Metal oxidation with N2O5: The nitrosylium nitrates (NO)Cu(NO3)3, (NO)2[Zn(NO3) 4] and (NO)6[Ni4(NO3) 12](NO3)2·(HNO3)

Article abstract of DOI:10.1002/ejic.201100565

The oxidation of copper, zinc and nickel by N₂O₅ led, respectively, to turquoise-coloured single crystals of (NO)Cu(NO ₃)₃ [monoclinic, P2₁/m, Z = 2, a = 465.90(5), b = 1111.7(1), c = 700.7(1) pm, β = 100.70(2)°, wR₂ = 0.0566], light-yellow single crystals of (NO)₂[Zn(NO ₃)₄] [orthorhombic, Fdd2, Z = 8, a = 1522.8(2), b = 2346.4(3), c = 596.18(7) pm, wR₂ = 0.0452] and green single crystals of (NO)₆[Ni₄(NO₃)₁₂](NO ₃)₂·(HNO₃) [orthorhombic, P2 ₁2₁2₁, Z = 4, a = 1167.68(4), b = 1791.97(6), c = 1834.11(6) pm, wR₂ = 0.0762]. In (NO)Cu(NO₃) ₃, the Cu²⁺ ion is coordinated by six oxygen atoms of monodentatenitrate groups in the form of a tetragonal distorted octahedron. The nitrate groups are connected to further copper ions leading to a two-dimensional network. In contrast, in (NO)₂[Zn(NO₃)₄], the nitrate anions are coordinated to only one Zn²⁺, ion and the coordination polyhedron is a distorted octahedron. The complex nitrate (NO) ₆[Ni₄(NO₃)₁₂](NO₃) ₂·(HNO₃) exhibits anionic ribbon chains according to _∞¹{[Ni(NO₃)_1/1(NO ₃)_4/2]}₂^2- with octahedrally coordinated Ni²⁺ ions as well as non-coordinating nitrate ions and HNO₃ molecules. The thermal decomposition of the copper and zinc nitrates are multistep processes and lead to a mixture of Cu and Cu₂O in the case of the copper compound and to ZnO for the zinc complex. Copyright

Full text of DOI:10.1002/ejic.201100565

FULL PAPER
DOI: 10.1002/ejic.201100565
Metal Oxidation with N2O5: The Nitrosylium Nitrates (NO)Cu(NO3)3,
(NO)2[Zn(NO3)4] and (NO)6[Ni4(NO3)12](NO3)2·(HNO3)
Steffen Gagelmann,[a] Katja Rieß,[a] and Mathias S. Wickleder*[a]
Keywords: Nitrogen oxides / Structure elucidation / X-ray diffraction / Thermal behavior
The oxidation of copper, zinc and nickel by N2O5 led, respec- ions leading to a two-dimensional network. In contrast, in
tively, to turquoise-coloured single crystals of (NO)Cu(NO3)3
[monoclinic, P21/m, Z = 2, a = 465.90(5), b = 1111.7(1), c =
700.7(1) pm, β = 100.70(2)°, wR2 = 0.0566], light-yellow single
crystals of (NO)2[Zn(NO3)4] [orthorhombic, Fdd2, Z = 8, a =
1522.8(2), b = 2346.4(3), c = 596.18(7) pm, wR2 = 0.0452] and
green single crystals of (NO)6[Ni4(NO3)12](NO3)2·(HNO3) [or-
thorhombic, P212121, Z = 4, a = 1167.68(4), b = 1791.97(6), c
= 1834.11(6) pm, wR2 = 0.0762]. In (NO)Cu(NO3)3, the Cu2+
ion is coordinated by six oxygen atoms of monodentate
nitrate groups in the form of a tetragonal distorted octa-
hedron. The nitrate groups are connected to further copper
(NO)2[Zn(NO3)4], the nitrate anions are coordinated to only
one Zn2+, ion and the coordination polyhedron is a distorted
octahedron. The complex nitrate (NO)6[Ni4(NO3)12](NO3)2·
(HNO3) exhibits anionic ribbon chains according to
2–
1{[Ni(NO3)1/1(NO3)4/2]}2
with octahedrally coordinated
ϱ
Ni2+ ions as well as non-coordinating nitrate ions and HNO3
molecules. The thermal decomposition of the copper and zinc
nitrates are multistep processes and lead to a mixture of Cu
and Cu2O in the case of the copper compound and to ZnO
for the zinc complex.
by the reaction of Cu(NO3)2 and N2O4,[4] and later on by
the reaction of Cu(NO3)2 and fuming HNO3.[5] In addition
to the new preparative route, we describe here its thermal
behaviour for the first time. In the reaction of the metal
with N2O5, the nickel nitrate (NO)6[Ni4(NO3)12](NO3)2·
(HNO3) is formed instead of the expected copper and zinc
congener (NO)n[Ni(NO3)2+n], clearly due to a slight con-
tamination of the reaction mixture with water.
Introduction
Investigations of the synthetic potential of dinitrogen
tetroxide N2O4 and later dinitrogen pentoxide N2O5 can be
traced back to the work of Addison from the early 1960s.
Addison succeeded in preparing a number of nitrosylium
nitratometallates, (NO)n[Mm+(NO3)m+n], which can be de-
composed to the corresponding anhydrous nitrates in some
cases.[1] Several of these compounds have subsequently been
analysed by X-ray diffraction, and – for example – the
structures of (NO)2[Co(NO3)4] and (NO)Mn(NO3)3 have
been reported.[2] Our interest in these nitrates was strongly
triggered by their potential to function as precursors for the
deposition of metals and metal oxides on various surfaces.
They seem to be very attractive, because they are carbon-
Results and Discussion
Crystal Structures
(NO)Cu(NO3)3 crystallizes in the monoclinic space
free and should lead to decomposition products without group P21/m with two formula units in the structure cell
any contamination. One striking example is the compound (Figure 1). The Cu2+ ion is situated on a centre of sym-
(NO2)[Au(NO3)4], which we obtained from the reaction of metry (Wyckoff symbol 2c). One of the nitrate groups,
–
Au with N2O5.[3] This compound can be decomposed to N(2)O3 , and the nitrosylium ion NO+ are bisected by a
elemental gold, induced by the electron beam of an electron mirror plane (Wyckoff symbol 2e).
microscope. These results encouraged us to perform further
The copper ion is coordinated by six oxygen atoms be-
reactions of metals with N2O5 and to investigate the com- longing to two crystallographically different nitrate groups,
–
pounds obtained and their thermal behaviour. In this paper N(1)O3– and N(2)O3 . It lies in the centre of an octahedron,
we show that copper and zinc are readily oxidized by N2O5 which is tetragonally distorted as a result of a Jahn–Teller
to give the nitrates (NO)Cu(NO3)3 and (NO)2[Zn(NO3)4] in effect on Cu2+ (Figure 2). The axial distances [Cu–O13
single-crystalline form. The copper compound was ob- 253.5(2) pm (2ϫ)] are significantly elongated relative to the
tained and structurally investigated for the first time in 1973 equatorial distances [Cu–O21 198.8(2) pm (2ϫ); Cu–O11
194.8(2) pm (2ϫ)]. The octahedron is further distorted with
[a] Universität Oldenburg, Institut für Reine und Angewandte
respect to the observed O–Cu–O angles, some of which dif-
Chemie,
fer significantly from 90°, that is, the line O13–Cu–O13 de-
Carl von Ossietzky Str. 9–11, 26111 Oldenburg, Germany
E-mail: mathias.wickleder@uni-oldenburg.de
fined by the Cu2+ ion and the apical oxygen atoms is signifi-
5160
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Metal Oxidation with N2O5
= 1/4 and 3/4, respectively. The N–O distance in the NO+
ion is 99.0(5) pm. This is shorter than the theoretical value
but in accordance with the findings for other NO+-contain-
ing salts.[6]
The zinc nitrate (NO)2[Zn(NO3)4] crystallizes in the or-
thorhombic crystal system with the non-centrosymmetric
space group Fdd2 and with eight formula units in the unit
cell (Figure 3).
Figure 1. Projection of the crystal structure of (NO)Cu(NO3)3 onto
the (001) plane.
cantly tilted with respect to the square plane defined by the
equatorial oxygen atoms O11 and O21.
Figure 3. Projection of the crystal structure of (NO)2[Zn(NO3)4]
onto the (001) plane.
In contrast to the copper compound, in (NO)2[Zn-
(NO3)4] the nitrate groups are exclusively coordinated to
one Zn2+ ion, that is, the complex anion [Zn(NO3)4]2– is
formed, which is similar in form to the previously observed
cesium nitrate Cs2[Zn(NO3)4].[7] Within the anion the zinc
atom is surrounded by six oxygen atoms. Four of these oxy-
gen atoms are at shorter Zn–O distances of 201.0(2) pm
(2ϫ) and 203.9(2) pm (2ϫ), the remaining two being found
at a distance of 236.9(2) pm (2ϫ). The shorter Zn–O dis-
tances cause a strongly distorted tetrahedron around the
Zn2+ ion (Figure 4).
The oxygen atoms belong to two crystallographically dif-
–
ferent nitrate groups, N(1)O3– and N(2)O3 . The O13–Zn1–
O13 angle within the tetrahedron is nearly ideal [108.5(1)°],
whereas the O23–Zn1–O23 angle is enlarged up to
138.7(1)°. This results in a widening of one edge of the tet-
rahedron allowing for additional coordination of the oxy-
gen atom O21. Thus, the nitrate group N(2)O3– can be seen
as an asymmetrically chelating ligand. The charge of the
Figure 2. Coordination of the Cu2+ ion in the crystal structure of
(NO)Cu(NO3)3.
–
The copper ions are linked by four bridging N(1)O3
–
groups in the [100] direction and by two N(2)O3 ions in [Zn(NO3)4]2– complex anion is compensated by two nitro-
the [010] direction. In this way layers of ϱ2[Cu(NO3)6/2]– are sylium ions that belong crystallographically to the same
formed. The charge balance for the layers is achieved by species. The distance between the nitrogen and oxygen
NO+ ions, which occupy available sites in the lattice at y/b atoms within the nitrosylium ion is 104.7(4) pm.
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S. Gagelmann, K. Rieß, M. S. Wickleder
FULL PAPER
The remaining two nitrate groups are bidentate bridging
ligands and connect the dimers in the [100] direction to
form infinite double chains (Figure 6). These can be formu-
Figure 4. Coordination of the Zn2+ ion in the structure of
(NO)2[Zn(NO3)4].
The formation of (NO)6[Ni4(NO3)12](NO3)2·(HNO3) is
clearly a result of a slight contamination by water of the
N2O5 prepared. The complex crystallizes in the orthorhom-
bic space group P212121 with four formula units per unit
cell. The four crystallographically different Ni2+ ions each
show the same distorted octahedral coordination of one
chelating and four monodentate nitrate groups. Although
the Ni–O distances lie in a narrow range from 200.8(5) to
210.0(5) pm, the distortion of the octahedra is especially
significant for the O–Ni–O angles involving those oxygen
atoms belonging to the chelating nitrate groups (O11, O12,
O21, O22, O31, O32, O41, O42), which were found to be
between 62.2(2) and 63.2(2)°. The nitrate ions that are
bonded in a monodentate fashion can be divided into two
categories according to their connectivity modes: two of the
four anions act as monodentate bridging ions and lead to
a linkage of two [NiO6] octahedrons to form a dimer (Fig-
ure 5).
2–
Figure 6. Double chains of
(NO)6[Ni4(NO3)12](NO3)2·(HNO3).
1{[Ni(NO3)1/1(NO3)4/2]}2
in
ϱ
Figure 5. Dimer of two [NiO6] octahedra in the crystal structure of (NO)6[Ni4(NO3)12](NO3)2·(HNO3).
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Metal Oxidation with N2O5
Figure 7. Projection of the crystal structure of (NO)6[Ni4(NO3)12](NO3)2·(HNO3) onto the (100) plane.
2–
lated as 1{[Ni(NO3)1/1(NO3)4/2]}2 according to Niggli’s mately 36%, but there is no distinct plateau in the TG
ϱ
formalism.
curve. However, it is known that copper nitrate decomposes
The crystal structure exhibits two crystallographically with the formation of CuO (mass loss: calcd. 39.5%) as an
different double chains that show, however, essentially iden- intermediate.[9]
tical bond lengths and angles. The chains are arranged into
puckered layers that are stacked in the [001] direction of the
unit cell (Figure 7). Between these layers are located non-
coordinated nitrate ions as well as the charge-balancing
NO+ ions. The N–O distances for the nitrate ions [123.8(8)–
130.2(8) pm] and the nitrosylium cations [96.3(9)–
111.4(9) pm] are in accordance with reported values.
Furthermore, the interlayer spacing contains a nitric acid
molecule, which can be clearly identified on the basis of the
observed N–O distances. These are 120.7(9) and
125.7(8) pm for two of the oxygen atoms and 139.8(8) pm
for the third, which indicates the presence of an H atom at
this oxygen atom. This is in accordance with the findings
for other nitric acid adducts.[8]
Figure 8. DTA/TG diagram of the thermal decomposition of (NO)
Cu(NO3)3.
Thermal Decomposition
The thermal decomposition of (NO)Cu(NO3)3 proceeds
Upon further heating, continuous weight loss is ob-
in at least two steps (Figure 8). The first step has an onset served, but again no plateau occurs in the TG curve. An-
temperature of 115 °C and ends at 183 °C with two endo- other endothermic peak at 975 °C is not associated with a
thermic maxima at 118 and 157 °C (Table 1). The product loss of mass. On the other hand, the temperature fits well
formed in this step is probably Cu(NO3)2 (mass loss: calcd. with the temperature reported for the decomposition of
32.9%; found 34.8%). The second step consists of two not CuO to Cu2O. We assume that gradual degradation of CuO
well-resolved stages. One significant DTA peak is observed starts after its formation and causes the decline of the TG
at 286 °C. The overall mass loss for this step is approxi- curve. The final decomposition product is a mixture of
Eur. J. Inorg. Chem. 2011, 5160–5166
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S. Gagelmann, K. Rieß, M. S. Wickleder
FULL PAPER
Table 1. Data for the thermal decomposition of (NO)Cu(NO3)3 and (NO)2[Zn(NO3)4].
Compound
Stage
Tonset
[°C]
Tend
[°C]
Tmax
[°C]
Mass loss [%]
calcd.
found
(NO)Cu(NO3)3
1. formation of Cu(NO3)2 (endo)
2. formation of CuO (exo)
3. formation of Cu2O and Cu (endo)
115
255
950
183
302
1010
118; 157
286
975
34.8
36.0
–
32.9
39.5
10
[a]
75.5
82.4
(NO)2[Zn(NO3)4]
1. unknown (endo)
2. formation of (NO)Zn(NO3)3 (endo)
3. unknown (endo)
61
99
158
81
133
18.5
8.9
13.9
26.8
68.1
120
24.5 (steps 1 + 2)
[a]
–
4. formation of ZnO (endo)
308
379
342
42.6 (steps 3 + 4)
77.1
[a] Not determined with reliability.
Cu2O and Cu, as can be seen from the X-ray powder
pattern (Figure 9). The complete mass loss was higher than
expected for the two decomposition products (Cu: 77.3%;
Cu2O: 74.4%), which may be explained by the difficulties
encountered in the sample preparation mentioned above.
Figure 10. DTA/TG diagram of the thermal decomposition of
(NO)2[Zn(NO3)4].
Figure 9. XRD powder diffractogram of the residue of the decom-
position product of (NO)Cu(NO3)3.
The first step of the thermal decomposition of
(NO)2[Zn(NO3)4] starts with an onset temperature of 61 °C
and finishes at 99 °C (Figure 10). The mass loss of 18.5%
is difficult to interpret, but, with the second step, which
occurs between 120 and 158 °C, the overall mass loss corre-
sponds to the formula (NO)Zn(NO3)3. Two further decom-
position steps are observed in the TG curve with mass
losses of 13.9 and 26.8%, respectively. The corresponding
temperatures in the DTA curve are reliable only for the sec-
ond step.
Figure 11. XRD powder diffractogram of the residue of the decom-
position product of (NO)2[Zn(NO3)4].
The overall mass loss is 68.1%, which is also significantly
smaller than that calculated for the formation of ZnO as
residue, as shown by the X-ray powder pattern (Figure 11).
The difference between the observed and calculated mass
Conclusions
In this paper we have presented the structures and the
loss seems reasonable if one takes into account the fact that thermal behaviour of (NO)Cu(NO3)3 and the new nitrosyl-
the initial sample may have contained a significant amount ium complex (NO)2[Zn(NO3)4]. Both compounds were ob-
of unreacted N2O5. Nevertheless, the suitability of the com- tained by the reaction of N2O5 with the elemental metals.
pound to act as precursor to ZnO has been clearly demon- (NO)Cu(NO3)3 forms a two-dimensional network through
strated.
bridging nitrato ligands, whereas (NO)2[Zn(NO3)4] contains
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Metal Oxidation with N2O5
IR Spectroscopy: IR spectra were recorded in the range of 600–
discrete nitrate anions. The thermal decomposition of the
complexes leads to a mixture of Cu + Cu2O and ZnO,
respectively. We were also able to obtain the unique com-
plex nitrate (NO)6[Ni4(NO3)12](NO3)2·(HNO3) by the reac-
4000 cm–1 with a Bruker Tensor 27 spectrometer equipped with a
“GoldenGate” diamond-ATR unit. (NO)Cu(NO ) : ν = 2340 (m),
˜
3 3
1538 (m), 1423 (s), 1330 (s), 1290 (s), 1040 (m), 1010 (m), 800 (m),
790 (s), 710 (s) cm–1. (NO) [Zn(NO ) ]: ν = 2310 (m), 1575 (s),
˜
2
3 4
tion of N2O5 with nickel. It consists of double chains of
1364 (m), 1298 (s), 955 (sh), 905 (s), 792 (m), 767 (m), 702 (m)
2–
1{[Ni(NO3)1/1(NO3)4/2]}2 that are arranged into layers
cm–1.
ϱ
housing NO+ cations, non-coordinating nitrate ions and
free HNO3 molecules.
X-ray Crystallography: Appropriate crystals of the compounds
were selected, and diffraction data were collected by using an image
plate diffractometer (IPDS I, STOE & CIE) and CCD dif-
fractometer (Kappa APEX II, Bruker). The structures were solved
successfully by direct methods by the program SHELXS-97 as-
suming the space group P21/m for the copper complex, Fdd2 for
the zinc complex and P212121 for the nickel compound.[11] For the
subsequent full-matrix least-squares refinement, the program
SHELXL-97 was used.[12] A numerical absorption correction was
applied to the data with the help of the programs X-RED and
X-SHAPE.[13,14] The data are summarized in Table 2. Further de-
tails on the crystal structure investigations may be obtained from
the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-
Leopoldshafen, Germany (Fax: +49-7247-808-666; E-mail:
crysdata@fiz-karlsruhe.de), on quoting the depository numbers
CSD-422032 {for (NO)2[Zn(NO3)4]}, -422033 [for (NO)Cu-
(NO3)3] and -422792 {for (NO)6[Ni4(NO3)12](NO3)2·(HNO3)}.
Experimental Section
Syntheses: All compounds were obtained by the reaction of N2O5
with the metals at room temperature. N2O5 was prepared by the
reaction of fuming HNO3 with P4O10 according to a literature pro-
cedure.[10] It was directly condensed onto small amounts of ground
copper, zinc and nickel powder. The copper compound was pre-
pared in a Schlenk tube at room temperature. The reaction of liquid
N2O5 with the metal resulted in a green solution after a few days.
During the evaporation of unreacted N2O5 in a stream of N2, tur-
quoise-coloured crystals grew. Light-yellow single crystals of the
zinc complex grew after several days when the reaction mixture was
kept in a sealed glass ampoule. The reaction of nickel powder and
N2O5 was also performed in a sealed glass tube by heating at
100 °C to yield green single crystals. For copper and zinc, the reac-
tions were almost quantitative with respect to the initial metal con-
tent. The reaction with nickel afforded some green crystals (approx-
imately 10–15% based on the initial metal amount), but the yellow-
green solution indicated that there was still some metal dissolved.
Concentration of this solution after recovering the green crystals
led to a yellow powder of low crystallinity and unknown composi-
tion. All compounds are very moisture-sensitive and have to be
handled under a protective gas. Crystals of (NO)6[Ni4(NO3)
12](NO3)2·(HNO3) turned cloudy and changed to a brown-yellow
colour even in a glovebox so that no further characterization has
been performed on this compound.
Thermal Analysis: DTA/TG measurements for (NO)Cu(NO3)3 and
(NO)2[Zn(NO3)4] were performed by using a thermal analyser
(TGA/SDTA 851e, Mettler-Toledo). For this purpose, about 10 mg
of the substance was placed in a corundum container. The samples
were prepared in a glove box due to the extreme moisture sensitivity
of the compounds. Nevertheless, for the zinc compound, the com-
plete removal of all traces of N2O5 was not possible due to its
sensitivity. The samples also had to be protected during the transfer
to the thermoanalyser. The corundum crucibles were heated at a
constant rate of 10 K/min under a flow of nitrogen, and the ther-
mal decomposition was monitored from 25 to 1050 °C. Character-
istic points such as the onset and end temperatures of the thermal
Table 2. Crystallographic data for (NO)Cu(NO3)3, (NO)2[Zn(NO3)]4 and (NO)6[Ni4(NO3)12](NO3)2·(HNO3).
(NO)Cu(NO3)3
(NO)2[Zn(NO3)4]
(NO)6[Ni4(NO3)12](NO3)2·(HNO3)
Crystal size [mm]
Molar mass [g/mol]
Crystal system
Space group
a [pm]
b [pm]
c [pm]
β [°]
Cell volume
0.30ϫ0.07ϫ0.05
279.58
0.44ϫ0.54ϫ0.60
373.43
orthorhombic
Fdd2 (No. 43)
1522.8(2)
2346.4(3)
596.18(7)
0.14ϫ0.07ϫ0.02
1346.06
orthorhombic
P212121 (No. 19)
1167.68(4)
1791.97(6)
1834.11(6)
monoclinic
P21/m (No. 11)
465.90(5)
1111.7(1)
700.7(1)
100.70(2)
356.62(7)
2
153
Mo-Kα
71.07
3.131
2130.2(5)
8
153
Mo-Kα
71.07
2.416
3837.8(2)
4
153
Mo-Kα
71.07
2.121
No. of formula units
Temperature [K]
Radiation
λ [pm]
μ [mm–1]
Extinction coefficient
Measured reflections
Unique reflections
with Io Ͼ 2σ(I)
Rint/Rσ
R1, wR2 [Io Ͼ 2σ(I)]
R1, wR2 (all data)
Goodness of fit
Flack x parameter
–
4294
706
581
0.0332/0.0249
0.0230; 0.0551
0.0308; 0.0566
1.044
0.0002(1)
6258
1068
–
53559
6745
3838
0.0960/0.0944
0.0398; 0.0762
0.0841; 0.0856
0.810
979
0.0633/0.0342
0.0222; 0.0448
0.0251; 0.0452
1.496
–
0.24(1)
0.16(2)
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S. Gagelmann, K. Rieß, M. S. Wickleder
FULL PAPER
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cedures by using the software delivered with the analyser.[15] The
data are summarized in Table 1. The residues of the decomposition
reactions were investigated by X-ray powder diffraction (STADI P,
STOE & CIE); the samples were prepared on a flat sample holder,
and the diffraction patterns were analysed by using the dif-
fractometer’s software.[16]
[8] M. D. Moran, D. S. Brock, H. P. A. Mercier, G. J. Schrobilgen,
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tal Structures, University of Göttingen, Göttingen, 1997.
[12] G. M. Sheldrick, SHELXL-97 – Program for the Refinement of
Crystal Structures, University of Göttingen, Göttingen, 1997.
[13] X-RED 1.22 – Program for Data Reduction for STADI4 and
IPDS, Stoe & Cie, Darmstadt, 2001.
Acknowledgments
The authors are grateful to Wolfgang Saak for collecting the X-ray
data.
[14] X-SHAPE 1.06 – Program for Crystal Optimisation for Numeri-
cal Absorption Correction, Stoe & Cie, Darmstadt, 1996.
[15] STARe, Software for control of DTA/TGA apparatus and
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Received: June 3, 2011
Published Online: October 14, 2011
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