipyramid
coordination of copper(II) by five O atoms.9 For instance, the
average lengths of the axial and equatorial bonds in the trigonal
bipyramid coordination of the Cu(2) atom in the Cu2OSO4
structure 10 are very close to the corresponding distances found
in the structure II. On the other hand, the O-Cu-O angles in
Cu2OSO4 are somewhat different: the angles between the axial
[Cu2(CF3COO)6]2- anions with two crystallographically
independent units. Both copper(II) atoms are coordinated by
four bridging trifluoroacetate groups binding the copper ions
into a dimer and two terminal CF3COO groups (one group for
each copper atom) (Fig. 2).
The fully ordered coordination polyhedron of the Cu2 atom is a
distorted trigonal bipyramid formed by five O atoms of
trifluoroacetate groups (Fig. 2, Table 2). The O2, O5 and Cu2
atoms form an axial axis (the O2-Cu2-O5 angle is 175.2о), which
is nearly perpendicular to the equatorial plane which includes
O4, O8, and O11. The angles in the equatorial plane are
considerably different (86, 134, and 140o) because different
coordination types of trofluoroacetate groups (bridging and
terminals) are involved.
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and equatorial planes deviate significantly from 90о, whereas all bipyramid coordination in I to the square pyramidVcieowoArrdticinleaOtniloinne
the three angles in the plane are closer to 120о than the angles can be represented as a movement of the axial axis [O3Cu1O7]
DOI: 10.1039/C6DT04526J
in structure II.
and [O2Cu2O5] toward each other, with a simultaneous
increase of the angles O1Cu1O6 and O4Cu2O8 (Fig. 2).
It is interesting to note that the dimeric fragment (the “chinese
lantern”) in the structure of anhydrous copper(II)
trifuoroacetate Cu(CF3COO)2 characterized by the Cu···Cu
12, 13
distance of 3.10 Å
is an intermediate form between a
“classical” chinese lantern and the trifluoroacetate complex
studied in our work The coordination of the copper atom in the
Cu(CF3COO)2 structure can be described as a distorted trigonal
bipyramid (Table 3), whereas the bridging trifluoroacetate
groups are located in the axial positions. As a result, the dimers
form an infinite chain.12 However the authors of 13 consider the
polyhedron of a copper atom as a distorted square pyramid.
This assumption is based on the elongation of the Cu-O distance
to one of the equatorial O atoms approaching 2.44 Å.
Fig. 2. Structure of the binuclear [Cu2(CF3COO)6] anion in the
crystal structure of (BMIm)2[Cu2(CF3COO)6]. Fluorine atoms are
not shown.
Conclusions
А new synthetic approach was successfully used for the
preparation of solutions of anhydrous nitrates by interaction of
dinitrogen tetraoxide with metals in a medium of ionic liquids.
It was expected and it was found that an ionic liquid will not only
Table 3. Coordination of copper(II) in the known dimeric
trifluroacetate complexes: selected bond lengths (Å) and angles
(o).
12
11
-
assist in dissociation of N2O4 into NO+ and NO3 , which is a
Cu2(CF3COO)4
Cu2(CF3COO)4](CH3CN)2
Square pyramid(1)
necessary prerequisite for the dissolution of a metal, but will
also take part in the formation of complexes as a source of
cations and/or anions.
Coordination Trigonal bipyramid/
polyhedra
Axial apex
square pyramid
CuO4
1.909(2) Cu1O4
1.964(3)
1.969(2)
1.970(2)
1.972(2)
2.114(2)
164.5(1)
98.1(1)
Depending on the composition of the ionic liquid, different
crystalline products can be isolated from the solution, with the
nature of the anion of the ionic liquid playing the major role. So,
the bis(triflate) imide anion is a weaker field anion as compared
to the nitrate anion, whereas trifluoroacetate is a stronger field
anion. As a result, crystals of nitrosonium nitratocuprate are
formed from a solution of copper(II) nitrate in BMIm(CF3SO2)2N,
while the trifluoroacetate dimeric complex is formed from a
solution of BMIm(CF3COO). In the case of BMIm(BF4), NOBF4 is
the least soluble and, therefore, this salt is precipitated from the
solution.
CuO2
CuO3
CuO1
CuO1’
1.917(2) Cu1O3
Equatorial
apex
1.967(2) Cu1O2
2.058(2) Cu1O1
2.441(2) Cu1N1
Axial axis
Axial axis – O4CuO1’ 88.1(1)
equatorial
plane
O4CuO2 175.63(9) O3Cu1O4
O3Cu1N1
O3Cu1O2
O3Cu1O1
O4CuO1 90.8(1)
O4CuO3 90.3(1)
91.2(1)
87.8(1)
O3CuO1 147.07(9) O1Cu1O2
O1CuO1’ 77.07(1) N1Cu1O2
O3CuO1’ 135.97(9) N1Cu1O1
164.5(1)
97.9(1)
97.5(1)
Angles in
equatorial
plane
In general, the results obtained provide evidence for the
efficient use of ionic liquids for inorganic syntheses. Note that
earlier ionic liquids have been already proven as benign media
in organic syntheses. Thus, the nature of the ionic liquid (Cat+An-
) in the interaction of copper with N2O4 governs the formation
Cu···Cu
3.097(1)
2.766(1)
1 In this case, the axial axis is chosen randomly as one of the diagonals of the base
of the square pyramid.
a
variety of products, including both NO+An- and
Due to the presence of four bridged CF3COO groups, the copper
atoms form characteristic dimers resembling a “chinese
lantern” (Fig. 2). In this structure, the O atoms of each bridged
carboxylate group take the equatorial position with respect to
one copper atom and the axial position with respect to the
other. The Cu···Cu distance is anomalously elongated (3.15 Å).
For comparison, the Cu···Cu distance of 2.77 Å was found for the
crystal structure of the dimer complex Cu2(CF3COO)4(CH3CN)2
having a tetragonal pyramid coordination of Cu atoms, with the
nitrogen atom of an acetonitrile molecule taking the position of
the apex of the pyramid (Table 3).11 Such a shortening of the
Cu···Cu distance is related to changing geometry of the
coordination polyhedron. So, the transfer from the trigonal
of
Cat2[Me2An6]. The application of this approach in studying the
interaction of other metals will presumably result in the new
complexes with interesting catalytic and optical properties, in
line with the strategy of synthesis of complex molecular systems
and hybrid materials14.
Acknowledgements
L.M. Kustov acknowledges the financial support by the Ministry
of Education and Science of the Russian Federation in the
framework of Increase Competitiveness Program of NUST
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explosive nitration products can be formed. Such mixtures
must not be heated without detailed sDtuOdI:ie10s.1a0n3Vd9ie/pwCr6AeDrtliiTcml0e4iOn5na2li6rnyJe
small-scale experiments.
I. V. Morozov, O. B. Bondarenko, E. V. Karpova, A. S.
Pryadchenko, Yu. M. Korenev, S. I. Troyanov and N. V. Zyk,
Russ. Chem. Bull., 2010, 59, 1921.
J. C. Evans, H. W. Rinn, S. J. Kuhn and G. A. Olah, Inorg. Chem.
1964, 3, 857.
Powder diffraction database PDF-4+ 2015, ICDD. PDF number
00-017-0253 (NOBF4).
Powder diffraction database PDF-4+ 2015, ICDD. PDF number
01-080-8772 (NO[Cu(NO3)3]).
A. F. Wells, Structural inorganic chemistry, 5th edition, Oxford
University Press, Oxford, 1984.
«MISiS» (No. К1-2015-045). Е.B. Deeva acknowledges the
support of Russian Foundation for Basic Research (My First
Grant Program, grant no. 16-33-01131-a).
5
Notes and references
6
7
8
9
‡
Experimental section
Materials
A Cu powder (99.99% purity) and Pb(NO3)2 (99.8% purity) were used. The ionic
liquids (BMIm)A (A-= [BF4]-, (CF3SO2)2N-, CF3COO-) were prepared by anion exchange
of MBImCl with the corresponding Li salts with further purification and drying. The
water content was below 50 ppm as controlled by the Fischer method.
XRD analysis was performed using a DRON-4-07 reflecting type diffractometer with
Cu Kα radiation and scintillation detector. In order to prevent the contact with air
during the X-ray diffraction pattern measurements, the hygroscopic samples were
placed in a quartz sample holder in an atmosphere of dry argon and were sealed
with a polypropylene film. The assessment of the diffraction patterns and phase
analysis were performed using an STOE WinXPow software.
Single crystal XRD studies were performed for single crystals of (NO)[BF4] and
(BMIM)2[Cu2(TFA)6] using an IPDS diffractometer (Stoe) with monochromatized Mo
Kα radiation (λ = 0.71073 Å). The structures were solved and anisotropically refined
with the SHELX package. The details of the data collection and structure refinement
are given in Table 1. Selected interatomic distances and angles for
(BMIM)2[Cu2(TFA)6] are summarized in Table 2.
Liquid N2O4 was prepared by thermal decomposition of lead nitrate according to the
procedure described elsewhere.15 Lead nitrate was preliminarily heated at 150оС for
3 h to remove traces of water and was decomposed in a flask supplied with a drying
column with P2O5 and a direct assending condenser with a trap cooled to 0оС. A
brown liquid (the boiling point of liquid N2O4 is 20oC) formed a crystalline specimen
upon cooling to below -10oC, which corresponded to the melting point of N2O4. The
absence of a blueish color confirmed the absence of traces of water and NO in N2O4.2
Portions (2-4 g) of dinitrogen tetraoxide synthesized were sealed in glass ampoules
for further experiments.
10 H. Effenberger, Monatshefte Chem., 1985, 116, 927.
11 E. V. Karpova, A. I. Boltalin, M. A. Zakharov, N. I. Sorokina, Yu.
M. Korenev and S. I. Troyanov, Z. Anorg. Allg. Chem., 1998,
624, 741.
12 E. Karpova, A. Boltalin, Yu. Korenev, and S. Troyanov, Russ. J.
Coord. Chem. 2000, 26, 361.
13 F. A. Cotton, E. V. Dikarev, M. A. Petrukhina, Inorg. Chem.,
2000, 39, 6072.
14 V. P. Ananikov, K. I. Galkin, M. P. Egorov, A. M. Sakharov, S. G.
Zlotin, E. A. Redina, V. I. Isaeva, L. M. Kustov, M. L. Gening, N.
E. Nifantiev, Mendeleev Commun., 2016, 26, 365.
15 Handbuch der präparativen anorganischen Chemie, Band 2
(Herausgeber Georg Brauer) F. Enke Verlag, 1978.
Interaction of N2O4 with ionic liquids. Synthesis of NO[BF4]. In the case of each of
the three ionic liquids studied in this work, the cooled (10оС) portion of N2O4 (1 g or
0.5 cm3) and an equal volume of the ionic liquid under study (10оС) were placed in a
glass ampoule with magnetic stirring bars, the ampoule was sealed and the content
was stirred on a magnetic stirrer (a hot plate) at 35-40оС for 1 week. Nitrosonium
tetrafluoroborate was prepared by the interaction of N2O4 with BMIm[BF4] (IL1). In
this case, the sealed ampoule was kept for 1.5 months in order to produce large
crystals suitable for X-ray structure analysis. The crystals were isolated by
centrifugation, then the ampoule was opened in a dry glove box and the crystals
were kept on a porous filter to remove the liquid. Colorless plate-shape crystals of
NO[BF4] are rapidly decomposed in air in the presence of moisture, they are
dissolved in water with evolution of NO and NO2 gases, which is typical for
nitrosonium salts.
Dissolution of copper in mixtures of an ionic liquid and dinitrogen tetraoxide.
Synthesis of (BMIm)2[Cu2(CF3COO)6]. A loading of copper powder was placed in a
glass ampoule, cooled to 0oC and a mixture of dinitrogen tetraoxide and an ionic
liquid was added at 0oC. The ampoule supplied with a drying column with P2O5 was
placed in a Dewar vessel with ice. For all the studied ionic liquids, dissolution of
copper was observed with evolution of NO. The dissolution process proceeded for
several days, then the reaction mixture was allowed to warm up to room
temperature. An excess of unreacted dinitrogen tetraoxide was removed from the
solutions by keeping them at room temperature, the ampoules were sealed and kept
for crystallization. After 1-4 weeks, crystals were precipitated in all the cases. They
were separated by centrifugation, the ampoules were opened in a dry glove box and
the crystals were kept on a porous filter to remove the liquid. The crystals obtained
were studied by powder and single crystal X-ray diffraction.
1
2
E. Ahmed and M. Ruck, Coord. Chem. Rev., 2011, 255, 2892.
C. Addison and N. Logan, In: Preparative Inorganic Reactions,
1964, Vol. 1, Ed. by W. L. Jolly, New York, Interscience.
R. A. Sheldon, I. Arends and U. Hanefeld, Green Chemistry and
Catalysis, Wiley-VCH, Weinheim, 2007.
Caution! One should use mixtures of N2O4 with organic
compounds with extreme precautions, because potentially
3
4
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DOI: 10.1039/C6DT04526J
ꢀ
N2O4 + IL → NO+ + NO3 , IL=ionic liquid
BMIm+BF4 + N2O4 → BMIm+NO3 + NO+BF4
Cu + BMIm+(CF3SO2)2Nꢀ + N2O4→ NO+[Cu(NO3)3]ꢀ
Cu + BMIm+CF3COOꢀ + N2O4 → (BMIm)2[Cu2(CF3COO)6] (a “chinese lantern” structure)
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+