The first simple, donor-free salt of the Sb(OTeF5)6- anion: Synthesis, structure, characterization, and thermochemistry of Cs[Sb(OTeF5)6]

Article abstract of DOI:10.1021/ic010217+

Large and nonbasic anions are needed to stabilize novel and highly electrophilic/oxidizing cations. The Sb(OTeF₅)₆^- anion is suitable for this purpose and can now be introduced as a counterion by metathesis of the here reported Cs salt with MF₆^- salts (M = As, Sb) since CsMF₆ is insoluble in many solvents.

Full text of DOI:10.1021/ic010217+

4488
Inorg. Chem. 2001, 40, 4488-4490
methods have been described elsewhere.8 Additional information is
found in the Supporting Information.
The First Simple, Donor-Free Salt of the
Sb(OTeF5)6 Anion: Synthesis, Structure,
-
Reaction Utilizing CsBr. Anhydrous CsBr (0.165 g, 0.775 mmol)
was weighed into a 10 mm (o.d.) thick-walled NMR tube, and a stock
solution of Ag[Sb(OTeF5)6] in SO2 (2.0 mL, 0.319 M, 0.638 mmol)
was transferred9 onto the CsBr. Immediately, a yellow beige precipitate
formed that is likely AgBr; see below. Additional SO2 was condensed
up to a height of 5.5 cm onto the frozen mixture, and NMR spectra
were obtained. The solution was then decanted10 into a one bulb vessel.
The remaining material (insoluble in SO2) was soluble in aqueous
Na2S2O3 solution and weighed 0.193 g (calcd for AgBr, 0.120 g).
Successive reduction of the solvent of the filtrate and cooling to 4 °C
afforded colorless crystals of Cs[Sb(OTeF5)6], which were isolated (0.88
g, 81%).
Characterization, and Thermochemistry of
Cs[Sb(OTeF5)6]
T. Stanley Cameron,†,1 Ingo Krossing,‡,§ and
Jack Passmore*,|
Chemistry Department, Dalhousie University, Halifax,
Nova Scotia, Canada, Institut fu¨r Anorganische Chemie,
Universita¨t Karlsruhe, Engesser Str. Geb. 30.45,
76128 Karlsruhe, Germany, and Chemistry Department,
University of New Brunswick, Fredericton,
New Brunswick E3B 6E2, Canada
Reaction Utilizing CsI. Solid beige Ag[Sb(OTeF5)6] (1.727 g, 1.040
mmol) and anhydrous CsI (0.330 g, 1.269 mmol) were weighed into a
10 mm (o.d.) thick-walled NMR tube. Immediately after the mixing, a
reaction occurred at some spots (brownish color). Approximately 4 g
of SO2 (5.5 cm height) was condensed onto the solid mixture and
immediately gave a dark violet solution (iodine color) over a yellow
precipitate. All volatiles were removed in vacuo, and the solid residue
was exposed to a dynamic vacuum for 2 h. However, after redissolution
in approximately 4 g of SO2, the color of the solution was only slightly
less intense, but further evacuation to remove the last traces of iodine
was avoided in order not to risk decomposition as observed in the case
of the silver salt. A 19F NMR spectrum of this sample only showed
ReceiVed February 23, 2001
Introduction
Highly resistant and weakly coordinating anions have been
the focus of much recent work,2 and, therefore, a series of
-
hexateflatometalates M(OTeF5)6 (M ) As, Sb, Bi, Nb) has
been prepared as NR4+ (R ) Me, Et)3 and silver salts.4 However,
we showed that for Ag[Sb(OTeF5)6] the silver cation remained
coordinated by a small but undetermined number of CH2Cl2
solvent molecules, which reacted with some of our desired
products.5 When SO2ClF was used as a solvent, incomplete
substitution and formation of Ag[Sb(Clx)(OTeF5)6-x] resulted.6
Cationic silver-chalcogen complexes such as [Ag2Se6(SO2)2]-
[Sb(OTeF5)6]2 were formed from mixtures of Ag[Sb(OTeF5)6]
and chalcogen halides EnHal2 (E ) S, Se, n ) 3-5),7
presumably due to the highly polarizing nature of the Ag+
cation. In fact, it is so polarizing that the Ag+ cation in Ag-
[Sb(OTeF5)6] is sufficient to oxidize elemental tellurium to give
[Te4][Sb(OTeF5)6]2.5 Therefore, an alternative starting material
was needed to introduce the Sb(OTeF5)6- anion by a metathesis
reaction. Herein, we present the synthesis, characterization, and
X-ray crystal structure of unsolvated Cs[Sb(OTeF5)6], 1. Cs+
is less polarizing than Ag+, and so this salt is highly useful in
introducing the Sb(OTeF5)6- anion by a metathesis reaction with
halides or hexafluorometalates MF6- (M ) As, Sb), especially
since CsMF6 is poorly soluble in SO2, our standard solvent for
reactions.
lines attributable to the Sb(OTeF5)6 anion [δ19F ) -40.7, J(19F-
125Te) ) 3597 Hz]. Decantation by a direct connection10 and removal
of all volatiles led to a grayish/metallic appearing microcrystalline
material that a gave a very intense Raman spectrum identical to that of
solid iodine (ν ) 181 cm-1).
-
1
Results and Discussion
Ag[Sb(OTeF5)6]11 reacted cleanly with CsBr in SO2 solution
to give insoluble AgBr and the very SO2-soluble Cs[Sb(OTeF5)6]
(1) salt in 81% recovered yield (eq 1).
CsBr + Ag[Sb(OTeF5)6] f Cs[Sb(OTeF5)6] (1) + AgBr
(1)
The in situ 19F NMR spectrum of this reaction only showed
a signal attributable to the Sb(OTeF5)6- anion at δ19F ) -40.7
[1J(19F-125Te) ) 3565 Hz), which is unchanged compared to
the original signal of Ag[Sb(OTeF5)6] in SO2 (δ19F ) -40.6)5
and comparable to those reported for the Sb(OTeF5)6- anion in
CH2Cl2 (δ19F ) -41.4 to -41.8).3,4 The expected AB4 spin
system of the OTeF5 group was not observed; rather, the
spectrum collapsed to a single line, in agreement with earlier
findings.3-5
Experimental Section
Reactions were carried out in thick-walled 10 mm (o.d.) NMR tubes
fitted with a special J. Young NMR valve. General techniques and
† Dalhousie University.
‡ Part of this work has been presented at the 5th RSC/GDCh conference
(Inorganic Chemistry) in Brighton, U.K., 1999.
§ Universita¨t Karlsruhe.
(8) Murchie, M. P.; Kapoor, R.; Passmore J.; Schatte, G.; Way, T. Inorg.
Synth. 1996, 31, 80.
| University of New Brunswick.
(9) The transfer vessel was built from a graded cylinder glass blown onto
a J. Young valve and a glass tube suitably equipped to attach the valve
of a 10 mm NMR tube. The latter connection includes a Rotoflo valve
to flame dry the evacuated connection prior to use. To ensure complete
transfer of the stock solution, small amounts of the solvent were
condensed three times into the cylinder and poured back to the reaction
vessel.
(10) Direct connection: A 0.25 in. glass tubing incorporating one valve to
allow flame drying. The reaction vessels were connected to the direct
connection by Gyro Lock fittings (Swage Lock Corp.). A short (2
cm) Teflon tubing was inserted into the glass tubing within the Gyro
Lock to avoid contact of metal and solution. A variation of this device
is described in ref 8.
(1) X-ray crystal structure determination.
(2) For recent reviews, see: (a) Reed, C. Acc. Chem. Res. 1998, 31, 133.
(b) Strauss, S. H. Chem. ReV. 1993, 93, 927.
(3) E(OTeF5)6- (E ) As, Sb, Bi): Mercier, H. P. A.; Saunders, J. C. P.;
Schrobilgen, G. T. J. Am. Chem. Soc. 1994, 116, 2921 and references
therein.
-
(4) E(OTeF5)6 (E ) Sb, Nb): Van Seggen, D. M.; Hurlburt, P. K.;
Anderson, O. P.; Strauss, S. H. Inorg. Chem. 1995, 34, 3453.
(5) Cameron, T. S.; Decken, A.; Krossing, I.; Passmore, J. Manuscript in
preparation.
(6) Gerken, M.; Kolb, P.; Wegner, A.; Mercier, H. P. A.; Borrmann, H.;
Dixon, D. A.; Schrobilgen, G. J. Inorg. Chem. 2000, 39, 2813.
(7) Decken, A.; Krossing, I.; Passmore, J. Submitted to Chem. Commun.
(11) Containing a small but undetermined number of CH2Cl2 molecules.
10.1021/ic010217+ CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/19/2001

Notes
Inorganic Chemistry, Vol. 40, No. 17, 2001 4489
Table 1. Observed Raman Frequencies (Relative Areas under the
-
Peak) of the Sb(OTeF5)6 Anion in 1 Compared to and Assigned on
the Basis of Those Found in [NMe4][Sb(OTeF5)6]3
assignment
νas(TeF4)
[NMe4][Sb(OTeF5)6]
Cs[Sb(OTeF5)6]
707 (12)
693 (3)
737 (8)
731 (9)
722 (sh)
706 (50)
659 (100)
643 (18)
426 (8)
397 (22)
334 (19)
304 (16)
236 (14)
139 (34)
130 (17, sh)
108 (15)
90 (9)
νs(Te-F)
sym(TeF4)
723 (50)
666 (100)
633 (13)
409 ( 20 (20, broad)
ν
νas(TeF4)
νas(Te-O)a
Figure 1. Section of the solid-state structure of Cs[Sb(OTeF5)6] (1).
One Sb(OTeF5)6- anion and all Cs- -F contacts are shown on the left;
thermal ellipsoids are drawn at the 25% probability level. The solid-
state packing omitting all Te and F atoms is shown on the right (SbO6
octahedra and Cs ellipsoids).
δas(F-TeF4)
337 (17)
305 (11)
239 (15)
140 (15)
δ
sym(F-TeF4)
δ
ciss(TeF4)
δ(Te-O-Sb)
δ(Te-O-Sb)
and lattice modes
110 (sh)
85 (3)
respective van der Waals radii of 3.60 Å (see Figure 1). Utilizing
the Brown approach,15 the sum of the valency units (vu) of the
Cs+ ion was estimated as +0.90 vu, which is in good agreement
with the univalent character of the Cs+ monocation.
a Coupled with Sb-O.3
The Cs+ ion in this structure is tetrahedrally coordinated by
However, when CsBr was replaced by CsI, an intensely red
violet colored solution resulted (color of iodine). The Raman
spectrum of the soluble material of this reaction was identical
to that of elemental iodine, which implies that the I- in CsI
was oxidized to I2, and indeed, a thermochemical evaluation of
this reaction showed that the oxidation of I- by Ag+ (in SO2)
-
four Sb(OTeF5)6 anions. Two of the anions coordinate with
two different OTeF5 groups monodentate to the Cs+ ion, and
the other two anions coordinate with three different OTeF5
groups monodentate to the Cs+ ion. The Cs-F contacts in 1
may be compared to those found in Cs(LiF2)16 [and Cs(SbF6)].17
In these salts, the Cs atom is coordinated by six shorter Cs- -F
contacts at 2.96-3.15 Å (3.12 Å) and two (six) longer contacts
is exothermic but that of Br- 12 is endothermic. The in situ 19
F
NMR spectrum of the last reaction only showed a signal
attributable to the Sb(OTeF5)6- anion at δ19F ) -40.7 [1J(19F-
125Te) ) 3597 Hz); no other fluorine containing species were
found. In this case, Raman spectroscopy showed only a very
intense iodine band. However, for 1 the Raman spectrum of
Cs[Sb(OTeF5)6] (actual spectrum deposited) exclusively showed
(13) A crystal of 1 (0.03 × 0.06 × 0.08 mm) was mounted on a RIGAKU
AFC5R diffractometer, and subsequent measurements were performed
at 213 ( 1 K with graphite-monochromated Mo KR radiation (λ )
0.710 69 Å). Cell constants and an orientation matrix for data collection
were obtained by least-squares refinement of 25 carefully centered
reflections in the range of 15.97° < 2Θ < 28.81° and correspond to
a tetragonal primitive unit cell with a ) 14.260(3) Å, c ) 14.618(5)
Å, and V ) 2972.8(8) Å3 (Z ) 4, CsF30O6SbTe6, FW ) 1686.20, d
) 3.77 g/cm3). Data were collected in the ω - 2Θ scan technique up
to a maximum of 2Θ of 50.1° with an ω-scan width of 1.37 + 0.35
tan Θ° at a scan speed of 8° min-1. Weak reflections (I < 15σ) were
rescanned up to a maximum of six scans and the counts were
accumulated. Stationary background counts were recorded on each
side of the reflection with a peak/background counting time ratio of
-
bands attributable to the Sb(OTeF5)6 anion indicating an
unsolvated Cs+ cation. The Raman bands of the Sb(OTeF5)6
-
anion are collected in Table 1 and are compared to and assigned
on the basis of those reported for [N(CH3)4+][Sb(OTeF5)6-]3.
The bands of both anions are in very good agreement. The
asymmetric stretching vibrations νas(TeF4) in 1 are at lower
energy than those in the NMe4 salt. No indication of
coordinated solvent SO2 was found in Cs[Sb(OTeF5)6] (1).
+
2: 1. Of the 2682 reflections recorded, 2474 were unique (Rint
)
0.042), equivalent reflections were merged. The intensities of three
representative standard reflections were measured every 150 reflections
and decreased during the data collection by 11.9%. A linear correction
factor was applied to account for this phenomenon. An empirical
absorption correction correction (µ ) 81.13 cm-1) based on azimuthal
scans of several reflections was applied which resulted in transmission
factors ranging from 0.81 to 1.00. Data were corrected for Lorentz
and polarization effects. The systematic absences uniquely determined
the space group to be P42/n. The structure was solved using direct
methods and all atom positions were identified by interpretation of
the subsequent difference Fourier maps using the TEXSAN14 crystal-
lographic software package of Molecular Structure Corp. Only the
Cs atom was refined anisotropically; all other atoms were refined
isotropically. The final cycle of the full-matrix least-squares refine-
ments on F was based on 366 observed reflections [I > 3σ(I)] and 92
variable parameters and converged with weighted and unweighted
The solid-state structure of a colorless single crystal of Cs-
[Sb(OTeF5)6] was determined.13,14 Due to the small size of the
crystal, the collected data set was weak, and consequently, the
data-parameter ratio was only 4:1 rendering extensive structural
discussions inadequate. However, we can reasonably give a
general description of the structure and obtain thermochemical
volumes and radii. Compound 1 forms an ionic lattice built from
unsolvated Cs+ cations and Sb(OTeF5)6 anions that adopt a
-
zinc blend type structure. The Cs atom is coordinated by six
stronger Cs- -F contacts at 3.09-3.14 Å and four weaker
contacts at 3.42-3.43 Å that are below the sum of their
agreement factors of R ) Σ(|Fo| - |Fc|)/Σ|Fo|) ) 0.058 and Rw
1.22 e-/A3).
)
2
(12) The oxidation of gaseous I- (∆fH ) -188 kJ/mol) by Ag+ (∆fH )
+1017 kJ/mol) with formation of Ag0 (∆fH ) +285 kJ/mol) and 0.5
I2 (∆fH ) 31 kJ/mol) is thermochemically possible (∆rH ) -513
kJ/mol). Adding the calculated [Born equation, dielectric constant 14
(SO2 at room temperature)] solvation energies of Ag+ (r ) 1.29 Å;
501 kJ/mol) and I- (r ) 2.06 Å; 313 kJ/mol) as well as the
experimental atomization energy of Ag0 (285 kJ/mol) and the
experimental sublimation enthalpy of 0.5 I2 (31 kJ/mol) into a suitable
Born-Fajans-Haber cycle allows the estimation of the heat of the
reaction Ag+(solv) + I-(solv) f Ag0(c) + 0.5 I2 (c) as slightly exothermic
(∆rH ) -13 kJ/mol). Due to the higher electron affinity of bromine
(325 vs 294 kJ/mol for iodine) and the higher solvation energy of the
Σ(w|Fo| - |Fc|)2/ Σw|Fo| ) ) 0.051 (GOF ) 1.77, ∆F ) +1.37/-
(14) Molecular Structure Corp. (1997-1999). teXsan for Windows. Single-
Crystal Structure Analysis Software. Version 1.06. MSC, 9009 New
Trails Drive, The Woodlands, TX 77381.
(15) The contacts s (in valency units vu) have been defined as s ) (R/
R0)-N, where R is the observed distance, R0 is the covalent bond
distance (bond order ) 1) of the bond in question, and N is a
empirically derived constant. For Cs- -F contacts N ) 4.61 and R0 )
1.904 Å, see: Brown, I. D. In Structure and Bonding in Crystals; M.
O’Keefe, M., Navrotsky, A., Eds.; Academic Press: London, 1981;
Vol. 2, 1.
smaller Br-
ion (r ) 1.82 Å, 354 vs 313 kJ/mol for I-(solv)) the
(16) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Clarendon
Press: Oxford, 1984.
(solv)
homologous reaction (giving liquid Br2) is endothermic for bromine
(∆rH ) +54 kJ/mol).
(17) Nolte, M. J.; de Beer, H. J. Acta Crystallogr. B 1979, 1208.

4490 Inorganic Chemistry, Vol. 40, No. 17, 2001
Notes
at 3.50 and 3.53 Å (3.38 Å) that are similar to the distances
found in 1 (3.04-3.14 and 3.42-3.49 Å). The geometry of the
Sb(OTeF5)6- anion is unremarkable. Average bond lengths and
bond angles are d(Sb-O)av ) 1.90(5) Å, d(Te-O)a. ) 1.81(5)
Å, d(Te-F)av ) 1.74(6) Å and (Sb-O-Te)av ) 149(3)° and
known lattice potential enthalpies of CsBr (∆HLatt ) 647 kJ/
mol) and AgBr (∆HLatt ) 905 kJ/mol)19 and estimating that of
Ag[Sb(OTeF5)6] (∆HLatt ) 365 kJ/mol)18 allowed us to establish
the solid-state enthalpy of eq 1 as exothermic by 256 kJ/mol
{[Sb] ) Sb(OTeF5)6}:
-
agree well with those reported for other Sb(OTeF5)6 anions,
∆H(eq 1) ) ∆HLatt(CsBr) + ∆HLatt{Ag[Sb]} -
∆HLatt(AgBr) - ∆HLatt{Cs[Sb]} )
e.g., in [NMe4][Sb(OTeF5)6] with d(Sb-O)avg ) 1.91(1) Å,
d(Te-O)av ) 1.78(1) Å, d(Te-F)avg ) 1.75(2) Å, and (Sb-
O-Te)av ) 150.9(8)°3. The crystal packing is best described
∆H(eq 1) ) 647 + 365 - 905 - 363 )
∆H(eq 1) ) -256 kJ/mol
-
as a cubic close packing of the large spherical Sb(OTeF5)6
anions (radius 4.79 Å, see below) where the Cs+ ions [Gold-
schmidt radius: 1.65 Å] occupy every second tetrahedral hole
(rcat/ran ) 0.344) (see Figure 1). The zinc blend structure is in
agreement with the radius ratio rules, which require a cation-
anion radius ratio between 0.225 and 0.414 for this lattice type.
The unsolvated nature of the cation in this crystal structure
allowed us to establish the thermochemical volume (radius) of
Concluding Remarks
The synthesis of the unsolvated Cs[Sb(OTeF5)6] salt was
achieved in good yield and is exothermic by 256 kJ/mol. The
-
Sb(OTeF5)6 anion may then be introduced into other salts by
-
a metathesis reaction with halides or hexafluorometalates MF6
(M ) As, Sb). Due to the large size of the Sb(OTeF5)6- anion,
the lattice potential energies of the resulting species are
dramatically decreased and may lead to hitherto unknown
species and structures.
-
the Sb(OTeF5)6 anion, which is needed to obtain lattice
potential enthalpy estimates of known and unknown Sb(OTeF5)6-
salts. The volume (radius) of the Cs+ cation is 19 Å3 (1.65 Å),18
-
and therefore, the volume (radius) of the Sb(OTeF5)6 anion
followed as
Acknowledgment. This work was supported by the Natural
Science and Engineering Research Council of Canada NSERC
(J.P., T.S.C.). We thank Isabelle Dionne M.Sc. for the Raman
spectra. Dr. Ingo Krossing is grateful to the Alexander von
Humboldt Foundation in Bonn, Germany, for providing a
Feodor-Lynen Fellowship.
V[Sb(OTeF5)6 ] ) [(unit cell volume/Z) - V(Cs+)] )
-
[(2973/4) - 19] ) 724 Å3
r[Sb(OTeF5)6 ] ) d(Cs-Sb) - r(Cs+) )
-
Supporting Information Available: Details of the Experimental
Section and a copy of the Raman spectrum of 1. A CIF File containing
details of the X-ray structure determination is also deposited. This
material is available free of charge via the Internet at http://pubs.acs.org.
6.44-1.65 ) 4.79 Å
Using Jenkins, Passmore, et al.’s generalized volume-based
Kapustinskii equation,18 the lattice potential enthalpy of the Cs-
[Sb(OTeF5)6] salt was estimated as 363 kJ/mol. Utilizing the
IC010217+
(18) Roobottom, H. K.; Jenkins, H. D. B.; Passmore, J.; Glasser, L. Inorg.
Chem. 1999, 38, 3609.
(19) Lide, D. R., Ed. Handbook of Chemistry and Physics, 80th ed.; CRC
Press: Boca Raton, London, New York, Washington DC, 1999.