Rare-earth iodides in ionic liquids: The crystal structure of [SEt 3]3[LnI6] (Ln = Nd, Sm)

Article abstract of DOI:10.1021/ic051533h

Crystals of [SEt₃]₃[LnI₆] (Ln = Nd, Sm) were obtained by the reaction of LnI₂ with the ionic liquid [SEt ₃][Tf₂N] [Tf₂N = bis-(trifluoromethanesulfonyl) imide]. The compounds are characterized by octahedral [LnI₆] ^3- units that are surrounded by a distorted cube of triethylsulfonium cations.

Full text of DOI:10.1021/ic051533h

Inorg. Chem. 2005, 44, 8168−8169
Rare-Earth Iodides in Ionic Liquids: The Crystal Structure of
SEt ] [LnI ] (Ln Nd, Sm)
[
)
3
3
6
Arash Babai and Anja-Verena Mudring*
Insititut f u¨ r Anorganische Chemie, UniVersit a¨ t zu K o¨ ln, Greinstrasse 6, D-50939 K o¨ ln, Germany
Received September 8, 2005
Crystals of [SEt
reaction of LnI
3
]
3
[LnI
6
] (Ln
)
Nd, Sm) were obtained by the
][Tf N] [Tf bis-
because SmI
versatile reduction reagents used in organic chemistry. We
were able to obtain long-time stable solutions of SmI (and
YbI ) in, for example, [mppyr][Tf N] (mppyr ) 1-methyl-
-propylpyrrolidinium). In contrast, a solution of SmI (as
well as a solution of NdI ) in the sulfonium-based IL [SEt ]-
Tf N] leads to the reduction of the cation of the IL. The IL
2
, the so-called Kagan reagent, is one of the most
6
2
with the ionic liquid [SEt
3
2
2
N )
(trifluoromethanesulfonyl)imide]. The compounds are characterized
2
]3- units that are surrounded by a distorted
2
2
by octahedral [LnI
cube of triethylsulfonium cations.
6
3
1
2
2
3
[
2
decomposes to a dark-brown liquid of higher viscosity and
evolves a smell reminiscent of garlic when exposed to the
atmosphere. To determine the product of decomposition on
Symmetric trialkylsulfonium-based ionic liquids (ILs) have
1
gained considerable attention as electrolytes, especially with
7
-
the bis(trifluoromethanesulfonyl)imide (Tf
2
N ) anion because
the side of the rare-earth cation, the respective rare-earth
their conductivities are among the highest found for aliphatic
2
diiodides, LnI
2
3
(Ln ) Nd, Sm), were reacted with [SEt ]-
onium-based room-temperature ILs (RTILs). Although
8
-
[Tf N] at elevated temperatures. After slow cooling of the
2
trialkylsulfonium Tf
2
N ILs show a large electrochemical
reaction mixture, room-temperature crystals of sufficient
quality for single-crystal X-ray structure analysis were
window, the cathodic limit of decomposition is generally
shifted downward compared to similar quaternary am-
monium-based ILs and reaches values (in the cathodic range)
9
obtained.
2
The structures of the isotopic compounds [SEt ] [LnI ]
3
3
6
that are otherwise typically found for imidazolium ILs. The
(
Ln ) Nd, Sm; Figure 1) are characterized by a nearly ideal
chemical lability of trialkylsulfonium ILs toward reduction
not only influences the electrochemistry but also strongly
influences the chemistry.
3
-
[LnI
6
]
octahedron. The mean interatomic distances of
d(Nd-I) ) 311 pm and d(Sm-I) ) 309 pm are well in the
expected range and reflect the radii contraction along the
series of trivalent rare-earth cations.
We are currently studying the chemistry of divalent rare-
earth compounds in miscelleaneous ILs because the proper-
ties of this class of solvents can be tuned in such a way as
Especially noteworthy is the second coordination sphere
of the rare-earth cations. Each of the triangular faces of the
3
to stabilize highly reducing species. It has been well-
3-
[LnI
6
]
octahedron is capped by a triethylsulfonium cation,
established now that the redox potentials of divalent rare-
earth cations cover a wide range and can reach values similar
to those of alkali metals.4 Particularly, investigations on the
(
6) Smith, M. B., March, J., Eds. March’s AdVanced Organic Chemis-
try: Reactions, Mechanisms, and Structure; Wiley-Interscience: New
York, 2001. Kagan, H. B. New J. Chem. 1990, 14.
,5
2
reactivity of SmI in different ILs are of eminent interest
(
7) So far we have been unable to determine the exact identity of the
decomposition products, which apparently are of a complex nature.
Reduction of the triethylsulfonium cation apparently leads to cleavage
of the S-C bond and subsequent polymerization. When exposed to
the atmosphere, hydrolysis takes place and sulfanes are formed.
*
To whom correspondence should be addressed. E-mail: a.mudring@
uni-koeln.de. Tel: +49 221 4703921. Fax: +49 221 4705083. Web page:
www.anjamudring.de.
(
1) Stegemann, H.; Rode, A.; Reiche, A.; Schnittke, A.; F u¨ llbier, H.
Electrochim. Acta 1990, 37, 379. Paulsson, H.; Hagfeldt, A.; Kloo,
L. J. Phys. Chem. B 2003, 107, 13665. Paulsson, H.; Berggrund, M.;
Vantesson, E.; Hagfeldt, A.; Kloo, L. Sol. Energy Mater. Sol. Cells
(8) Experimental information: [SEt3][[Tf2N] was prepared according to
2
the literature procedure. LnI2 (Ln ) Sm, Nd) was prepared by the
reduction of LnI3 with the corresponding Ln metal in a sealed tantalum
container, jacketed with an evacuated silica tube. LnI3 was prepared
from metal (chips, Chempur, 99.5%) and iodine (Riedel de H a¨ en,
2004, 82, 345. Li, X.; Johnson, K. E. Can. J. Chem. 2004, 82, 491.
13
(
(
2) Matsumoto, H.; Matsuda, T.; Miyazaki, Y. Chem. Lett. 2000, 1430.
3) Mudring, A.; Babai, A.; Arenz, S.; Giernoth, R. Angew. Chem. 2005,
99.8%) according to the procedure described in the literature. Storage
and manipulation of the starting materials and products were handled
under drybox conditions (MBraun, Garching, Germany). The reaction
of LnI2 (0.22 mmol, ∼88 mg) with [SEt3][Tf2N] (1.8 mmol, 0.73 g,
0.5 mL) was carried out in an evacuated and sealed silica tube at 393
K for 12 h. Yellow (Sm) and pale-green (Nd) single crystals of [SEt3]3-
[LnI6] formed as an insoluble product after subsequent cooling (2
K/min) to room temperature. The product was separated by filtration.
Estimated yields: ∼15%.
117, 5621; Angew. Chem., Int. Ed. 2005, 34, 5485.
(
4) Meyer, G. Chem. ReV. 1988, 88, 93.
(
5) Morss, L. In Handbook of the Physics and Chemistry of Rare Earth;
Gschneidner, K. A., Eyring, L., Choppin, G. R., Lander, G. H., Eds.;
Elsevier: New York, 1994; Vol. 8, Chapter 122. Strange, P.; Svane,
A.; Temmermann, W. M.; Szotek, Z.; Winter, H. Nature 1999, 399,
756.
8168 Inorganic Chemistry, Vol. 44, No. 23, 2005
10.1021/ic051533h CCC: $30.25
© 2005 American Chemical Society
Published on Web 10/21/2005

COMMUNICATION
Figure 2. First and second coordination sphere of Ln3 in [SEt3]3[LnI6].
+
Figure 1. Crystal structure of [SEt3]3[LnI6]. Hydrogen atoms and disorder
in the SEt3 part of the structure are omitted for clarity.
+
+
Hydrogen atoms and disorder in the SEt3 structure part are omitted for
clarity.
leading to the formation of a (distorted) cube (Figure 2). This
structural feature has already been predicted by molecular
[
(
MX
6
]x- a second coordination sphere of a cube of cations
of the IL) is a common structural feature.
The high conformational flexiblity of the triethylsulfonium
3-
10
dynamic studies to occur for [LnCl
6
]
in imidazolium ILs
and has been observed in compounds obtained from the IL
1
1
[
mppyr][Tf
2
N]. A similar structural motif has recently been
cation, which, on the one hand, is a prerequisite for a cation
of an IL, becomes a crucial problem when trying to get
crystals of sufficient quality for X-ray structure analysis. As
-
found for [PF
6
]
6
in the IL [dmim][PF ] (dmim ) 1,3-
12
dimethylimidazolium). Therefrom, the general conclusion
can be drawn that for anionic octahedral units such as
-
3
2
has already been noted for the Tf N anion, conformational
flexiblity and a well-shielded or delocalized charge often lead
to strong disorder in the crystal. However, in the case of
(
9) Crystal data: Suitable single crystals were mounted under inert
conditions in glass capillaries. Intensity data sets were collected on
an IPDS II diffractometer (Stoe, Darmstadt, Germany). The crystal
structures were solved by direct methods (SIR-92; Altomare, A.;
Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl. Crystallogr.
3 3 6
[SEt ] [NdI ], we were able to obtain high-quality crystals,
which allowed not only positioning of the cations but also
their anisotropic refinement and even refinement of hydrogen
positions after the riding model. Thus, the structure of the
triethylsulfonium cation could be determined reliably. Aware-
ness has to be drawn to the fact that the cation is far from
being planar, as has been mentioned occasionally in the
1
993, 26, 343). Subsequent difference Fourier analyses revealed the
remaining atom positions. The structures were refined with SHELXL-
7 (Sheldrick, G. M., Institut f u¨ r Anorganische Chemie der Universit a¨ t,
9
Tammanstrasse 4, G o¨ ttingen, Germany, 1998). Numerical absorption
correction after crystal shape optimization was performed using the
programs X-Red 1.01 and X-Shape 1.01 (Stoe, Darmstadt, Germany).
[
(
2
7
SEt3]3[NdI6]: S3C9H45NdI6, M ) 1251.3, orthorhombic, a ) 1942.6-
2) pm, b ) 1816.3(3) pm, c ) 2143.5(4) pm, U ) 7563.1(2) Å, T )
1,2
literature, but shows a strong tetrahedralization at the
-
1
98 K, space group Pbca (No. 61), Z ) 8, µ(Mo KR) ) 6.442 mm ,
central sulfur atom with C-S-C bonding angles of about
1 340 reflections measured, 8902 unique (Rint ) 0.404), which were
used in all calculations. The final R1 was 0.093, and the final wR2
was 0.159 (observed data). [SEt3]3[SmI6]: S3C9H45SmI6, M ) 1257.4,
orthorhombic, a ) 1936.8(1) pm, b ) 1807.07(7) pm, c ) 2116.47-
1
01°.
Acknowledgment. A.-V.M. thanks the Deutsche For-
(
8) pm, U ) 7407.47(6) Å, T ) 170 K, space group Pbca (No. 61),
-1
schungsgemeinschaft (Grant SPP 1166, “Lanthanoidspezi-
fische Funktionalit a¨ ten”) and the Fonds der Chemischen
Industrie (supplies and Liebig fellowship) for their support
as well as Prof. Dr. G. Meyer for his interest in our ongoing
research.
Z ) 8, µ(Mo KR) ) 6.761 mm , 79 255 reflections measured, 8117
unique (Rint ) 0.101), which were used in all calculations. The final
R1 was 0.051, and the final wR2 was 0.076 (observed data). Hydrogen
positions were treated with the “riding model”, and disorder was taken
into account.
(
(
(
10) Chaumont, A.; Wipff, G. J. Phys. Chem. B 2004, 108, 3311.
11) Babai, A.; Mudring, A.-V. J. Alloys Compd. 2005, in press.
12) Hardacre, Ch.; McMath, S. E. J.; Niewenhuyzen, M.; Bowron, D. T.;
Soper, A. K. J. Phys.: Condens. Matter 2003, 15, 159.
13) Corbett, J. D. Inorg. Synth. 1983, 22, 31. Meyer, G. In Synthesis of
Lanthanide and Actinide Compounds; Meyer, G., Morss, L., Eds.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1991; pp
Supporting Information Available: Further crystallographic
information are available in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org.
(
135-144.
IC051533H
Inorganic Chemistry, Vol. 44, No. 23, 2005 8169