Pertechnetyl fluorosulfate, [TcO3]+[SO 3F]-

Article abstract of DOI:10.1002/zaac.200700485

A one step synthesis of [TcO₃]⁺[SO₃F] ^- is reported. The compound is volatile at room temperature and has according to calculations a tetrahedral coordination around Tc and a monodentate SO₃F group. In the solid state the [SO₃F]^- anion bridges three [TcO₃]⁺ cations, and vice versa. Space group P2₁/c, Z = 4, lattice dimensions at 173 K: a = 695.4(11), b = 808.6(12), c = 893.3(14) pm, β = 97.36(8)°.

Full text of DOI:10.1002/zaac.200700485

DOI: 10.1002/zaac.200700485
Pertechnetyl Fluorosulfate, [TcO3]؉[SO3F]؊
Joanna Supeł, Adelheid Hagenbach, U. Abram, and Konrad Seppelt*
Berlin, Freie Universität, Institut für Chemie, Anorganische und Analytische Chemie
Received October 16th, 2007.
Abstract. A one step synthesis of [TcO3]ϩ[SO3F]Ϫ is reported. The
compound is volatile at room temperature and has according to
calculations a tetrahedral coordination around Tc and a mono-
dentate SO3F group. In the solid state the [SO3F]Ϫ anion bridges
three [TcO3]ϩ cations, and vice versa. Space group P21/c, Z ϭ 4,
lattice dimensions at 173 K: a ϭ 695.4(11), b ϭ 808.6(12), c ϭ
893.3(14) pm, β ϭ 97.36(8)°.
Keywords: Technetium; Fluorosulfate
Introduction
In the following we present our results on the generation
of [TcO3]ϩ[SO3F]Ϫ.
Isolated trioxides of transition metal elements are of
theoretical interest. The best examples may be molecular
MoO3 and WO3, which have been detected in matrices.
According to their i.r. spectra and DFT calculations, these
molecules have a singlet ground state and a trigonal pyr-
amidal structure with OϪMϪO bond angles around
106Ϫ108° [1]. In other words, these species violate strongly
the VSEPR model [2], which would predict a trigonal
planar structure for such compounds, as is indeed observed
in molecular SO3. Together with the non-octahedral struc-
tures of M(CH3)6 (M ϭ Mo, W, Re) [3], these trioxides
present the most serious discrepancies from the VSEPR
model.
Results and Discussion
Due to the restrictions in the handling of radioactive Tc
compounds, we have chosen a simple system, namely
fluorosulfate as a weakly (but not very weakly) coordinat-
ing anion. All the modern very weakly coordinating anions
[9] would need solvents, which together with the small
Ϫ
amounts of usable TcO4 starting materials (<40 mg) and
its high oxidation power would make any isolation very dif-
ficult.
At first we have reacted [NH4]ϩ[TcO4]Ϫ with HSO3F. The
reaction mixture produces in vacuum some volatile mate-
rial, namely [NH4]ϩ[SO3F]Ϫ as colorless needles, and a very
small crop of yellow, Tc containing crystals, which have
been identified as [TcO3]ϩ[SO3F]Ϫ, see below. In order to
circumvent the formation of volatile [NH4]ϩ[SO3F]Ϫ, we
turned to Kϩ[TcO4]Ϫ as starting material, and reacted this
with fluorosulfuric acid containing some SO3.
In search of similar transition metal trioxide systems that
may be obtained in chemical, not matrix, environments, we
ϩ
turned to the cations MO3 (M ϭ Mn, Tc, Re). A good
candidate would be MnO3ϩ because of the small size of the
metal atom. There is no indication that largely unsolvated
ϩ
MnO3 cation has ever been observed. We have tried to
react MnO3F with fluoride attracting Lewis acids such as
AsF5 and SbF5, only to find no reaction at all [4].
TcO3F, a fluoride bridged dimer in the solid state, reacts
with AsF5 or SbF5 under formation of [TcO2F2]ϩ[(As, Sb)
F6]Ϫ [5]. ReO3F, finally, is an oxygen and fluoride bridged
chain polymer [6]. Fluoride ion abstraction would give no
Kϩ[TcO4]Ϫ ϩ 2HSO3F ϩ SO3 Ǟ
Kϩ[SO3F]Ϫ ϩ [TcO3]ϩ[SO3F]Ϫ ϩ H2SO4
Upon sublimation at room temperature in vacuum, a
larger amount of yellow material with some excess of
HSO3F can be sublimed away. After slow cooling to Ϫ78°,
yellow crystals are formed. It is difficult to free them of
adhering fluorosulfuric acid, but a crystal structure deter-
mination is easily done.
ϩ
isolated ReO3 ions. In summary, the best candidate for a
largely unsolvated MO3 cation is TcO3ϩ. Solvated TcO3
ϩ
ϩ
has been already described in the complex [TcO3ϩ (triazacy-
clonane ) Br]Ϫ [7], whereas for [ReO3]ϩ[ (solvate) X]Ϫ there
are many examples [8].
Gaseous TcO3SO3F
* Prof. Dr. K. Seppelt
Freie Universität Berlin
Institut fuer Chemie und Biochemie
Fabeckstraße 34-36
D-14195 Berlin, Germany
Tel. ϩϩ49 30 838 54289, Fax: ϩϩ49 30 838 53310
E-mail: seppelt@chemie.fu-berlin.de
We have no experimental evidence for the structure of the
volatile TcO3SO3F, and therefore have to trust DFT calcu-
lations, see table 1 and figure 1.
ϩ
These calculations show clearly that isolated TcO3 is
ϩ
pyramidal, with OϪTcϪO ϭ 107.75°. Planar TcO3 is a
646
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 634, 646Ϫ648

Pertechnetyl Fluorosulfate, [TcO3]ϩ[SO3F]Ϫ
Table 1 DFT calculated structures of [TcO3]ϩ containing molecules.
Energy/a.u.
TcO distances/pm
OTcO angles/°
rel. energy/ kcal molϪ1
TcO3, C3v
TcO3, D3h
Ϫ306.153544
Ϫ306.1287903
167.9
168.3
107.75
120.0
0.0
15.51
TcO3ϪOϪSO3F C1
Ϫ1030.4802779
Ϫ1030.4802027
168.0-168.1, 191.6
169.0-168.1, 191.6
109.5-110.5
109.6-110.5
0.0
0.04
Cs
TcO3···O2SOF, Cs
Ϫ1030.4728308
168.0-168.1
221.1 (2x)
105.3-108.1
63.7
4.64
octahedral, with Tc···O distances of 223.8 Ϫ 227.6(6) pm.
In spite of the smaller size of oxygen than nitrogen atoms,
these contact distances are longer than the Tc···N distances
in [TcO3]ϩ [(triazacyclononane)Br]Ϫ [7].
Table 2 Bond lengths/pm and angles/° of [TcO3]ϩ[SO3F]Ϫ in the
crystal
TcϪO
Tc···O
SϭO
167.3(6)
168.6(6)
169.1(6)
OϪTcϪO
O···Tc···O
OϭSϭO
FϪSϭO
104.9(3)
104.8(3)
105.9(3)
223.8(6)
225.6(6)
227.6(6)
74.0(2)
73.7(2)
75.1(2)
144.2(6)
144.5(5)
144.6(5)
114.9(3)
113.1(3)
114.7(3)
Figure 1 Calculated structures of molecular TcO3SO3F, numerical
values see table 1. Top: monodentate SO3F group. The overall ener-
getic minimum has no (C1) symmetry, with a torsional angle of
9.5° away from Cs symmetry. Bottom: bidentate SO3F group,
saddle point.
SϪF
153.3(5)
104.1(3)
103.2(3)
104.9(3)
saddle point, 15.5 kcal mol higher in energy. Molecular oxy-
gen bridged TcO3SO3F could have three structures, namely
single, double, or triple oxygen bridged. The adhesion be-
ϩ
tween cation the TcO3 and SO3FϪ is very fluxional.
Ground state turns out to be the single oxygen bridged mol-
ecule. The two molecular components can rotate essentially
free against each other. A Cs symmetric and a C1 symmetric
orientation, the latter with a torsional angle of 9.5°, differ
only by 0.04 kcal molϪ1 in energy, which is way below the
accuracy of such calculations. The double oxygen bridged
molecule is 4.6 kcal molϪ1 higher in energy and a saddle
point on the energy hypersurface (with one imaginary fre-
quency). The triple oxygen bridged species could not be cal-
culated.
Figure 2 The structure of [TcO3]ϩ[SO3F]Ϫ in the solid state,
ORTEP representation, 50 % probability ellipsoids. Shown is one
ϩ
TcO3 cation and its closest contacts to three SO3FϪ anions.
The high volatility of TcO3SO3F is therefore best ex-
plained if one assumes a distorted tetrahedral coordination
around the Tc atom in the gaseous phase, see figure 1.
Conclusion
The compound [TcO3]ϩ[SO3F]Ϫ is probably the one with
Solid state of [TcO3]؉[SO3F]؊
ϩ
the most isolated TcO3 cation so far, however it is still far
ϩ
from being a free ion. In the gaseous phase the TcO3 ion
The result of the crystal structure solution is shown in table
2 and figure 2. Here the pyramidal TcO3 cation (with
with SO3FϪ as counter ion turns into a molecular species.
ϩ
OϪTcϪO angles 104.8 Ϫ 105.9(3)°) is weakly bridged by
three oxygen atoms of three different SO3FϪ anions, and
vice versa. The TcϭO distances have the expected shortness
(167.3-169.5(6) pm). The Tc environment is now distorted
Experimental Section
Caution. Handling anhydrous HF or compounds that produce HF
upon hydrolysis requires eye and skin protection. 99Tc is a weak
Z. Anorg. Allg. Chem. 2008, 646Ϫ648
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
647

J. Supeł, A. Hagenbach, U. Abram, K. Seppelt
β-emitter. Manipulations of 99Tc compounds are performed in a
laboratory approved for the handling of such materials.
DFT calculations are done with the GAUSSIAN package [13], the
Becke3 parameter hybrid, and the correlation functional of Lee,
Yang, and Parr, all as implemented in [13]. Basis sets for O, S, F:
6Ϫ311 ϩρ(d,p). Tc: for 28 core electrons energy consistent pseudo-
Materials. [NH4]ϩ[TcO4]Ϫ is purchased from Oakridge NEI
Laboratories, Kϩ[TcO4]Ϫ is prepared by reaction of it with KCl
in water as the least soluble precipitate. Fluorosulfuric acid from
laboratory stock is distilled in vacuum into a Ϫ30°C trap to free it
from HF or SO3, while H2SO4 remains behind. Sample handling
is performed in a Teflon-PFA (perfluoroether-tetrafluoroethylene
copolymer) double-U-tube.
potentials from the Stuttgart group [14], and
a basis set
s8p7d6[s6p5d3] from the Pacific Northwest Laboratory [15].
We thank the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie for support of this work.
References
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sec per frame. 2θmax ϭ 61°, 1800 frames, covering a full sphere.
Semiempirical absorption correction is done by equalizing sym-
metry equivalent reflections (SADABS). The structure is solved
and refined with the Sheldrick programs [11]. Experimental
details are given in Table 3.
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TcO3SO3F. a) [NH4]ϩ[TcO4]Ϫ (30 mg) is filled into the sealed end
of the double-U-PFA tube, and 1 ml HSO3F is added to it. The
salt readily dissolves under formation of a yellow color. The open
end of the double-U-tube is connected to a vacuum line through a
metal valve. The first U-tube is cooled to Ϫ78 °C, the second to
Ϫ196 °C holding back all volatile (radioactive) materials. Upon
heating to 100 °C, a mainly colorless sublimation starts, together
with distillation of excess HSO3F. In the first U-tube colorless
needles are formed, together with a very small amount of yellow
plates. The colorless needles are crystallographically identified as
[NH4]ϩ[SO3F]Ϫ [12]. The yellow crystals are TcO3SO3F, see below.
b) Kϩ[TcO4]Ϫ(35 mg) is given into the sealed end of the double-
U-tube, and 1 ml HSO3F, containing 0.2 ml disulfuric acid is given
to it. The salt dissolves only slowly upon heating to r.t., the mixture
turns yellow. Distillation/sublimation from room temperature into
Ϫ78 °C and Ϫ196 °C affords a liquid phase in the Ϫ78 °C trap.
Slow cooling from Ϫ10 °C to Ϫ78 °C brings out yellow crystal
plates that are often packed together. Results see table 2 and 3.
Further crystallographic data are deposited with the Fachinforma-
tionszentrum Karlsruhe, Gesellschaft fuer wissenschaftliche techni-
sche Zusammenarbeit mbH, D-76344 Eggenstein-Leopoldshafen,
with the CSD number 418710. Details can be obtained on quoting
the depository number, names of authors, and the journal citation.
[14] Institut für Theoretische Chemie, Universitaet Stuttgart, Ger-
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[15] Extensive Computational Chemistry Environment Basis Set
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Northwest Laboratory: Richmond, USA.
648
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 646Ϫ648