Fluoride ion donor properties of group 13 trifluorides (MF3, M = Al, Ga, In, Tl) and crystal structures of InF3·3SbF 5, TlF3·3SbF5 and TlF 3·AsF5·2HF

Article abstract of DOI:10.1039/c0nj00514b

Reactions between strong Lewis acids (i.e. AsF₅, SbF ₅) and MF₃ (M = Al, Ga, In, Tl) in anhydrous hydrogen fluoride at ambient temperature proceeded only in three cases, yielding InF ₃·3SbF₅, TlF₃·3SbF₅, TlF₃·AsF₅·2HF and TlF₃· AsF₅. Crystal structure of InF₃·3SbF₅ consists from infinite chains of In atoms connected by three SbF₆ units, with two bridging fluorine atoms (F_b) in cis-position. Due to the strong interaction of SbF₆ units with In³⁺, the Sb-F_b bonds are significantly elongated (200.7(4) pm). Such long Sb-F_b bonds have been observed in the crystal structure of SbF ₅. The crystal structure of TlF₃·3SbF₅ is built from slabs where thallium atoms are connected by SbF₆ units. The thallium is nine-fold coordinated by fluorine atoms in the shape of a tricapped trigonal prism. In the crystal structure of TlF₃· AsF₅·2HF there are puckered layers, composed of rectangular rings made of Tl and F atoms. The seven-fold coordination around each Tl is completed by three axial fluorine atoms, provided by one HF molecule and two AsF₆ units arranged below and above the puckered layers forming infinite slabs on that way. The second molecule of HF is placed between the slabs. Vibrational spectra of isolated InF₃·3SbF₅, TlF₃·3SbF₅, and TlF₃·AsF ₅ are consistent with the presence of highly deformed SbF ₆/AsF₆ octahedra. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/c0nj00514b

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www.rsc.org/njc | New Journal of Chemistry
Fluoride ion donor properties of group 13 trifluorides (MF3, M = Al,
Ga, In, Tl) and crystal structures of InF3ꢀ3SbF5, TlF3ꢀ3SbF5 and TlF3ꢀ
AsF5ꢀ2HFw
Zoran Mazej* and Evgeny Goreshnik
Received (in Victoria, Australia) 2nd July 2010, Accepted 20th August 2010
DOI: 10.1039/c0nj00514b
Reactions between strong Lewis acids (i.e. AsF5, SbF5) and MF3 (M = Al, Ga, In, Tl) in
anhydrous hydrogen fluoride at ambient temperature proceeded only in three cases, yielding
InF3ꢀ3SbF5, TlF3ꢀ3SbF5, TlF3ꢀAsF5ꢀ2HF and TlF3ꢀAsF5. Crystal structure of InF3ꢀ3SbF5 consists
from infinite chains of In atoms connected by three SbF6 units, with two bridging fluorine atoms
(Fb) in cis-position. Due to the strong interaction of SbF6 units with In3+, the Sb–Fb bonds are
significantly elongated (200.7(4) pm). Such long Sb–Fb bonds have been observed in the crystal
structure of SbF5. The crystal structure of TlF3ꢀ3SbF5 is built from slabs where thallium atoms
are connected by SbF6 units. The thallium is nine-fold coordinated by fluorine atoms in the shape
of a tricapped trigonal prism. In the crystal structure of TlF3ꢀAsF5ꢀ2HF there are puckered layers,
composed of rectangular rings made of Tl and F atoms. The seven-fold coordination around each
Tl is completed by three axial fluorine atoms, provided by one HF molecule and two AsF6 units
arranged below and above the puckered layers forming infinite slabs on that way. The second
molecule of HF is placed between the slabs. Vibrational spectra of isolated InF3ꢀ3SbF5,
TlF3ꢀ3SbF5, and TlF3ꢀAsF5 are consistent with the presence of highly deformed SbF6/AsF6
octahedra.
stronger than SbF5. Actual pFꢁ values for solid MF3 are
Introduction
certainly lower because in the case of polymeric solids pFꢁ
According to Brønsted and Lowry definition, an acid is a
values have to be corrected for association energies resulting in
smaller pFꢁ values than for free molecules.2
proton donor and a base is a proton acceptor. An acid–base
reaction always involves a transfer of proton allowing a
In the present work the results of reactions between MF3
quantitative comparison of different Brønsted acids. Estimating
(M = Al, Ga, In, Tl) and Lewis acids (AsF5, SbF5) in
the strength of Lewis acids represents a problem, since no such
anhydrous hydrogen fluoride (aHF) are described.
common relationship exists. Various approaches have been
used for a qualitative description of strengths of Lewis acids.1
Results and discussion
A quantitative scale (pFꢁ scale) for Lewis acidity based on
fluoride ion affinities of free gaseous molecules was reported
first time in 2001.2 Fluoride ion has a small size and high
basicity and because of that it reacts essentially with all Lewis
acids. Therefore the fluoride ion affinity (or enthalpy of
reaction between Lewis acid and fluoride ion) could serve as
a quantitative scale of Lewis acids.1
Synthesis
InF3 and TlF3 completely dissolved in anhydrous hydrogen
fluoride (aHF), acidified with large excess of SbF5, yielding
colourless solutions from which colourless MF3ꢀ3SbF5
(M = In, Tl) were isolated (eqn (1)). The analogous reactions
with AlF3 and GaF3 did not proceed:
Group 13 trifluorides (MF3, M = Al, Ga, In) are according
to the pFꢁ scale very strong Lewis acids placed between SbF5
and AsF5. The SbF5 has been for a long time considered as the
strongest Lewis acid. Recent high level electronic calculations3
confirmed previous experimental results (i.e. [AsF4]+[PtF6]ꢁ is
known,4 meanwhile analogue compound with between AsF5
and SbF5 is not) that MF5 (M = Os, Ir, Pt, Au) are even
HF
MF3 þ 3SbF5 ꢁ! MF3 ꢀ 3SbF5 ðM ¼ In; TlÞ ð1Þ
298 K
InF3 dissolves in aHF, only when aHF is acidified with large
excess of SbF5, i.e. when molar ratio n(InF3) : n(SbF5) is much
higher than 1 : 3. This could be explained by the fact that
acidity of fluorine-bridged SbnF5n (n = 1, 2, 3, 4) and of n
monomeric SbF5 molecules increases with increasing
n
(i.e. fluoride ion affinities of SbF5(g) = 503–515 kJ molꢁ1),
Jozˇef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia.
E-mail: zoran.mazej@ijs.si; Fax: (+386) 1 477 3155;
Tel: (+386) 1 477 3301
w Electronic supplementary information (ESI) available: X-ray
powder diffraction pattern of TlF3ꢀAsF5 (Table S1), Infrared spectra
of ground crystals of TlF3ꢀAsF5ꢀ2HF (Fig. S1 and S2) and vibrational
spectra of TlF3ꢀAsF5 (Fig. S3). CSD reference numbers
783217–783219. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c0nj00514b
Sb2F10(g) 556–559 kJ molꢁ1, Sb3F15(g) = 572 kJ molꢁ1
Sb4F20(g) = 580 kJ molꢁ1, 2SbF5(g) = 667–671 kJ molꢁ1
3SbF5(g) = 728–767 kJ molꢁ1, and 4SbF5(g) = 855 kJ molꢁ1).5
The lack of observed reactions in the case of Al and Ga
could be also due to kinetic inertness. For example, it is well
known that a-AlF3 is nonreactive with little or no catalytic
,
,
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activity, meanwhile b- and other forms (Z-, y-, k-) of AlF3 are
more reactive.6,7 The highest reactivity is observed for X-ray
amorphous so called high surface HS-AlF3 which does not
have a regular bulk structure.8,9 Alfa phase has a closed-
packed structure, whereas beta and other phases, structurally
related to b-AlF3, have more open structures. Because of that,
reaction between KAlF4 and excess of SbF5 in aHF has been
also tried (eqn (2)). An attempt was made to prepare
AlF3ꢀnSbF5 from KAlF4 in situ by displacement of a weaker
Lewis acid (AlF3) with a stronger one (SbF5).
HF
KAlF3 þðnþ2ÞSbF5 ꢁ!KSb2F11 þAlF3 ꢀnSbF5 ð2Þ
298K
Instead of the desired AlF3ꢀnSbF5 phase only AlF3 was
observed with by-product KSb2F11.
Reaction with AsF5 in aHF proceeded only in the case of
TlF3. First unstable TlF3ꢀAsF5ꢀ2HF is formed which further
decomposes during the pumping on a high vacuum to
TlF3ꢀAsF5 (eqn (3)).
Fig. 2 Part of the infinite chain in the crystal structure of InF3ꢀ3SbF5.
Symmetry operations used for generation of equivalent atoms:
(i) x ꢁ y, ꢁy, 0.5 ꢁ z (ii) x ꢁ y, ꢁ1 + x, ꢁz (iii) 1 + y, 1 ꢁ x + y,
ꢁz (iv) 2 ꢁ x, ꢁy, ꢁz (v) 2 ꢁ x + y, 1 ꢁ x, z (vi) 1 ꢁ y, ꢁ1 + x ꢁ y, z.
pumping
HF
long Sb–Fb(–In) bond distance (200.7(4) pm) is comparable
with the Sb–Fb bond lengths [198(5)–206(5) pm] found in
the crystal structure of solid SbF5,4 where SbF5 units are
connected in tetrameric rings [(SbF5)4] by cis-fluorine atoms.
Although, there are numerous examples of fluorine bridged
adducts, in neither of them such elongation of Sb–Fb
TlF3 þAsF5 ꢁ! TIF3 ꢀAsF5 ꢀ2HF ꢁ! TIF3 ꢀAsF5
298K
ꢁ2HF
ð3Þ
From a purely thermodynamic standpoint, the fluoride ion
affinity is only one of the factors that will determine if reaction
would proceed or not. Neglecting the entropy, difference
between lattice energies of reactants and products is another
governing factor. Unsuccessful attempts to synthesize
MF3ꢀnSbF5 (M = Al, Ga) could be ascribed to their higher
lattice energies of AlF3 and GaF3 in comparison to InF3 and
TlF3.10,11 For the latter, fluoride ion affinity of SbnF5n (n Z 1)
and lattice energies of InF3ꢀ3SbF5 and TlF3ꢀ3SbF5 are enough
to overcome the lattice energies of starting trifluorides
and make reaction between InF3/TlF3 and SbF5 thermo-
dynamically favourable.
bond has been observed, i.e. Sb–Fb
= 196.4(3) pm
([Au(HF)2](SbF6)2ꢀHF),12 195.15(5) pm (CrF5ꢀSbF5),13
195.4(16) and 199.0(14) pm (UF5ꢀ2SbF5),14 194.2(6) pm
(MoF4OꢀSbF5),15 192.7(4) pm (TcO2F3ꢀSbF5),16 194.5(4) pm
(ReO2F3ꢀSbF5).16 Much longer Sb–Fb bond length has been
theoretically predicted (210.38 pm) only in so far unknown
dinuclear anion [F5Auꢀ ꢀ ꢀFꢀ ꢀ ꢀSbF5]ꢁ.17 what is in agreement
with higher Lewis acidity of AuF5 in comparison to SbF5.
Bond lengths between Sb and terminal fluorine atoms (Ft) in
the crystal structure of InF3ꢀ3SbF5 are in the range
183.9(4)–184.9(4) pm and are close to Sb–Ft distances in solid
SbF5 (177(5)–187(5) pm).4 Fluorine atoms around indium
metal form quite regular octahedra with bond lengths In–F =
207.5(4) pm similar as to that in InF3 (205.3(3) pm).5 The
F–In–F bond angles in InF6 octahedra are 87.67(16) and
92.33(16)1, respectively. Although the bridging fluorine atoms
are closer to antimony than to indium atoms, the SbF6
octahedra are strongly deformed (F–Sb–F bond angles are
in the range from 81.5(2) to 99.5(3)1). Therefore a description
InF3ꢀ3SbF5 is more preferable than In(SbF6)3.
Crystal structures
Crystal structure of InF3ꢀ3SbF5. Crystal structure of
InF3ꢀ3SbF5 consists of infinite chains (Fig. 1) of indium atoms
connected by three SbF6 units, with two bridging fluorine
atoms (Fb, i.e. F2) in cis-position (Fig. 2). In1 atom occupies
ꢀ
the 2b Wyckoff position with 3 symmetry, and the Sb1 atom is
located at a site with twofold symmetry (Wyckoff 6f). Very
Crystal structure of TlF3ꢀ3SbF5. The crystal structure of
TlF3ꢀ3SbF5 consists of slabs (Fig. 3) where thallium atoms are
connected by SbF6 units (Fig. 4). Tl1 atom is at a 2d site with
three-fold symmetry.
Each SbF6 unit bridges to two thallium atoms, with three
bridging fluorine atoms in facial position (Fig. 5). As expected,
Sb–Fb bond lengths (Sb–Fb = 189.4(6) pm, 197.0(6) pm, and
197.7(6) pm) are longer than Sb–Ft ones (183.1(6) pm, 183.3(6)
pm, 183.4(6) pm). Although the Sb–Fb bond lengths are
shorter than Sb–Fb distances in InF3ꢀ3SbF5, the longest two
bonds are still significantly longer then Sb–Fb bonds observed
in other fluorine bridged adducts. This indicates that TlF3 is
Fig. 1 Packing of infinite –[In–(F–SbF4–F)3–In]– chains in the crystal
structure of InF3ꢀ3SbF5.
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Fig. 6 Nine-fold coordination of Tl atom in the shape of a tricapped
trigonal prism (a) and one triangular face of trigonal prism is staggered
against the other one (b) in TlF3ꢀ3SbF5. Symmetry operations used for
generation of equivalent atoms: (i) 1 ꢁ x + y, 1 ꢁ x, z (ii) 1 ꢁ y,
x ꢁ y, z.
Fig. 3 View along a-axis showing the packing of slabs in the crystal
structure of TlF3ꢀ3SbF5.
The Tl–F3 and Tl–F8 bond lengths are significantly shorter
(218.4(6) and 220.5(6) pm, respectively) than Tl–F6 distances
(259.3(8) pm), however, this difference is balanced by
respective distances to the Sb atoms as Sb–(F3/F8) (197.7(6)/
197.0(6) pm) are considerably longer than Sb–F6 (189.4(6) pm).
For comparison, in TlF3 (where Tl is 8-fold coordinated),
Tl–F distances are 1 ꢂ 209 pm; 2 ꢂ 220 pm, 2 ꢂ 223 pm,
1 ꢂ 224 pm and 2 ꢂ 249 pm.18
Crystal structure of TlF3ꢀAsF5ꢀ2HF. In the crystal structure
of TlF3ꢀAsF5ꢀ2HF, thallium atoms are connected via fluoride
anions, resulting in the formation of puckered layers,
composed of rectangular rings (Fig. 7).
Fig. 4 View along c-axis (perpendicular on the slab) in the crystal
structure of TlF3ꢀ3SbF5.
The seven-fold coordination around each Tl is completed by
three axial fluorine atoms, provided by HF molecule and two
AsF6 units arranged below and above the puckered layers
(Fig. 8). In this way infinite slabs are formed which are
connected via hydrogen bonds only. There are ‘‘free’’
molecules of HF placed between the slabs. Another example
of a compound with coordinated and non-coordinated HF
molecules is Au(SbF6)2ꢀ4HF.12
In each AsF6 unit there are four short [As–F5: 167.9(8),
As–F4: 168.3(7), As–F3: 170.8(7), As–F2: 170.9(8) pm] and
two long As–F bonds [As–F1: 178.0(7) pm, As–F6: 178.8(7) pm].
The latter are bridging ones and connect AsF6 units to Tl
atoms (Fig. 9). Both sets of bond distances are in the range of
previously reported bond lengths between As and terminal or
bridging fluorine atoms, respectively.19
There are three ideal geometries known for coordination
number seven: monocapped octahedron, monocapped trigonal
prism in which a seventh ligand has been added to a rectangular
face and a pentagonal bipyramid. The coordination of fluorine
Fig. 5 SbF6 units, with three bridging fluorine atoms in facial
position, connecting two Tl atoms in the crystal structure of TlF3ꢀ
3SbF5. Symmetry operations used for generation of equivalent atoms:
(i) 1 ꢁ x, 1 ꢁ y, 1 ꢁ z (ii) 1 ꢁ y, x ꢁ y, z (iii) y, 1 ꢁ x + y, 1 ꢁ z.
also a poor fluoride ion donor, although much better than
InF3. Although the elongation of Sb–Fb bonds in TlF3ꢀ3SbF5
is not so pronounced as in InF3ꢀ3SbF5, the former formulation
is still more appropriate than ionic one, i.e. Tl(SbF6)3.
The polyhedron around the metal center is basically a
tricapped trigonal prism (Fig. 6a), whose triangular faces are
formed by fluorine ligands provided by six SbF6 units. All
rectangular faces of the prism are capped by fluorine ligands.
This way coordination number nine is achieved for the Tl
atom. One triangular face of trigonal prism is staggered by
B51 with respect to the other one (Fig. 6b).
Fig. 7 Part of the puckered layer in the crystal structure of
TlF3ꢀAsF5ꢀ2HF showing rectangular rings (HF molecules and AsF6
units are omitted for clarity).
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The Tl–F(–Tl) bond lengths (Tl1–F7i
=
207.0(6),
Tl1–F8iii = 207.5(6), Tl1–F8 = 214.7(6) and Tl1–F7 =
216.5(6) pm) are significantly shorter than Tl–F(–AsF5)
[Tl1–F9 = 228.4(6), Tl1–F6ii = 230.7(7)] and Tl–F(–H)
[Tl1–F1 = 241.6(7) pm] bond distances. In KTlF4 where Tl
is also coordinated by seven fluoride ligands, the Tl–F
distances are in the range from 202 to 249 pm.20
It’s well known that oxygen and fluorine atoms are
sometimes technically difficult to distinguish by X-ray
diffraction. In the crystal structure of TlF3ꢀAsF5ꢀ2HF the
positions of hydrogen atoms could not be unambiguously
determined. Therefore, grown crystals could hypothetically
also have composition TlF3ꢀAsF5ꢀ2H2O, TlF3ꢀAsF5ꢀ2H2O/HF
or even (H3O)Tl(F)F2(AsF6), if we assume that non-
coordinated HF is [H3O]+ cation and that, instead of Tl atom
coordinated HF, we have only terminal fluorine atom. Both
options are highly unlikely. The first option could be excluded
because in AsF5/aHF superacid systems water behaves as a
very strong base and consequently displaces the weaker base
HF from [H2F]+, thus forming [H3O]+ ions directly in
solution.21 The second option is also not very reliable because
there would be a highly electronegative terminal fluorine atom
in the neighbourhood of three protons belonging to [H3O]+
cation. The final proof for TlF3ꢀAsF5ꢀ2HF composition came
from infrared spectra (see Fig. S1 and S2w) of ground crystals,
where no vibrational bands were observed in 1000–4000 cmꢁ1
region. In that region [H3O]+ salts give very sharp and
moderately strong band at around 1600 cmꢁ1 [das(H3O+)]
and very broad double band in 3000–3500 cmꢁ1 region
[nas(H3O+) and ns(H3O+)].22 The vibrations belonging to
molecules of water are found in the same ranges (bending
Fig. 8 Fragment of the crystal structure of TlF3ꢀAsF5ꢀ2HF showing
the packing of slabs.
and stretching vibrations at around 1600 and 3200–3500 cmꢁ1
respectively).23
,
Fig. 9 Part of the crystal structure of TlF3ꢀAsF5ꢀ2HF showing the
connectivity of Tl atoms and AsF6 units with bridging fluorine atoms
in cis positions. Symmetry operations used for generation of equiva-
lent atoms: (i) 1 ꢁ x, 0.5 + y, 1.5 ꢁ z.
Vibrational spectroscopy
Vibrational spectra of InF3ꢀ3SbF5 and TlF3ꢀ3SbF5 are shown
in Fig. 11 and 12 and frequencies are given in Table 1 and 2.
atoms around Tl in TlF3ꢀAsF5ꢀ2HF is irregular (C.N. = 7)
and it could be hardly described with idealized structures
(Fig. 10).
Fig. 10 Part of the crystal structure of TlF3ꢀAsF5ꢀ2HF, showing the
coordination around Tl atom. Symmetry operations used for generation
of equivalent atoms: (i) 1 ꢁ x, 0.5 + y, 1.5 ꢁ z (ii) 1 ꢁ x, ꢁ0.5 + y,
1.5 ꢁ z (iii) 2 ꢁ x, ꢁ0.5 + y, 1.5 ꢁ z.
Fig. 11 Vibrational data of: (a) InF3ꢀ3SbF5, (b) liquid SbF5,
(c) InSbF6.28
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Table 2 Vibrational data of TlF3ꢀ3SbF5
TlF3ꢀ3SbF5
IRa
R
733(sh)
721(s)
727(20)
712(sh)
704(vs)
670(sh)
714(90)
702(100)
662(sh)
639(50)
626(m)
591(sh)
537(5)
491(3)
495(vs)
478(vs)
455(5)
392(7)
376(m)
357(5)
309(5)
256(70)
202(10)
Fig. 12 Vibrational data of TlF3ꢀ3SbF5 [(a) powder; (b) single crystal]
a
Intensities are given in parenthesis; m = medium, s = strong,
vs. = very strong, sh = shoulder.
and (c) TlSbF6.
25,27
Table 1 Vibrational data of InF3ꢀ3SbF5 and liquid SbF5
Raman spectra of TlF3ꢀ3SbF5 (Fig. 12, Table 2) were taken
on powdered samples obtained by syntheses (eqn (1)) and also
on selected single crystals. They were found to be identical.
Vibrational spectra of TlF3ꢀ3SbF5 together with Raman
spectrum of TlSbF6 are shown in Fig. 12, and frequencies
given in Table 2. As a consequence of the lowering of the
symmetry of SbF6 unit in the solid state (site symmetry and
correlation effects) and the strong cation–anion interactions in
the crystal lattice, some vibrations which are otherwise Raman
or infrared inactive in Oh symmetry, becomes active, and
additionally, splitting of some vibrations may also occurs.
Since TlF3ꢀ3SbF5 gave very complex vibrational spectra no
detailed assignment has been done. Similar as in the case of
InF3ꢀ3SbF5, a strong doublet at 478/495 cmꢁ1 was observed in
infrared spectrum of TlF3ꢀ3SbF5. Its intensity and position are
typical for compounds where strong interactions between two
metal centers are present (M–Fb–Sb bridges).
InF3ꢀ3SbF5
SbF5 (liquid)
Tentative Assignmentsa
IRb
730(s)
R
IR
742(s)
R
n(SbꢁFt)
n(SbꢁFt)
n(SbꢁFt)
n(SbꢁFt)
707(vs)
713(vs)
665(m) 657(s)
718(s)
670(s)
705(s)
669(s)
533(m)
496(m)
n(SbꢁFbꢁIn)
n(SbꢁFbꢁIn)
450(w,br)
349(w)
310(w,br) 302(w)
Deformation modes
Deformation modes
268(mw) Deformation modes
316(w)
269(m)
221(w)
231(w)
189(w)
Deformation modes
Deformation modes
200(w,br)
a
b
= stretching mode. Intensities are given in parenthesis;
n
w = weak, mw = medium weak, m = medium, s = strong, vs. = very
strong, sh = shoulder.
The Raman intensity of an XY6 octahedra (molecule or
anion) normally follows the order I(n1) > I(n2) > I(n5), where
n1, n2 and n5 belong to symmetric stretching, asymmetric
stretching and bending of XY6 group, respectively. Typical
example represents Raman spectrum of TlSbF6 (Fig. 12) with
the most intensive band at 647 cmꢁ1 (n1), two weaker bands at
275/287 cmꢁ1 (n5) and one weak band 566 cmꢁ1 (n2). In the
Raman spectrum of TlF3ꢀ3SbF5 the most intensive band is
observed at much higher value (B708 cmꢁ1). Additionally, it
is split into two bands (702 and 714 cmꢁ1) and for both of
them the corresponding bands (704 and 721 cmꢁ1) could be
found in the infrared spectrum of TlF3ꢀ3SbF5. We could not
find any similar example in available literature. Similar case
was with Raman spectrum of TlF3ꢀAsF5 (ESI, Figure S3w).
The significance of the vibrational spectra is that they
demonstrate that the products of reactions between MF3
(M = In, Tl) and SbF5 in aHF, used to record the Raman
spectra, could be better formulated as MF3ꢀ3SbF5 than purely
ionic M(SbF6)3 compounds.
Crystal structure of solid SbF5 consists of tetramers built
from four SbF6 octahedra sharing joint vertices.24 SbF6 units
are linked by cis-bridging fluorine atoms. Vibrational spectra
of liquid SbF5 argues in favour of a cis-fluorine-bridged
polymer.25 Because of that, the great similarity between
vibrational spectra of InF3ꢀ3SbF5 and liquid SbF5 is not
surprising (Table 1, Fig. 11). In both cases we have strongly
deformed SbF6 units with two strongly elongated Sb–Fb bonds
with Fb in cis-position and four much shorter Sb–Ft bonds.
The bands in the 665–742 cmꢁ1 region are assigned to stretching
modes (Sb–Ft) between Sb atom and terminal fluorine atoms,
meanwhile bands in the 450–533 cmꢁ1 range are typical
for Sb–Fb–M (M = metal atom) bridging.26 Bands below
350 cmꢁ1 were assigned to bending deformations.
Conclusions
Experimental results of reactions between group 13 metal
trifluorides (MF3, M = Al, Ga, In, Tl) and strong Lewis acids
(SbF5, AsF5) in anhydrous HF as a solvent confirmed in
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2810 New J. Chem., 2010, 34, 2806–2812 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010

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Table 3 Mass balances and chemical analyses of InF3ꢀ3SbF5, TlF3ꢀ3SbF5, and TlF3ꢀAsF5
Mass balance
Calculated
/g
Chemical analyses
Calculated
Obtained
/g
Obtained
%In/Tl
%In/Tl
%Sb/As
%F
%Sb/As
%F
Product
InF3ꢀ3SbF5
TlF3ꢀ3SbF5
TlF3ꢀAsF5
0.600
0.866
0.647
0.632
0.9284
0.647
13.97
22.42
47.39
44.43
40.07
17.37
41.60
37.52
35.24
12.0
22.2
48.3 ꢃ 0.8
44.0
/
18.1 ꢃ 0.3
40.6
37.4
34.6
literature expressed expectations29 that preparation of cationic
species by fluoride ion abstraction from MF3 (M = Al, Ga, In, Tl)
is highly unlikely. Nonreactivity of AlF3 and GaF3 is a
consequence of their higher lattice energies in comparison to
InF3 and TlF3. The isolated solids could be better formulated
as fluorine-bridged polymeric adducts, i.e. MF3ꢀ3SbF5
(M = In, Tl) and TlF3ꢀAsF5, than ionic M(SbF6)3 and
TlF2(AsF6) compounds. Extremely elongated Sb–Fb(–In)
bonds observed in the crystal structure of InF3ꢀ3SbF5, shows
very high Lewis acidity of In3+, meanwhile the acidity of Tl3+
is lower.
recorded on Renishaw Raman Imaging Microscope System
1000, with He–Ne laser with wavelength 632.8 nm.
Reactions between MF3 (M = Al, Ga, In, Tl) and AsF5/SbF5
in aHF. All experiments between MF3 and SbF5/AsF5 were
made in a similar manner, so only preparation of InF3ꢀ3SbF5
is described. In a dry-box 0.73 mmol (0.125 g) of InF3 was
loaded into FEP reaction vessel. Then aHF (1.5 ml) was
condensed onto InF3 and excess of SbF5 (1.40 g, 6.46 mmol)
was added, both at 77 K. After warming of reaction mixture to
the room temperature the solid phase completely dissolved
and clear colourless solution was obtained in few hours. The
solution was left stirring for 24 h and volatiles aHF and SbF5
were pumped away.
In the case of weaker Lewis acid, AsF5, reaction proceeded
only with TlF3. It seems that only in this case, the fluoride ion
affinity of AsF5 is capable to overcome the unfavourable
difference in the lattice energies between the reactants
(i.e. TlF3) and the products (i.e. TlF3ꢀAsF5), where the lattice
energy of the former should be much higher then the lattice
energy of the latter. The intermediate compound TlF3ꢀAsF5ꢀ2HF
is a metastable phase.
There was no reaction observed in the MF3 (M = Al, Ga)/
SbF5/aHF and MF3 (M = Al, Ga, In)/AsF5/aHF systems.
Mass balances and chemical analysis of isolated InF3ꢀ3SbF5,
TlF3ꢀ3SbF5, and TlF3ꢀAsF5 are given in Table 3.
Crystal growth of InF3ꢀ3SbF5, TlF3ꢀ3SbF5 and TlF3ꢀAsF5ꢀ
2HF. Single crystals preparation of InF3ꢀ3SbF5 was carried
out in a T-shaped apparatus made of two FEP tubes (19 mm
o.d., and 6 mm o.d.). About 0.35 g of InF3ꢀ3SbF5 was
dissolved in B2 ml aHF at 273 K. Clear solution was poured
into the narrower tube. The evaporation of solvent from this
solution was carried out by maintaining temperature gradient
of about 10 K between wider and narrower tube of the
apparatus for one month. Colourless single crystals of
InF3ꢀ3SbF5 formed.
Experimental
Caution
Anhydrous HF and some fluorides are highly toxic and must
be handled using appropriate apparatus and protective gear.
Apparatus and reagents. Volatile materials (SbF5, AsF5,
aHF) were handled in an all-Teflon vacuum line equipped
with Teflon valves. The manipulation of the non-volatile
materials was done in a dry box (M. Braun). The residual
water in the atmosphere within the dry box never exceeded 2 ppm.
The reactions were carried out in FEP (tetrafluoroethylene-
hexafluoropropylene) reaction vessels (length 250–300 mm,
i.d. 15.5 mm, o.d. 18.75 mm) equipped with Teflon valves
and Teflon coated stirring bars. Prior to use, all reaction
vessels were passivated with elemental fluorine. Fluorine was
used as supplied (Solvay). Anhydrous HF (Fluka, Purum) was
treated with K2NiF6 (Ozark Mahoning) for several hours
prior to use. AlF3 (Aldrich, 99.95%), GaF3 (Aldrich,
99.99%) and InF3 (Aldrich, 99.9%) were used as supplied.
Since commercial ‘‘TlF3’’ was yellow, it was treated by 20 bar
of elemental fluorine at 473 K for three days in a 100 ml nickel
reaction vessel. Resulted TlF3 was colorless. Compounds SbF5
and AsF5 were synthesized by pressure fluorination of SbF3
(Alfa Aesar, 99%) or As2O3 (Fluka, 99.5%), respectively, with
elemental fluorine in a nickel reactor at 573 K.30
In the case of TlF3ꢀ3SbF5, 100 mg of the sample was
dissolved in 2 ml of aHF, and clear solution was decanted
into the narrower tube. The latter was kept at 273 K,
meanwhile the wider one was cooled down, First to 257 K
for 2 weeks, then to 232 K for additional 5 days. Colourless
single crystals of TlF3ꢀ3SbF5 formed.
TlF3 was dissolved in 2 ml of aHF acidified with 1.0 g of
AsF5. Clear solution was poured into the narrower tube. The
evaporation of the solvent from these solutions was carried
out by maintaining a temperature gradient corresponding to
about less then 10 K between both tubes for 8 months. The
result of this treatment was to slowly condense the aHF from
the narrower into the wider tube, leaving behind the crystals.
Attempts to speed the crystallization (for example, higher
temperature gradient) resulted in immediate precipitation
of powdered non-crystalline product. Grown crystals of
TlF3ꢀAsF5ꢀ2HF were isolated at 273 K.
Crystallization products were immersed in a perfluorinated
oil (ABCR, FO5960, melting point 263 K) in a dry-box. Single
crystals were then selected from the crystallization products
under the microscope (at temperatures from 265 to 273 K)
Techniques. Infrared spectra were taken on a Perkin-Elmer
FTIR 1710 spectrometer on powdered samples between AgCl
windows in a leak tight brass-cell. Raman spectra were
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010 New J. Chem., 2010, 34, 2806–2812 2811

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Table
4
Summary of crystal data and refinement results for
References
InF3ꢀ3SbF5, TlF3ꢀ3SbF5 and TlF3ꢀAsF5ꢀ2HF
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InF3ꢀ3SbF5
Trigonal
TlF3ꢀ3SbF5
Trigonal
TlF3ꢀAsF5ꢀ2HF
Monoclinic
P21/c
555.33(4)
576.52(5)
2192.87(19)
93.279(4)
0.70092(10)
4
471.31
4.466
200
27.87
0.0593
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Crystal system
Space group
a/pm
b/pm
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ꢀ
P3c1
ꢀ
P3
871.90(6)
871.90(6)
952.19(9)
/
0.62688(9)
2
822.07
4.355
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940.8(16)
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911.62
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a
R1
wR2
0.0398
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b
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package WinGX.33 In the structure of TlF3ꢀAsF5ꢀ2HF
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details of the structure refinement are given in Table 4. Further
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from the Fachinformationszentrum Karlsruhe, D-76344
Eggenstein-Leopoldshafen, Germany, on quoting the depository
numbers CSD-421923 (InF3ꢀ3SbF5), CSD-421924 (TlF3ꢀ3SbF5)
and CSD-421925 (TlF3ꢀAsF5ꢀ2HF).
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Acknowledgements
The authors gratefully acknowledge the Slovenian Research
Agency (ARRS) for financial support of the present study
within the research program: P1-0045 Inorganic Chemistry
and Technology.
c
2812 New J. Chem., 2010, 34, 2806–2812 This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010