Theoretical Evidence for Two New Intermediate Xenon Species: Xenon Azide Fluoride, FXe(N3), and Xenon Isocyanate Fluoride, FXe(NCO)

Article abstract of DOI:10.1021/ic9613671

The reaction behavior of xenon difluoride, XeF₂, toward HN₃, NaN₃, and NaOCN was investigated in H₂O, aHF (anhydrous HF), and SO₂ClF solution. The analysis of the final reaction products (XeF₂ + HN₃ (NaN₃) in H₂O → HF, N₂, N₂O, Xe; XeF₂ + HN₃ in aHF → N₂, Xe, N₂F₂; XeF₂ + HOCN (NaOCN) in H₂O → HF, N₂, N₂O, NH₃, CO₂, Xe) indicated the intermediate formation of FXe(N₃) and FXe(NCO) and revealed different reaction mechanisms for both compounds. Both intermediates, FXe(N₃) and FXe(NCO), were studied on the basis of ab initio computations at HF and correlated MP2 levels using a quasirelativistic LANL2DZ pseudopotential for Xe. Both were shown to possess stable minima at HF and MP2 levels (no imaginary frequencies) with the following structural parameters (MP2/LANL2DZ). FXe(N₃): C_s; d(F-Xe) = 2.051, d(Xe-N1) = 2.318, d(N1-N2) = 1.241, d(N2-N3) = 1.180 ?; <(FXeN1) = 178.1, <(XeN1N2) = 112.2, <(N1N2N3) = 174.7°. FXe(NCO): C_s; d(F-Xe) = 2.024, d(Xe-N) = 2.206, d(N-C) = 1.194, d(C-N) = 1.231 ?; <(FXeN) = 178.7, <(XeNC) = 125.4, <(NCO) = 174.2°. The experimentally unobserved cyanate isomer, FXe(OCN), was calculated to be higher in energy than the isocyanate isomer FXe(NCO): ΔE = 19.8 (HF), 18.3 (MP2) kcal mol^-1.

Full text of DOI:10.1021/ic9613671

Inorg. Chem. 1997, 36, 1929-1933
1929
Theoretical Evidence for Two New Intermediate Xenon Species: Xenon Azide Fluoride,
FXe(N3), and Xenon Isocyanate Fluoride, FXe(NCO)†
Axel Schulz‡ and Thomas M. Klapo1tke*,‡
Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, U.K.
ReceiVed NoVember 14, 1996X
The reaction behavior of xenon difluoride, XeF2, toward HN3, NaN3, and NaOCN was investigated in H2O, aHF
(anhydrous HF), and SO2ClF solution. The analysis of the final reaction products (XeF2 + HN3 (NaN3) in H2O
f HF, N2, N2O, Xe; XeF2 + HN3 in aHF f N2, Xe, N2F2; XeF2 + HOCN (NaOCN) in H2O f HF, N2, N2O,
NH3, CO2, Xe) indicated the intermediate formation of FXe(N3) and FXe(NCO) and revealed different reaction
mechanisms for both compounds. Both intermediates, FXe(N3) and FXe(NCO), were studied on the basis of ab
initio computations at HF and correlated MP2 levels using a quasirelativistic LANL2DZ pseudopotential for Xe.
Both were shown to possess stable minima at HF and MP2 levels (no imaginary frequencies) with the following
structural parameters (MP2/LANL2DZ). FXe(N3): Cs; d(F-Xe) ) 2.051, d(Xe-N1) ) 2.318, d(N1-N2) )
1.241, d(N2-N3) ) 1.180 Å; (FXeN1) ) 178.1, (XeN1N2) ) 112.2, (N1N2N3) ) 174.7°. FXe(NCO):
Cs; d(F-Xe) ) 2.024, d(Xe-N) ) 2.206, d(N-C) ) 1.194, d(C-N) ) 1.231 Å; (FXeN) ) 178.7, (XeNC)
) 125.4, (NCO) ) 174.2°. The experimentally unobserved cyanate isomer, FXe(OCN), was calculated to be
higher in energy than the isocyanate isomer FXe(NCO): ∆E ) 19.8 (HF), 18.3 (MP2) kcal mol-1
.
Introduction
Xe-N bond have been reported. The first Xe-N compound
FXeN(SO2F)2 was prepared by DesMarteau et al. in 1974,6 and
it was not before 1987 that Schrobilgen et al. reported the XeF+
cation bonded to H-CN, i.e. [HCtN-Xe-F]+.7 Further
xenon-nitrogen-bonded derivatives of the -N(SO2F)2 and
-N(SO2CF3)2 groups8 as well as XeF+ cations bonded to other
organo-nitrogen ligands have been reported.9
We have been studying various neutral compounds and
cations containing a direct main-group-element-azide bond.1 Due
to the lability of the nitrogen-iodine bond (all binary N-I
species and more than a few compounds containing a direct
N-I bond are very unstable and often explosive), we especially
+
focused on iodine azide compounds, e.g. IN3, (IN3)x, I(N3)2
,
+ 2
and I2N3
.
This pronounced instability of many N-I com-
Experimental Section
pounds has facilitated both experimental and theoretical research
exploring the thermodynamics of such compounds and espe-
cially the N-I bond energy.3,4
Caution! Neat hydrazoic acid is shock sensitive, and proper safety
precautions, such as working on a small scale and using safety shields,
should be taken when the material is handled.
Materials. XeF2 (Fluorochem), NaN3 (Aldrich), and NaOCN
(Aldrich) were used as supplied. HF (Merck) was dried by storage
over BiF5.10 HN3 was prepared from NaN3 and stearic acid at 110-
130 °C.11
Apparatus. All reactions were carried out on a vacuum line
constructed largely from 316 stainless steel and nickel to which the
reaction vessel was connected via ≈1 ft length, 1/4 in. o.d. flexible FEP
tubing. The T-shaped reaction vessel originally described by Bartlett
et al. was constructed from FEP tubing (Bohlender). The commonly
We now want to explore xenon azide compounds since Xe
is the next neighbor of iodine. (N.B. Although XeF+ is a well-
known and stable cation, the isoelectronic counterpart to I2,
XeI+, is still an unknown species.) For an excellent review
covering the history of xenon chemistry see ref 5.
Whereas numerous examples of xenon bonded to oxygen or
fluorine are known, much fewer compounds containing a direct
* Corresponding author. Tel: 011 49 89 5902 630. Fax: 011 49 89 5902
382. E-mail: tmk@anorg.chemie.uni-muenchen.de.
† Dedicated to Professor Neil Bartlett on the occasion of his 65th birthday.
‡New address: Institute of Inorganic Chemistry, LMU Munich, Meis-
erstrasse 1, D-80333 Munich, Germany.
(7) Emara, A. A. A.; Schrobilgen, G. J. J. Chem. Soc., Chem. Commun.
1987, 1646.
(8) (a) DesMarteau, D. D. J. Am. Chem. Soc. 1978, 100, 6270. (b)
DesMarteau, D. D.; LeBlond, R. D.; Hossain, S. F.; Nothe, D. J. Am.
Chem. Soc. 1981, 103, 7734. (c) Sawyer, J. F.; Schrobilgen, G. J.;
Sutherland, S. J. Inorg. Chem. 1982, 21, 4064. (d) Schumacher, G.
A.; Schrobilgen, G. J. Inorg. Chem. 1983, 22, 2178. (e) Faggiani, R.;
Kennepohl, D. K.; Lock, C. J. L.; Schrobilgen, G. J. Inorg. Chem.
1986, 25, 563. (f) Foropoulos, J.; DesMarteau, D. D. J. Am. Chem.
Soc. 1987, 104, 4260.
(9) (a) Emara, A. A. A.; Schrobilgen, G. J. J. Chem. Soc., Chem. Commun.
1988, 257. (b) Schrobilgen, G. J. J. Chem. Soc., Chem. Commun. 1988,
1506. (c) Emara, A. A. A.; Schrobilgen, G. J. Inorg. Chem. 1992, 31,
1323.
X Abstract published in AdVance ACS Abstracts, April 1, 1997.
(1) (a) Tornieporth-Oetting, I. C.; Klapo¨tke, T. M. Angew. Chem. 1995,
107, 509; Angew. Chem., Int. Ed. Engl. 1995, 34, 511. (b) Klapo¨tke,
T. M. Chem. Ber. (Review), in press.
(2) (a) Hargittai, M.; Molnar, J.; Klapo¨tke, T. M.; Tornieporth-Oetting, I.
C.; Kolonits, M.; Hargittai, I. J. Phys. Chem. 1994, 98, 10095. (b)
Buzek, P.; Klapo¨tke, T. M.; Schleyer, P. v. R.; Tornieporth-Oetting,
I. C.; White, P. S. Angew. Chem. 1993, 105, 289; Angew. Chem., Int.
Ed. Engl. 1993, 32, 275. (c) Tornieporth-Oetting, I. C.; Klapo¨tke, T.
M.; Schulz, A.; Buzek, P.; Schleyer, P. v. R. Inorg. Chem. 1993, 32,
5640. (d) Tornieporth-Oetting, I. C.; Buzek, P.; Schleyer, P. v. R.;
Klapo¨tke, T. M. Angew. Chem. 1992, 104, 1391; Angew. Chem., Int.
Ed. Engl. 1992, 31, 1338.
(10) Christe, K. O.; Wilson, W. W.; Schack, C. J. J. Fluorine Chem. 1978,
11, 71.
(3) Otto, M.; Lotz, S. D.; Frenking, G. Inorg. Chem. 1992, 31, 3647.
(4) Schulz, A.; Tornieporth-Oetting, I. C.; Klapo¨tke, T. M. Inorg. Chem.
1995, 34, 4343.
(5) Laszlo, P.; Schrobilgen, G. J. Angew. Chem. 1988, 100, 495; Angew.
Chem. Int. Ed. Engl. 1998, 27, 479.
(6) LeBlond, R. D.; DesMarteau, D. D. J. Chem. Soc., Chem. Commun.
1974, 555.
(11) (a) Krakow, B.; Lord, R. C.; Neely, G. O. J. Mol. Spectrosc. 1968,
27, 198. (b) Klapo¨tke, T. M.; Tornieporth-Oetting, I. C. Nichtmet-
allchemie; VCH: Weinheim, New York, 1994.
(12) (a) Zemva, B.; Hagiwara, T.; Casteel, W. J., Jr.; Lutar, K.; Jesih, A.;
Bartlett, N. J. Am. Chem. Soc. 1990, 112, 4846. (b) Zemva, B.; Lutar,
K.; Chacon, L.; Fele-Beuermann, M.; Allman, J.; Shen, C.; Bartlett,
N. J. Am. Chem. Soc. 1995, 117, 10025.
S0020-1669(96)01367-5 CCC: $14.00 © 1997 American Chemical Society

1930 Inorganic Chemistry, Vol. 36, No. 9, 1997
Schulz and Klapo¨tke
Table 1. Gaseous Products of the Reactions of XeF2 with HN3/
NaN3 and XeF2 with NaOCN
structure. In the quantum mechanical computation (NBO analysis,
subjecting the HF density matrix as represented in the localized NBOs
to a second-order perturbative analysis), the energy for the donor-
acceptor interaction was computed according to eq 1 with hF being the
Fock operator.15
reaction
solvent IR/cm-1
assignment
ref
HN3 + XeF2
HN3 + XeF2
aHF
H2O
990a
3338 vwb ν(N-H), HN3
2565 w
2 × ν3, N2O
ν5, νas(N-F), trans-N2F2 21
3
22
3
22
3
3
22
3
2
æ|hF|æ*
2298 vw 2 × νs(NNN), HN3
(2)
ææ*
E
) -2
(1)
2225 s
2140 m
2075 vw δ (NNN), HN3
1285 m
1151 w
590 w
ν1(NN), N2O
Eæ* - Eæ
νas(NNN), HN3
Reaction of HN3 with XeF2 in aHF. In a typical reaction, XeF2
(0.51 g, 3.01 mmol) was dissolved in aHF (5 mL) in one arm of an
FEP T-reactor and HN3 (0.13 g, 3.02 mmol) was dissolved in aHF (5
mL) in the other arm. Both solutions were cooled to -78°C. The
HN3 solution was slowly added to the XeF2 solution. When the addition
was complete, the colorless solution was allowed to slowly warm to
room temperature. No reaction was observed at or below -20 °C. At
ca. -18 °C, the fast reaction started with evolution of gaseous products.
Cessation of the gas evolution signaled completion of the reaction. The
gaseous products were analyzed by gas IR spectroscopy (Table 1).
ν3(NO), N2O
νs(NNN), HN3
ν2(δ, NNO), N2O
22
NaN3 + XeF2
H2O
H2O
2225 s
2140 m
2075 vw δ (NNN), HN3
1285 m
1151 w
590 w
ν1(NN), N2O
22
3
3
22
3
22
νas(NNN), HN3
ν3(NO), N2O
νs(NNN), HN3
ν2(δ, NNO), N2O
23
NaOCN + XeF2
3718 m
3618 m
2568 w
2355 vs
2228 s
1282 m
720 m
CO2
CO2
23
23
22
23
22
22
23
23
23
Reaction of HN3 with XeF2 in H2O. This reaction was carried out
as described above for the reaction of XeF2 with HN3 in aHF with the
difference that both solutions were reacted at 0 °C (HN3, 0.13 g, 3.02
mmol; in 3 mL of H2O/XeF2, 0.51 g, 3.01 mmol; in 7 mL of H2O). A
pinkish color appeared for a short moment. The total volume of the
gaseous products formed corresponded to 7.0 mmol of gas (calculated
from expansion of the reaction products from the known-volume
reaction vessel into the calibrated vacuum line). Variation of the
temperature at which the reaction vessel was held revealed ca. 3.4 mmol
of N2, 1.1 mmol of N2O, and 2.5 mmol of Xe (bp: N2, -196 °C; N2O,
-88.5 °C; Xe, -108.1 °C).11b The gaseous products were analyzed
by gas IR spectroscopy (Table 1). The mass spectrum of the gaseous
products which were volatile at -196 °C revealed the presence of a
large amount of N2 (and traces of O2, the level of which was close to
that of the “background” air).
2 × ν3, N2O
ν3(ν,OCO), CO2
ν1(NN), N2O
ν3(NO), N2O
23
CO2
665 s
ν2(δ, OCO), CO2
a Beside HF, NH3, and small amounts of HN3. b Beside HF.
3
used reactor was constructed from /4 in. o.d. FEP tubes which were
joined at right angles by a Teflon valve (Bohlender).12
Spectroscopy. Gas infrared spectra were recorded at 20 °C (2
mmHg, 10 cm Monel cell, NaCl windows) on a Philips PU9800 FTIR
spectrometer. The NMR spectra (14N, 19F) were recorded in 10 mm
NMR tubes using a Bruker WP 200 SY spectrometer operating at
14.462 MHz (14N) or 188.313 MHz, respectively. NMR spectra in
aHF solution were recorded in 8 mm FEP NMR tubes fitted into 10
mm glass NMR tubes. All spectra are reported in ppm on the δ scale
and are referred to external MeNO2 (14N) or CFCl3 (19F), respectively.
Good 14N spectra could usually be obtained after 5000 scans and a
pulse width of 48 µs, and 19F spectra, after 20 scans and a pulse width
of 2 µs. Peak positions appearing downfield (high frequency) of the
reference are reported as plus and those upfield (low frequency) of the
reference are reported as minus.
Reaction of NaN3 with XeF2 in H2O. This reaction was carried
out as described above for the reaction of XeF2 with HN3 in H2O at 0
°C (NaN3, 0.20 g, 3.08 mmol/XeF2, 0.51 g, 3.01 mmol). The gaseous
products were analyzed by gas IR spectroscopy (Table 1).
NMR Experiment: Reaction of HN3 with XeF2 in aHF. In an
NMR experiment, XeF2 (0.38 g, 2.24 mmol) was reacted with HN3
(0.01 g, 2.24 mmol) in 5 mL of aHF. Below -20 °C, HN3 (14N NMR)
and XeF2 (19F NMR) were detected. During the rapid reaction, no
spectrum could be obtained due to bubbling of the solution. Im-
mediately after cessation of the gas evolution, the sample was recooled
to -40 °C and N2F2 was detected in the 14N NMR spectrum.
We also attempted to observe 129Xe NMR spectra (55.316 MHz;
directly referenced to external XeOF4); however, the only resonance
found could be assigned to XeF2 (δ ) -1680 ppm, triplet, 2JXe-F
(
129Xe
Before reaction: 14N NMR (-30 °C, aHF) -134 (N2, HN3), -162
satellites) ) 5604 Hz.).9c
(N3, HN3), -318 ppm (N1, HN3);16 19F NMR (-30 °C, aHF) -175
2
ppm (XeF2), JXe-F
(
129Xe satellites) ) 5611 Hz.17
Computational Methods. The structures and the vibrational spectra
of the molecules FXe(N3), FXe(NCO), and FXe(OCN) were computed
ab initio at the HF and electron-correlated MP2 levels of theory with
the program package Gaussian 94.13 For C, N, O, and F, a 6-31G(d)
basis set was used; for Xe, a quasi-relativistic pseudopotential
(LANL2DZ)14 was used where the basis functions for the valence s
and p electrons consist of the standard double-ú basis set (notation HF/
LANL2DZ or MP2/LANL2DZ). An NBO analysis was carried out to
account for non-Lewis contributions to the most appropriate valence
After reaction: 14N NMR (-40 °C, aHF) +67 ppm, t, 1JN-F ) 137
Hz (trans-N2F2);18 19F NMR (-40 °C, aHF) +95 ppm s, br (trans-
a
N2F2).18a
NMR Experiment: Reaction of HN3 with XeF2 in SO2ClF. The
NMR experiment in SO2ClF was performed with the same amounts of
XeF2 and HN3 as described above for the NMR experiment in aHF.
Before the reaction started, only HN3 and XeF2 were detected in the
14N and 19F NMR spectra. After the reaction started (Tmax ) -20 °C),
however, before it was complete, the NMR tube was rapidly recooled
to -80 °C. The spectra obtained at this temperature were indicative
for a mixture of the starting materials (XeF2 and HN3) and the final
products; however, no intermediate was detected. N2F2 could not be
detected in the 19F NMR spectrum of the quenched-reaction mixture
due to the strong solvent resonance of SO2ClF at +100 ppm.
(13) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; Johnson,
B. G.; Robb, M. A.; Cheeseman, J. A.; Keith, T.; Petersson, G. A.;
Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski,
V. G.; Ortiz, J. V.; Foresman, J. B.; Peng, C. Y.; Ayala, P. Y.; Chen,
W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.; Baker, J.;
Stewart, J. P.; Head-Gordon, M.; Gonzalez, C.; Pople, J. A. Gaussian
94, Revision B.2; Gaussian, Inc.: Pittsburgh, PA, 1995.
(14) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (b) Wadt,
W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284. (c) Hay, P. J.; Wadt,
W. R. J. Chem. Phys. 1985, 82, 299.
(15) (a) Reed, A.; Curtiss, L. A.; Weinhold, F. Chem. ReV. 1988, 88, 899.
(b) Reed, A.; Schleyer, P. v. R. J. Am. Chem. Soc. 1987, 109, 7362.
(c) Reed, A.; Schleyer, P. v. R. Inorg. Chem. 1988, 27, 3969. (d)
Klapo¨tke, T. M.; Schulz, A. Quantenmechanische Methoden in der
Hauptgruppenchemie; Spektrum: Heidelberg, Oxford, 1996.
(16) Klapo¨tke, T. M.; White, P. S.; Tornieporth-Oetting, I. C. Polyhedron
1996, 15, 2579 and references therein.
(17) Schrobilgen, G. J.; Holloway, S. H.; Granger, P.; Brevard, C. Inorg.
Chem. 1978, 17, 980.
(18) (a) Gmelin Handbook of Inorganic Chemistry, 8th ed.; Springer:
Berlin, New York, 1986; p 391 and references therein. (b) Jander, G.;
Blasius, E. Lehrbuch der analytischen und pra¨paratiVen Chemie;
Hirzel: Leipzig, 1979.

Theoretical Evidence for Intermediate Xe Species
Inorganic Chemistry, Vol. 36, No. 9, 1997 1931
Before reaction: 14N NMR (-30 °C, SO2ClF) -136 (N2, HN3),
Scheme 1. Pathways for the Formation and Decomposition
of FXeN3 and FXe(NCO)
-169 (N3, HN3), -324 ppm (N1, HN3);16 19F NMR (-30 °C, SO2ClF)
2
-174.8 ppm (XeF2), JXe-F
(
129Xe satellites) ) 5605 Hz.17
Recooled during reaction: 14N NMR (-80 °C, SO2ClF) +63 ppm,
s, br (trans-N2F2),18a -136 (N2, HN3), -172 (N3, HN3), -324 ppm
(N1, HN3);16 19F NMR (-80 °C, SO2ClF) -175.0 ppm (XeF2),
2JXe-F 129Xe satellites) ) 5606 Hz.17
(
Reaction of NaOCN with XeF2 in H2O. In a typical reaction, XeF2
(0.51 g, 3.01 mmol) was dissolved in H2O (6 mL) in one arm of an
FEP T-reactor and NaOCN (0.20 g; 3.08 mmol) was dissolved in H2O
(6 mL) in the other arm. Both solutions were cooled to 0 °C. The
NaOCN solution was slowly added to the XeF2 solution. The fast
reaction started immediately with evolution of gaseous products. A
pinkish color appeared for a short moment. Cessation of the gas
evolution signaled completion of the reaction. The gaseous products
were analyzed by gas IR spectroscopy (Table 1). Ammonia was
detected by its characteristic odor and identified as [Hg2NI‚H2O].18b
NMR Experiment: Reaction of NaOCN with XeF2 in aHF. In
an NMR experiment, XeF2 (0.38 g, 2.24 mmol) was reacted with
NaOCN (0.15 g, 2.31 mmol) in 5 mL of aHF. Below -20 °C, HNCO
(formed from NaOCN in aHF; 14N NMR) and XeF2 (19F NMR) were
detected. During the rapid reaction, no spectrum could be obtained
due to bubbling of the solution. Immediately after cessation of the
gas evolution, the sample was recooled to -40 °C.
reaction in water, NH3 was only detected as a reaction product
+
in the reaction of NaOCN with XeF2 (14N NMR, NH4 in
solution; analytically in H2O solution, Experimental Section).
Moreover, the volumetric analysis of the gaseous products
formed in the reaction of HN3 with XeF2 in water revealed that
for 4 equiv of reacted XeF2 (or HN3; cf. Scheme 1 and
Experimental Section) and 9.4 equiv of gaseous products were
found (N2, 4.5; N2O, ca. 1.5; Xe, ca. 3.4 equiv). This
corresponds within experimental errors to mechanism A (Scheme
1), where one would expect the total formation of 10 equiv of
gas (i.e.: N2, 4.0; N2O, 2.0; Xe, 4.0 equiv), rather than to
mechanism B (total 9 equiv: N2, 0.0; N2O, 5.0; Xe, 4.0 equiv).
(N.B. The volumetric analysis for the products of the isocyanate
reaction was not conclusive due to the high solubility of
ammonia and carbon dioxide in water.) The brief observation
of the pinkish color (see Experimental Section) for both the
cyanate and the azide reactions with XeF2 in aqueous solution
indicates a short-lived derivative of the aqueous system only.
So far, we have been unable to identify this species; it could,
for example, be a short-lived product of the interaction of HON
(formed from HON3 or HONCO) with water.
Before reaction: 14N NMR (-30 °C, aHF) -304 ppm (HNCO);19
19F NMR (-30 °C, aHF) -175.1 ppm (XeF2), JXe-F
(
129Xe satellites)
2
) 5611 Hz.17
After reaction: no 14N NMR (-40 °C, aHF) resonance found.
NMR Experiment: Reaction of NaOCN with XeF2 in H2O. This
reaction was carried out as described above for the reaction of XeF2
with NaOCN in aHF with the difference that both solutions were reacted
at 0 °C (NaOCN, 0.15 g, 2.31 mmol/XeF2, 0.38 g, 2.24 mmol).
Immediately after cessation of the gas evolution, the NMR spectrum
was recorded at 0 °C and NH4+ was detected in the 14N NMR spectrum.
After reaction: 14N NMR (0 °C, aHF) -355.0 ppm (NH4+).20
Due to the very poor solubility of NaOCN in SO2ClF, no attempt
was made to obtain NMR data in this solvent.
Both mechanisms (A and B) can easily be understood by
initial hydrolysis of the Xe-F and Xe-N bonds according to
their polarity (eqs 2 and 3). It is known that thermal fragmenta-
Results and Discussion
F-Xe-N3 + H2O f H-O-N3 + HF + Xe
(2)
Reactions in Water. It is well-known that fluorine gas reacts
at room temperature with moist NaN3 or with NaN3 suspended
in H2O/HF to intermediately form N3F, which thermally
decomposes into N2 and NF radicals, which then combine to
give N2F2.24 However, in no experiment in which we reacted
NaN3, HN3, or NaOCN with XeF2 in aqueous conditions did
we observe the formation of N2F2 (see below for reaction of
NaN3 in aHF). Although we cannot completely rule out that
any N2F2 formed in the course of the reaction could have entirely
hydrolyzed by the time the reaction was over, it is far less likely
that XeF2 behaves as a simple fluorination agent in these
reactions but intermediately forms F-Xe-N3 or F-Xe-NCO,
respectively (cf. Scheme 1). Both intermediates (F-Xe-N3 and
F-Xe-NCO) are not expected to be stable in water but are
expected to hydrolyze according to mechanism A or B shown
in Scheme 1.
F-Xe-NCO + H2O f H-O-NCO + HF + Xe (3)
tion of covalently bound azides, XN3, is induced not by breaking
the X-N3 bond but rather by dissociation into XN and N2 (i.e.,
HN3 decomposes into HN and N2).3,25 Therefore, HON3 will
dissociate into N2 and HON radicals which will combine into
hyponitrous acid, i.e. trans-(HNO)2 (eq 4).26 Although neat
hyponitrous acid is known,27 a the compound rapidly decom-
poses to form N2O and H2O (eq 5).27b In case of mechanism
HON3 f {HON} + N2 f
1/2 trans-HO-NdN-OH + N2 (4)
trans-HO-NdN-OH f N2O + H2O
(5)
Whereas N2O was identified by IR spectroscopy (Table 1)
as one of the products of the azide as well as of the isocyanate
B (isocyanate reaction), the initially formed H-O-NCO (eq
3) reacts with water according to eq 6 to form (i) carbonic acid,
which liberates CO2 (eq 7), and (ii) hydroxylamine, which
decomposes into a complex mixture of NH3, N2O, and H2O
(19) Logan, N. In Nitrogen NMR; Witanowski, M., Webb, G. A.. Eds.;
Plenum: London, New York, 1973; Chapter 6.
(20) Geissler, P.; Klapo¨tke, T. M.; Kroth, H.-J. Spectrochim. Acta 1995,
51A, 1075.
(21) King, S.-T.; Overend, J. Spectrochim. Acta 1966, 22, 689.
(22) (a) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed.; Wiley, New York, Chichester,
1986. (b) Mecke, R.; Langenbucher, F. Infrared Spectra; Heyden:
London, 1965; Serial No. 106.
(23) Mecke, R.; Langenbucher, F. Infrared Spectra; Heyden: London, 1965;
Serial No. 6.
(24) Gmelin Handbook of Inorganic Chemistry, 8th ed.; Springer: Berlin,
New York, 1986; p 385 and references therein.
(25) (a) Richardson, W. C.; Setser, D. W. Can. J. Chem. 1969, 47, 2725.
(b) Alexander, M. H.; Werner, H.-J.; Dagdigian, P. J. J. Chem. Phys.
1988, 89, 1388.
(26) (a) Harteck, P. Ber. Dtsch. Chem. Ges. 1933, 66, 423. (b) McGraw,
G. E.; Bernitt, D. L.; Hisatsune, I. C. Spectrochim. Acta 1967, 23A,
25. (c) Lu¨ttke, W.; Skancke, P. N.; Traetteberg, M. Theor. Chim. Acta
1994, 87, 321.
(27) (a) Hughes, M. N. Q. ReV., Chem. Soc. 1968, 22, 1. (b) Greenwood,
N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford,
1984; p 527. (c) Ibid., pp 495-496.

1932 Inorganic Chemistry, Vol. 36, No. 9, 1997
Table 2. Ab Initio Calculated Energies and Structural Parameters of FXeN3, FXeNCO, and FXe(OCN) (Notation: F-Xe-A-B-C)
FXeN3 FXeNCO FXe(OCN)
Schulz and Klapo¨tke
HFa
MP2a
HFa
MP2a
HFa
MP2a
-E/a.u.
277.681 89
278.415 03
281.608 47
282.286 74
281.576 83
282.257 64
d(F-Xe)/Å
d(Xe-A)/Å
d(A-B)/Å
1.980
2.184
1.218
1.107
178.2
114.6
177.2
2.051
2.318
1.241
1.180
178.1
112.2
174.7
1.944
2.138
1.192
1.158
178.9
134.5
177.4
2.024
2.206
1.194
1.231
178.7
125.4
174.2
1.910
2.139
1.265
1.142
178.5
119.2
178.8
2.009
2.207
1.292
1.192
179.1
113.7
179.1
d(B-C)/Å
(FXeA)/deg
(XeAB)/deg
(ABC)/deg
a For C, N, O, and F, a 6-31G(d) basis set was used; for Xe, a quasi-relativistic pseudopotential (LANL2DZ)14 was used where the basis functions
for the valence s and p electrons consist of the standard double-ú basis set (notation: HF/LANL2DZ or MP2/LANL2DZ).
Table 3. Ab Initio Calculated Frequencies (cm-1), Intensities in Parentheses (km mol-1), and Zero-Point Energies (zpe) of FXeN3, FXeNCO,
and FXe(OCN) (Notation: F-Xe-A-B-C)
FXeN3
FXeNCO
FXe(OCN)
approx assign
HFa
MP2a
HFa
MP2a
HFa
MP2a
νas(ABC), A′
νs(ABC), A′
2425 (1245)
1375 (492)
759 (10)
694 (27)
511 (411)
403 (57)
243 (28)
221 (38)
118 (8)
2246 (836)
1251 (24)
645 (1)
551 (6)
470 (92)
277 (1)
186 (15)
172 (21)
95 (5)
2439 (2521)
1519 (49)
756 (62)
713 (73)
562 (261)
385 (152)
233 (48)
240 (41)
82 (5)
2300 (1147)
1325 (25)
637 (14)
580 (24)
482 (165)
344 (16)
199 (29)
200 (30)
86 (29)
2572 (464)
1256 (248)
697 (44)
622 (32)
608 (212)
402 (108)
228 (25)
236 (32)
108 (12)
9.62
2194 (140)
1325 (25)
586 (24)
497 (10)
482 (138)
350 (0)
187 (18)
200 (15)
98 (9)
δ(ABC), A′
γ(ABC), A′′
ν(FXe), A′
ν(XeABC), A′
δ(FXeABC),A′
γ(FXeABC),A′′
δ(FXeABC), A′
zpe/kcal mol-1
9.65
8.44
9.91
8.80
8.16
a For C, N, O, and F, a 6-31G(d) basis set was used; for Xe, a quasi-relativistic pseudopotential (LANL2DZ)14 was used where the basis functions
for the valence s and p electrons consist of the standard double-ú basis set (notation: HF/LANL2DZ or MP2/LANL2DZ).
(eq 8) (occasionally, some N2 is formed as well during the
decomposition of hydroxylamine).27c
H-O-NCO + 2H2O f HONH2 + (HO)2CO
(HO)2CO f H2O + CO2
(6)
(7)
HONH2 f 1/4N2O + 3/4H2O + 1/2NH3
(8)
Figure 1. Structures of FXeN3, FXeNCO, and FXe(OCN).
Computational Aspects. The structures of both observed
intermediates, FXeN3 and FXe(NCO), as well as the structure
of the cyanate isomer, FXe(OCN), were computed ab initio at
the HF and electron-correlated MP2 levels of theory and were
fully optimized within Cs symmetry (Table 2, Figure 1). For
xenon, a quasi-relativistic pseudopotential was used. All three
molecules represent true minima at the energy hypersurface (no
imaginary frequencies; Table 3). The experimentally unob-
served cyanate isomer FXe(OCN) (N.B. Neither H2O2 nor
HOCNsthe most likely products of the decomposition of the
hypothetical FXe(OCN), i.e. of HO-OCNswas detected) was
found to be 19.8 kcal mol-1 (HF level) and 18.3 kcal mol-1
(MP2 level) higher in energy than the isocyanate form FXe-
(NCO) (Table 2). This finding nicely compares to the fact that
OdC-N-N-CdO is also much lower in energy than the O-O
bound isomer NtC-O-O-CtN (e.g., isocyanate radicals,
OdCdN•, are much more stable than cyanate radicals NtC-
O•).29,30
Reactions in aHF. Whereas we do have evidence for the
intermediate formation of FXeN3 and FXe(NCO) in water, the
final products from the reactions carried out in aHF are in accord
with both (i) the intermediate formation of FXeN3 and FXe-
(NCO) and (ii) the behavior of XeF2 as a fluorinating agent,
yielding FN3 and or FNCO, respectively, and HF (NaF). We
unequivocally identified small amounts of trans-N2F2 from the
IR and 14N/19F NMR spectra looking at the products formed
from the reaction of HN3 and XeF2 in aHF (eq 9).
FN3 aHF8 {FN} + N2 f 1/2 trans-N2F2 + N2
(9)
Thermodynamic Aspects. The formation of FXeN3 and
FXe(NCO) from XeF2 and HN3 or HNCO is thermodynamically
feasible (largely due to the strong H-F bond) as indicated by
an energy cycle describing the gas phase reactions according
to eqs 10 and 11. The upper (i.e., in reality, more negative)
XeF2(g) + HN3(g) f FXeN3(g) + HF(g)
(10)
(28) (a) Bond enthalpy terms at 298.15 K (all values in kcal mol-1): Xe-F
(XeF2), 31.3;11b H-N (HN3), 92.2;28b H-F (HF), 135.6.11b (b)
Illenberger, E.; Comita, P. B.; Brauman, J. I.; Fenzlaff, H.-P.; Heni,
M.; Heinrich, N.; Koch, W.; Frenking, G. Ber. Bunsen-Ges. Phys.
Chem. 1985, 89, 1026.
XeF2(g) + HNCO(g) f FXeNCO(g) + HF(g) (11)
(29) (a) Klapo¨tke, T. M.; Schulz, A. Inorg. Chem. 1996, 35, 4791. (b) Maier,
G.; Naumann, M.; Reisenauer, H. P.; Eckwert, J. Angew. Chem. Int.
Ed. Engl. 1996, 35, 1696. (c) Klapo¨tke, T. M.; Schulz, A. Inorg. Chem.
1996, 35, 7897.
values for ∆H° could be estimated using the literature data for
the bond enthalpies and taking the Xe-N bond dissociation
enthalpy equal to zero:28 ∆H°(10) < -12.1 kcal mol-1; ∆H°(11)
< -12.1 kcal mol-1
.
(30) Thomson, C.; Wishart, B. Theor. Chim. Acta 1974, 35, 361.

Theoretical Evidence for Intermediate Xe Species
Inorganic Chemistry, Vol. 36, No. 9, 1997 1933
The MP2-computed F-Xe bond lengths for FXeN3 and FXe-
(NCO) of 2.05 and 2.02 Å are just slightly longer than the
experimentally determined value of 1.97 Å for the F-Xe bond
in the covalent molecule FXeN(SO2F)2, which also contains
divalent xenon directly bound to one fluorine and one nitrogen
atom (cf. XeF2, d(Xe-F) ) 1.977 Å).6,8,9c Whereas the Xe-N
bond length of 2.20 Å in FXeN(SO2F)26,8 compares well to the
calculated value of 2.21 Å in FXe(NCO), the Xe-N bond in
the azide was computed to be 2.32 Å and is therefore expected
to be substantially weaker than that in the iminodisulfuryl
derivative. On the other hand, the Xe-N bond length in FXeN3
is still substantially shorter than the calculated Xe-N bond
length in the cationic adduct [FXe(NCH)]+ (2.42 Å).9c The
relatively weak Xe-N bond in FXeN3 can be rationalized in
the localized picture by an NBO analysis. A strong donor-
acceptor interaction (negative hyperconjugation) which weakens
the Xe-N bond was found for FXeN3: σ(Xe-N1) f π*(N2-
N3), 52 kcal mol-1. (N.B. This interaction is much stronger in
FXeN3 than in FXe(NCO).)
From the experimental and theoretical results discussed in this
paper, the following conclusions can de drawn: (i) The
formation of the observed hydrolysis products in the reaction
of XeF2 with HN3 (or NaN3) and HNCO (or NaOCN) in water
can mechanistically be better explained by an intermediate
formation of FXe(N3) and FXe(NCO) than by a simple
fluorination of the azide and isocyanate. No experimental
evidence was found for the formation of the isomeric cyanate
compound FXe(OCN). (ii) Xenon azide fluoride, FXe(N3), and
xenon isocyanate fluoride, FXe(NCO), both possess minimum
structures (true minima; no imaginary frequencies) on their
energy hypersurface at HF and electron-correlated MP2 levels
of theory. (iii) The isomeric cyanate compound FXe(OCN) also
represents true minima at HF and MP2 levels; however, this
isomer is higher in energy than the isocyanate species by 19.8
kcal mol-1 (HF level) and 18.3 kcal mol-1 (MP2 level).
Acknowledgment. We thank Mr. Jim Gall for the multi-
nuclear NMR measurements. Financial support from the
University of Glasgow and the Deutsche Forschungsgemein-
schaft is gratefully acknowledged.
Conclusions
The reaction behavior of XeF2 toward azides and isocyanates
has been studied experimentally in aqueous solution and in aHF.
IC9613671