Structural and electrochemical properties of YbIII in various ionic liquids

Article abstract of DOI:10.1002/ejic.201000323

Solvation and ligand exchange reactions of ytterbium(III) as a model for the late trivalent f-elements have been studied in triflate and bistriflylamide ionic liquids (ILs) with the purpose of contributing to a wider understanding of f-element organometallic catalysis, as well as separation and nuclear fuel reprocessing, in ILs. Using the compounds [C₄mpyr] ₃[Yb(OTf)₆] and [C₄mpyr][Yb(Tf ₂N)₄] [C₄mpyr = N-methyl-N-propylpyrrolidinium; OTf = triflate, trifluoromethanesulfonate; Tf₂N = bistriflylamide, bis(trifluoromethanesulfonyl)amide] we were able to structurally characterize the local surroundings of Yb³⁺ in the ILs [C₄mpyr][OTf] and [C₄mpyr][Tf₂N]unequivocally. The formation of [C ₄mpyr]₃[Yb(OTf)₆][C₄mpyr][Tf ₂N] from a solution of Yb(Tf₂N)₃ in [C ₄mpyr][OTf] shows that the stronger coordinating OTf^- anion completely replaces the less Lewis basic Tf₂N^- anion in the first coordination sphere of the lanthanide ion. As expected, such a ligand exchange could not be observed for Yb(OTf)₃ in [C ₄mpyr][Tf₂N]. The ion exchange in the lanthanide coordination sphere can be efficiently monitored by means of cyclic voltammetry (CV). CV measurements also indicate that Yb³⁺ adopts a mixed OTf ^-/Tf₂N^- coordination environment when Yb(OTf)₃ is dissolved in [C₄mpyr][Tf₂N]. The measured half-wave potentials of the studied systems can be linked to the electron-donor properties of the metal cation. Solvation and ligand exchange reactions of ytterbium(III) as a model for the later trivalent lanthanides have been studied in triflate and bistriflylamide ionic liquids (ILs) with the purpose of contributing to a wider understanding of organometalliccatalysis, as well as separation and nuclear fuel reprocessing, in ILs.

Full text of DOI:10.1002/ejic.201000323

FULL PAPER
DOI: 10.1002/ejic.201000323
Structural and Electrochemical Properties of YbIII in Various Ionic Liquids
Arash Babai,[a] Slawomir Pitula,[a] and Anja-Verena Mudring*[a]
Keywords: Lanthanides / Ionic liquids / Solvation / Structure elucidation / Ytterbium
Solvation and ligand exchange reactions of ytterbium(III) as
a model for the late trivalent f-elements have been studied
in triflate and bistriflylamide ionic liquids (ILs) with the pur-
pose of contributing to a wider understanding of f-element
organometallic catalysis, as well as separation and nuclear
fuel reprocessing, in ILs. Using the compounds [C4mpyr]3-
[Yb(OTf)6] and [C4mpyr][Yb(Tf2N)4] [C4mpyr = N-methyl-N-
propylpyrrolidinium; OTf = triflate, trifluoromethanesulfonate;
Tf2N = bistriflylamide, bis(trifluoromethanesulfonyl)amide]
we were able to structurally characterize the local surround-
ings of Yb3+ in the ILs [C4mpyr][OTf] and [C4mpyr][Tf2N]
unequivocally. The formation of [C4mpyr]3[Yb(OTf)6]-
[C4mpyr][Tf2N] from a solution of Yb(Tf2N)3 in [C4mpyr]-
[OTf] shows that the stronger coordinating OTf– anion com-
pletely replaces the less Lewis basic Tf2N– anion in the first
coordination sphere of the lanthanide ion. As expected, such
a ligand exchange could not be observed for Yb(OTf)3 in
[C4mpyr][Tf2N]. The ion exchange in the lanthanide coordi-
nation sphere can be efficiently monitored by means of cyclic
voltammetry (CV). CV measurements also indicate that Yb3+
adopts a mixed OTf–/Tf2N– coordination environment when
Yb(OTf)3 is dissolved in [C4mpyr][Tf2N]. The measured half-
wave potentials of the studied systems can be linked to the
electron-donor properties of the metal cation.
media. So far only a few experimental[7] and theoretical[8]
studies have appeared. However, catalytic properties are
crucially determined by the surroundings of the metal cat-
ion. This finding is also observed in the areas of separation
chemistry and fuel reprocessing. In order to gain a basic
understanding of the processes in the ligand shell of cat-
ionic lanthanide ions in hydrophobic ILs, which are of
interest for the above-mentioned applications, we investi-
gated the solvation behavior of trivalent ytterbium in
triflate and bistriflylamide-based ILs by means of structural
analysis and electrochemistry.
Introduction
Dissolution, solvation, as well as ligand exchange reac-
tions, of f-element cations in conventional inorganic sol-
vents, such as water or liquid ammonia, or classical organic
solvents, like tetrahydrofuran or acetonitrile, are nowadays
quite well understood, as extensive studies have been under-
taken in the past.[1] In contrast, little is known about lan-
thanide ions in ionic liquids (ILs).[2] However, ILs are of
immense interest with respect to liquid–liquid extraction for
the separation and purification of lanthanides, as well as
for the separation of fission materials from reusable fissile
materials. Hydrophobic ILs have been discussed in this con-
text as alternatives to the conventionally used volatile or-
ganic compounds/solvents.[3] The processing of nuclear fuel
by high-temperature molten salt extraction has been exten-
sively studied in the past.[4] ILs, especially room-tempera-
ture ionic liquids (RTILs), and hence room-temperature
molten salts, offer the advantage that they work at much
lower temperatures. In addition, lanthanide salts of weakly
Lewis basic anions, like triflate or bistriflylamide, have
shown to be efficient Lewis acid catalysts.[5] Although more
and more reports on highly efficient lanthanide catalysis in
ILs appear,[6] little is known about the local surroundings
of the lanthanide ion in these comparatively new reaction
Results and Discussion
Crystal Structures
Crystalline [C4mpyr][Yb(Tf2N)4] was obtained by care-
fully cooling a supersaturated solution of Yb(Tf2N)3 in
[C4mpyr][Tf2N] to room temperature. Structural analysis
revealed that the asymmetric unit of [C4mpyr][Yb(Tf2N)4]
contains two crystallographically independent lanthanide
cations. Both exhibit Yb3+ in an oxygen atom surrounding
that can be described as a trigonal dodecahedron (Fig-
ure 1a). This coordination polyhedron is mostly preferred
over a cube when ligand–ligand repulsion, like in case of
the Tf2N– anions, plays a role for coordination number
eight. The mean Yb–O interatomic distance in [C4mpyr]-
[Yb(Tf2N)4] is 229.3 pm, which is in the expected range for
eightfold-coordinated Yb3+ and is slightly shorter than the
mean distance in [Yb(H2O)8][C(SO2CF3)3]·H2O (232 pm).[9]
View this journal online at
[a] Anorganische Chemie I – Festkörperchemie und Materialien,
Fakultät für Chemie und Biochemie, Ruhr-Universität
Bochum,
44780 Bochum, Germany
Fax: +49-234-32-29028
E-mail: anja.mudring@rub.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000323.
wileyonlinelibrary.com
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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FULL PAPER
One crystallographically independent ytterbium cation
(Yb1) is coordinated to four chelating Tf2N– ligands with
two of the ligands in s-cis and two in s-trans conformation.
The s-trans Tf2N– ligands both have λ configuration. Simi-
larly, the other crystallographically independent lanthanide
cation in [C4mpyr][Yb(Tf2N)4] is coordinated to four che-
lating Tf2N– ligands, of which two adopt s-cis and two s-
trans conformation. But here disorder between λ- and δ-
configured s-trans ligands was observed (Figure 1a). In
[C4mpyr][Yb(Tf2N)4], a mean S–O interatomic distance of
146.6 pm was found for the coordinating oxygen atoms,
whereas the mean S–O interatomic distance for the “free”
S–O bonds was 140.5 pm. This distance compares well to
that of the free anion. A small but distinct change in the S–
O interatomic distances within the Tf2N ligand upon coor-
dination was detected. A similar change has already been
noted for the compounds [C4mpyr]2[Ln(Tf2N)5] (Ln = Nd,
Tb) and [C4mpyr][Ln(Tf2N)4] (Ln = Tm, Lu),[10] the latter
two crystallizing isotypically with [C4mpyr][Yb(Tf2N)4], as
well as [C4mpyr]2[Eu(Tf2N)5], [Cxmim][Eu(Tf2N)4] (x = 3,
4)[11] (mim
=
N-methylimidazole), and [C4mim]-
[Y(Tf2N)4].[12] The change in the S–O bond length is far
more pronounced in the trivalent complex compound
[C4mpyr][Yb(Tf2N)4] than in the analogous divalent com-
plex compound [C3mpyr]2[Yb(Tf2N)4], where values of
144 pm for the S–O bond with the coordinating oxygen
atom and 141 pm for the noncoordinating oxygen atom
were observed.[13] This indicates, together with a shorter
Yb–O interatomic distance (in [C3mpyr]2[Yb(Tf2N)4], a
Yb2+–O interatomic distance of 250 pm was found), a
stronger interaction of the Tf2N oxygen atoms with the
higher oxidized ytterbium. For tables compiling the in-
teratomic distances for all the compounds see Supporting
Information. In [C4mpyr][Yb(Tf2N)4] a mean N–S–N angle
of 127° and a mean S–N distance of 155 pm was found. In
all cases no significant changes in the mean N–S–N angle
or in the S–N bonding distance relative to noncoordinated
Tf2N were observed.
In order to obtain structural data on the coordination
sphere of the later trivalent lanthanides in triflate ILs,
Yb(OTf)3 was treated with [C4mpyr][OTf] to yield the com-
pound [C4mpyr]3[Yb(OTf)6]. To the best of our knowledge,
this is the first structurally characterized homoleptic triflate
complex. In this compound all OTf– ligands coordinate in
a monodentate, nonbridging fashion, which yields isolated
octahedra embedded in a [C4mpyr] matrix (Figure 1b). The
OTf anions are all trans and arranged in a way to minimize
steric repulsion. In the equatorial positions the CF3 groups
are directed oppositely in such a way that the trans stereo-
chemistry is also realized with the axial CF3 groups. The
Yb–O distances are in the range 216 to 220 pm. These are
significantly shorter than those observed in [C4mpyr][Yb-
(Tf2N)4] with eightfold-coordinated trivalent Yb3+ but are
similar to those found for sixfold-coordinated Yb3+, as
in hexakis(tetramethylurea-O-)ytterbium(III) perchlorate
(218 pm).[14] The S–O bonds of the coordinating oxygen
Figure 1. (a) Coordination of Yb(1) in [C4mpyr][Yb(Tf2N)4] (left),
disorder of Tf2N around Yb(2) (right); (b) the asymmetric unit of
[C4mpyr]3[Yb(OTf)6]; (c) part of the crystal structure of [C4mpyr]4-
[Yb(OTf)6][Tf2N] where noncoordinating Tf2N ligands are en-
circled and coordinating SO3R-groups are shown as tetrahedra.
In order to investigate ligand exchange reactions,
Yb(Tf2N)3 was dissolved in the IL [C4mpyr][OTf]. Ligand
exchange was evident in the crystalline compound [C4mpyr]4-
[Yb(OTf)6][Tf2N] (Figure 1c), in which the Tf2N– anions
are incorporated in the crystal structure only in a nonco-
ordinating fashion. The ytterbium cation is surrounded so-
lely by OTf– anions in an octahedral fashion as in [C4mpyr]3-
[Yb(OTf)6].
Cyclic Voltammetry
Cyclic voltammetry is a well-suited tool used to monitor
atoms are slightly elongated (145.2 pm on the average) in ligand displacement reactions in solution. The cyclic vol-
contrast to those of the “free” oxygen atoms (143.5 pm). tammograms of 0.025  solutions of Yb(Tf2N)3 in
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Structural and Electrochemical Properties of YbIII in Various Ionic Liquids
[C4mpyr][Tf2N] (Figure 2a), Yb(OTf)3 in [C4mpyr][Tf2N] 100 mV/s are shown in Figure 2 (for other scan rates see
(Figure 2b), Yb(OTf)3 in [C4mpyr][OTf] (Figure 2c), and Supporting Information). The half-wave potentials (HWP)
Yb(Tf2N)3 in [C4mpyr][OTf] (Figure 2d) at a scan rate of versus Fc/Fc+ are found at –0.34 V, –0.79 V, –1.35 V, and
–1.35 V, respectively. The large difference between the oxi-
dation and the reduction peaks in the cyclic voltammog-
rams indicate a nonreversible process. Lower scan rates led
to a smaller separation of the two peaks (see Supporting
Information). But even with a scan rate as low as 10 mV/s,
the redox process is irreversible. It seems that the viscosity
of the IL plays an important role. [C4mpyr][Tf2N] has a
lower viscosity (95 mPas at 20 °C) than [C4mpyr][OTf]
(158 mPas at 20 °C)[15] and, indeed, lowering the scan rate
does affect the separation of the reduction and the oxi-
dation peaks more for [C4mpyr][Tf2N] than for [C4mpyr]-
[OTf]. When comparing the HWP of a solution of
Yb(Tf2N)3 in [C4mpyr][Tf2N], where YbIII is solely coordi-
nated to Tf2N– (HWP = –0.34 V), with the HWP of a solu-
tion of Yb(OTf)3 in [C4mpyr][OTf], where YbIII is coordi-
nated to OTf– (HWP = –1.35 V), a distinct difference is
observed. For the OTf solutions a substantially higher re-
dox potential YbIII/YbII was measured. This observation is
in agreement with the stronger Lewis basicity of the OTf
ligand compared to that of Tf2N. Generally higher redox
potentials are observed for metal cations if the ligand sur-
roundings it is able to donate more electron density to the
metal and hence has a higher donor number or stronger
Lewis basicity. A comparison of the cyclic voltammograms
of Yb(Tf2N)3 in [C4mpyr][OTf] and Yb(OTf)3 in [C4mpyr]-
[OTf] reveals the striking observation that the reduction
peaks of the trivalent species are both located at –1.35 V.
From this we conclude that the Tf2N– ligands in the coordi-
nation sphere of YbIII get replaced by OTf– upon dissol-
ution of Yb(Tf2N)3. This is backed by the fact that
[C4mpyr]4[Yb(OTf)6][Tf2N] crystallizes from such a solu-
tion. For a solution of Yb(OTf)3 in [C4mpyr][Tf2N] such a
complete ligand exchange obviously does not occur and the
determined HWP of –0.79 V lies between those of Yb-
(OTf)3 in [C4mpyr][OTf] and Yb(Tf2N)3 in [C4mpyr][Tf2N],
pointing to a mixed OTf–/Tf2N– coordination.
Conclusions
Combining all the gathered information, the following
reaction paths can be presented for dissolving YbIII in
Tf2N- and OTf-based ILs [Equations (1), (2), and (3)]:
Yb(Tf2N)3 + [C4mpyr][Tf2N] Ǟ [C4mpyr][Yb(Tf2N)4]
(1)
Yb(Tf2N)3 + 6[C4mpyr][OTf] Ǟ
[C4mpyr]4[Yb(OTf)6][Tf2N] + 2[C4mpyr][Tf2N] (2)
Yb(OTf)3 + 3[C4mpyr][OTf] Ǟ [C4mpyr]3[Yb(OTf)6]
(3)
Yb(Tf2N)3 dissolves upon complex formation in Tf2N
ILs. As a comparatively small trivalent lanthanide ion,
YbIII is surrounded by four Tf2N ligands coordinating bi-
dentately through their oxygen atoms. Similarly, Yb(OTf)3
dissolves in the OTf IL, [C4mpyr][OTf], upon forming the
Figure 2. Cyclic voltammograms of (a) Yb(Tf2N)3 in
[C4mpyr][Tf2N]; (b) Yb(OTf)3 in [C4mpyr][Tf2N]; (c) Yb(OTf)3 in
[C4mpyr][OTf]; (d) Yb(Tf2N)3 in [C4mpyr][OTf].
Eur. J. Inorg. Chem. 2010, 4933–4937
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A. Babai, S. Pitula, A.-V. Mudring
FULL PAPER
complex anion [Yb(OTf)6]3–. Dissolution of Yb(Tf2N)3 in
[C4mpyr][OTf] yields [C4mpyr]4[Yb(OTf)6][Tf2N], in which
the Tf2N– ligand has been replaced by the stronger Lewis
metal dissolves readily to give a colorless solution. The water from
the acidic solution was removed, and the resulting colorless solid
was dried for 24 h at 200 °C under reduced pressure (10–3 mbar).
base OTf– in the coordination sphere of Yb3+. In contrast, [C4mpyr][Yb(Tf2N)4] (1) and [C4mpyr]3[Yb(OTf)6] (2): Compounds
1
and
2
were synthesized from equimolar amounts of
we have no evidence for such a complete ligand exchange
when Yb(OTf)3 is dissolved in [C4mpyr][Tf2N]. Cyclic vol-
tammetry proved to be a powerful tool to monitor the li-
gand exchange in solution.
[C4mpyr][Tf2N] and Yb(Tf2N)3, and [C4mpyr][OTf] and Yb(OTf)3,
respectively. The starting materials were placed in a Schlenk tube
and stirred for 2 h at 120 °C until a homogeneous compound was
obtained. By cooling to room temperature colorless solids were ob-
tained. Single crystals of compounds 1 and 2 formed as insoluble
products after cooling the reaction mixture to room temperature
(5 °C/min).
Experimental Section
[C4mpyr]4[Yb(OTf)6][Tf2N] (3): Single crystals of 3 formed from a
solution of Yb(Tf2N)3 in [C4mpyr][OTf]. Yb(Tf2N)3 was dissolved
at 120 °C in [C4mpyr][OTf] until a homogeneous solution was ob-
tained. As the solution was cooled to room temperature, colorless
single crystals of 3 precipitated out.
The compounds synthesized in this work, as well as the starting
materials, are air- and moisture-sensitive. Therefore, the materials
were prepared and stored under inert gas. The reactions were car-
ried out by using either the standard “Schlenk technique” with a
vacuum/argon line or by using glass ampoules in an argon glovebox
(MBraun, Garching). The reaction ampoules were sealed under dy-
namic vacuum outside the glovebox while connected to a vacuum
line. All the reaction vessels were carefully dried for several hours
in a drying oven before use. All the starting materials were sublimed
prior to use. The ILs were synthesized according to the given pro-
cedures, purified until they exhibited CV-grade purity, and dried
for at least 24 h at 120 °C under reduced pressure (10–3 mbar).
X-ray Crystallography
To obtain structural information on the respective lanthanide com-
plex compounds, single crystals for X-ray analysis were grown out
of the respective ILs by supersaturating the IL with the respective
salt while hot. Subsequent careful cooling of the solution yielded
crystals of sufficient quality for structural analysis. However, crys-
tals of comparatively poor quality are a commonly encountered
problem when crystals are grown from ILs because the synthesis of
ILs generally employ ions that have a poor tendency to crystallize
but rather show packing frustration and disorder.[19] It took huge
effort to get the presented single-crystal X-ray diffraction data
shown here. For most of the checked specimens we were just able
to determine the cell parameters but the collected data were of too
poor quality to allow for a full structure refinement. Single-crystal
X-ray diffraction data were obtained with the aid of an image plate
diffraction system with graphite monochromated Mo-Kα radiation
(IPDS, Stoe&Cie, Darmstadt, Germany). Crystal structure solu-
tions were accomplished by direct methods using the SHELXS-97
software package.[20] The remaining atomic positions were localized
by subsequent difference Fourier analyses and least-squares refine-
ments with the SHELXL-97 software package.[21] For [C4mpyr]3-
[Yb(OTf)6], hydrogen atoms were placed in idealized positions and
constrained to reside on their respective parent atom. Because of
the lower data quality for [C4mpyr][Yb(Tf2N)4] and [C4mpyr]4-
[Yb(OTf)6][Tf2N], treatment of hydrogen atoms were omitted. Data
reduction was carried out with the program package X-Red,[22] and
numerical absorption corrections were performed with the program
X-Shape.[23] For crystal structure drawings, the program Diamond
was employed.[24]
[C4mpyr][Tf2N]: The IL [C4mpyr][Tf2N] was synthesized following
a modified literature procedure.[16] First, N-butyl-N-methylpyrrol-
idinium bromide was obtained by solvent-free alkylation of N-
methylpyrrolidine with 1-bromobutane at 80 °C. The crude product
was recrystallized from acetonitrile/toluene, dried in vacuo to re-
move the solvent mixture, and subsequently dissolved in water. One
equivalent of Li(Tf2N) in water was added, and the mixture was
stirred for 24 h at room temperature. The product that formed a
second phase to water was separated, purified by addition of acti-
vated charcoal, and filtered through aluminum oxide. It was dis-
solved in dichloromethane and washed with small aliquots of water
until no bromide residues could be detected in the extract (AgNO3
test). The resulting IL was dried for 48 h in a Schlenk tube at
150 °C under reduced pressure and rigorous stirring. 1H NMR
(200 MHz, [D6]DMSO): δ = 0.985 (t, J = 7.29 Hz, 3 H), 1.365 (sext,
J = 7.25, 7.43 Hz, 2 H), 1.748 (m, J = 7.80, 7.47 Hz, 2 H), 2.156
(m, 4 H), 3.037 (s, 3 H), 3.349 (m, 2 H), 3.503 (m, 4 H) ppm. 19F
NMR (300 MHz, CDCl3): δ = –79.43 (s, 6 H) ppm.
[C4mpyr][OTf]: The IL [C4mpyr][OTf] was prepared following a lit-
erature procedure.[17] [C4mpyr]Cl (44.4 g, 0.25 mol) was dissolved
in dichloromethane (50 mL), and Li(OTf) (39.0 g, 0.25 mol) was
added. The suspension was stirred overnight and filtered. The de-
canted solution was washed with several aliquots of water until no
chloride residues could be detected (AgNO3 test). The solvent was
removed, and the IL was dried in vacuo at 120 °C overnight. 1H
NMR (300 MHz, D2O): δ = 0.98 (t, J = 7.42 Hz, 3 H, 9-H), 1.41
(sext., J = 7.42 Hz, 2 H, 8-H), 1.79 (quint., J = 8.43 Hz, 2 H, 7-
H), 2.23 (br. s, 4 H, 3-H, 4-H), 3.04 (s, 3 H, 10-H), 3.29–3.38 (m,
2 H, 6-H), 3.42–3.59 (m, 4 H, 2-H, 5-H) ppm. 13C NMR (75 MHz,
D2O): δ = 12.8 (s, C-9), 19.2 (s, C-8), 21.3 (s, C-3, C-4), 25.1 (s, C-
7), 48.0 (s, C-10), 64.2 (m, C-2, C-5, C-6) ppm.
Crystal Data for [C4mpyr] [Yb(Tf2N)4] (1): C17H20F24N5O16S8Yb,
Mr = 1435.90 g/mol, monoclinic, P2/c (no. 13), a = 2013.33(15) pm,
b = 14.8617(9) pm, c = 1620.65(11) pm, β = 113.182(5)°, V =
4457.7(5)ϫ106 pm3, Z = 4, ρ = 2.140 g/cm3, µ = 2.649 mm–1. 68174
reflections were collected, of which 9973 were unique (Rint
0.0743). GOF = 1.048. R1/R2 = 0.0913/0.2412 [IϾ2σ(I)].
=
Crystal Data for [C4mpyr]3[Yb(OTf)6] (2): C66H120F36N6O36S12Yb2,
Mr 2988.49 g/mol, monoclinic, P21/c (no. 14),
=
a
=
2539.07(13) pm, b = 2027.26(6) pm, c = 2472.95(13) pm, β =
119.493(4)°, V = 11489.8(9)ϫ106 pm3, Z = 4, ρ = 1.728 g/cm3, µ =
1.969 mm–1. 61158 reflections were collected, of which 15020 were
unique (Rint = 0.0424). GOF = 1.052. R1/R2 = 0.0540/0.1318
[IϾ2σ(I)].
Yb(Tf2N)3: Yb(Tf2N)3 was synthesized by dissolving ytterbium
metal in aqueous HTf2N and subsequent removal of the liquid
phase.[18] The crude product was sublimed at 280 °C under reduced
pressure (10–3 mbar) to give Yb(Tf2N)3.
Yb(OTf)3: Yb(OTf)3 was synthesized in a procedure similar to that
used for Yb(Tf2N)3 by dissolving Yb metal in aqueous HOTf. The
Crystal Data for [C4mpyr]4[Yb(OTf)6][Tf2N] (3): C77H140F42N8O40-
S14Yb2, Mr = 3410.90 g/mol, monoclinic, P21/c (no. 14), a =
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Structural and Electrochemical Properties of YbIII in Various Ionic Liquids
enne, P. Hesemann, J. J. J. Moreau, I. Billard, C. Gaillard, S.
Mekki, G. Moutiers, Chem. Eur. J. 2006, 12, 3074; X. Sun, D.
Wu, J. Chen, D. J. Li, J. Chem. Technol. Biotechnol. 2007, 82,
267.
2542.0(3) pm,
b = 2056.78(12) pm, c = 2967.3(3) pm, β =
91.990(8)°, V = 15504(2)ϫ106 pm3, Z = 4, ρ = 1.573 g/cm3, µ =
1.543 mm–1. 81633 reflections were collected, of which 14473 were
unique (Rint = 0.1484). GOF = 0.926. R1/R2 = 0.0826/0.2037
[IϾ2σ(I)].
[4] A. I. Bhatt, H. Kinoshita, A. L. Koster, I. May, C. Sharrad,
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the supplementary crystallographic data for this paper. These data
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Autolab PGStat-12 instrument (Metrohm, Filderstadt, Germany).
A platinum working disc electrode, a glassy carbon counter elec-
trode and a silver-rod quasi reference electrode were used. All mea-
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rates of 10, 50, 100, and 200 mV/s. The electrodes were polished
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and acetone, and dried prior to use. The cyclic voltammograms
and half-wave potentials are given with respect to the Fc/Fc+ redox
couple. In order to do so, the Fc/Fc+ redox potential was measured
in the corresponding ILs first and a numerical correction was ap-
plied to the measured data afterwards.
Supporting Information (see footnote on the first page of this arti-
cle): Tables with selected interatomic distances and further infor-
mation on cyclic voltammetry measurements at different scan rates.
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The Deutsche Forschungsgemeinschaft (DFG) is acknowledged for
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