Lewis acid base reactions between boron trifluoride and complex oxoanions as a versatile access to fluorooxoanions: Synthesis of sodium (Trifluoroborato)sulfate

Article abstract of DOI:10.1002/zaac.201200033

Na₂SO₄BF₃, synthesized in a closed vessel from BF₃ and Na₂SO₄ at 603 K, crystallizes in the triclinic space group P1 (a = 6.6033(2), b = 6.6328(2), c = 6.6349 (1) A, α = 84.542(2), β = 84.458(1) and γ = 65.762(1)°). The novel fluorooxo anion [SO₄BF₃]^2- displays a structure similar to the disulfate anion S₂O₇ ^2-. Heating the title compound in the absence of BF₃ in the gas phase leads to decomposition even at 553 K, which is below the temperature of synthesis under BF₃ pressure. Copyright

Full text of DOI:10.1002/zaac.201200033

SHORT COMMUNICATION
DOI: 10.1002/zaac.201200033
Lewis Acid Base Reactions between Boron Trifluoride and Complex
Oxoanions as a Versatile Access to Fluorooxoanions: Synthesis of Sodium
(
Trifluoroborato)sulfate
[a]
[a]
Thomas Pilz and Martin Jansen*
Keywords: BF adduct; Boron; Fluorine; Fluorooxo anions; X-ray diffraction; Lewis acid base reaction
3
2 7
O
2–. Heating the
Abstract. Na
Na SO at 603 K, crystallizes in the triclinic space group P1 (a =
.6033(2), b = 6.6328(2), c = 6.6349 (1) Å, α = 84.542(2), β =
2
SO
4
BF
3
, synthesized in a closed vessel from BF
3
and
displays a structure similar to the disulfate anion S
title compound in the absence of BF in the gas phase leads to decom-
position even at 553 K, which is below the temperature of synthesis
under BF pressure.
¯
2
4
3
6
8
2
–
4.458(1) and γ = 65.762(1)°). The novel fluorooxo anion [SO
4
BF
3
]
3
Introduction
Na
SO BF , which has the same number of valence electrons
2 4 3
as Na S O .
2
2 7
Complex fluorooxoanions of main group or transition ele-
A detailed search of the literature has revealed that this con-
ments offer a number of promising prospects. Varying the oxy- cept was tried before; however, apparently no conclusive or
gen to fluorine ratio is providing another degree of freedom, reproducible results were obtained. The first report dates back
allowing for even more diverse primary, secondary and tertiary to 1936, when Baumgarten and Müller observed that solid
structural features, compared to pure oxo- or fluoroanions. The K SO absorbs BF in a molar ratio of 1:1, with only elemental
2
4
3
–
2–
[4]
pronounced differences in the polarizabilities of F and O
analyses given. This study was extended to further phos-
would result in significant changes in the dielectric, including phates and sulfates.[ In a more recent investigation, non-
5]
[6]
non-linear optical properties, when (partially) substituting flu- integer M SO (M = Na, Tl)/BF ratios were found. The latest
2
4
3
orine for oxygen in solids constituted of complex oxoanions, reference is from 1974, reporting on 1:2 and 1:3 adducts of
and vice versa. As another favorable aspect, terminally bound CrO42– and SO4 with BF , and the formation of unstable
2–
3
–
2–
2–
fluorine will exert weaker trapping of, e.g. alkali metal ions in intermediates with NO , CO
ionic conductors than terminal oxygenatoms. Motivated by this sumed to decompose to B O and [BF ] . In neither of the
and SO3 , which were as-
3
3
–
[7]
2
3
4
latter option, we have started to prepare and characterize lith- studies mentioned, compositions or constitutions were con-
ium fluorooxoborates.[
1–3]
In the course of these studies, we firmed.
were relying on acid-base reactions in the solid state. Boron
oxide or alkali oxoborates have served as acids, alkali fluorides
or tetrafluoroborates as fluoride bases. However, the respective
solid state syntheses have proven to be time consuming and
Results and Discussion
Na SO BF was synthesized from BF , generated in situ by
2
4
3
3
–
tedious, because the comparatively weak basicity of F pro-
thermal decomposition of LiBF (p(BF , 603 K) = 0.87
calcd.
4
3
vides a low driving force and requires carefully elaborating
the tight parameter windows in temperature and reaction time
applicable. In order to broaden the synthetic access to complex
fluorooxoanions, we have considered to investigate the reac-
tion of basic oxoanions with molecular Lewis acids, beginning
with BF . Indeed, we have observed that gaseous BF readily
5
[8]
ϫ 10 Pa ), and Na SO at 603 K, in a sealed quartz ampoule
2
4
(Equation (1)). The formation of Na SO BF proceeds in com-
2 4 3
petition with a side reaction leading to minor amounts of
NaBF , the only additional crystalline phase recorded. For the
4
formation of NaBF we suggest a reaction according to Equa-
4
3
3
tion (2), assuming that boron oxide and sodium catena-polysul-
fates are present in an amorphous state. Under the reaction
conditions (603 K) the new solid is only stable in an atmo-
2
–
reacts with, e.g. SO4 in the solid state, yielding new
sphere of BF , otherwise it decomposes, even at lower tem-
*
Prof. Dr. M. Jansen
3
Fax: +49-711-689-1502
E-Mail: M. Jansen@fkf.mpg.de
peratures. By heating the sample at 553 K for a couple of hours
in an argon floated tube, Na SO is recovered. Thermogravi-
2
4
[
a] Max-Planck-Institut für Festkörperforschung
Heisenbergstraße 1
metric investigations show the onset of decomposition at
19 K. The title compound is sensitive to air, exposition to
moisture yields mainly NaBF , Na SO and an unidentified
7
0569 Stuttgart, Germany
5
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201200033 or from the au-
thor.
4
2
4
amorphous product.
Z. Anorg. Allg. Chem. 2012, 638, (5), 733–736
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
733

T. Pilz, M. Jansen
SHORT COMMUNICATION
Na
2
SO
4
+ BF
3
Ǟ Na
2
SO
4
BF
3
(1)
(2)
(3+n) Na
2
SO
4
+ 8 BF
3
4 2 3 n+3 4n+9
Ǟ 6 NaBF + B O + Na2nS O
The products as obtained are relatively hard, coarse crystal-
line and contain crystals of good quality, suitable for single-
crystal X-ray structure analysis. The crystallographic data
given in Table 1 indicate a monoclinic pseudo-symmetry. The
triclinic unit cell and space group was confirmed by a le Bail
fit of the powder data, also the internal R values of the inten-
sity data collected was unacceptably high when assuming mo-
noclinic symmetry.
Table 1. Crystallographic data for Na
2
SO
4
BF
3
.
Temperature /K
Formula weight
Space group, Z
Lattice constants /Å
298
209.85
¯
P1, 2
a = 6.6033(2)
b = 6.6328(2)
c = 6.6349(1)
α = 84.542(2) °
β = 84.458(1) °
γ = 65.762(1) °
263.25 (1)
ρ = 2.647
0.08ϫ 0.06ϫ 0.04
SMART APEX I
(from powder data)
Volume /Å3
Density (calculated) /g·cm–3
Crystal size / mm
Diffractometer
(Bruker AXS Karlsruhe)
X-ray radiation, λ /Å
Monochromator
Mo-K , 0.71073
graphite
0.802
α
Absorption coefficient μ /mm–1
θ range /°
Figure 1. The discrete anion of Na
2
SO
4
BF
3
(a) coordinates to two
3.1–25
crystallographic different sodium atoms with coordination numbers 5
and 6 (b). Only F2(i) and O4(i) among the ligands of coordinating Na1
belong to the same anion. Pairs of distorted edge sharing octahedra
and distorted trigonal bipyramides with central sodium atoms are
building up layers (c) between the anions.
Index range
–7 Յ h Յ 7
–
–
7 Յ k Յ 7
7 Յ l Յ 7
Independent reflections
Transmission tmin, tmax
No. of parameters
925
0.6083, 0.7468
100
0.0395, 0.1198
–0.60, 0.62
2
2
2
R
1
[F Ͼ 2σ(F )], wR(F )
Although the constituting building units are of comparable size
and shape, interestingly the structures appear to be substan-
tially different. We attribute this phenomenon to the distinct
Δρmin, Δρmax /e·Å–3
Na SO BF
3
comprises the novel complex anion coordination requirements of the terminal fluorine as compared
2
4
2
–
[11]
[
F BOSO ] , which is a structural analogue to and isovalen- to oxygen atoms. Calculations of the valence sums
give
3
3
2
–
ceelectronic with S O7 (Figure 1a).
conclusive evidence for such an explanation. As can be seen
2
Boron and sulfur atoms are in tetrahedral environments, from Table 3, the terminal fluorine atoms accumulate expected
with terminal B–F and S–O bond angles varying from 105.2(3) valence sums of about 1, whereas the corresponding oxygen
to 112.0(3)° and 104.4(2) to 113.3(2)°, respectively (Table 2). atoms range around 2. This is reflecting on one hand the
As expected, the distance between the sulfur atom and the stronger S–O bonding, as compared to B–F, and on the other
bridging oxygen atom (O1) is significantly larger (1.532(2) Å) hand the different contributions of the coordinating sodium
than those to terminal oxygen atoms (O2: 1.447(3) Å, O3: atoms to the valence sums of fluorine in Na SO BF and the
2
4
3
[9]
1.449(2) Å, and O4: 1.449(3) Å) (Table 2).
The torsion corresponding terminal oxygen atoms in Na S O .
2 2 7
angles and the angle at the bridging oxygen atom are very
The redistribution of the sodium atoms in Na SO BF com-
2
4
3
[9]
close to those found in Na S O
(Na SO BF : 17.0(4)°, pared to Na S O is in accordance with the low affinity of the
2 4 3 2 2 7
2
2
7
1
4.1(2)°, 12.8(3)°; Na S O : 17.0(2)°, 14.3(1)°, 11.5(1)°) (B1– BF4– ions to cations, which has been addressed as an “innocent
2 2 7
[12]
O1–S1, 128.2(3)°; S1–O4–S1, 125.7(1)°). The atom Na1 is in anion to precipitate cations“.
a distorted octahedral and the atom Na2 in a distorted trigonal (triflates)[13,14] M(F C–SO ) (M = Li, Na) the stronger coordi-
In trifluoromethylsulfonates
3
3
bipyramidal coordination by oxygen and fluorine atoms nation of cations to oxygen in comparison to fluorine atoms is
Table 2, Figure 1b). The three dimensional structure is charac- even more pronounced.
terized by layers consisting of the complex anions and sodium Figure 2 shows the IR spectrum, which proofs the absence
ions, stacked in an alternating sequence, approximately along of OH groups that would absorb at around 3500 cm , how-
111] (Figure 1 c). We have compared the structures of ever, they cannot be distinguished from fluorine by X-ray dif-
(
–1
[
Na SO BF and Na S O using the CMPZ algorithm.[
10]
fraction.
2
4
3
2 2 7
7
34
www.zaac.wiley-vch.de
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2012, 733–736

Synthesis of Sodium (Trifluoroborato)sulfate
2 4 3
Table 2. Selected distances /Å and the bond angles /° of Na SO BF ,
estimated standard deviations are given in brackets.
B1–
F3
F1
F2
O1
1.381(5)
1.383(4)
1.405(5)
1.489(5)
S1–
O2
O3
O4
O1
1.447(3)
1.449(2)
1.449(3)
1.532(2)
Na1–
F3
F2
2.314(3)
2.331(3)
2.337(3)
2.342(3)
2.369(3)
2.395(3)
Na2–
O2i
F2
2.377(3)
2.396(3)
2.449(3)
2.476(3)
2.494(3)
i
ii
v
O3
O4
O2
O3
iii
vi
iv
vii
F1
F1
i
O4
O1–B1–F3
F1–B1–F2
F2–B1–F3
O1–B1–F2
F1–B1–F3
F1–B1–O1
O1–B1–F3
F1–B1–F2
F2–B1–F3
O1–B1–F2
105.2(3)
108.6(3)
109.6(3)
109.8(3)
111.5(3)
112.0(3)
105.2(3)
108.6(3)
109.6(3)
109.8(3)
O1–S1–O2
O1–S1–O4
O1–S1–O3
O3–S1–O4
O1–S1–O3
O2–S1–O4
O1–S1–O2
O1–S1–O4
O1–S1–O3
O3–S1–O4
104.4(2)
107.4(1)
108.2(1)
110.4(2)
112.7(2)
113.3(2)
104.4(2)
107.4(1)
108.2(1)
110.4(2)
[i] (–x, –y+2, –z+2) [ii] (–x, –y+2, –z+1) [iii] (x–1, y+1, z) [iv] (x,
y+1, z) [v] (x–1, y, z+1) [vi] (–x, –y+1, –z+2) [vii] (x, y, z+1)
Table 3. Bond valence sums of terminal oxygen and fluorine atoms in
[
9]
Na
2
SO
4
BF
3
and Na
2
S
2
O
7
2 2 7
(ICSD collection code of Na S O :
413049). Atoms that contribute less than 5% are omitted.
Na
2
SO
4
BF
3
Na S O
2 2 7
O,F –S / –Na / –(S + Na)
O
–S / –Na / –(S + Na)
O2
O3
O4
F1
F2
F3
1.615 / 0.387 /2.002
1.605 / 0.398 / 2.003
1.603 / 0.435 / 2.038
0.761 / 0.264 / 1.025
0.715 / 0.314 / 1.029
0.764 / 0.195 / 0.959
O1 1.630 / 0.408 / 2.110
O2 1.638 / 0.447 / 2.085
O3 1.673 / 0.404 / 2.077
O5 1.662 / 0.323 / 1.985
O6 1.653 / 0.326 / 1.979
O7 1.647 / 0.397 / 2.044
Figure 2. FT-IR spectrum of Na
2
SO
bottom 1400–400 cm range enlarged). Absorptions resulting from
minor amounts of NaBF are marked with an arrow.
4 3
BF (top whole range measured,
–
1
4
Experimental Section
All reactions were carried out by using standard Schlenk technique
The compound was also investigated by solid-state NMR,
and glove boxes under dry argon atmosphere. LiBF
anhydrous, ultra dry, 99.9995%) is placed at the bottom of a quartz
ampoule. A quartz stick separates a silver crucible containing Na SO
99 +%, for analysis, anhydrous, Acros Organics, pre dried at 573 K
under vacuum for 4 days) from the LiBF . The ampoule was sealed
4
(Sigma Aldrich,
11
by acquiring the B MAS spectra with and without application
1
9
19
of F spin decoupling (data not shown). When efficient
F
2
4
[15]
decoupling is applied,
interaction is suppressed, and a more intense and narrower 11
the dephasing caused by the dipolar
(
B
4
–
1
resonance is observed in the spectrum. As the dipolar interac- under vacuum and heated up to 603 K at a heating rate of 100 K·h ,
tion scales down with the cube of the distance, this implies held 300 hours at 603 K, and cooled to a rate of 1 K·h– to room
1
4 3
temperature. During heating LiBF evolves BF (log p(Torr) = –4310
close proximity of the fluorine atom to the boron atom.
[
8]
K / T + 9.96 ).
Powder X-ray diffraction patterns were collected between 5 and 95°
θ with a Bruker D8 powder diffratometer (D8 ADVANCE, Bruker
Conclusions
2
The Lewis Acid base reaction of solid Na SO with gaseous AXS, Karlsruhe, Germany) using Cu-Kα radiation from a primary
2
4
BF3 represents a facile access to the (fluoroborato)sulfate Ge(111)-Johansson type monochromator. The sample was placed in a
2
–
Hilgenberg glass capillary (diameter: 0.5 mm) and sealed under argon.
anion [SBO F ] . With respect to the crystal structure, the
4
3
[
16]
[17]
The refinement was performed by using TOPAS.
gave the lattice constants as a = 6.60323(2) Å, b = 6.6328(2) Å, c =
.6349(1) Å, α = 84.542 (2)°, β = 84.4578(1)° and γ = 65.762(1)°.
A Le-Bail fit
sodium salt is reminiscent of sodium disulfate containing an
isovalenceelectronic anion. The sodium atoms, however, are
appreciably rearranged in order to comply with the distinct
coordination requirement of the terminal oxygen compared flu-
orine atoms. The synthetic procedure appears to be generally
6
Single crystal diffraction data were recorded at 298 K with a SMART-
APEX-I CCD X-ray diffractometer (Bruker AXS, Karlsruhe, Ger-
applicable and prolific. As a result of preliminary studies on many) using Mo-K radiation and a graphite monochromator. Reflec-
α
Na PO /BF we have isolated and characterized Na B PO F . tion integration and multi-scan adsorption correction were performed
3
4
3
3
2
5 4
Z. Anorg. Allg. Chem. 2012, 733–736
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
735

T. Pilz, M. Jansen
SHORT COMMUNICATION
with the Bruker suite software package[18] and SADABS.[19] The struc-
ture was solved by direct methods and refined with the SHELXTL
software package.[
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20]
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08.
6
Crystallographic data, atomic coordinates and the powder pattern are
given in Table 1, Table 4 and in the supporting information.
[
1
[
[
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1
2 4 3
Table 4. Atomic coordinates for Na SO BF .
5
Atom Site
x
y
z
U
eq
[
7] V. Gutmann, U. Mayer, R. Krist, Synth. React. Inorg. Met.-Org.
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Na1
Na2
B1
S1
O1
O2
O3
O4
F1
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
–0.2684(2)
–0.2772(3)
–0.1655(6)
0.2281(1)
0.0220(4)
0.3489(4)
0.1543(4)
0.3493(4)
–0.2356(4)
–0.0994(4)
–0.3322(4)
0.3835(3)
0.7662(3)
0.8455(2)
0.4009 (3) 0.0415 (5)
0.0303 (5)
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0.8557 (7) 0.8760 (6) 0.0200 (8)
0.7277(1)
0.8947(4)
0.8570(4)
0.6335 4)
0.5568(4)
0.7260(4)
0.7497(4)
0.0640(4)
0.6507(1)
0.0214 (3)
0.7619 (4) 0.0239 (6)
0.5623 (4) 0.0258 (6)
0.4993 (4) 0.0276 (6)
0.8000 (4) 0.0283 (6)
0.7740 (3) 0.0323 (6)
0.0669 (3) 0.0323 (6)
0.9006 (4) 0.0366 (6)
F2
F3
[13] R. Dinnebier, N. Sofina, M. Jansen, Z. Anorg. Allg. Chem. 2004,
6
30, 1613–1616.
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–1
Infrared spectra (range: 400–4000 cm ) were recorded using a Perkin–
Elmer FT-IR spectrometer Spectrum Two in a glove box.
6
[
[
[
[
[
15] C. V. Chandran, G. Hempel, T. Bräuniger, Solid State Nucl. Magn.
Reson. 2011, 40, 84–87.
Thermal analysis was performed with the instrument STA 409 C
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sis software, Version 3.0, Bruker AXS, Inc. Madison, USA, 2008.
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47.
18] Bruker Suite, Version 2008/3, Bruker AXS Inc., Madison, USA,
008.
–
1
(
Netzsch GmbH, Selb, Germany) at a heating rate of 10 K·min up
to 800 °C.
4
Supporting Information (see footnote on the first page of this article):
Indexed powder pattern of Na SO BF .
2 4 3
2
19] G. M. Sheldrick, SADABS, Bruker AXS area detector scaling and
adsorbtion, Version 2007/4, University of Göttingen, Germany,
Acknowledgments
2007.
[
20] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
The authors thank Dr. H. Nuss for collecting the single crystal inten-
sities and Dr. T. Bräuninger for the NMR measurement.
Received: January 26, 2012
Published Online: March 8, 2012
7
36
www.zaac.wiley-vch.de
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2012, 733–736