Ready Access to Anhydrous Anionic Lanthanide Acetates by Using Imidazolium Acetate Ionic Liquids as the Reaction Medium

Article abstract of DOI:10.1002/chem.202100141

Access to lanthanide acetate coordination compounds is challenged by the tendency of lanthanides to coordinate water and the plethora of acetate coordination modes. A straightforward, reproducible synthetic procedure by treating lanthanide chloride hydrates with defined ratios of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]) has been developed. This reaction pathway leads to two isostructural crystalline anhydrous coordination complexes, the polymeric [C₂mim]_n[{Ln₂(OAc)₇}_n] and the dimeric [C₂mim]₂[Ln₂(OAc)₈], based on the ion size and the ratio of IL used. A reaction with an IL : Ln-salt ratio of 5 : 1, where Ln=Nd, Sm, and Gd, led exclusively to the polymer, whilst for the heaviest lanthanides (Dy?Lu) the dimer was observed. Reaction with Eu and Tb resulted in a mixture of both polymeric and dimeric forms. When the amount of IL and/or the size of the cation was increased, the reaction led to only the dimeric compound for all the lanthanide series. Crystallographic analyses of the resulting salts revealed three different types of metal-acetate coordination modes where η²μκ² is the most represented in both structure types.

Full text of DOI:10.1002/chem.202100141

Accepted Article
Accepted Article
Title: Ready access to anhydrous anionic lanthanide acetates using
imidazolium acetate ionic liquids as the reaction medium
Authors: Guillaume Bousrez, Olivier Renier, Steven P. Kelley, Brando
Adranno, Elnaz Tahavori, Hatem M. Titi, Volodymyr Smetana,
Si-Fu Tang, Anja Verena Mudring, and Robin D. Rogers
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202100141
Link to VoR: https://doi.org/10.1002/chem.202100141
01/2020

10.1002/chem.202100141
Chemistry - A European Journal
FULL PAPER
Ready access to anhydrous anionic lanthanide acetates using
imidazolium acetate ionic liquids as the reaction medium
Guillaume Bousrez,[a] Olivier Renier,[a] Steven P. Kelley,[b] Brando Adranno,[a] Elnaz Tahavori,[a] Hatem
M. Titi,[c] Volodymyr Smetana,[a] Si-Fu Tang,[d] Anja-Verena Mudring*[a] and Robin D. Rogers*[a,e]
[a]
Dr. G. Bousrez, O. Renier, B. Adranno, E. Tahavori, Dr. V. Smetana, Prof. Dr. A.-V. Mudring, Prof. Dr. R. D. Rogers
Department of Materials and Environmental Chemistry
Stockholm University
Svante Arrhenius väg 16C, Stockholm 10691, Sweden
E-mail: anja-verena.mudring@mmk.su.se
Dr. S. P. Kelley
Department of Chemistry
University of Missouri
601, S. College Avenue, Columbia, Missouri 65211, United States
H. T. Titi
Department of Chemistry
McGill University
Montreal, QC H3A 0B8, Canada
Prof. Dr. S.-F. Tang
College of Chemistry and Pharmaceutical Sciences
Qingdao Agricultural University
Changcheng Road 700, Chengyang District, Qingdao 266109, China
Prof. Dr. R. D. Rogers
[b]
[c]
[d]
[e]
College of Arts & Sciences
The University of Alabama
Tuscaloosa, Alabama 35487, United States
E-mail: rdrogers@ua.edu
Supporting information for this article is given via a link at the end of the document.
Abstract: The access to lanthanide acetate coordination compounds
is challenged by the tendency of lanthanides to coordinate water and
the plethora of acetate coordination modes. We developed a
straightforward, reproducible synthetic procedure by reaction of
lanthanide chloride hydrates with defined ratios of the ionic liquid (IL)
1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]). This reaction
pathway leads to two isostructural crystalline anhydrous coordination
complexes, the polymeric [C2mim]n[{Ln2(OAc)7}n] and the dimeric
[C2mim]2[Ln2(OAc)8], based on the ion size and the ratio of IL used. A
reaction with an IL:Ln-salt ratio of 5:1 where Ln = Nd, Sm, and Gd led
exclusively to the polymeric, whilst for the heaviest lanthanides (Dy-
Lu) dimeric was observed. Reaction with Eu and Tb resulted in a
mixture of both polymeric and dimeric forms. By increasing the
amount of IL and/or the size of the cation, the reaction led to only the
dimeric compound for all the lanthanide series. Crystallographic
analyses of the resulting salts revealed three different types of metal-
acetate coordination modes where 22 is the most represented both
structure types.
larger metal ions such as alkaline earths (Ae2+), lanthanides (Ln3+),
or uranyl ([UO2]2+), structurally distinct anionic complexes form
structures ranging from isolated monomers chelated by [OAc]–, to
dinuclear oligomers and polymeric complexes with chelating,
bridging, and mixed coordination modes.[2] Some Ln3+ ions, e.g.,
Nd, have been found with up to three different metal/ligand ratios,
pointing towards the large hidden potential of these systems to
provide unique acetate complexes.[2] This wide range of
coordination modes which [OAc]– can adopt with the lanthanides
prompted us to explore reproducible routes to homoleptic anionic
salts of the series of 4f-elements. Only a few structures of
homoleptic 4f-element acetate complexes have been reported so
far.[3] A particular challenge in the preparation of homoleptic
complexes of trivalent lanthanides is their extreme oxophilicity,
ubiquitous water frequently enters their coordination environment.
As a vehicle to provide a high concentration of coordinating
ligands promoting the formation of homoleptic complexes, and
large stable cations (e.g., dialkylimidazolium cations, Figure 1,
left) which can stabilize large and potentially unusual coordination
complex anions, ionic liquids (ILs) have proven a valuable
synthetic tool, in particular for obtaining homoleptic complexes.[2,4]
Their tendency to promote coordination of large numbers of
anions and the exclusion of neutral solvent molecules has led to
new coordination numbers, various coordination modes, and
polymeric structures,[5] in addition to providing routes to new
luminescent and magnetic materials.[6]
Introduction
The simple acetate anion ([OAc]–) is ubiquitous in Nature and
offers an exciting coordination chemistry because of the plethora
of coordination modes it can accommodate with metal ions
(Figure 1, right), especially in anionic metal complexes.[1] With
1
This article is protected by copyright. All rights reserved.

10.1002/chem.202100141
Chemistry - A European Journal
FULL PAPER
La, Pr, Nd, Sm-Lu, x = 6 or 7) or with an excess of the IL
[C2mim][OAc] in a fixed molar ratio, driving off the water by
heating, and slowly cooling to obtain a crystalline product. The
crystalline complexes were characterized by powder and single
crystal X-ray diffraction (PXRD and SCXRD), differential scanning
calorimetry (DSC), and infrared (IR).
When using a 5:1 IL:Ln-salt molar ratio, a combination of PXRD
and SCXRD revealed the formation of two series of anhydrous,
homoleptic
lanthanide
acetate
complexes,
dimeric
[C2mim]2[Ln2(OAc)8] (Ln
=
Eu, Tb–Lu) and polymeric
[C2mim]n[{Ln2(OAc)7}n] (Ln = Nd, Sm-Tb). For the largest
lanthanides tested, La and Pr, only Ln(OAc)3(H2O) could be
isolated (Figure S4). A detailed description of their structures can
be found below. Whilst this reaction with light lanthanides (Nd, Sm,
and Gd) led to the formation of exclusively polymeric
[C2mim]n[{Ln2(OAc)7}n] (see Figure S1 for PXRD patterns of the
products), with the heaviest lanthanides (Dy-Lu) the formation of
dimeric [C2mim]2[Ln2(OAc)8] was observed (see Figure S2 for
PXRD patterns of the products). The reaction with the
intermediate lanthanides, Eu and Tb, resulted in a mixture of both
polymeric and dimeric forms (PXRD patterns are shown in Figure
S3, S5, and S6). The PXRD patterns of representatives for each
of the two compound series, [C2mim]n[{Ln2(OAc)7}n] (Ln = Gd) and
[C2mim]2[Ln2(OAc)8]) (Ln = Er) are shown in Figure 2. However,
even if in most cases the final products are obtained as phase
pure, for some lanthanides the PXRD patterns indicated that
some minor unidentified side products were generated during the
reaction.
Figure 1. (Top) General structure of dialkylimidazolium acetate ILs. (Bottom)
Observed coordination modes of the [OAc]– ion with trivalent lanthanide cations.
One feature of ILs, which renders them particularly interesting as
solvents and reaction media for the conversion of hydrates,
particularly for the readily hydrated lanthanide salts, is the stability
of ILs to temperatures above the boiling point of water. Certain ILs
with coordinating, and even weakly coordinating anions,[7] can be
reacted neat with hydrated metal salts on the benchtop and
heated, with or without vacuum, to drive off volatiles such as such
as H2O or even HCl.[8] Historically, access to anhydrous
lanthanide complexes has been limited because of their high
affinity for oxygen,[9] thus we have been exploring the use of ILs
to dehydrate metallic salts leading to ready access to new
compounds including [C2mim][UO2(OAc)3], [C2C2im][UO2(OAc)3],
[C4mim][UO2(OAc)3], [C2C2im]2[La(OAc)5], [C2mim]2[Nd(OAc)5],
and [C2mim]n[Sr(OAc)3]n (where (C2mim)
=
1-ethyl-3-
methylimidazolium, (C2C2im) = 1,3-diethylimidazolium, (C4mim) =
1-butyl-3-methyl-imidazolium).[2,4a,8] Interestingly, in these
reactions the formation of oxo- and hydroxy compounds, which
frequently occurs when attempting to dehydrate hydrates of
strongly Lewis basic metal salts, is suppressed. Moreover, while
readily accessible coordination chemistry is thus easily available,
systematic studies are still lacking.
In this work, we build upon our observation that the readily
available IL [C2mim][OAc] allows for easy and reliable access to
water-free f-element compounds and develop a general, reliable
synthetic procedure applicable across the entire range of 4f-metal
ions leading to anhydrous materials. Here, single crystal X-ray
diffraction analysis has allowed us to unveil the complex nature of
acetate coordination modes in these anhydrous, homoleptic
lanthanide anionic complexes across the entire lanthanide series.
.
Scheme 1. General scheme of the synthesis of anhydrous salts of anionic
4f/[OAc]- complexes and influence of the amount of IL introduced on the
selectivity of the final product. (*PXRD indicated that these compounds were
obtained, albeit along with unidentified side products.)
There are multiple effects which could result in the preferential
formation of each of the three compounds like the ion size or
lanthanide salt concentration in the IL, i.e. IL-Ln-salt ratio. To shed
more light on this, several experiments were conducted.
To investigate whether it is truly the decreasing ion size, and/or
the IL:Ln-salt ratio that leads to the preferential formation of
Results and Discussion
Synthesis
[C2mim]2[Ln2(OAc)8]
(which
would
correspond
to
The synthetic methodology developed (Scheme 1) is based on
reacting readily available starting salts such as LnCl3•xH2O (Ln =
[C2mim][OAc]•Ln(OAc)3) over [C2mim]n[{Ln2(OAc)7}n] (which
could be re-written as 0.5[C2mim][OAc]•Ln(OAc)3) different IL:Ln-
2
This article is protected by copyright. All rights reserved.

10.1002/chem.202100141
Chemistry - A European Journal
FULL PAPER
salt ratios, namely 3:1 and 10:1 molar equivalents (eq) were
tested (Scheme 1).
Stability and Chemical Reactivity
Neat products which were carefully washed with acetonitrile to
remove all excess IL, showed no detectable degradation over two
months. However, it was noted that degradation occurred
whenever excess IL was present (Figure S7 and S8). The dimeric
compounds degraded faster than the polymeric ones, even in a
sample containers sealed under ambient atmosphere, the powder
turning partially into a colorless oil, presumably due to the
formation of acetic acid generated from the reaction with moisture
in the air as the samples developed the characteristic smell of
acetic acid. By way of illustrative example, the polymer
[C2mim]n[{Gd2(OAc)7}n] and the dimer [C2mim]2[Er2(OAc)8] were
followed using PXRD. Without washing with acetonitrile, after four
weeks under ambient conditions, the PXRD pattern of the
remaining powder indicated that no more dimer was present and
indicated the presence of the polymeric form, as well as some
undetermined crystalline compounds (Figure S7). This was later
When the reactions were conducted with 3 eq of IL, the large
lanthanides (Pr, Nd, and Sm) yielded only Ln(OAc)3(H2O) as a
phase pure compound. To re-call when a 5:1 ratio was used,
[C2mim]n[{Ln2(OAc)7}n] formed for Nd and Sm. For Pr, the 5:1 ratio
already led to Pr(OAc)3(H2O). Thus, there is a stronger tendency
for the earlier lanthanides to form Ln(OAc)3(H2O). In order to
prevent its formation, a higher IL:Ln-salt ratio has to be used.
For that reason we tested a 10:1 Ln-salt ratio. Raising the amount
of IL to 10 eq led to the dimeric compound even for Pr, Nd, and
Sm, which otherwise were only obtained for the heavier
lanthanides. However, close examination of the PXRD patterns
revealed that only [C2mim]2[Sm2(OAc)8] was phase pure, whilst
for the Pr and Nd reactions, mixtures with other, yet, unidentified
crystalline phases were observed.
In summary, the larger the lanthanide is, the higher the IL
concentration has to be used to lead to anhydrous complexes.
confirmed by means of
a unit cell check via SCXRD.
[C2mim]n[{Gd2(OAc)7}n] was also phase pure after reaction, but
after four weeks degraded to Gd(OAc)3(H2O) with other unknown
phases (Figure S8). This last observation confirms that larger
lanthanides seems to have a certain tendency to generate the
monohydrate lanthanide either with a lower amount of IL or after
degradation.
Structural Results
The two isostructural series of anhydrous, polymeric
[C2mim]n[{Ln2(OAc)7}n] and dimeric [C2mim]2[Ln2(OAc)8] with their
unit cell parameters are provided in Table 1. We next describe
each series of compounds from a structural point of view.
[C2mim]2[Ln2(OAc)8] (Ln
[C2C2im]2[La2(OAc)8]
=
Pr, Nd, Sm, Eu, Tb–Lu),
This family of thirteen isomorphous salts containing the discrete,
dimeric [Ln2(OAc)8]2- ion all crystallized in the monoclinic space
group P21/n with one half of the dimeric anion (Figure 3) residing
around a crystallographic center of inversion and one [C2mim]+
cation in the asymmetric unit. The [C2mim]+ cations are
disordered with the ethyl CH3 group being spread over three
positions emulating both cis and trans conformations of a
hypothetical [C2C2im]+ cation, while the [C2C2im]+ cation in the La
structure was observed solely in the cis-conformation. This
degree of freedom explains the isostructurality of both the
[C2C2im]+ and [C2mim]+ structures.
Figure 2. (Top) Experimental PXRD pattern of [C2mim]n[{Gd2(OAc)7}n] (Red) vs
theoretical pattern (Black). (Bottom) Experimental PXRD pattern of
[C2mim]2[Er2(OAc)8] (Blue) vs theoretical pattern (Black).
Figure 3. [Ln2(OAc)8]2– dimeric unit in the crystal structures of
[C2mim]2[Ln2(OAc)8] and [C2C2im]2[La2(OAc)8]. Coordination modes are
indicated according to Figure 1.
3
This article is protected by copyright. All rights reserved.

10.1002/chem.202100141
Chemistry - A European Journal
FULL PAPER
The Ln3+ cations are 9-coordinated with the oxygen atoms in the
form of a slightly distorted tricapped trigonal prism. The dimeric
units (Figure 3) have Ci symmetry, while each Ln coordination
polyhedron is asymmetric. The Ln-O distances range from 2.27(1)
to 2.66(1) Å including minor variations with coordination mode,
different data collection temperatures, and following the
lanthanide contraction. The [OAc]– ions exhibit three coordination
modes – 322, 22, and 222 (Figure 1).
Table 1. Comparison of cell parameters for the crystal structures determined in this study.
Compound
SG
a, Å
b, Å
[C2mim]2[Ln2(OAc)8]
12.315(2)
c, Å
, 
V, Å3
IL:Ln ratio
CCDC
[C2mim]2[Pr2(OAc)8]*
[C2mim]2[Nd2(OAc)8]
[C2mim]2[Sm2(OAc)8]*
[C2mim]2[Eu2(OAc)8]*
[C2mim]2[Tb2(OAc)8]*
[C2mim]2[Dy2(OAc)8]*
[C2mim]2[Dy2(OAc)8]
[C2mim]2[Ho2(OAc)8]
[C2mim]2[Er2(OAc)8]
[C2mim]2[Tm2(OAc)8]
[C2mim]2[Yb2(OAc)8]
[C2mim]2[Lu2(OAc)8]
P21/n
P21/n
P21/n
P21/n
P21/n
P21/n
P21/n
P21/n
P21/n
P21/n
P21/n
P21/n
9.535(2)
9.543(1)
9.487(1)
9.489(8)
9.476(1)
9.449(1)
9.458(5)
9.466(8)
9.439(2)
9.426(2)
9.421(4)
9.408(6)
16.599(3)
16.727(2)
16.576(2)
15.563(1)
16.557(2)
16.595(2)
16.690(9)
16.700(1)
16.698(5)
16.685(3)
16.683(8)
16.652(9)
93.830(3)
93.596(3)
93.709(5)
94.220(3)
94.239(9)
94.155(2)
93.963(2)
93.965(3)
93.968(9)
94.065(5)
94.113(2)
94.209(2)
1944.8(7)
1990.4(4)
1924.0(5)
1795.8(3)
1898.2(3)
1905.1(3)
1938.2(2)
1939.8(3)
1922.5(9)
1922.3(5)
1921.1(2)
1912.0(2)
10:1
10:1
10:1
5:1
1920417
1920416
1920418
1920419
1920420
1920421
1920422
1920423
1920424
1920425
1920426
1920427
12.493(1)
12.260(2)
12.193(2)
12.132(9)
12.181(1)
12.308(7)
12.300(9)
12.227(3)
12.254(2)
12.255(5)
12.237(7)
5:1
5:1
5:1
5:1
5:1
5:1
5:1
5:1
[C2C2im]2[Ln2(OAc)8]
[C2C2im]2[La2(OAc)8]*
P21/n
9.570(3)
12.473(4)
16.853(5)
93.685(2)
2007.4(1)
10:1
1920428
[C2mim]n[{Ln2(OAc)7}n]
[C2mim]n[Nd2(OAc)7]n*
[C2mim]n[Eu2(OAc)7]n
[C2mim]n[Gd2(OAc)7]n
[C2mim]n[Tb2(OAc)7]n
Pca21
Pca21
Pca21
Pca21
19.240(1)
19.303(3)
19.281(5)
19.302(1)
7.847(5)
7.841(1)
7.833(2)
7.868(6)
19.118(1)
2886.5(3)
2896.5(9)
2886.8(9)
2902.7(3)
5:1
5:1
5:1
5:1
1920432
1920433
1920434
1920435
19.138(3)
19.113(5)
19.113(1)
*Measured at 100 K.
[C2mim]n[{Ln2(OAc)7}n] (Ln = Nd, Eu-Tb)
The 222 (4) mode in [C2mim]2[Nd2(OAc)8] represents the
shortest Nd-O distances in the structure – 2.41(1)–2.43(1) Å,
while the 22 (2) distances are longer (2.50(1)–2.53(1) Å) as a
result of partial repulsion between two O atoms binding to the
same metal cation. This correlates well with the Nd–O distances
observed in [C2mim]2[Nd(OAc)5] (2.53(1)–2.64(1) Å) represented
solely by the 22 mode. Consequently, the 322 (5) mode lies
in between with Nd-O = 2.437(4) and 2.541(4)–2.622(4) Å
depending on how many oxygen atoms have been bound to the
same metal center.
This second isostructural series is very sensitive to the lanthanide
size and the reaction ratio (5:1 IL:Ln-salt). Here the acetate ligand
again shows its versatility by allowing a lower number of
coordinating acetates by forming anionic polymers. These
compounds crystallize in the orthorhombic space group Pca21
with two independent Ln positions and one independent cation in
the asymmetric unit. The linear polymeric anion consists of
repeating [Ln2(OAc)7]– where each Ln is coordinated by nine
oxygen atoms in the form of a slightly distorted tricapped trigonal
prism. Ln1 is coordinated to two chelating and five unidentate
acetate ligands, while Ln2 to three chelating and three unidentate
ligands. The distribution of unidentate and chelating ligands
violates any possible mirror symmetry for a trigonal prism, and as
a result the polymer chains are chiral with the metal ion acting as
the chiral center. Both positions alternate along the b axis being
connected by three acetate bridges. The [OAc]– ions exhibit
322 (5), 22 (2), and 222 (4) coordination modes similar to
[C2mim]2[Ln2(OAc)8]; however, the proportion of the terminating
22 mode is significantly lower (Figure 4).
Dimeric [Ln2(OAc)8]2- units are known in the literature and even
found in some applications in cryogenics,[10] but are extremely
rare. The only previously published compound that contains this
unit with identical coordination modes is
macrocycle complex
(C2H3O2)2][Gd2(C2H3O2)8]•C6H6•4CHCl3) where [Gd2(OAc)8]2-
plays the role of
counterion.[11] Hydrates such as
a
Gd hexaaza
(2[Gd(C22H26N6)-
a
[Ln2(OAc)8(H2O)2] have been observed with a few lanthanides
(La-Sm),[12] but with different acetate coordination modes (three
22 and one 322 per Ln atom). Other pure, dimeric Ln tetra-
To
analyze
the
bonding
patterns
we
will
use
carboxylato
[Ho2(butenoate)8]2- with rather large aromatic counterions.[13]
Lastly, similar tri-carboxylato dimers
complexes
include
[Eu2(CH3BzO)8]2-
and
[C2mim]n[{Nd2(OAc)7}n] as an example. In addition to two
symmetry-independent Nd positions, there are seven
independent acetate ions resulting in a wide spread of the Nd−O
bonds (2.36(1)−2.77(1) Å). Although the Nd−O bonds in different
coordination modes show partial overlap, the monodentate
coordinated [OAc]– (222 and in part 322 similarly to
[C2mim]2[Nd2(OAc)8]) cover the lower range of that spectrum –
2.365(7)–2.497(6) Å, while the bidentate [OAc]– (22 and
322) partially overlapping the upper one, 2.446(7)–2.767(6) Å.
[Ln2(CH3COO)6(H2O)4]nH2O[10,14] have been observed for the
heavier Ln (Eu-Lu) exhibiting the same 22 and 322 modes
as the latter. Though the 222 coordination mode could still be
obtained in the fluorinated Tb2(CF3COO)6(H2O)6, all initial 322
bridges have been distorted resulting in 222.
4
This article is protected by copyright. All rights reserved.

10.1002/chem.202100141
Chemistry - A European Journal
FULL PAPER
These distances are also comparable to those in the two known
Nd acetates[15] (see below).
[C2mim]2[Er2(OAc)8], there are now three peaks for the acetate at
1404 (CH3 deformation), 1566 (C-O stretching) and 1608 (C-O
stretching) cm-1 (Figure S16). The deformation of the methyl
group seems to be similar whatever the type of coordination is.
However, there are two types of carbon-oxygen stretching signals,
which confirm the presence of, at least, two different types of
coordination modes in the compound.[20] It could be also related
to the crystal structure bond lengths. The ligands only coordinated
to one metal center have bond lengths (C-O) around 2.41 Å
whereas when the acetate ligand bridged the two metal centers
the bond lengths are between 2.31-2.57 Å.
In the polymeric [C2mim]n[{Gd2(OAc)7}n], there are four bands at
1405 (CH3 deformation), 1433 (CH3 deformation), 1566 (C-O
stretching), and 1605 (C-O stretching) cm-1 (Figure S15). It seems
that in this case the methyl group vibrational frequency is
impacted by the type of coordination because of the hydrogen
bonding between some CH3 groups and the oxygen from the
bridged acetates. Nevertheless, in the polymeric compounds the
C-O bonds lengths are very similar (2.30-2.42 Å) except one (2.86
Å) from the 322 coordination mode.
In summary, IR can be used to distinguish between the two
different complexes via the stretching signals of the C-O and CH3
functions. The differences between the bands can be correlated
to the bond lengths and coordination modes as observed from the
SCXRD analyses.
Figure 4. Polymeric chain [{Nd2(OAc)7}n]– in the crystal structure of
[C2mim]n[{Nd2(OAc)7}n]. Coordination modes are indicated according to Figure
1.
Among the published Nd acetates, [C2mim]n[{Nd2(OAc)7}n] is
structurally
closer
to
the
acetate
hemihydrate
Nd(OAc)3•0.5H2O[15a] or the Pr acetate monohydrate[16] than to the
anhydrous Nd(OAc)3.[15b] The two former exhibits a linear
polymeric chain with similar acetate coordination modes – only
322 and 222. Both crystallographically independent Ln
positions in Nd(OAc)3•0.5H2O and Pr(OAc)3•H2O are nine-
coordinated in the form of distorted tricapped trigonal prisms.
Nd(OAc)3 crystallizes with ten independent Nd positions and in
addition to 322 introduces two new coordination modes −
332 (6) and 432 (7). The Nd positions are mostly 9-
coordinated with coordination polyhedra that are significantly
more irregular capped trigonal prisms. Polymeric chains are also
present in the structure, but due to additional Nd(OAc)n groups,
with the new coordination modes 332 and 432, they merge
into layers.
Thermal Properties
To elucidate the thermal properties of the two structure series,
differential scanning thermograms of the two representatives for
the two series, [C2mim]2[Er2(OAc)8], and [C2mim]n[{Gd2(OAc)7}n],
were recorded. Upon heating [C2mim]n[{Gd2(OAc)7}n] (Figure 5,
top) two clear endothermic phase transitions close to each other
can be observed. The first transition starts at 180.2 °C, followed
by a second at 188.5 °C. Polarized optical microscopy (POM)
indicated a transition of the crystalline solid to a higher order
mesophase (Figure S17) before melting into an isotropic liquid.
During the cooling, vitrification can be observed around 33 °C.
This reversible process occurs around 35 °C during the second
heating. The compound recrystallized upon heating at 86.5 °C (a
small feature of this recrystallization process can be even
detected in the first heating cycle) and yielded to the mesophase
at 179.4 °C, becoming an isotropic liquid at 187.8 °C. Noteworthy,
the second heating shows a slightly better separation between the
phase transitions from solid to liquid. Indicating that repeated
heating and cooling cycle help to enhance crystallinity. All
subsequent heating and cooling cycles are fully reproducible.
The reversible cold crystallization and melting of coordination
polymers upon heating is well known among halometallate[21] and
other organometallic ILs.[5h,22] The metal coordination
environment and complex formation in such systems can vary
under different conditions of temperature and pressure even
when the composition is held constant.[23] Anhydrous imidazolium
salts of [Ln(OAc)5]2- ions had not been reported to crystallize
under the conditions explored here.[3] The unpredictable nature of
polymeric metal containing ILs along with the highly flexible
coordination chemistry of the chosen anion ([OAc]–) along with
some unreported experimental data strongly imply the existence
of yet more undiscovered complexes in the [Cnmim][OAc]/Ln3+
systems, which we hope to continue to explore..
Among the related polymeric Ln acetates an even more complex
connectivity has been observed in catena-(4-acetato)-(3-
acetato)-bis(2-acetato)-aqua-di-europium(II)[17]
introducing
another coordination mode 542 (8) resulting in a denser
layered motif. It is also worth noting that the acetate anion may
offer plenty of other coordination modes, e.g., 442, 552 or
652, though they have so far not been observed in pure
lanthanide compounds.
Vibrational Spectroscopy
The different coordination modes also show in the infrared spectra
of
the
compounds.
[C2mim]2[Er2(OAc)8],
and
[C2mim]n[{Gd2(OAc)7}n], were chosen as representatives for each
of the two structure series.
Acetates have been intensively studied by vibrational
spectroscopy since the 1950s.[18] Conveniently, sodium acetate
was used as a standard for the comparison of acetates. It is
known to show two significant peaks at 1440 (CH3 deformation)
and 1578 (C-O stretching) cm-1.[19] IR data for the IL [C2mim][OAc]
shows the values of the two peaks of the anion be shifted to 1377
(CH3 deformation) and 1560 (C-O stretching) cm-1 (Figure S13).
IR spectra of the dimeric and polymeric compounds reveal the
inequivalency of the acetate oxygen atoms. In the dimeric
5
This article is protected by copyright. All rights reserved.

10.1002/chem.202100141
Chemistry - A European Journal
FULL PAPER
The DSC trace of the first heating of the dimeric compound
connectivity. This might also be the reason, why the polymeric
compound features a mesophase, while the coordination dimer
displays only a second crystalline phase.
[C2mim]2[Er2(OAc)8] (Figure 5, bottom) shows
a
broad
endothermic event between 60 °C to 130 °C which is attributed to
the loss of residual acetonitrile. A broad signal at 146.4 °C
indicated a melting from solid to isotropic liquid. Upon cooling a
vitrification can be observed around 0 °C. The devitrification
occurred around 3.5 °C during subsequent heating. A cold
recrystallization was observed at 43.4 °C followed by a solid-solid
phase transition at 76.6 °C. This seems to indicate that the
compound could have another structural conformation. However
it has not been possible to determine it. The compound started to
melt at 153.4 °C again with the event extending over several
degrees. The second cooling was similar to the previous one with
again only one vitrification around 0 °C, and the subsequent third
heating cycle was similar to the second.
Conclusion
In summary, we developed a straightforward synthetic route,
based on ionic liquids, towards two anhydrous lanthanide acetate
series from their corresponding metal salt hydrates, polymeric
[C2mim]n[{Ln2(OAc)7}n] and dimeric [C2mim]2[Ln2(OAc)8]. PXRD
data indicated that for IL:Ln-salt ratios of 5:1, for the heavier
lanthanides, i.e. Ln = Dy–Lu, the formation of [C2mim]2[Ln2(OAc)8]
is preferred, whilst for the lighter lanthanides Ln = Nd, Sm, Gd
polymeric [C2mim]n[{Ln2(OAc)7}n] is exhibited. The crossover of
structural preference is found at Ln = Eu and Tb, where both
structures are found. Under the same conditions for La and Pr,
only Ln(OAc)3(H2O) was isolated. From this one could conclude,
that the larger the lanthanide ion is, the higher the tendency to
form the lanthanide acetate hydrate. When reducing the IL:Ln-salt
ratio to 3:1, even for Ln = Pr, Nd, and Sm, Ln(OAc)3(H2O) forms.
When a higher IL:Ln-salt ratio of 10:1 is employed, even for Ln =
Pr, Nd and Sm, the formation of the dimeric structure is observed.
Thus, it appears that a large (e.g. 10-fold) excess of IL the
formation of the dimer [C2mim]2[Ln2(OAc)8] is favoured for all
lanthanides, regardless of their size. This appears to be plausible,
as the IL:Ln-salt ratio is higher in [C2mim]2[Ln2(OAc)8] (which
corresponds to 1:1 of [C2mim][OAc]•Ln(OAc)3) than in
[C2mim]n[{Ln2(OAc)7}n] (which just has a 1:2 ratio according to its
composition 0.5[C2mim][OAc]•Ln(OAc)3)). For La, the use of an IL
with a bulkier cation, i.e. [C2C2im]2[OAc] allowed access the dimer
[C2C2im]2[La2(OAc)8], even from aqueous solution.
Both the dimeric and polymeric structures reveal the same
acetate coordination modes, namely 322, 22, and 222,
though with slightly different proportion. The dimeric complexes
show low lanthanide size selectivity, though the largest in the
series, La, could be crystallized isostructurally only with a larger
cation. On the other hand, the acetate anion has been found to
be very “creative,” offering extended variety of connectivities with
the lanthanide cations and, as a result, multiple formations with
the same metal enhancing our interest for further investigations.
The formation of the different complexes with their different
coordination modes can be easily identified through IR
spectroscopy according to the different stretching modes of the
C-O and CH3 groups. The thermal properties of both compound
series can be related well to their structural features. As expected,
due to the higher degree of condensation, i.e. connectivity, the
compounds with polymeric structure melt higher (about 50 °C)
than the dimeric ones. For both compounds, before melting the
formation of another form is observed. In case of the dimeric
material, this is a second solid crystalline phase, whilst in case of
the polymeric structure polarizing optical microscopy reveals the
formation of a mesophase.
The straightforward methodology established in this work has
allowed the formation of extremely rare dimeric [Ln2(OAc)8]2- units
with a large number of lanthanides which could lead to potential
applications depending on the Ln used (magnetism, optical
properties, etc.). Moreover some reactions generated either
undiscovered phases from the thermal behavior or some
undetermined compounds as minority phases observed in PXRD.
Taking into account the simplicity of the ligand combined with a
Figure 5. (Top) DSC thermograms of [C2mim]n[Gd2(OAc)7]n and (Bottom)
[C2mim]2[Er2(OAc)8].
The dimer melts about 50 °C before the polymer. This can be
attributed on the one hand to the lower degree of condensation,
i.e. less polymeric character of the dimer, but also to reduced
6
This article is protected by copyright. All rights reserved.

10.1002/chem.202100141
Chemistry - A European Journal
FULL PAPER
La(OAc)3(H2O). White solid. FTIR (ʋ (cm-1)): 3262, 1601, 1523, 1402, 1335,
1052, 1015, 942, 663, 614, 465, 419.
huge variety of coordination modes it can deliver, the IL/Ln-
acetate systems still lack deeper understanding and represent a
considerable interest in terms of designed synthesis of specific
anhydrous lanthanide complexes. There is obviously much room
left to explore.
Pr(OAc)3(H2O). Light green solid. FTIR (ʋ (cm-1)): 3273, 1682, 1531, 1395,
1341, 1170, 1052, 1024, 1007, 956, 943, 748, 670, 642, 610, 502, 477,
421.
[C2mim]n[{Nd2(OAc)7}n]. White solid. FTIR (ʋ (cm-1)): 3148, 3119, 3090,
3079, 2987, 2929, 1634, 1569, 1391, 1335, 1254, 1167, 1121, 1090, 1048,
1015, 940, 867, 808, 774, 646, 620, 500. ESI TOF m/z (negative mode)
700.4110 (calculated m/z = 700.9145).
Experimental Section
Syntheses
[C2mim]n[{Sm2(OAc)7}n]. White solid. FTIR (ʋ (cm-1)): 3142, 3117, 3098,
3079, 2975, 2931, 1609, 1554, 1402, 1336, 1247, 1166, 1118, 1086, 1047,
1013, 942, 869, 808, 775, 641, 666, 611, 489. ESI TOF m/z (negative
mode) 718.6951 (calculated m/z = 718.9356).
1-Methylimidazole (98%, Alfa Aesar, Karlsruhe, Germany) and 1-
ethylimidazole (> 98%, Tokyo Chemical Industry, Tokyo, Japan) were
distilled over KOH before use. Lanthanide chloride hydrates were obtained
from the reaction between Ln2O3 (HEFA Rare Earth Canada Co. Ltd,
Richmond, British Columbia, Canada) and HCl (37%, VWR Chemicals,
Fontenay-sous-Bois, France). Ethyl bromide (98%, Alfa Aesar, Karlsruhe,
Germany) and sodium acetate (99%, Alfa Aesar, Karlsruhe, Germany)
were used as received. All solvents were ‘solvent grade’ and used as
received without additional purification.
[C2mim]n[{Eu2(OAc)7}n] and [C2mim]2[Eu2(OAc)8] (mixture). White solid.
FTIR (ʋ (cm-1)): 3380, 3143, 3093, 2999, 2984, 2943, 1605, 1565, 1432,
1404, 1335, 1300, 1249, 1160, 1095, 1045, 1015, 953, 932, 868, 787, 680,
666, 642, 626, 613, 504, 469. [C2mim]n[{Eu2(OAc)7}n] ESI TOF m/z
(negative
mode)
716.6241
(calculated
m/z
=
716.9348).
Synthesis of [C2Cnim][Br]
[C2mim]2[Eu2(OAc)8] ESI TOF m/z (negative mode) 387.6951 (calculated
m/z = 387.9743).
In a flask under argon were introduced 1-alkylimidazole (50 mmol, 1.0 eq.),
ethyl bromide (55 mmol, 1.1 eq.) and acetonitrile (5 mL). The mixture was
heated under reflux for three days. After cooling to room temperature the
solution was washed with ethyl acetate and put in a cold bath (-78 °C) to
allow the crystallization of the product. The white precipitate was washed
several times and then dried under vacuum at room temperature.
[C2mim]n[{Gd2(OAc)7}n]. White solid. FTIR (ʋ (cm-1)): 3143, 3093, 2984,
1606, 1566, 1434, 1405, 1336, 1300, 1161, 1095, 1045, 1016, 954, 933,
868, 787, 667, 651, 643, 626, 613, 505, 469. ESI TOF m/z (negative mode)
730.6341 (calculated m/z = 730.9448).
[C2mim]n[{Tb2(OAc)7}n] and [C2mim]2[Tb2(OAc)8] (mixture). Brown solid.
FTIR (ʋ (cm-1)): 3550, 3526, 3360, 3150, 3109, 2994, 2932, 1643, 1590,
1543, 1407, 1351, 1338, 1162, 1099, 1054, 1018, 949, 939, 861, 787, 742,
691, 668, 643, 615, 506, 484, 468, 453, 425. [C2mim]n[{Tb2(OAc)7}n] ESI
TOF m/z (negative mode) 730.6166 (calculated m/z = 730.9444).
[C2mim]2[Tb2(OAc)8] ESI TOF m/z (negative mode) 394.6952 (calculated
m/z = 394.9791).
[C2mim][Br] FTIR (ʋ (cm-1)): 3422, 3136, 3065, 3027, 2975, 2866, 2822,
1770, 1731, 1670, 1571, 1519, 1467, 1446, 1423, 1386, 1366, 1340, 1302,
1251, 1171, 1110, 1093, 1032, 957, 909, 865, 789, 704, 665, 649, 621,
599, 418.
[C2C2im][Br] FTIR (ʋ (cm-1)): 3129, 3056, 2976, 2938, 2796, 2730, 2608,
1563, 1544, 1447, 1408, 1384, 1347, 1295, 1247, 1165, 1122, 1087, 1028,
956, 821, 802, 755, 688, 625, 592.
[C2mim]2[Dy2(OAc)8]. White solid. FTIR (ʋ (cm-1)): 3546, 3372, 3238, 3150,
3109, 3002, 2933, 1592, 1544, 1408, 1351, 1162, 1099, 1053, 1018, 950,
940, 900, 861, 788, 692, 669, 644, 616, 508, 470, 441, 428, 417. ESI TOF
m/z (negative mode) 398.6946 (calculated m/z = 398.9817).
Synthesis of [C2Cnim][OAc]
[C2Cnim][Br] (50 mmol, 1.0 eq) and sodium acetate (4.10 g, 50 mmol, 1.0
eq.) were dissolved in acetone (50 mL) in a round bottom flask. The
mixture was stirred overnight then filtrated. The filtrate was evaporated
under reduced pressure to yield to a colorless oil.
[C2mim]2[Ho2(OAc)8]. Light pink solid. FTIR (ʋ (cm-1)): 3142, 3092, 3002,
2985, 2945, 1609, 1568, 1435, 1406, 1347, 1335, 1301, 1248, 1161, 1095,
1045, 1015, 957, 934, 871, 808, 788, 751, 682, 668, 644, 607, 508, 466.
ESI TOF m/z (negative mode) 400.7019 (calculated m/z = 400.9841).
[C2mim][OAc] FTIR (ʋ (cm-1)): 3139, 2975, 3030, 2866, 2748, 1560, 1451,
1427, 1377, 1328, 1256, 1174, 1090, 1002, 1034, 958, 899, 804, 702, 599,
454.
[C2mim]2[Er2(OAc)8]. Light pink solid. FTIR (ʋ (cm-1)): 3385, 3143, 3092,
2985, 1608, 1566, 1404, 1335, 1301, 1249, 1161, 1094, 1045, 1016, 958,
934, 871, 789, 682, 668, 645, 614, 509, 469, 426. ESI TOF m/z (negative
mode) 402.6986 (calculated m/z = 402.9851).
[C2C2im][OAc] FTIR (ʋ (cm-1)): 3422, 3136, 3064, 2978, 2933, 1562, 1410,
1165, 1123, 1090, 1045, 1009, 956, 921, 830, 802, 760, 688, 642, 622,
527, 461.
[C2mim]2[Tm2(OAc)8]. White solid. FTIR (ʋ (cm-1)): 3396, 3154, 3118, 2993,
1560, 1400, 1347, 1169, 1048, 1016, 981, 963, 945, 905, 867, 845, 670,
652, 617, 516, 496, 471. ESI TOF m/z (negative mode) 404.6964
(calculated m/z = 404.9880).
General procedure for the synthesis of anhydrous lanthanide compounds
In a round-bottom flask were introduced LnCl3•xH2O (x = 6 or 7) (1.0 mmol,
1.0 eq) and [C2mim][OAc] (850 mg, 5.0 mmol, 5.0 eq). The mixture was
heated at 100 °C under stirring overnight. The flask was then transferred
to a pre-heated oven at 100 °C. A program was run to slowly decrease the
temperature (1 °C/h) to 25 °C to allow a better crystallization of the final
products. The final complexes have been obtained with yields 80 % and
higher.
[C2mim]2[Yb2(OAc)8]. White solid. FTIR (ʋ (cm-1)): 3388, 3153, 3090, 2995,
1618, 1570, 1404, 1345, 1299, 1249, 1169, 1097, 1047, 1018, 959, 930,
878, 793, 687, 671, 643, 618, 512, 474, 425. ESI TOF m/z (negative mode)
409.0997 (calculated m/z = 409.4923).
[C2mim]2[Lu2(OAc)8]. White solid. FTIR (ʋ (cm-1)): 3384, 1638, 1540, 1453,
1412, 1169, 1049, 1022, 957, 839, 759, 688, 642, 613, 509. ESI TOF m/z
(negative mode) 410.6987 (calculated m/z = 410.9945).
7
This article is protected by copyright. All rights reserved.

10.1002/chem.202100141
Chemistry - A European Journal
FULL PAPER
Compounds obtained with a 3:1 (IL/Ln-ratio)
samples were cooled to -60 °C. Given temperatures correspond to the
onset.
Nd(OAc)3(H2O). Light purple solid. FTIR (ʋ (cm-1)): 3276, 1682, 1598, 1528,
1395, 1341, 1052, 1024, 1006, 956, 942, 863, 744, 670, 642, 609, 571,
504, 477.
A SYNAPT G2-S HDMS Q-ToF Mass Spectrometer (Waters, Manchester,
United Kingdom) with an electrospray ionization (ESI) operated in the
positive and negative ion mode, was used in this study. The ion source
was set up as follows: capillary voltage: 2500 V, extractor: 1.0 V, RF lens:
0.5 V, ion source temperature: 120 °C and desolvation temperature 250 °C.
Nitrogen was used as both the cone and desolvation gas at a flow of 70
L/h and 500 L/h, respectively. Argon was used as a collision gas at a
pressure of 2.95⋅10–4 mbar.
Sm(OAc)3(H2O). White solid. FTIR (ʋ (cm-1)): 3336, 1705, 1531, 1415,
1263, 1051, 1018, 951, 674, 643, 612, 501, 464.
Compounds obtained with a 10:1 (IL/Ln-ratio)
[C2mim]2[Pr2(OAc)8]. Light green solid. ESI TOF m/z (negative mode)
376.6848 (calculated m/z = 376.9609).
The infrared spectroscopy (IR) was conducted with a Bruker Alpha-P ATR-
spectrometer (Bruker AXS, Karlsruhe, Germany) in attenuated total
reflection configuration in the range of 4000–400 cm–1. The data evaluation
was carried out with the program OPUS (Bruker, Ettlingen, Germany).
[C2mim]2[Nd2(OAc)8]. Light purple solid. ESI TOF m/z (negative mode)
378.6852 (calculated m/z = 378.9627).
Optical analyses were made by heated-stage polarized optical microscopy
(POM) with an Axio Imager A1 microscope (Carl Zeiss Micro Imaging
GmbH, Göttingen, Germany) equipped with a hot stage, THMS600
(Linkam Scientific Instruments Ltd, Surrey, United Kingdom), and Linkam
TMS 94 temperature controller (Linkam Scientific Instruments Ltd, Surrey,
United Kingdom). Images were recorded at a magnification of 100× as a
video with a digital camera. During heating and cooling, the sample was
placed between two cover slips. Heating and cooling rates were 10 °C/min
[C2mim]2[Sm2(OAc)8]. White solid. FTIR (ʋ (cm-1)): 3144, 3094, 2999, 2984,
2931, 1602, 1564, 1430, 1404, 1336, 1300, 1249, 1160, 1095, 1045, 1015,
951, 930, 866, 786, 679, 665, 641, 626, 613, 502, 469, 429. ESI TOF m/z
(negative mode) 388.6932 (calculated m/z = 388.9747).
General procedure for the synthesis of [C2C2im][La2(OAc)8]
In a round-bottom flask were introduced LaCl3•7H2O (371 mg, 1.0 mmol,
1 eq), [C2C2im][OAc] (1.840 g, 10 mmol, 10 eq), and water (5 mL). The
mixture was heated at 100 °C under stirring overnight. The flask was then
transferred to a pre-heated oven at 100 °C. A program was run to slowly
decrease the temperature (1 °C/h) to allow a better crystallization of the
final product.
ORCID
Guillaume Bousrez: 0000-0002-0265-7431
Olivier Renier: 0000-0002-1227-547X
Steven P. Kelley: 0000-0001-6755-4495
Brando Adranno: 0000-0001-6221-4109
Elnaz Tahavori: 0000-0002-4753-5462
Volodymyr Smetana: 0000-0003-0763-1457
Hatem M. Titi: 0000-0002-0654-1292
Si-Fu Tang: 0000-0002-7151-9876
Anja-Verena Mudring: 0000-0002-2800-1684
Robin D. Rogers: 0000-0001-9843-7494
Instrumentation
PXRD data were recorded at ambient temperature on a PANalytical X’pert
PRO diffractometer (Malvern Panalytical, Malvern, United Kingdom),
operating at 45 kV and 40 mA and using Cu Kα1 radiation. The data were
recorded in reflection mode from 5° to 70° with a step size of 0.01° for 60
min.
The data for single crystal analysis at Stockholm University were collected
on a Bruker Venture diffractometer (Bruker AXS, Karlsruhe, Germany)
using Cu Kα radiation (λ = 1.54178 Å at 297 K) at room temperature or at
low temperature (100 K). The crystal structures were solved and refined
using SHELXT and SHELXL subroutines within the APEX3 software
package.[24] Absorption corrections were carried out with the program
SADABS. Hydrogen atoms for all structures were assigned geometrically
using a riding atom model. To illustrate the crystal structures, the program
Diamond 3 (CrystalImpact, Bonn, Germany) was used.[25]
The crystal structural measurements at The University of Alabama were
carried out on a Bruker SMART APEX II CCD diffractometer (Mo Kα
radiation; λ = 0.71073 Å) at 100 K. The intensity data of the reflections and
scaling were integrated using SAINT within the APEX3 software
package.[26] SADABS[27] was used for the absorption corrections. The
crystal structure solution was performed by direct methods using
SHELXT.[28] SHELXL-97[26] and SHELXL-2013[24c] were used for
subsequent difference Fourier analyses and least-squares refinement. All
non-hydrogen atoms were refined anisotropically, whereas hydrogen
atoms were assigned geometrically using a riding atom model.
Acknowledgements
This research was supported, in part, by the Royal Swedish
Academy of Science through the Göran Gustafsson prize to A.-
V.M., by the Swedish Research Council (Vetenskapsrådet, VR)
through Grant 2020-05405 (A.-V.M.), by a Tage Erlander Guest
Professorship to R.D.R. (VR Grant 2018-00233), and by U.S.
Department of Energy, Office of Science, Office of Basic Energy
Sciences, Heavy Elements program under Award DE-
SC0019220 (to R.D.R.). S.-F.T. acknowledges financial support
from the Qingdao Science and Technology Program (19-6-1-43
nsh).
Differential scanning calorimetry (DSC) was performed with a computer-
controlled PhoenixDSC 204 F1 thermal analyzer (Netzsch, Selb,
Germany). Measurements were carried out at a heating rate of 5 °C/min
from -60 °C to 210 °C in sealed aluminum crucible with a nitrogen flow rate
of 40 mL/min. The samples were placed in aluminum pans which were
cold-sealed and punctured. Before recording the DSC thermogram the
8
This article is protected by copyright. All rights reserved.

10.1002/chem.202100141
Chemistry - A European Journal
FULL PAPER
[22] A.-V. Mudring, Aust. J. Chem. 2010, 63, 544-564.
Keywords: Anhydrous lanthanide complexes • Dimer • Polymer
• 1-Ethyl-3-methylimidazolium acetate
[23] J. Estager, J. D. Holbrey, M. Swadzba-Kwasny, Chem. Soc. Rev. 2014,
43, 847-886.
[24] a) Bruker, 2015; b) G. M. Sheldrick, Acta Crystallogr., Sect. A 2015, 71,
3-8; c) G. M. Sheldrick, Acta Crystallogr., Sect. C 2015, 71, 3-8.
[25] K. Brandenburg, H. Putz, Crystal Impact GbR, Bonn, Germany 2011.
[26] G. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr 2008, 64,
112-122.
[1]
a) S. Bette, J. Stelzner, G. Eggert, T. Schleid, G. Matveeva, U. Kolb, R.
E. Dinnebier, Angew. Chem. Int. Ed. 2020, 59, 9438-9442; b) U. Kumar,
J. Thomas, N. Thirupathi, Inorg. Chem. 2010, 49, 62-72.
[2]
[3]
V. Smetana, S. P. Kelley, H. M. Titi, X. Hou, S.-F. Tang, A.-V. Mudring,
R. D. Rogers, Inorg. Chem. 2020, 59, 818-828.
[27] L. Krause, R. Herbst-Irmer, D. Stalke, J. Appl. Crystallogr. 2015, 48,
1907-1913.
a) G. G. Sadikov, G. A. Kukina, M. A. Porai-Koshits, L. A. Pospelova, J.
Struct. Chem. 1968, 9, 128-129; b) G. Meyer, D. Gieseke-Vollmer, Z.
Anorg. Allg. Chem. 1993, 619, 1603-1608; c) C. J. Kepert, L. Wei-Min, P.
C. Junk, B. W. Skelton, A. H. White, Aust. J. Chem. 1999, 52, 437-458.
a) S. P. Kelley, V. Smetana, S. D. Emerson, A.-V. Mudring, R. D. Rogers,
Chem. Commun. 2020, 56, 4232-4235; b) S.-F. Tang, V. Smetana, M. K.
Mishra, S. P. Kelley, O. Renier, R. D. Rogers, A.-V. Mudring, Inorg.
Chem. 2020, 59, 7227-7237; c) D. Yaprak, E. T. Spielberg, T. Bäcker, M.
Richter, B. Mallick, A. Klein, A.-V. Mudring, Chem. Eur. J. 2014, 20,
4704-4712
[28] G. M. Sheldrick, Acta Crystallogr., Sect. A 2015, 71, 3-8.
[4]
[5]
a) D. Prodius, A.-V. Mudring, in Handbook on the Physics and Chemistry
of Rare Earths, Vol. 50 (Eds.: J.-C. G. Bünzli, V. K. Pecharsky), Elsevier,
2016, pp. 395-420; b) A. Babai, A.-V. Mudring, Chem. Mater. 2005, 17,
6230-6238; c) A. Babai, S. Pitula, A. V. Mudring, Eur. J. Inorg. Chem.
2010, 2010, 4933-4937; d) A. Babai, A.-V. Mudring, Inorg. Chem. 2006,
45, 3249-3255; e) A. Babai, A.-V. Mudring, Dalton Trans. 2006, 1828-
1830; f) S.-F. Tang, A.-V. Mudring, Cryst. Growth Des. 2009, 9, 2549-
2551; g) S. Tang, A.-V. Mudring, Cryst. Growth Des. 2011, 11, 1437-
1440; h) E. T. Spielberg, E. Edengeiser, B. Mallick, M. Havenith, A.-V.
Mudring, Chem. Eur. J. 2014, 20, 5338-5345.
[6]
[7]
a) B. Mallick, B. Balke, C. Felser, A. V. Mudring, Angew. Chem. Int. Ed.
2008, 47, 7635-7638; b) A. Getsis, A. V. Mudring, Z. Anorg. Allg. Chem.
2010, 636, 1726-1734; c) S. Tang, A. Babai, A.-V. Mudring, Angew.
Chem. Int. Ed. 2008, 47, 7631-7634; d) B. Mallick, B. Balke, C. Felser,
A.-V. Mudring, Angew. Chem. Int. Ed. 2008, 47, 7635-7638.
a) A. S. Chesman, M. Yang, N. D. Spiccia, G. B. Deacon, S. R. Batten,
A. V. Mudring, Chem. Eur. J. 2012, 18, 9580-9589; b) A. S. Chesman, M.
Yang, B. Mallick, T. M. Ross, I. A. Gass, G. B. Deacon, S. R. Batten, A.-
V. Mudring, Chem. Commun. 2012, 48, 124-126.
[8]
[9]
C. C. Hines, D. B. Cordes, S. T. Griffin, S. I. Watts, V. A. Cocalia, R. D.
Rogers, New J. Chem. 2008, 32, 872-877.
S. Cotton, Lanthanide and Actinide Chemistry, John Wiley & Sons,
Chichester, 2013.
[10] a) G. Lorusso, O. Roubeau, M. Evangelisti, Angew. Chem. Int. Ed. 2016,
55, 3360-3363; b) M. Evangelisti, O. Roubeau, E. Palacios, A. Camón,
T. N. Hooper, E. K. Brechin, J. J. Alonso, Angew. Chem. Int. Ed. 2011,
50, 6606-6609.
[11] P. H. Smith, R. R. Ryan, Acta Crystallogr., Sect. C 1992, 48, 2127-2130.
[12] H. Sawase, Y. Koizumi, Y. Suzuki, M. Shimoi, A. Ouchi, Bull. Chem. Soc.
Jpn. 1984, 57, 2730-2737.
[13] a) B. V. Bukvetskii, I. V. Kalinovskaya, Russ. J. Inorg. Chem. 2011, 56,
721-725; b) A. M. Atria, M. T. Garland, R. Baggio, Acta Crystallogr., Sect.
C 2012, 68, m185-m188.
[14] a) R. Vaďura, J. Kvapil, Mater. Res. Bull. 1971, 6, 865-873; b) B. Barja,
R. Baggio, M. T. Garland, P. F. Aramendia, O. Peña, M. Perec, Inorg.
Chim. Acta 2003, 346, 187-196; c) J. W. Bats, R. Kalus, H. Fuess, Acta
Crystallogr., Sect. B 1979, 35, 1225-1227; d) C. J. Kepert, L. Wei-Min, P.
C. Junk, B. W. Skelton, A. H. White, Aust. J. Chem. 1999, 52, 437-458;
e) L. Cañadillas-Delgado, O. Fabelo, J. Cano, J. Pasán, F. S. Delgado,
F. Lloret, M. Julve, C. Ruiz-Pérez, CrystEngComm 2009, 11, 2131-2142.
[15] a) S. Gomez Torres, Thesis, Köln, Germany, 2007; b) S. Gomez Torres,
G. Meyer, Z. Anorg. Allg. Chem. 2008, 634, 231-233.
[16] S. Ganapathy, V. P. Chacko, R. G. Bryant, M. C. Etter, J. Am. Chem.
Soc. 1986, 108, 3159-3165.
[17] P. Starynowicz, J. Alloys Compd. 1998, 268, 47-49.
[18] K. Ito, H. J. Bernstein, Can. J. Chem. 1956, 34, 170-178.
[19] L. H. Jones, E. McLaren, J. Chem. Phys. 1954, 22, 1796-1800.
[20] D. G. Karraker, J. Inorg. Nucl. Chem. 1969, 31, 2815-2832.
[21] B. Mallick, A. Metlen, M. Nieuwenhuyzen, R. D. Rogers, A.-V. Mudring,
Inorg. Chem. 2012, 51, 193-200.
9
This article is protected by copyright. All rights reserved.

10.1002/chem.202100141
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents
We describe a straightforward pathway to synthesize anhydrous lanthanide acetate complexes from lanthanide chloride hydrates and
the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]). The combination of the lanthanide size and the amount of IL
introduced allows the selective formation of two isostructural crystalline anhydrous compound the dimeric, [C2mim]2[Ln2(OAc)8], and
the polymeric, [C2mim]n[{Ln2(OAc)7}n].
10
This article is protected by copyright. All rights reserved.