Stabilization of SF5- with Glyme-Coordinated Alkali Metal Cations

Article abstract of DOI:10.1021/acs.inorgchem.8b02655

The stabilization of complex fluoroanions derived from weakly acidic parent fluorides is a significant and ongoing challenge. The [SF₅]^- anion is recognized as one such case, and only a limited number of [SF₅]^-

Full text of DOI:10.1021/acs.inorgchem.8b02655

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
−
Stabilization of SF5 with Glyme-Coordinated Alkali Metal Cations
Kazuhiko Matsumoto,*,† Yuki Haruki,† Shunsuke Sawada,† Shigeyuki Yamada,‡ Tsutomu Konno,‡
and Rika Hagiwara†
†Graduate School of Energy Science, Kyoto University, Yoshida, Sakyo-ku, Kyoto, 606-8501, Japan
‡Faculty of Molecular Chemistry and Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan
S
* Supporting Information
ABSTRACT: The stabilization of complex fluoroanions derived from
weakly acidic parent fluorides is a significant and ongoing challenge. The
[SF5]− anion is recognized as one such case, and only a limited number
of [SF5]− salts are known to be stable at room temperature. In the
present study, glyme-coordinated alkali metal cations (K+, Rb+, and Cs+)
are employed to stabilize [SF5]−, which provides a simple synthetic route
to a [SF5]− salt. The reactivities of KF and RbF with SF4 are significantly
enhanced by complexation with G4, based on Raman spectroscopic
analyses. A new room-temperature stable salt, [Cs(G4)2][SF5] (G4 =
tetraglyme), was synthesized by stoichiometric reaction of CsF, G4, and
SF4. The vibrational frequencies of [SF5]− were assigned based on
quantum chemical calculations, and the shift of the G4 breathing mode accompanying coordination to metal cations was
confirmed by Raman spectroscopy. Single-crystal X-ray diffraction revealed that Cs+ is completely isolated from [SF5]− by two
G4 ligands and [SF5]− is disordered along the crystallographic two-fold axis. Hirshfeld surface analysis reveals that the H···H
interaction between two neighboring [Cs(G4)2]+ moieties is more dominant on the Hirshfeld surface than the interaction
between the H atom in glyme molecules and the F atom in [SF5]−, providing a CsCl-type structural model where the large and
spherical [Cs(G4)2]+ cations contact each other and the [SF5]− anions occupy interstitial spaces in the crystal lattice. The
[SF5]− anion, combined with [Cs(G4)2]+, exhibits a very limited deoxofluorinating ability toward hydroxyl groups in both neat
conditions and THF solutions.
SF4 and new [SF5]− salts, [HNC5H3(CH3)2 ]2F−[SF5 ]·nSF4
+
−
INTRODUCTION
■
(n = 1 or 4) and [HNC5H4N(CH3)2 ]2[SF5−]F−·
+
Sulfur tetrafluoride functions as both a Lewis acid and base and
can form [SF3]+ and [SF5]− by reacting with a F− acceptor or
donor, respectively.1−6 The [SF5]− anion exists with several
counter-cations, including Rb[SF5 ],2 Cs[SF5 ],3
Cs6[SF5]4[FHF]2,2 [N(CH3)4][SF5],4 [((CH3)2N)3S][SF5],5
and [Cs(18-crown-6)][SF5],6 but only a limited number of
examples are vacuum-stable owing to the low Lewis acidity of
SF4.7,8 Scheme 1 summarizes the preparative routes for the
known [SF5]− salts along with information on the SF4
dissociation pressure.
Although introduction of a strong fluoride ion donor,
including the fluorides of large alkali metal or organic cations,
is the usual method used to stabilize such anions,11−14 the Rb+
and [N(CH3)4]+ salts have clearly been reported to have
significant SF4 dissociation pressures and are unstable at room
temperature throughout this series.2,4 The stability of Cs[SF5]
has been a controversial topic in previous reports. Two early
reports stated that the reaction between CsF and SF4 did not
proceed.1,4 Later, Tullock et al. mentioned Cs[SF5] was stable
at room temperature and released SF4 at elevated temper-
atures, although a high reaction temperature of 250 °C is
required to complete this reaction.3 Gerken et al. extended this
field with their recent work and reported adducts of SF4 with
an organic nitrogen base as well as S···F interactions in pure
5
CH2Cl2.9,15−17 The bulky cations, ((CH3)2N)3S+ and Cs-
6
(18-crown-6)2 , provide stable salts with [SF5]−. Another
recent report showed that nucleophilic activation of SF6 by
phosphine provided a stable substituted phosphonium [SF5]−
salt.10 Even in the cases where such salts have a certain degree
of stability, the synthetic methods suffer from low yields,
complicated procedures, or an expensive organic cation is
required.
+
In the present study, a new series of [SF5]− salts has been
synthesized by a simple reaction which introduces glyme-
coordinated alkali metal cations. Although the strategy to
stabilize [SF5]− in this study is related to previous work using
crown ether (18-crown-6),6 glymes have more structural
flexibility than crown ethers and form complex cations with
alkali metals in various coordination modes.18,19 They can also
function as the solvent because most glymes are liquids under
ambient conditions. Enhancement of reactivities of alkali metal
fluorides (MF) with SF4 in the presence of tetraglyme (G4)
and the structure of the room-temperature stable Cs salt will be
discussed.
Received: September 18, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b02655
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a
Scheme 1. Summary of the Preparative Methods for Previously Known [SF5]− Salts
a
The compounds in red and blue denote [SF5]− salts with and without an appreciable SF4 dissociation pressure at room temperature, respectively.
Abbreviations DMPy, DMAP, TASF, and NIiPr refer to dimethylpyridine, 4-(dimethylamino)pyridine, tris(dimethylamino)sulfonium fluoride, and
2−4
1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidenamino, respectively. References: Rb[SF5],2 Cs[SF5],
Cs6[SF5]4[FHF]2,2 [N(CH3)4][SF5],4
[DMPyH]2F[SF5]·nSF4 (n = 1 or 4)),9,17 [DMAPH]2F[SF5]·CH2Cl2,17 [Cs(18-crown-6)][SF5],6 and [P(NIiPr)3F][SF5]10.
overnight after a 24 h reaction period resulted in no increase in
RESULTS AND DISCUSSION
Reactivity of Alkali Metal Fluorides with SF4. The
reaction of MF and SF4 in the presence of G4 at 25 °C resulted
in the formation of [M(G4)n][SF5] (eq 1):
■
mass with respect to the KF/G4 mixture, which indicated that
K[SF5] is unstable under vacuum (it should be noted that G4
has a negligible vapor pressure and does not contribute to mass
changes (∼2 Pa at 25 °C)).20 However, the product for RbF
leads to a significant mass increase and volume increase of the
white powder. Prolonged evacuation of the Rb salt at 25 °C for
several days resulted in the appearance of a liquid phase, which
suggested a small SF4 dissociation pressure for this product.
These observations indicated that [K(G4)n][SF5] and [Rb-
(G4)n][SF5] are only stable under a SF4 pressure, although the
dissociation pressure over [Rb(G4)n][SF5] was quite low. The
reaction was also carried out in the absence of G4 to clarify the
effects of G4. Raman spectroscopy under 1.2 atm of SF4
revealed that even reaction for over 2 days did not result in the
formation of K[SF5], whereas the formation of Rb[SF5] was
confirmed. The coordination of G4 to M+ was suggested by the
shift of the G4 breathing mode to a higher wavenumber
(Figure 1a,b) (see below for the details of this shift).
MF + SF + nG4 → [M(G4)n][SF](M+ = K+, Rb , andCs+)
+
4
5
(1)
The reactivity of MF toward SF4 depends on the nature of
M+. Figure 1 shows the Raman spectra of the products from
Synthesis of [Cs(G4)2][SF5]. The stoichiometric reaction
(CsF: G4: SF4 = 1:2:1 in mol) in the case of CsF gave the
white powdery [Cs(G4)2][SF5], whereas the reaction in G4
solvent (meaning the reaction with excess G4) resulted in a G4
solution of [Cs(G4)n][SF5]. The mass increase indicated a
99% conversion, which was significantly greater than without
G4, that is, the reaction between solid CsF and gaseous SF4 in
the absence of G4 was reported to hardly occur at room
temperature, and the yield was 94% for the reaction at 250
°C.3 The reaction to form [Cs(18-crown-6)][SF5] requires 60
°C and still yields only a 77% conversion.6 Our Raman
spectroscopic trial also confirmed the formation of Cs[SF5] by
reaction of CsF and SF4 under 1.2 atm of SF4 (Figure 1e).
Although the dissociation pressure of SF4 over Cs[SF5] was
very low, gradual degradation of intensity of bands assigned to
[SF5]− occurred under vacuum by Raman spectroscopy. These
observations indicated that the present reaction with G4 is
Figure 1. Raman spectra of the products from the reactions of alkali
metal fluorides and SF4 with and without G4 at 25 °C: (a) KF + SF4
in G4, (b) RbF + SF4 in G4, (c) KF + SF4, (d) RbF + SF4, (e) CsF +
SF4, and (f) pure G4. The spectra (a−e) were recorded under an SF4
−
○
atmosphere of 1.2 atm. Symbols denote PFA reactor (*), [SF5] ( ),
and breathing mode of G4 (br-G4).
the reactions of MF and SF4 over 24 h in the presence of G4.
The spectrum of G4 is also shown for comparison. In the
Raman spectra where the sample is under an SF4 pressure of
1.2 atm, the bands assigned to [SF5]− were observed for both
the K+ and Rb+ salts (Figure 1a,b) (see below for the detailed
assignments). In the case of KF, evacuation of volatiles
B
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considered to be a simple and effective way to synthesize a
vacuum-stable [SF5]− salt at room temperature. Although the
exact coordination number in the liquid state was unclear, the
1:1:4.5 (CsF:SF4:G4 in molar ratio) reaction yielded a
completely liquid phase at room temperature. Differential
scanning calorimetry (DSC) and visual confirmation revealed
that the G4 complex salt, [Cs(G4)2][SF5], melted at 37 °C
(Figure S1 for DSC curve, Supporting Information). Only a
single peak was observed in the 19F NMR spectrum of
[Cs(G4)2][SF5] (61.0 ppm in the melt at 40 °C and 65.9 ppm
in a G4 solution at 25 °C). This implies a dissociative
intermolecular process by considering low Lewis acidity of SF4;
the SF4 molecule produced by dissociation of [SF5]−
undergoes Berry pseudorotation, followed by recombination
to effect chemical exchange. This observation was in agreement
with the previous report on [((CH3)2N)3S][SF5] at room
temperature (61.1 ppm (singlet) in CD3CN).5
X-ray Crystal Structure and Raman Spectrum of
[Cs(G4)2][SF5]. Slow recrystallization of [Cs(G4)2][SF5] from
the G4 solution gave single crystals suitable for structural
determination by X-ray diffraction. Crystallographic data are
summarized in Table S1, Supporting Information, and selected
geometrical parameters are listed in Table 1 (other geometrical
Figure 2. Thermal ellipsoid plots of (a) [Cs(G4)2]+ and (b) [SF5]−
and (c) disordered model of [SF5]− in [Cs(G4)2][SF5] at −160 °C.
Thermal ellipsoids are shown at the 50% probability level.
Table 1. Selected Experimental and Calculated Bonding
Lengths (Å) and Angles (deg) of [SF5]− and Contact
a
Distances for [Cs(G4)2]+ in [Cs(G4)2][SF5]
S1−F1
S1−F2
S1−F3
S1−F4
1.498(6) [1.604]
1.676(5) [1.740]
1.691(5) [1.740]
1.702(5) [1.740]
1.713(5) [1.740]
87.3(9) [85.3]
166.0(7) [170.5]
91.9(7) [89.6]
3.161(4)
F1−S1−F2
F1−S1−F3
F1−S1−F4
F1−S1−F5
F3−S1−F4
F3−S1−F5
F4−S1−F5
84.8(4) [85.3]
86.0(4) [85.3]
84.2(4) [85.3]
83.8(3) [85.3]
85.0(5) [85.3]
169.9(6) [170.5]
93.9(7) [89.6]
S1−F5
F2−S1−F3
F2−S1−F4
F2−S1−F5
Cs1···O20
Cs1···O50
Cs1···O80
Cs1···O11
Cs1···O14
3.168(4)
3.098(4)
3.180(4)
3.156(3)
a
Calculated geometrical parameters of [SF5]− (C4v) at PBE1PBE/
aug-cc-pVTZ are shown in square brackets. Experimental geometrical
parameters for the G4 molecule of [Cs(G4)2]+ in [Cs(G4)2][SF5] are
listed in Table S2, Supporting Information.
parameters including the C−H···F interactions are listed in
Tables S2 and S3). Figure 2 shows the X-ray structures of
[Cs(G4)2]+ and [SF5]− in [Cs(G4)2][SF5]. Figure 3 shows the
packing diagram of [Cs(G4)2][SF5] as viewed along the c-axis
(see Figure S2 for the view along the a-axis). The cation−
anion packing in the [Cs(G4)2][SF5] structure is best
described as the CsCl-type. The two G4 molecules coordinate
to the Cs+ center by 10 ether O atoms (five for each G4
molecule, Figure 2a). To the best of the authors’ knowledge,
this is the first crystallographic example of a [Cs(G4)2]+
complex cation. Whereas crown ether ligands can sandwich
alkali metal cations in [M(crown)2]+,21 the two G4 ligands in
[Cs(G4)2][SF5] surround Cs+ in a more spherical manner and
are related to each other by a two-fold rotation along the c-axis
at the Cs+ position. The Cs+···O contact distances fall within a
narrow range (3.098(4) to 3.161(4) Å) owing to the flexible
glyme structure and are shorter than those in [Cs(18-crown-
6)2][SF5] (3.184(9)−3.551(9) Å) in which the Cs+ ion is 12-
coordinate.21 The bond valences of Cs+ were calculated to
Figure 3. Packing diagram of [Cs(G4)2][SF5] along the c-axis.
Thermal ellipsoids are shown at the 50% probability level.
compare the coordination states in [Cs(G4)2][SF5] and
[Cs(18-crown-6)2][SF5] (see Table S4, Supporting Informa-
tion, for details pertaining to the bond valence calcula-
tion).22,23 The bond valence sum for Cs+ in [Cs(18-crown-
6)2][SF5] is 0.98, which is consistent with an oxidation state of
+1. However, Cs+ in [Cs(G4)2][SF5] has a bond valence sum
of 1.37, which suggests Cs+ is significantly overcoordinated in
this structure and is strongly bound by the G4 molecules. The
space-filling model of [Cs(G4)2]+ demonstrates the complete
isolation of the Cs+ core from the anion (Figure S3, Supporting
Information). The [SF5]− anion adopts a square-pyramidal
C
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geometry as expected from the valence shell electron repulsion
model of molecular geometry (Figure 2b),24,25 where the Fax−
S−Feq angles (Fax: F1 and Feq: F2−F5 in Figure 1b) are <90°
(83.8(3)−86.0(4)°) because of the lone pair occupies a
position trans to Fax (see Table 1 for comparison of
experimental and calculated geometric parameters at the
PBE1PBE/aug-cc-pVTZ level of theory). The S−Fax bond
(1.498(6) Å) was shorter than the S−Feq bonds (1.676(5)−
1.713(5) Å), as has been reported in previous works.2,5,9,15
The F atoms in [SF5]− were disordered into two positions
along the crystallographic two-fold axis, as shown in Figure 2c,
where the disordered Fax atoms were located at opposite sides
with respect to the equatorial plane and the Feq atoms were
also disordered into two positions. This is a different disorder
mode from the nearly octahedral geometry with equivalent site
occupancies that is observed in [Cs(18-crown-6)2][SF5].
There were several H···F distances (H in G4 and F in
[SF5]−) that were shorter than the sum of van der Waals radii
of H and F (H, 1.20 Å; F, 1.47 Å), but they were not
remarkably shorter (>2.39 Å). Details of the local interactions
are discussed in the section related to the Hirshfeld surface
analysis.
Table 2. Vibrational Frequencies, Intensities, and
a
Assignments for [SF5]− in [Cs(G4)2][SF5]
exptl
b
c
infrared
Raman
calcd (C4v)
assignment
A1, ν(SFax)
E, νas(SFeq 2)a/νas(SFeq 2
A1, νs(SF4)
E, δ(FaxSFeq 2)a/δ(FaxSFeq 2
A1, δumb(SF4)
B2, νs(SFeq 2)a − νs(SFeq 2
794(s)
788(60)
578(37)
522(49)
804(4)[131]
621(1)[604]
519(4)[0]
460(0)[115]
443(13)[21]
433(13)[0]
324(2)[0]
591(vs)
523(w)
465(m)
435(vw)
)
b
)
b
442(100)
424(92)
336(47)
287(66)
245(42)
)
b
B1, δ(SFeq 2)a + δ(SFeq 2
B2, ρt(SFeq 2)a − ρt(SFeq 2
E, ρw(SFeq 2)a/ρw(SFeq 2
)
b
254(0)[0]
)
b
235(0)[20]
)
b
a
Frequencies are given in cm−1. The experimental intensities for the
Raman spectra are scaled relative to the intensity of the δ(FaxSFeq 2)a/
δ(FaxSFeq 2)b mode of [SF5]−, which is assigned a value of 100. The
abbreviations, vw, w, m, s, and vs, denote very weak, weak, medium,
b
strong, and very strong. Values in parentheses denote calculated
Raman intensities (Å4 u−1) and values in square brackets denote
calculated infrared intensities (km mol−1). The vibrational data were
c
calculated at the PBE1PBE/aug-cc-pVTZ level of theory. The
symbols ν, δ, νs, δumr, νas, ρt, and ρw denote stretching, bending,
symmetric stretching, umbrella, asymmetric stretching, torsion, and
wagging modes, respectively.
The Raman spectrum of [Cs(G4)2][SF5] at 25 °C is shown
in Figure 4 (see Figure S4, Supporting Information, for the
quantum chemical calculations (Figure 4a). Previous work
relating to the salts with G4-coordinated alkali metal cations
revealed that the G4 breathing mode exhibited a blue-shift
relative to that of pure G4, owing to the interaction between
the alkali metal cation and O atom in G4.28,29 Such a shift with
respect to G4 was also observed for the spectrum of
[Cs(G4)2][SF5]; the Raman bands at 808, 828, and 851
cm−1 of pure G4 shifted to 834, 850, and 867 cm−1 (Figure
4c,d), which indicated complex formation of G4 with Cs+.
+
Hirshfeld Surface Analysis of Cs(G4)2 . Interactions of
[Cs(G4)2]+ in the [Cs(G4)2][SF5] crystal structure were
investigated by Hirshfeld surface analysis, which is an effective
way to analyze the intermolecular interactions by partitioning
space in the crystal into regions where the electron distribution
of a sum of spherical atoms for the molecule dominates the
corresponding sum over the crystal.30−33 Figure 5 shows the
Figure 4. Raman spectra of [Cs(G4)2][SF5] (a and c) and pure G4 (b
and d) at 25 °C. The top figure shows the spectra in the range 100−
1000 cm−1. The bottom figure shows the magnified spectra in the
Figure 5. Hirshfeld surfaces and projection of dnorm and the shape
index for [Cs(G4)2]+ in [Cs(G4)2][SF5]: (a) molecular structure, (b)
projection of dnorm, and (c) projection of shape index.
range 750−900 cm−1 to clarify the shift of the breathing mode of G4.
−
○
The symbols denote [SF5] ( ) and breathing mode of G4 (br-G4).
Hirshfeld surfaces and projection of the normalized contact
distance on the surface (dnorm) and shape index (S), for
[Cs(G4)2]+ in [Cs(G4)2][SF5] (see Figures S5 and S6,
Supporting Information, for the Hirshfeld surface analysis for
[Cs(18-crown-6)2]+ in [Cs(18-crown-6)2][SF5]). The [SF5]−
anion was treated in the disordered model by considering all
the orientations with their partial occupancies. On the dnorm
infrared spectrum). Table 2 lists detailed assignments of
vibrational modes, including infrared spectroscopic data, based
on quantum chemical calculations at the PBE1PBE/aug-cc-
pVTZ level of theory. The eight relatively strong Raman bands
of [SF5]− agree with those reported in previous studies6,26,27
and were assigned to its fundamental modes based on the
D
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surface, intermolecular contacts, shorter and longer than the
sum of their van der Waals radii, are highlighted in red and
blue, respectively, and contacts around the sum of van der
Waals radii are shown in white. When [Cs(G4)2]+ is regarded
as cubical, the eight red regions at the corners (each region
further has some spots) correspond to the H···F contacts that
are shorter than the sum of their van der Waals radii (Figure
5b). Projection of S on the Hirshfeld surface can be used to
identify complementary hollows (red) and bumps (blue)
where two molecular surfaces touch one another. Comparison
of the dnorm and S surfaces (the orientation of [Cs(G4)2]+ is
shown in Figure 5a) suggests that the hollows appearing along
the gap between two G4 molecules on the [Cs(G4)2]+ surface
(red regions in Figure 5c) have contacts around the sum of van
der Waals radii (white regions in Figure 5b). These hollows are
well-fitted by G4 molecules of the six neighboring [Cs(G4)2]+
complex cations.
The two-dimensional (2D) fingerprint of the Hirshfeld
surface provides a visual summary of the frequency for each
combination of de and di, where de and di are the distances
from the surface to the nearest nucleus, external, and internal,
respectively. This 2D plot indicates that intermolecular
interactions are present in the crystal and shows the relative
area of the surface corresponding to each kind of interaction.
Figure 6 shows the 2D fingerprint plots of [Cs(G4)2]+ in
[Cs(G4)2]+ in [Cs(G4)2][SF5] is 0.82, indicating that this
complex cation can be considered a pseudosphere (cf. the
identical G-value is calculated for [Cs(18-crown-6)2]+ in its
[SF5]− salt, as shown in the Supporting Information). The
large contribution of H···H interaction to the Hirshfeld surface
and the large globularity lead to the CsCl-type structural
model, where the roughly spherical [Cs(G4)2]+ cations
(volume based on Hirshfeld surface analysis: 674.06 Å3)
contact each other and the [SF5]− anions are located in the
interstitial spaces in the crystal lattice. The large interstitial
volume among the [Cs(G4)2]+ cations allows disordering of
the anionic moiety, which is reflected in the larger volume of
the disordered [SF5]− anion in [Cs(G4)2][SF5] (85.32 Å3)
than the volume of the ordered [SF5]− anion in [DMPyH]-
F[SF5]·4SF4 (77.82 Å3).9
Deoxofluorinating Ability of [SF5]−. Although SF4 gas is
well-known as a deoxofluorinating reagent,34,35 the deoxo-
fluorinating ability of [SF5]− is considered to be weaker than
the parent SF4 because it is stabilized in the anionic form. This
was confirmed by the reaction of [Cs(G4)2][SF5] with 3-
phenyl-1-propanol. The reactions in THF solutions at 50 °C
proceeded giving only low yields (1% for 1.0 equiv of
[Cs(G4)2][SF5] and 6% for 1.4 equiv of [Cs(G4)2][SF5]).
Even the reaction in the neat [Cs(G4)2][SF5] solution at 100
°C did not significantly improve the yield (7% for 1.0 equiv of
[Cs(G4)2][SF5] and 9% for 2.0 equiv of [Cs(G4)2][SF5]).
These results suggested a highly stabilized state for [SF5]− with
the [Cs(G4)2]+ countercation.
CONCLUSIONS
■
In conclusion, herein the formation of [SF5]− salts with glyme-
coordinated alkali metal fluorides (KF, RbF, and CsF) is
reported. Although only a limited number of examples were
known for [SF5]− salts, even KF, which is the weakest fluoride
ion donor in this series, forms a complex salt with SF4 in the
presence of G4. This is in contrast to the nonreactivity (or
negligibly low-reactivity) of KF and SF4 in the absence of G4.
The reactivity with SF4 increases with increasing size of the
alkali metal cation, and Cs+ forms a vacuum-stable salt,
[Cs(G4)2][SF5]. According to single-crystal X-ray diffraction
studies, this salt is comprised of Cs+ that is entirely surrounded
by two G4 ligands and highly isolated [SF5]−. A Hirshfeld
surface analysis reveals that the H···H interaction between two
neighboring [Cs(G4)2]+ moieties is more dominant on the
Hirshfeld surface than the interaction between the H atom in
glyme molecules and the F atom in [SF5]−. This corresponds
to a CsCl-type lattice, in which the large and spherical
[Cs(G4)2]+ cation contact each other and the [SF5]− anions
occupy the interstitial spaces in the crystal lattice. The
stabilized [SF5]− anion exhibits only a limited deoxofluorinat-
ing activity.
Figure 6. 2D fingerprint plots of [Cs(G4)2]+ in [Cs(G4)2][SF5]. The
two insets highlight the H···H and H··F contacts. The symbols, de and
di, are the distances from the surface to the nearest nucleus, external
and internal, respectively.
This study shows that the bulkiness of glyme-coordinated
alkali metal cations can stabilize fluorocomplex anions of the
parent fluorides with weak fluoride ion affinities, instead of
needing to introduce organic cations. The structural flexibility
and low melting point of the glyme species enable wide
applicability of this strategy to other fluorocomplex systems,
and investigations on systems are currently in progress.
[Cs(G4)2][SF5]. The contribution of the H···H contact
(72.7%, symmetric with respect to the diagonal) is significantly
larger than that of the H···F contact (23.1%, asymmetric with
respect to the diagonal), suggesting that the interaction
between two neighboring glyme molecules is more dominant
on the Hirshfeld surface than the interaction between the H
atoms in glyme molecules and the F atoms in [SF5]−.
Globularity (G) of a molecule is defined as the Ssphere/Sh ratio
(e.g., 1.0 for a perfect sphere), where Sh and Ssphere are the
surface areas of the Hirshfeld surface of the molecule and of a
sphere of the same volume, respectively. The G-value of
EXPERIMENTAL SECTION
■
Apparatus and Materials. Volatile materials were handled in a
vacuum line constructed using stainless steel, Pyrex glass, and
tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA). Non-
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volatile materials were handled under a dry argon atmosphere in a
glovebox. Alkali metal fluorides, KF (Wako Pure Chemical Industries,
purity 99.0%), RbF (Aldrich, 99.8%), and CsF (Wako Pure Chemical
Industries, purity 97%), were dried under vacuum at 150 °C.
Tetraglyme (G4) (Kishida Chemical, purity 98.0%, water content <30
ppm) was used as supplied. Sulfur tetrafluoride (SynQuest
Laboratories, 94%) was treated with KF to remove HF prior to use.
Caution! Sulfur tetrafluoride and its derivatives are potentially
hazardous materials and must be handled using appropriate protective
gear with immediate access to proper treatment procedures.
Reactivity of Metal Fluorides with SF4. The reactivity of metal
fluorides with SF4 was confirmed by Raman spectroscopy under 1.2
atm of SF4. The following provides the details of reaction procedure.
Reactivity of KF with SF4. Inside the drybox, 0.132 g of KF (2.28
mmol) was loaded to a 10 mm o.d. PFA reactor equipped with a
stainless steel valve (volume: ∼13 mL). After the PFA reactor was
connected to the vacuum line and evacuated, an excess of SF4 (∼1.2
atm) was introduced into the reactor on the vacuum the reaction line
(∼110 mL). The valve of the PFA reactor was kept open during the
reaction to ensure an excess amount of SF4 gas. After reaction for 48
h, the extent of reaction was confirmed by Raman spectroscopy.
Reactivity of RbF with SF4. The same procedure as in the case for
KF was used for RbF (0.218 g, 2.09 mmol). After reaction for 48 h,
the extent of reaction was confirmed by Raman spectroscopy.
Reactivity of CsF with SF4. The same procedure as in the case for
KF was used for CsF (1.023 g, 6.73 mmol). After reaction for 48 h,
the extent of reaction was confirmed by Raman spectroscopy.
Reactivity of Metal Fluorides with SF4 in G4. Reactivity of
metal fluorides with SF4 in G4 was confirmed by Raman spectroscopy
under 1.2 atm of SF4. The following provides details of reaction
procedure.
Reactivity of KF with SF4 in G4. In the drybox, 0.120 g of KF (2.07
mmol) was loaded into a 10 mm o.d. PFA reactor equipped with a
stainless steel valve (volume: ∼13 mL), and 1.130 g (5.09 mmol) of
G4 was added to it. After the PFA reactor was connected to the
vacuum line and evacuated, an excess of SF4 (∼1.2 atm) was
introduced to it on the vacuum (∼107 mL). The valve of the PFA
reactor was kept open during the reaction to ensure an excess amount
of SF4 gas. After reaction for 18 h, the extent of reaction was
confirmed by Raman spectroscopy. The Raman laser was focused on
the G4 solution.
Reactivity of RbF with SF4 in G4. The same procedure as in the
case for KF in G4 was used for RbF (0.229 g, 2.19 mmol) and G4
(0.978 mg, 4.41 mmol). After reaction for 18 h, the sample was
entirely solidified, and the reactivity was confirmed by Raman
spectroscopy. The Raman laser was focused on the white powder.
Synthesis of [Cs(G4)2][SF5]. Inside the drybox, 3.418 g of CsF
(22.49 mmol) and 10.00 g (44.99 mmol) of G4 were transferred into
a 1 in. o.d. PFA reactor. After evacuating the PFA reactor, 1.55 atm of
SF4 (22.6 mmol in 357 mL (volume of the reactor and reaction line))
was introduced into the mixture of CsF and G4 at room temperature.
Agitation of the mixture for 20 h resulted in the formation of a white
powder which was recovered in the drybox (15.681 g, 22.27 mmol).
19F NMR (376 MHz, CFCl3, G4): δ 65.9 (s), 19F NMR (376 MHz,
CFCl3, neat): δ 61.0 (s,br). See the main text and Table 2 for the
Raman and IR spectroscopic data, respectively.
in total). To this solution, 0.022 g of 3-phenyl-1-propanol (0.16
mmol) was added, and the mixture was stirred under anhydrous
conditions at 50 °C for 25 h. Yield: 6%.
Reaction in Neat [Cs(G4)2][SF5] Liquid (1.0 equiv of [Cs(G4)2]-
[SF5]). Inside the drybox, 0.020 g of 3-phenyl-1-propanol (0.15 mmol)
was added to 0.103 g of [Cs(G4)2][SF5] (0.148 mmol). The mixture
was stirred under anhydrous conditions at 100 °C for 8 h. Yield: 7%.
Reaction in Neat [Cs(G4)2][SF5] Liquid (2.0 equiv of [Cs(G4)2]-
[SF5]). Inside the drybox, 0.020 g of 3-phenyl-1-propanol (0.15 mmol)
was added to 0.207 g of [Cs(G4)2][SF5] (0.294 mmol). The mixture
was stirred under anhydrous conditions at 100 °C for 8 h. Yield: 9%.
Spectroscopic and Thermal Analyses. Raman spectra were
recorded (Bruker Optics, MultiRAM FT-Raman spectrometer) at
room temperature using the 1064 nm line of a Nd:YAG laser as the
excitation line (laser power 200 mW) with a resolution of 2 cm−1. The
samples for Raman spectroscopy were loaded into 5 mm o.d. Pyrex
glass tubes under dry Ar and sealed with a plastic cap. The spectra
under a SF4 atmosphere were recorded in 10 mm o.d. PFA tubes.
Infrared spectra were recorded at room temperature. Infrared spectra
were recorded (Bruker Optics, Alpha FT-IR spectrometer) in an
attenuated total reflection mode at room temperature with a
resolution of 4 cm−1. The entire spectrometer was placed under a
dry air atmosphere in an open dry chamber. The 19F NMR spectra
(376 MHz) were measured with a Bruker AVANCE III 400 NMR
spectrometer using CDCl3 as the external lock solvent containing
CFCl3 (δF = 0 ppm) as the internal standard. Differential scanning
calorimetry (DSC) was performed using a DSC-8230 Thermo Plus
EVO II Series (Rigaku Corp.) at a scan rate of 5 °C min−1. The
samples for DSC were sealed in an airtight Al cell under an
atmosphere of dry Ar.
Single-Crystal X-ray Diffraction. Inside the drybox, G4 was
added to a several hundred mg of [Cs(G4)2][SF5] in the vertical arm
of a 1/2 in. PFA T-shaped reactor equipped with a stainless steel valve
until a saturated solution was formed at room temperature. Crystals of
[Cs(G4)2][SF5] were grown by slowly cooling down the G4 solution
to −21 °C, and the supernatant was decanted into the side arm of the
T-shaped reactor. Suitable crystals were selected and transferred into a
quartz capillary (0.5 mm o.d., dried under vacuum at 500 °C prior to
use) under a dry argon atmosphere. The capillary was temporarily
plugged with vacuum grease and sealed using an oxygen torch. Single-
crystal X-ray diffraction data were obtained using a R-axis Rapid II,
Rigaku X-ray diffractometer controlled by the program RAPID
AUTO 2.4036 and equipped with an imaging plate area detector
which used the program RAPID XRD 2.3.3.37 A graphite-
monochromated Mo Kα radiation (0.71073 Å) was used. The
measurements consisted of 12 ω scans (130−190°, 5°/frame) at the
fixed φ (30°) and χ (45°) angles and 32 ω scans (0−160°, 5°/frame)
at the fixed φ (180°) and χ (45°) angles. Integration, scaling, and
absorption corrections were performed using RAPID AUTO 2.40.
The structure was solved using SIR-9238 and refined by SHELXL-9739
linked to Win-GX.40 Anisotropic displacement factors were
introduced for all atoms except for hydrogen.
Calculations. The energy-minimized gas-phase structures, vol-
umes, and vibrational frequencies and intensities were calculated at
the PBE1PBE level of theory using the aug-cc-pVTZ basis set.
Quantum chemical calculations were carried out using the program
Gaussian 03.41 The CrystalExplorer 17.5 program was used for
Hirshfeld surface analyses.42 The disorder of [SF5]− was modeled
based on the averaged structure by considering all orientations with
their partial occupancies.
Reactivity of [Cs(G4)2][SF5] with 3-Phenyl-1-propanol. The
following is the experimental procedure for the fluorination of 3-
phenyl-1-propanol with [Cs(G4)2][SF5]. The fluorinated product, 1-
fluoro-3-phenylpropane, was identified by its signal at δ = −218.9
ppm (tt, JH−F = 46.3, 30.1 Hz) in 19F-NMR. The yield was
determined by 19F NMR relative to an internal standard
benzotrifluoride.
Reaction in THF (1.0 equiv of [Cs(G4)2][SF5]). Inside the drybox,
0.11 g of [Cs(G4)2][SF5] (0.15 mmol) was dissolved in THF (0.4 M
in total). To this solution, 0.022 g of 3-phenyl-1-propanol (0.16
mmol) was added, and the mixture was stirred under anhydrous
conditions at 50 °C for 25 h. Yield: 1%.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b02655.
Crystallographic, vibrational spectroscopic, thermoana-
lytical, and Hirshfeld surface analysis data (PDF)
Reaction in THF (1.4 equiv of [Cs(G4)2][SF5]). Inside the drybox,
0.15 g of [Cs(G4)2][SF5] (0.22 mmol) was dissolved in THF (0.4 M
F
DOI: 10.1021/acs.inorgchem.8b02655
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Article
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Accession Codes
CCDC 1861202 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB21EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: k-matsumoto@energy.kyoto-u.ac.jp.
(19) Watanabe, M.; Thomas, M. L.; Zhang, S. G.; Ueno, K.; Yasuda,
T.; Dokko, K. Application of ionic liquids to energy storage and
conversion materials and devices. Chem. Rev. 2017, 117, 7190−7239.
(20) Kuczynski, M.; Hart, W.'t; Westerterp, K. R. Binary vapor-
liquid-equilibria of methanol with sulfolane, tetraethylene glycol
dimethyl ether and 18-crown-6. Chem. Eng. Process. 1986, 20, 60.
(21) Steed, J. W. First- and second-sphere coordination chemistry of
alkali metal crown ether complexes. Coord. Chem. Rev. 2001, 215,
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ORCID
Kazuhiko Matsumoto: 0000-0002-0770-9210
Shigeyuki Yamada: 0000-0002-6379-0447
Tsutomu Konno: 0000-0002-5146-9840
Notes
The authors declare no competing financial interest.
(22) Altermatt, D.; Brown, I. D. The automatic searching for
chemical-bonds in inorganic crystal-structures. Acta Crystallogr., Sect.
B: Struct. Sci. 1985, 41, 240−244.
ACKNOWLEDGMENTS
■
This work was supported by JSPS KAKENHI Grant Number
17K14544.
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Acta Crystallogr., Sect. B: Struct. Sci. 1991, 47, 192−197.
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