In pursuit of the PO2+ cation. The reaction of KPO2F2 and SbF5 leads to an eight-membered antimony-oxygen-phosphorus-bridged ring

Article abstract of DOI:10.1002/1521-3749(200104)627:4<631::AID-ZAAC631>3.0.CO;2-C

The reaction of KPO₂F₂ with the strong Lewis acid SbF₅ was studied as a potential pathway to the unknown PO₂⁺ cation. The resulting product has the desired PO₂SbF₆ composition but consists of an eight-membered, antimony-oxygen-phosphorus-bridged ring that was characterized by vibrational and NMR spectroscopy, ab initio methods, and a single crystal x-ray diffraction study. The preferred formation of the ring and its mechanism are discussed. Wiley-VCH Verlag GmbH, 2001.

Full text of DOI:10.1002/1521-3749(200104)627:4<631::AID-ZAAC631>3.0.CO;2-C

+
In Pursuit of the PO Cation. The Reaction of KPO F and SbF
2
2 2
5
leads to an Eight-membered Antimony-Oxygen-Phosphorus-bridged Ring
a
b
b
c
a
Stefan Schneider , Ashwani Vij , Jeffrey A. Sheehy , Fook S. Tham , Thorsten Schroer ,
a,b
and Karl O. Christe
*
a
Los Angeles, California/USA, Loker Hydrocarbon Research Institute, University of Southern California, University Park
Edwards, California/USA, Air Force Research Laboratory
Riverside, California/USA, University of California
b
c
Received December 12th, 2000.
Professor Josef Goubeau in memoriam
Abstract. The reaction of KPO F with the strong Lewis acid
single crystal x-ray diffraction study. The preferred formation
of the ring and its mechanism are discussed.
2
2
SbF5 was studied as a potential pathway to the unknown
+
PO2 cation. The resulting product has the desired PO SbF6
2
composition but consists of an eight-membered, antimony-
oxygen-phosphorus-bridged ring that was characterized by
vibrational and NMR spectroscopy, ab initio methods, and a
Keywords: Phosphorus; Vibrational spectroscopy; NMR
spectroscopy; Crystal structure; Ab inito calculations
+
Auf der Suche nach demPO 2 Kation. Die Reaktion von KPO F mit SbF
2 2
5
f uÈ hrt zu einemachtgliederigen Sb±O±P verbruÈckten Ring
+
Inhalts uÈ bersicht. Auf der Suche nach PO2 Kationen wurde
gungsspektroskopischen, NMR, und ab initio Methoden,
die Reaktion von KPO F mit der starken Lewiss aÈ ure SbF
sowie einer Einkristallr oÈ ntgenstrukturuntersuchung charak-
terisiert wurde. Der Mechanismus und die bevorzugte Bil-
dung des sauerstoffverbr uÈ ckten Ringes werden diskutiert.
2
2
5
untersucht. Das resultierende Produkt mit der gew uÈ nschten
Zusammensetzung PO SbF besteht aus einem achtglied-
2
6
rigen sauerstoffverbr uÈ ckten Ring der anhand von schwin-
±
Introduction
between PO2F2 and two AsF molecules >eq. >1), Fig-
5
+
ure 1) and no PO F or PO were observed.
2
2
In viewof the long kno wn existence, great stability
and general utility of CO , SiO and NO , it is sur-
prising that the closely related PO2 cation is pre-
sently still unknown. The only data available is an
ab initio calculation on the free gaseous ion [1]. Very
little is also known about its parent molecule, phos-
+
2
2
2
KPO F + 2 AsF ® K[PO F ´ 2 AsF ]
>1)
2
2
5
2
2
5
+
+
The failure to generate the PO2 cation in this reac-
tion can be attributed to PO F having a Lewis acidity
comparable to that of AsF [6, 7]. Therefore, PO F
shares its oxygen ligands with AsF through the for-
mation of a donor-acceptor adduct rather than give up
fluoride ions to form PO F or the PO cation. Since
SbF5 and particularly oligomeric SbF5 are much
stronger Lewis acids than AsF [6], it was hoped that
the replacement of AsF in reaction >1) by an excess
of SbF might lead to PO .
Another highly interesting aspect is the most plausi-
ble structure of PO . Whereas the minimum energy
structure of the free gaseous PO2 ion is a di-coordi-
nated linear monomer [1] as in CO and NO , the
condensed phase structure of PO2 is more proble-
matic. Since phosphorus seeks a coordination number
higher than two, the PO2 cations would either have
2
±
5
2 2
phoryl fluoride [2, 3], however, the corresponding an-
5
±
ion, PO F , is well known and characterized [4].
2
2
+
Since anions can generally be converted to the corre-
sponding parent molecules and cations by treatment
with a strong Lewis acid, it was interesting to study
the reaction of a PO2F2 salt with strong Lewis acids.
In a previous study in our laboratory, the interaction
2
2
5
±
5
+
5
2
between KPO F and AsF had been studied [5]. Sur-
prisingly, only an oxygen-bridged polynuclear anion
2
2
5
+
2
+
+
2
2
*
Prof. Dr. Karl O. Christe,
+
University of Southern California,
Loker Hydrocarbon Research Institute,
Los Angeles, CA 900089-1661, USA
e-mail: karl.christe@edwards.af.mil
+
to polymerize, as isoelectronic SiO does, or undergo
2
Z. Anorg. Allg. Chem. 2001, 627, 631±637
Ó WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0044±2313/01/627631±637 $ 17.50+.50/0
631

S. Schneider, A. Vij, J. A. Sheehy, F. S. Tham, T. Schroer, K. O. Christe
Table 1 Crystal data and structure refinement for
>
SbF O PF )
4 2 2 2
Empirical formula
Space group
Unit cell dimensions
F
12
O
4
P
2
Sb
2
P1 triclinic
Ê
Ê
Ê
a = 5.565>4) A a = 88.685>16)°
b = 7.406>6) A b = 76.367>16)°
c = 7.443>6) A c = 83.364>16)°
±
Ê
3
Volume/A
296.1>4)
3.350
Fig. 1 Polynuclear anion [PO F ´ 2AsF ] .
2
2
5
±3
q
>calculated)/g cm
Z
2
Formula weight
l/mm
597.44
5.001
±1
fluorine or oxygen bridging with the anions. Of these
two choices, the first one is less likely because it
would result in an accumulation of mutually repelling
positive charges.
Temperature/K
k >MoKa)/A
Crystal size/mm
Theta range for data collection h/°
Index ranges >hkl)
Reflections collected
Independent reflections
F>000)
203>2)
0.71073
Ê
0.20 ´ 0.12 ´ 0.10
2.77 to 26.37
±6 £ h £ 6, ±9 £ k £ 9, ±9 £ l £ 9
2845
1202 [R>int) = 0.0469]
272
0.565765 and 0.406416
R1 = 0.0406, wR2 = 0.0987
R1 = 0.0416, wR2 = 0.0997
2.174 and ±1.864
SADABS
Experimental
Max. and min. transmission
a)
R
R
[I > 2r>I)]
>all data)
Materials and Methods
a)
Ê
3
Largest diff. peak and hole >e A )
Absorption correction
Goodness-of-fit on F
Data/restraints/parameters
Refinement method
All volatile materials were handled in either a stainless-steel
vacuum line [8] equipped with Teflon-FEP U-traps, 316
stainless-steel bellows-seal valves, and a Heise Bourdon
tube-type pressure gauge, or a flamed-out Pyrex glass va-
cuum line equipped with grease-free Kontes glass Teflon
valves. Nonvolatile materials were handled in the dry nitro-
gen atmosphere of a glove box.
2
1.168
1202/0/91
Full-matrix least-squares on F
2
a)
R = R|Fo| ± |Fc| |/R|Fo|.
Infrared spectra were recorded in the range of 4000±
4
Table 2 Atomic coordinates >´ 10 ) and equivalent isotro-
pic displacement parameters >A ´ 10 )
±
1
4
1
00 cm on a Midac FT-IR Model 1720 at a resolution of
Ê
2
3
±
1
cm . Spectra of solids were obtained by using dry powders
a)
pressed between AgCl windows in an Econo press >Barnes
Engineering Co.). Spectra of gases were obtained by using a
stainless steel cell of 5 cm path length equipped with AgCl
windows. Raman spectra were recorded in the range of
x
y
z
U>eq)
Sb>1)
P>1)
F>1)
F>2)
F>3)
F>4)
O>2)
O>1)
F>6)
F>5)
4170>1)
2277>2)
6657>6)
1648>6)
2636>8)
6091>8)
4353>8)
2190>7)
±202>6)
2419>7)
7691>1)
11935>2)
9178>5)
6397>5)
8157>6)
5603>5)
12637>6)
9927>5)
12778>5)
12638>5)
2440>1)
1685>2)
2470>6)
2075>5)
4885>5)
2912>6)
276>6)
1761>6)
1420>5)
3522>5)
20>1)
20>1)
32>1)
29>1)
38>1)
39>1)
28>1)
26>1)
33>1)
33>1)
±
1
4
000±10 cm on a Bruker Equinox 55 FT-RA spectrophoto-
meter using a NdYag laser at 1064 nm. Pyrex melting point
capillaries or NMR tubes, that were baked out at 300 °C for
4
8 h at 10 mtorr vacuum, were used as sample containers.
The F and P NMR spectra were recorded on a Bruker
19
31
AM-360 spectrometer equipped with a 8.45556-T cryomagnet.
Samples were measured in heat sealed 4 mm glass tubes and
a)
U
i j i j i j
eq = >1/3) R R Uij a*a*a*a )
19
31
referenced to CFCl > F) and 85% H PO > P) with positive
3
3
4
shifts being to high frequency of the reference compounds.
Commercially available urea, KH PO >Aldrich),
NH HF >Riedel-de-Haen) and SO >Matheson) were used
as received. SbF >Ozark Mahoning) was purified by distilla-
tion prior to use. A literature method was used for the pre-
paration of KPO [9] and it showed no impurities detect-
Data were integrated using the SAINT [11] software pack-
age, and the rawdata was corrected for absorption using the
SADABS [12] program. The structure was solved by the Pat-
terson method using the SHELXS-97 [13] program and re-
2
4
4
2
2
5
2
fined by the least squares method on F using SHELXL-97
2 2
F
[
14]. The crystal did not showany significant decomposition
able by vibrational spectroscopy.
during the data collection. The experimental and refinement
parameters, and the atomic coordinates and thermal displa-
cement parameters are listed in Tables 1 and 2, respectively.
Single crystals of >SbF O PF ) were grown by slow sub-
4
2
2 2
limation at 90 °C. They were mounted on the goniometer
head by the oil-drop method using perfluoropolyether
>
PFPE) oil and precentered Nylon Cryoloops equipped with
a magnetic base. The crystal structure was determined at
03 K using a Bruker diffractometer equipped with a CCD
Computational Methods
2
detector and a lowtemperature, LT3, device. The 3-circle
platform with a fixed v-axis was controlled by the SMART
Infrared and Raman spectra for oxygen- and fluorine-
bridged >SbF O PF ) complexes were computed by the
4
2
2 2
[
10] software package. The unit cell parameters were deter-
density-functional approach using the B3LYP functional
[15]. The so-called DFT/DZVP all-electron basis set [16, 17],
supplemented with one f function with an exponent of
0.3854 taken from the polarization functions of Ahlrichs
[18], was used for antimony, and 6-311G>d) basis sets of
Pople et al. [19] were used for oxygen, phosphorus, and
mined from three runs of data with 30 frames per run using
a scan speed of 30-seconds per frame. A complete hemi-
sphere of data was collected using 1271 frames at 30 sec/
frame, including 50 frames that were collected at the begin-
ning and end of the data collection to monitor crystal decay.
632
Z. Anorg. Allg. Chem. 2001, 627, 631±637

+
In Pursuit of the PO2 Cation
fluorine. Cartesian coordinates taken from crystal structure
determinations were used as a starting point for the geome-
try optimizations. The calculations were carried out on IBM
RS/6000 Model 260 workstations using the Gaussian 98 [20]
program system.
agree well with those observed by us for
SbF O PF ) >crystalline solid, stable at 95 °C). Also
>
4
2
2 2
the reported IR spectrum >1230 vs, 1175 s, 1095 w,
042 s, 961 m, 735 s, 705 vs, etc) shows only fair agree-
1
31
ment with our data >see below), but their P NMR
spectrum agrees well with that observed in this study.
Although in our opinion, Kr uÈ ger, Dehnicke and Shiha-
da had probably prepared the same compound and
suggested, by analogy with related known compounds,
the correct oxygen-bridged dimeric structure, their
compound may have been of poor purity and was not
well characterized.
Syntheses of ꢀSbF O PF ) and KPO F ´ 2 SbF
4
2
2 2
2
2
5
2 2
In the drybox, KPO F >6.39 mmol) was placed into a
flamed-out Pyrex glass reaction vessel equipped with a
grease-free Kontes glass Teflon valve. On the metal vacuum
line, a large excess of SbF >34.23 mmol) and a fewml of
5
SO2 were added to the reaction vessel. After keeping the
mixture at room temperature for several hours, the SO and
2
unreacted SbF5 were pumped off and pure, crystallinic
Crystal structure of ꢀSbF O PF )
2 2
4
2
>
SbF O PF ) was obtained in high yield by vacuum subli-
4 2 2 2
mation at 95 °C. The colorless solid residue consisted of
KSbF6 that was identified by vibrational spectroscopy and
the observed mass balance.
The crystals of >SbF O PF ) belong to the centro-
4
2
2 2
symmetric space group P1. The asymmetric unit cell
contains one half of the dimer and the other half is
generated by the symmetry operation ±x + 1, ±y + 2, ±
z. The structure of >SbF O PF ) >Figure 2, Table 3)
In another experiment,
13.52 mmol) and SbF5 >27.2 mmol) was placed into a
flamed-out Pyrex glass vessel. After a couple of weeks at
room temperature, all the liquid SbF had reacted with
KPO resulting in a dry colorless powder. A comparison
of the vibrational spectra of the product with those of the
KPO ´ 2AsF polyanion [5] showed, that the product had
the composition KPO ´ 2 SbF
Raman spectral data for KPO F ´ 2 SbF >dry powder)
a 1 : 2 mixture of KPO2F2
>
4
2
2 2
shows that the molecule contains an eight-membered
Sb±O±P±O] ring which adopts a chair conformation
5
[
F
2
2
2
where two SbF units are bridged by two ±OP>F )O-
4
2
2
F
2
5
groups. The phosphorus and oxygen atoms are co-
planar with a maximum mean plane deviation of
2
F
2
5
.
Ê
2
2
5
0.0186 A and the antimony atoms are located above
±1
[
cm >relative intensity)]: 232>12.8), 294>38.5), 598>2.6),
Ê
and belowthis plane at 1.1418 A . There is a significant
613>5.1), 659>100), 689>15.4), 956>7.7).
distortion of the octahedral environment around the
antimony atoms due to the two bridging oxygen li-
gands having considerably longer bonds and, there-
fore, being less repulsive. The fluorine atoms F1 and
F2 are located in a quasi-axial position and are longer
Heating of KPO F ´ 2SbF to 95 °C resulted in the subli-
2
2
5
mation of >SbF O PF ) . Further heating of >SbF O PF )
4
2
2 2
4
2
2 2
led to slowPOF 3 evolution and produced a colorless liquid
of undetermined composition.
Ê
Ê
by 0.02 A >average Sb±F = 1.865 A) compared to
the equatorial fluorine atoms F3 and F4 >average
Results and Discussion
Ê
Synthesis and Properties of ꢀSbF O PF )
2 2
Sb±F = 1.845 A). The two Sb-O distances are practi-
cally identical at 2.004>4) A. Due to the presence of
4
2
Ê
The room-temperature reaction of KPO F with ex-
2
2
the two longer Sb±O bonds, the F1±Sb1±F2 angle is
compressed to 171.2>2)° from the ideal value of 180°,
the O±Sb±O angle is compressed to 86.4>2), and the
F3±Sb1±F4 angle is widened to 93.6>2)°. A compari-
cess SbF in the presence of a suitable solvent, such as
5
SO , followed by the removal of the solvent and ex-
2
cess SbF and a vacuum sublimation at 95 °C, pro-
5
duces KSbF and a product of the desired composition
6
PO SbF >eq. >2)).
2
6
KPO F + 2 SbF ® ªPO SbF º + KSbF
>2)
2
2
5
2
6
6
The more volatile ªPO SbF º can be readily separated
2
6
from the KSbF by vacuum sublimation at 95 °C and
6
was obtained in high yield and purity. As will be
shown below, this compound does not have a simple
+
±
PO SbF structure but consists of eight-membered,
2
6
oxygen-bridged >SbF O PF ) units.
4
2
2 2
A compound with such a structure has been pro-
posed previously by Kr uÈ ger, Dehnicke, and Shihada
[
21±23]. It was isolated in 4% yield from the reaction
of SbF with HOPOF >eq. >3)).
5
2
HOPOF + SbF ® F Sb>O PF ) + HF
>3)
2
5
4
2
2
However, its reported properties >fine, white crystals,
Fig. 2 Ortep Plot of >SbF O PF ) ; thermal ellipsoids are
4
2
2 2
m.p. 65 °C, decomp.p. 70 °C with POF loss) do not
shown at the 30% probability level.
3
Z. Anorg. Allg. Chem. 2001, 627, 631±637
633

S. Schneider, A. Vij, J. A. Sheehy, F. S. Tham, T. Schroer, K. O. Christe
son of the bond distances and angles for >SbF O PF )
2 2
also explored. It resulted in a significantly higher R
factor and larger thermal parameters and was there-
fore rejected. Further support for the oxygen-bridged
model comes from the vibrational spectra and theore-
tical calculations.
4
2
with those of closely related SbCl derivatives [22, 23]
4
is listed in Table 4 and shows good agreement.
The crystal packing diagram of >SbF O PF ) along
4
2
2 2
the b-axis is shown in Figure 3. The chair-form mole-
cules make contacts with the neighboring molecules
resulting in a polymeric chain. The closest contact dis-
Vibrational Spectra and Theoretical Calculations
Ê
tances are P1 ´ ´ ´ F2 and P1 ´ ´ ´ F3 at 3.295 and 3.277 A,
The Raman and infrared spectra of >SbF O PF ) are
4
2
2 2
respectively.
shown in Figure 4. The observed and calculated fre-
quencies and IR and Raman intensities are summa-
rized in Table 5. For comparison, the calculated spectra
of the fluorine-bridged model have also been listed in
this table. As can be seen from Table 5, the observed
spectra agree only with the oxygen-bridged but not
with the fluorine-bridged model. In a fluorine-bridged
structure, the P±O bonds would possess significant
double bond character and their antisymmetric
Since oxygen and fluorine atoms are often difficult
to distinguish in crystal structures, the possibility of re-
fining our data set for a fluorine-bridged model was
Ê
Table 3 Bond lengths/A and selected angles/° for
>
SbF O PF )
4 2 2 2
Sb>1)±F>3)
Sb>1)±F>4)
Sb>1)±F>2)
Sb>1)±F>1)
Sb>1)±O>2)#1
Sb>1)±O>1)
P>1)±O>1)
P>1)±F>5)
1.841>4)
1.851>4)
1.861>3)
1.870>4)
2.003>4)
2.004>4)
1.493>4)
1.497>4)
1.499>4)
1.502>3)
F>3)±Sb>1)±F>2)
F>2)±Sb>1)±F>1)
F>2)±Sb>1)±O>2)#1
F>4)±Sb>1)±O>1)
O>2)#1±Sb>1)±O>1)
O>1)±P>1)±F>5)
O>1)±P>1)±O>2)
F>5)±P>1)±O>2)
O>1)±P>1)±F>6)
F>5)±P>1)±F>6)
93.0>2)
171.1>2)
86.3>2)
176.4>2)
86.4>2)
110.4>2)
117.3>2)
106.6>2)
106.8>2)
104.5>2)
110.6>2)
136.8>3)
138.7>3)
±1
stretching vibrations should occur in the 1500 cm
region.
The assignments for >SbF O PF ) were made in
4
2
2 2
point group C , in accord with the results from the
i
crystal structure determination and the theoretical cal-
culations which show that >SbF O PF ) possesses
P>1)±O>2)
P>1)±F>6)
4
2
2 2
only a symmetry center and that no atoms lie on this
center. A total of 54 fundamental vibrations are ex-
pected out of which one half of them is symmetric
O>2)±P>1)±F>6)
P>1)±O>2)±Sb>1)#1
P>1)±O>1)±Sb>1)
>
g
A modes) and the other half is antisymmetric >Au
Symmetry transformations used to generate equivalent atoms:
1 ±x + 1, ±y + 2, ±z
#
modes) to the symmetry center. The A modes are
g
due to the in-phase motions of the symmetry related
Ê
groups and are only Raman active, while the Au
Table 4 Comparative bond distances/A and angles/° >in
>
SbF O PF ) , >SbCl O PCl ) and >SbCl O PMe )
modes represent the out-of-phase motions of these
4
2
2 2
4
2
2 2
4
2
2 2
groups and are only infrared active. Since the vibra-
a)
2
>
SbF
4
O
2
PF
2
)
>SbCl
4
O
2
PCl
2
)
2
>SbCl
[23]
4 2 2 2
O PMe )
tional coupling between the corresponding A and Au
g
[22]
modes is relatively weak, their frequency separations
are small, except for the four highest frequency modes
that are due to the antisymmetric and symmetric in-
Sb±O >av)
Sb±X
2.004>4)
1.856>4)
2.06
2.30
2.01
2.35
>
X = F or Cl) >av)
P±O >av)
O±Sb±O
O±P±O
1.496>4)
86.4>2)
117.3>2)
1.50
83
116
1.55
87
113
a)
present work
4 2 2 2
Fig. 3 Packing diagram of >SbF O PF ) along the b-axis
showing the formation of a layered chain polymer through
P ´ ´ ´ F bridges.
Fig. 4 IR and Raman spectra of >SbF
4 2 2 2
O PF ) .
634
Z. Anorg. Allg. Chem. 2001, 627, 631±637

+
In Pursuit of the PO2 Cation
phase and out-of-phase stretching motions of the PO2
groups. Therefore, it may appear that some of the
bands are active in both the infrared and the Raman
spectra, but a closer inspection reveals that their fre-
quencies differ enough to rule out this interpretation.
In viewof the complexity of the symmetry coordi-
nates for such a large system, a normal coordinate
analysis was not carried out for >SbF O PF ) . It
>SbF O PF ) are in very good agreement with those
4 2 2 2
previously reported for the analogous chlorine com-
pound >SbCl O PCl ) [24].
4
2
2 2
The total energies, calculated for the oxygen- and
the fluorine-bridged structures showthat the oxygen-
±
1
bridged model is favored by 130 kcal mol . This large
energy difference accounts for the preferred forma-
tion of the oxygen-bridged rings which can be ex-
plained by the following mechanism >Figure 5).
4
2
2 2
should also be noted that the vibrational spectra of
4 2 2 2
Table 5 Unscaled calculated and observed vibrational frequencies of the oxygen and fluorine bridged >SbF O PF )
±
1 a)
±1 b)
±1 a)
Calcd frequencies/cm
B3LYP
Obsd frequencies/cm
Calcd frequencies/cm
B3LYP
Assignment
in point
Oxygen-bridged
Fluorine-bridged
Group C
i
Raman
IR
Raman
1161 [3]
IR
Raman
IR
1
252 >1297)
1261 >vs)
1509 >289)
m 28 >A
u
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
1167 [10]dp
158 [4]p
1507
1147
m 1
m 2
>A
>A
g
g
1
1
137 >989)
1158 >vs)
1046 >s)
1144 >157)
744 >174)
m 29 >A
m 30 >A
u
u
9
91 >409)
9
9
85 [4]dp
07 [16]p
1048 [7]
960 [19]
742
m 3
m 4
>A
>A
g
717 >178)
g
8
7
99 >72)
24 >181)
952 >s)
708 >vs,br)
715
705
m 31 >A
m 32 >A
u
u
7
6
21 [3]p
95 [3]dp
710 [5]
702 >124)
652 >16)
m 5
m 6
>A
>A
g
g
6
6
93 >156)
85 >203)
684 >vs)
637 >m)
651
506
m 33 >A
u
6
6
87 [12]p
20 [21]p
691 [39]
m 7
>A
g
472 >94)
m 34 >A
u
632 [100]
467
461
m 8
m 35 >A
m 36 >A
>A
g
6
5
19 >1)
90 >63)
463 >881)
u
u
5
4
82 [0.2]p
91 [2]p
454 >0.3)
432 >630)
403 >27)
m 9
>A
g
g
509 [2]
m 10 >A
4
4
4
3
81 >95)
64 >134)
33 >13)
45 >45)
488 >s)
m 37 >A
m 11 >A
m 38 >A
m 12 >A
m 39 >A
m 13 >A
m 40 >A
m 14 >A
m 41 >A
m 42 >A
m 43 >A
m 15 >A
m 44 >A
u
4
4
3
2
70 [2]p
400
356
g
458 >sh)
u
40 [12]p
58 [0.4]p
76 [1]p
461 [11]
382 [1]
347 >9)
g
330
298
u
g
281 >120)
u
270 [26]
253
g
2
2
2
71 >261)
69 >114)
58 >44)
252 >97)
248 >102)
u
u
246
229
u
2
57 [2]p
253 [1]
240 [2]
245 >267)
g
2
52 >10)
u
2
46 [3]dp
222 >5)
215 >4)
208 >10)
m 16 >A
m 17 >A
g
g
2
43 [0.5]dp
2
37 >5)
m 45 >A
m 46 >A
m 18 >A
m 47 >A
u
2
29 >0.3)
204
186
u
2
17 [3]p
218 [4]
196 [2]
g
2
1
09 >0.1)
91 >4)
180 >0.3)
166 >19)
u
2
1
07 [1]dp
97 [2]p
172
m 19 >A
m 20 >A
m 48 >A
u
m 21 >A
m 22 >A
g
g
153
139
121
1
77 [1]p
g
1
70 [0.02]p
g
1
1
46 >1)
42 >0.1)
118 >0.04)
114 >2)
m 49 >A
m 50 >A
u
u
1
1
33 [0.1]dp
08 [1]dp
151 [2]
118 [2]
111
m 23 >A
m 24 >A
g
g
1
01 >0.01)
m 51 >A
m 25 >A
m 52 >A
m 26 >A
m 53 >A
m 27 >A
m 54 >A
u
5
4
3
2 [0.1]p
g
4
4
2
8 >0.8)
6 >0.9)
1 >0.7)
u
8 [0.02]p
2 [0.001]p
g
u
g
u
a)
±1
Ê
4
±1 b)
IR intensities given in parentheses [km mol ], and Raman intensities given in brackets [A amu ]. Relative IR and Raman intensities given in par-
entheses and brackets, respectively.
Z. Anorg. Allg. Chem. 2001, 627, 631±637
635

S. Schneider, A. Vij, J. A. Sheehy, F. S. Tham, T. Schroer, K. O. Christe
phorus seeks coordination numbers in excess of two.
+
Since the polymerization of PO2 is highly unlikely
due to the mutual repulsion of charges of the same
+
sign, PO2 exhibits a strong tendency to undergo oxy-
gen- or fluorine- bridging to achieve higher coordina-
+
tion. Even the possibility of approximating a PO2 ca-
±
tion by having a PO2F2 unit forming two fluorine-
bridges to very strong Lewis acids is thwarted by ener-
getics. In the eight-membered >SbF O PF ) rings, the
4
2
2 2
oxygen-bridged structure is favored over the fluorine-
±
1
bridged one by 130 kcal mol .
Fig. 5 Formation mechanism of >SbF O PF ) .
4
2
2 2
Acknowledgement. The work at USC was financially sup-
ported by the National Science Foundation and that at the
Air Force Research Laboratory by the Air Force Office of
Scientific Research and DARPA. Two of us >S. S. and T. S.)
gratefully acknowledge support by the Alexander von Hum-
boldt Foundation.
The first step involves the formation of an oxygen-
±
bridged polynuclear [PO F ´ 2 SbF ] anion, as in the
2
2
5
case of AsF . The important difference between AsF
5
5
and SbF is that antimony can expand its coordination
5
towards fluorine or oxygen past six, while arsenic
cannot [25]. This allows the SbF5 ligand of
±
2 2 5 2 2
±
References and Notes
[
PO F ´ 2 SbF ] to interact with a second PO F an-
ion, as shown in Figure 5. The SbF assisted elimina-
5
[1] P. Pyykk oÈ , Y. Zhao, Mol. Phys. 1990, 70, 701.
[2] U. Wannagat, J. Rademachers, Z. Anorg. Allg. Chem.
1957, 289, 66.
[3] D. W. Muenow, O. M. Uy, J. L. Margrave, J. Inorg. Nucl.
Chem. 1969, 31, 3411.
tion of two moles of KF then produces the final pro-
duct. The following experimental evidence supports
this mechanism. When a 2 : 1 molar mixture of SbF5
and KPO F was allowed to interact at room tempera-
2
2
[
4] A. Addou, P. Vast, P. Legrand, Spectrochim. Acta 1982,
8 A, 785, and references cited therein.
ture in the absence of a solvent, a colorless powder
was obtained that was identified by vibrational spec-
3
+
[5] K. O. Christe, R. Gnann, R. I. Wagner, W. W. Wilson,
troscopy as the K salt of the oxygen bridged
Eur. J. Solid State Inorg Chem. 1996, 33, 865.
±
[
PO F ´ 2 SbF ] polyanion. Heating of this salt to
2
2
5
[
6] J. W. Larson, T. B. McMahon, Inorg. Chem. 1987, 26,
018.
9
5 °C resulted in the sublimation of >SbF O PF ) and
4
2
2 2
4
a KSbF residue >see Experimental Section).
6
[7] K. O. Christe, D. A. Dixon, D. McLemore, W. W. Wil-
son, J. A. Sheehy, J. A. Boatz, J. Fluorine Chem. 2000,
1
01, 151.
NMR Spectra
[
8] K. O. Christe, R. D. Wilson, C. J. Schack, Inorg. Synth.
1986, 24, 3.
A solution of a fewsingle crystals of >SbF O PF ) in
4
2
2 2
SO was used to record NMR-spectra. The strongest
[9] U. Schuelke, R. Kayser, Z. Anorg. Allg. Chem. 1991,
00, 221.
[10] SMART V 4.045 Software for the CCD Detector Sys-
tem, Bruker AXS, Madison, WI 1999.
[11] SAINT V 4.035 Software for the CCD Detector Sys-
tem, Bruker AXS, Madison, WI 1999.
12] SADABS, Program for absorption correction for area
detectors, Version 2.01, Bruker AXS, Madison, WI
2000.
[13] G. M. Sheldrick, SHELXS-97, Program for the Solution
of Crystal Structure, University of G oÈ ttingen, Germany,
1997.
14] G. M. Sheldrick, SHELXL-97, Program for the Refine-
ment of Crystal Structure, University of G oÈ ttingen,
Germany, 1997.
2
3
1
6
signal in the P spectra was a triplet >d ±35.6 ppm,
1
JPF 1030 Hz) that is typical for a PO F group, but
2
2
the spectra also exhibited many signals that could not
1
be firmly assigned. The chemical shift and the J
PF
coupling constant observed for our triplet agree well
[
1
with those >d ±35.5 ppm, JPF 1039 Hz) previously re-
ported by Dehnicke et al. [21] for an SbF solution.
5
1
9
The F NMR-spectra were even more complicated.
In viewof this, it is not certain wh ether the eight-
membered ring persists in SO solution at room tem-
2
[
perature.
Conclusion
[
15] The B3LYP functional uses a three-parameter exchange
functional of Becke >B3) [A. D. Becke, J. Chem. Phys.
The reaction of KPO F with the strongest presently
2
2
1
993, 98, 5648; P. J. Stephens, C. F. Devlin, C. F. Chaba-
known Lewis acid, i. e., oligomeric SbF , does not pro-
5
lowski, and M. J. Frisch, J. Phys. Chem. 1994, 98, 11623]
and the Lee, Yang, and Parr >LYP) correlation gradi-
ent-corrected functional [C. Lee, W. Yang, and
R. G. Parr, Phys. Rev. B 1988, 37, 785].
+
duce PO2 salts but oxygen-bridged eight-membered
Sb±O±P rings with hexa-coordinated antimony and
tetra-coordinated phosphorus. The chances for prepar-
+
ing ionic salts that contain isolated PO2 cations must
[16] These local-spin-density-optimized Gaussian basis sets
were developed by Nathalie Godbout and Jan An-
be considered very slim because pentavalent phos-
636
Z. Anorg. Allg. Chem. 2001, 627, 631±637

+
In Pursuit of the PO2 Cation
dzelm, and are made available courtesy of Cray Re-
search, Inc. The general method by which they were de-
veloped is given in N. Godbout, D. R. Salahub, J. An-
dzelm, and E. Wimmer, Can. J. Chem. 1992, 70, 560.
mann, J. C. Burant, S. Dapprich, J. M. Millam, A. D. Da-
niels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi,
V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomel-
li, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson,
P. Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick, A. D.
Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski,
J. V. Ortiz, B. B. Stefanov, G. Liu, A. Liashenko, P. Pis-
korz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox,
T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
C. Gonzalez, M. Challacombe, P. M. W. Gill, B. G. John-
son, W. Chen, M. W. Wong, J. L. Andres, M. Head-Gor-
don, E. S. Replogle, and J. A. Pople, Gaussian, Inc.,
Pittsburgh, PA, 1998.
[
17] Basis sets were obtained from the Extensible Computa-
tional Chemistry Environment Basis Set Database, Ver-
sion, as developed and distributed by the Molecular
Science Computing Facility, Environmental and Mole-
cular Sciences Laboratory which is part of the Pacific
Northwest Laboratory, P.O. Box 999, Richland, Wash-
ington 99352, USA, and funded by the U.S. Department
of Energy. The Pacific Northwest Laboratory is a multi-
program laboratory operated by Battelle Memorial
Institute for the U.S. Department of Energy under con-
tract DE-AC06-76RLO 1830. Contact David Feller or
Karen Schuchardt for further.
[21] N. Kr uÈ ger, K. Dehnicke, Z. Anorg. Allg. Chem. 1978,
438, 169.
[22] A. W. Cooke, J. Pebler, F. Weller, K. Dehnicke, Z. An-
org. Allg. Chem. 1985, 524, 68.
[23] A. F. Shihada, F. Weller, Z. Anorg. Allg. Chem. 1981,
472, 102.
[
18] Polarization functions are unpublished supplements to
the basis sets described in A. Schafer, C. Huber, and
R. Ahlrichs, J. Chem. Phys. 1994, 100, 5829.
[
19] M. J. Frisch, J. A. Pople, and J. S. Binkley, J. Chem. Phys.
[24] K. Dehnicke, R. Schmitt, Z. Anorg. Allg. Chem. 1968,
358, 1.
1984, 80, 3265.
[
20] Gaussian 98, Revision A.7, M. J. Frisch, G. W. Trucks,
H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Chee-
seman, V. G. Zakrzewski, J. A. Montgomery, R. E. Strat-
[25] G. W. Drake, D. A. Dixon, J. A. Sheehy, J. A. Boatz,
K. O. Christe, J. Am. Chem. Soc. 1998, 120, 8392.
Z. Anorg. Allg. Chem. 2001, 627, 631±637
637