The octanuclear europium cluster [bmpyr]6[Eu8(μ 4-O)(μ3-OH)12(μ2-OTf) 14(μ1-Tf)2](HOTf)1.5 obtained from the ionic liquid [bmpyr][OTf]

Article abstract of DOI:10.1002/zaac.200600150

The octanuclear europium cluster compound [bmpyr]₆[Eu ₈(μ₄-O)(μ₃-OH)₁₂(μ ₂-OTf)₁₄(μ₁-OTf)₂](HOTf) _1.5 has been crystallized from the ionic liquid [bmpyr][OTf]. Structural characterization by single crystal X-ray diffraction revealed an Bug cluster unit which is centered by an oxide anion. The Bug-cluster polyhedron can be described as a bicapped octahedron or a triangulated dodecahedron. Each of the triangular faces of the cluster is capped by one μ₃-hydroxo group. Fourteen μ₂-triflate (CF₃SO₃ ^-) anions bridge via oxygen the cluster edges. Together with two μ₁-terminal coordinating triflate anions they complete the cluster unit. Six cations from the ionic liquid counterbalance the cluster charge. Additionally, 1.5 HOTf molecules per Bug-cluster unit are incorporated in the crystal structure of the title compound.

Full text of DOI:10.1002/zaac.200600150

DOI: 10.1002/zaac.200600150
The Octanuclear Europium Cluster [bmpyr] [Eu (µ -O)(µ -OH) (µ -OTf)
6
8
4
3
12
2
14
1
)
(
µ -Tf) ](HOTf) Obtained from the Ionic Liquid [bmpyr][OTf]
1
2
1.5
Arash Babai and Anja-Verena Mudring*
Köln, Institut für Anorganische Chemie der Universität
Received May 5th, 2006.
th
Dedicated to Professor Glen B. Deacon on the Occasion of his 70 Birthday
Abstract. The octanuclear europium cluster compound
bmpyr] [Eu (µ -O)(µ -OH)12(µ -OTf)14(µ -OTf) ](HOTf)1.5 has
been crystallized from the ionic liquid [bmpyr][OTf]. Structural
characterization by single crystal X-ray diffraction revealed an Eu
cluster unit which is centered by an oxide anion. The Eu -cluster
1
anions bridge via oxygen the cluster edges. Together with two µ -
terminal coordinating triflate anions they complete the cluster unit.
Six cations from the ionic liquid counterbalance the cluster charge.
Additionally, 1.5 HOTf molecules per Eu -cluster unit are incorpo-
8
rated in the crystal structure of the title compound.
[
6
8
4
3
2
1
2
8
8
polyhedron can be described as a bicapped octahedron or a trian-
gulated dodecahedron. Each of the triangular faces of the cluster
Ϫ
is capped by one µ
3
-hydroxo group. Fourteen µ
2
-triflate (CF
3
SO
3
)
Keywords: Rare-earth metals; Ionic liquids; Cluster compounds
europium(III)-triflate in the ionic liquid [bmpyr][OTf] as a colorless
compound. Single crystal X-ray structure analysis reveals an
octanuclear unit of europium atoms which can be understood as a
Lanthanide polyoxometallate cluster compounds offer a high po-
tential as luminescent, magnetic and catalytic functional materials
bicapped octahedron (see Fig.1, left). Such a [Eu
8
(µ
4 3
-O)(µ -
[1]. However, because of the high charge and the polarizing power
10ϩ
OH)12
Eu (DMF)
mixed
10[Eu
]
cluster core has been previously described for
of the trivalent rare earth cations, it is generally difficult to control
the process of oligomerization. In addition, the trivalent rare earth
ions generally show highly variable coordination numbers and geo-
metries with only small energy differences leading to a large num-
ber of different polyoxometallates. In case of (trivalent) europium,
hexa-, octa-, nona- and pentadecanuclear polyhydroxometallate
cluster compounds have been described [2]. Here, we report on the
synthesis and structural characterization of an oxygen-centered
octanuclear europium cluster compound obtained from the ionic
8
8
(µ
valent
(OC
4
-O)(µ
3
-OH)12(Se
3
)(Se
4
)
3
(Se
5
)
2
[3]. In case of the
cluster compound
6
] a distorted cubic ar-
octanuclear
i
H
8
O
8
6
H
3
Me
2
-2,6)10(O Pr)
2
(THF)
rangement of the eight europium atoms was found [4]. The Eu-Eu
distances in 1 with a mean value of 393.0(4) pm are well beyond
the Eu-Eu bonding region and significantly higher as in
Eu
the europium cations can alternatively be described as a Eu
fly sandwiched between two perpendicular Eu dimers. Such a
structural unit is known for octanuclear clusters like B
Cl [5]. In case of 1 the central Eu butterfly is centered by an
8
(DMF)
8
(µ
4
-O)(µ
3
-OH)12(Se
3
)(Se
4
)
3
(Se
5
)
2
. The arrangement of
4
butter-
2
liquid [bmpyr][OTf] (bmpyr
OTf ϭ trifluoromethanesulfonate, CF SO ).
3 3
ϭ
1-butyl-1-methylpyrrolidinium,
2Ϫ
8
H
8
and
Ϫ
B
8
8
4
oxide anion with a mean Eu-O interatomic distance of 254.4(3) pm.
Surpisingly this interatomic distance is about 18 pm longer than in
Results and Discussion
Eu
in [Eu
describe the hydroxide anion arrangement around the Eu
8
(DMF)
8
(µ
4
-O)(µ
3
-OH)12(Se
3
)(Se
4
)
3
(Se
O) (257 pm) [2c]. In order to
cluster
5 2
) but similar to the one
6
(µ -O)(µ
6
3
-OH)
8
(H O)24]I
2
8
(H
2
8
The europium cluster compound [bmpyr]
6 8 4 3 2
[Eu (µ -O)(µ -OH)12(µ -
8
OTf)14(µ -OTf) ](HOTf)1.5 (1) has been obtained from acidic
1
2
unit it is useful to view the cationic arrangement as a triangulated
dodecahedron. Each of the triangular faces of this polyhedron is
capped by a µ
distance of 237.1(3) pm which lies in the same region as found
for Eu (DMF) (µ -O)(µ -OH)12(Se )(Se (Se (241(6) pm) and
(µ -O)(µ -OH) (H O)24]I (H O) (239(1) pm). Sixteen triflate
3
-hydroxide anion with a mean Eu-O interatomic
*
Dr. Anja-Verena Mudring
)
3
5 2
)
Institut für Anorganische Chemie
Universität zu Köln
8
6
8
4
3
3
4
3
[Eu
6
8
2
8
2
8
Greinstraße 6
D-50939 Köln
Fax: (49) 221 470 5083
E-Mail: a.mudring@uni-koeln.de
http://www.anjamudring.de
(OTf) anions fill the coordination sphere of the europium cations.
Fourteen of the triflate anions coordinate in a bidentate chelating
mode through two oxygen atoms along the edges of the Eu cluster.
8
Two additional triflate anions coordinate only monodentately to
europium. The mean Eu-OTf interatomic distance of 239.8(3) pm is
in the expected range. All europium cations are crystallographically
independent. Six of them are coordinated by nine oxygen atoms in
the form of a monocapped square antiprism whereas two europium
1)
Paper presented at the XVIIIth Tage der Seltenen Erden (Terrae
Rarae 2005) at Bonn-Röttgen/Germany, November 30th Ϫ Decem-
ber 2nd, 2005 (www.Terrae-rarae.de).
1956
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 632, 1956Ϫ1958

An Octanuclear Europium Cluster
Fig. 1 Parts of the crystal structure of [bmpyr]
6
[Eu
8
(µ
4
-O)(µ
3
-OH)12(µ
2
-OTf)14(µ
1
-OTf)
2
](HOTf)1.5 (1): Eu
8
(µ
4
-O)(µ
(µ -O)(µ
4
3
-OH)12 cluster core
-OH)12(µ -OTf)14
4Ϫ
(
left), {[Eu
8
(µ
4
-O)(µ
3
-OH)12(µ
2
-OTf)14
}
, one oxygen and CF
3
groups omitted for clarity (middle), {[Eu
8
3
2
6Ϫ
(
µ -OTf) ]} cluster unit (right).
1 2
cations are surrounded by just eight oxygen atoms in the form of
a square antiprism. The coordination of the europium cations be-
longing to the inner Eu butterfly (Fig. 2, left) is accomplished by
4
one oxide anion, five hydroxide anions and three oxygen atoms
belonging to triflate anions that form a bridge to neighbouring
2
europium cations. In case of the perpendicular Eu units one eu-
ropium ion of each unit has the coordination number nine, which
is accomplished by four hydroxide anions, four triflate anions that
bridge to other europium cations and one terminal triflate ligand.
The other half of the europium cations has a coordination number
of eight with the terminal triflate ligand missing. The anionic
charge of the cluster is counterbalanced by six [bmpyr] cations from
8
the ionic liquid. Additionally, 1.5 HOTf molecules per Eu -cluster
unit are incorporated in the crystal structure of 1. Despite the
plethora of polynuclear hydroxo lanthanide clusters it seems that
certain cluster cores have a pronounced stability. In case of oxygen
centred hydroxo lanthanide clusters the hexanuclear cluster unit
Fig.
6 8 4 3
2 Europium coordination in [bmpyr] [Eu (µ -O)(µ -
OH) (µ -OTf) (µ -OTf) ](HOTf)1.5. Coordination of Eu cations
belonging to the central Eu butterfly (left). Coordination of one
half of Eu-cations belonging to the perpendicular Eu units (right),
in case of the other half the terminal monodentate triflate ligand
1
2
2
14
1
2
4
2
6
3
8ϩ
[
Ln
has been described for a plethora of different counter anions and
ligands [2, 6, 7]. The existence of Eu (DMF) (µ -O)(µ -OH)12(Se )-
Se (Se and together with the new example of [bmpyr] [Eu (µ
O)(µ -OH)12(µ -OTf)14(µ -OTf) ](HOTf)1.5 may justify the assump-
tion that the [Ln (µ -O)(µ cluster unit is also common
-OH)12 1
6
(µ -O)(µ -OH)
8
]
(Ln ϭ lanthanide) with a Ln
6
octahedron
is absent.
8
8
4
3
3
(
4
)
3
5
)
2
6
8
4
-
3
2
1
2
The
ionic
liquid
1-butyl-1-methylpyrrolidinium
triflate,
0ϩ
8
4
3
]
[bmpyr][OTf], was synthesized following a literature procedure [7].
to oxygen centred hydroxo lanthanide cluster compounds.
To
HOTf)1.5 120 mg of the acidic europium(III)-triflate and 0.2 ml of
bmpyr][OTf] were placed in a silica tube which was sealed under
obtain
6 8 4 3 2 1 2
[bmpyr] [Eu (µ -O)(µ -OH)12(µ -OTf)14(µ -Tf) ]-
(
[
Experimental Section
vacuum. The reaction mixture was heated at 393 K for 36 h. Color-
less, transparent single crystals of 1 form as an insoluble product
after cooling the reaction mixture to room temperature (2 K/min).
The product was separated by cannula-filtration from the ionic
liquid. Estimated yield: 20 %.
All operations were carried out under argon using standard
Schlenk-line and glovebox techniques.
[
bmpyr] [Eu (µ -O)(µ -OH) (µ -OTf)
6 8 4 3 12 2 14
(
µ -OTf) ](HOTf) (1)
Crystal structure determination of 1
1
2
1.5
(99.9 %, Chempur) were suspensed in 10 ml H
SO H ϭ HOTf; 98 %
Sigma-Aldrich) was added dropwise until a transparent acidic (pH
1) solution of europium(III)-triflate was obtained. Water was re-
5
00 mg Eu
2
O
3
2
O
After checking the crystal quality via Laue photographs a colorless
3
and trifluoromethanesulfonic acid (CF
3
3
fragment (0.3
F
ϫ
0.3
ϫ
0.2) mm of 1,
C
71.5
H
133.5Eu
8
Ϫ1
52.5 6 65.5
N O S17.5 (4899.57 g mol ) was selected for data collection.
<
Triclinic, P-1, a ϭ 1557.05(5) pm, b ϭ 1915.14(6) pm, c ϭ
2798.37(8) pm, Ͱ ϭ 104.950(2)°, β ϭ 92.324(2)°, γ ϭ 107.107(2)°,
moved in vacuo and the remaining colorless solid was dried for 12 h
at 300 °C under reduced pressure (10 mbar).
Ϫ2
˚
3
Ϫ3
Ϫ1
V ϭ 7644.0(4) A , Z ϭ 2, ρcalcd ϭ 2.129 g cm , µ ϭ 3.620 mm
.
Z. Anorg. Allg. Chem. 2006, 1956Ϫ1958
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 1957

A. Babai, A.-V. Mudring
X-ray diffraction data were collected on an IPDS II diffractometer
˚
with Mo-KͰ radiation (graphite monochromator, λ ϭ 0.71073 A)
[
1] Z. Zheng, Chem. Commun. 2001, 2521 and literature cited
therein.
at Ϫ150 °C, θmin/θmax ϭ 1.38°/27.00°. Indices: Ϫ19<ϭh<ϭ19,
Ϫ24<ϭk<ϭ24, Ϫ35<ϭl<ϭ35; F(000) ϭ 4770; 122252 reflections
collected, 33371 unique [R(int) ϭ 0.0471]. The X-Area program
package was used for data collection, unit cell refinement and data
reduction [8]; numerical absorption correction after crystal shape
optimization was performed using the programs X-Red 1.01 and
[2] (a) R. Wang, H. D. Selby, H. Liu, M. D. Carducci, T. Jin, Z.
Zheng, J. W. Anthis, R. J. Staples, Inorg. Chem. 2002, 41, 278;
(
b) M. Addamo, G. Bombieri, E. Foresti, M. D. Grillone, M.
Volpe, Inorg. Chem. 2004, 43, 1603; (c) T. Timofte, A. Babai,
A.-V. Mudring, Inorg. Chem. submitted.
X-Shape 1.01 [9, 10]. Structure solution with direct methods
2
[3] Ch. G. Pernin, J. A. Ibers, Inorg. Chem. 1997, 36, 3802.
(
[
SHELXS-97) [11] and refinement against F
12] led to R ϭ 0.0571, wR
ϭ 0.1653 for all data.
0
with SHELXH-97
ϭ 0.0665,
[
[
[
4] W. J. Evans, M. A. Greci, J. W. Ziller, Inorg. Chem. 2000, 39,
1
2
ϭ 0.1598 [I > 2σ(I)] and R
1
3213.
wR
2
5] L. J. Guggenberger, Inorg. Chem. 1969, 8, 2771; R. A.Jacob-
son, W. N. Lipscomb, J. Am. Chem. Soc. 1958, 80, 5571.
6] Z. Zheng, Chem. Commun. 2001, 2521 and literature cited
therein; Z. Zheng, Inorg. Synthesis 2004, 184; A. Babai, A.-V.
Mudring, Z. Anorg. Allg. Chem. 2005, 631, 261.
Crystallographic data for the structure have been deposited with
the Cambridge Crystallographic Data Centre, CCDC 604289.
Copies of the data can be obtained free of charge on application
to The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (Fax: int.code ϩ(1223)336-033; e-mail for inquiry:
fileserv@ccdc.cam.ac.uk).
[
7] L. Crowhurst, N. L. Lancaster, J. M. P e´ rez Arlandis, T. Wel-
ton, J. Am. Chem. Soc. 2004, 126, 11549.
8] X-Area, Stoe & Cie, Darmstadt, Germany, 2002.
9] X-Red 1.01, Stoe & Cie, Darmstadt, Germany, 2002.
[
[
[10] X-Shape 1.01, Stoe & Cie, Darmstadt, Germany, 2002.
Acknowledgements. This work has been supported by the Deutsche
Forschungsgemeinschaft (SPP 1166: Lanthanoidspezifische Funk-
tionalitäten) and the Fonds der Chemischen Industrie. The authors
thank Prof. Dr. Gerd Meyer for his continuous support.
[11] G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, 1997, Göttingen.
[12] G. M. Sheldrick, SHELXH-97, Program for Crystal Structure
Refinement, 1997, Göttingen.
1958
www.zaac.wiley-vch.de
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 1956Ϫ1958