Octahedral Hexachloro Environment of Dy3+ with Slow Magnetic Relaxation and Luminescent Properties

Article abstract of DOI:10.1002/ejic.202100143

The compound [BiCNIm]₃[DyCl₆] was synthesized from a nitrile-functionalized imidazolium ionic liquid [BiCNIm][Cl] and DyCl₃ ? 6H₂O in acetonitrile using solvothermal conditions. Structural characterization reveals that the Dy³⁺ ions are in a quasi-regular octahedral environment, formed by six chloride anions. The magnetic study indicates that this mononuclear compound exhibits a Single Ion Magnet behaviour. This behaviour is compared to that of other mononuclear compounds containing Dy³⁺ ions in various octahedral environment.

Full text of DOI:10.1002/ejic.202100143

Full Papers
doi.org/10.1002/ejic.202100143
Octahedral Hexachloro Environment of Dy3+ with Slow
Magnetic Relaxation and Luminescent Properties
Nesrine Benamara,[a, b] Mayoro Diop,[a] Cédric Leuvrey,[a] Marc Lenertz,[a] Pierre Gilliot,[a]
Mathieu Gallart,[a] Hélène Bolvin,[c] Fatima Setifi,[b] Guillaume Rogez,[a] Pierre Rabu,[a] and
Emilie Delahaye*[a, d]
The compound [BiCNIm]3[DyCl6] was synthesized from a nitrile-
functionalized imidazolium ionic liquid [BiCNIm][Cl] and
DyCl3 ·6H2O in acetonitrile using solvothermal conditions.
Structural characterization reveals that the Dy3+ ions are in a
quasi-regular octahedral environment, formed by six chloride
anions. The magnetic study indicates that this mononuclear
compound exhibits a Single Ion Magnet behaviour. This
behaviour is compared to that of other mononuclear com-
pounds containing Dy3+ ions in various octahedral environ-
ment.
Introduction
anisotropy, also called Single Ion Magnet (SIM), has been
explored. In particular, the pioneering works on bis
(phthalocyaninato)-lanthanide complexes have largely contrib-
uted to the success of this approach.[25,26] Since then, different
ligands were synthesized to tailor the coordination sphere
around the lanthanide ion, giving the possibility to establish
magneto-structural correlations, especially concerning the sym-
metries of the ligand field around the magnetic centre (C1, D5h,
D4d, C3v….).[27–34] Nevertheless, difficulties to reach certain
symmetries remain, principally related to the fact that lantha-
nide ions tends to present high coordination numbers.
Regarding SIMs, only few examples of mononuclear compounds
containing lanthanide ions in octahedral environment were
reported.[35–45]
Possibility to achieve unusual coordination environments
for Ln3+ ions was observed with the use of Ionic Liquids (ILs).[46]
In particular, the formation and stabilization of octahedral
entities of formula [LnCl6]3À in the solid state was described
using phosphonium or alkyl imidazolium ILs with Ln chloride
salts.[47–49] However, no information on possible slow relaxation
of the magnetization was reported for these compounds.
This article describes the synthesis and the characterization
of the compound [BiCNIm]3[DyCl6] obtained in solvothermal
conditions by reacting DyCl3 ·6H2O with the 1,3-bis
((cyanomethyl)imidazolium) chloride IL [BiCNIm][Cl]. [BiC-
NIm]3[DyCl6] is constituted of quasi-regular octahedral [DyCl6]3À
entities surrounded by imidazolium cations [BiCNIm]+. The
magnetic properties have been analyzed evidencing a SIM
behaviour for the Dy3+ ions in this environment. The detailed
analysis of the properties suggests a combination of Raman,
Orbach and Quantum Tunneling (QTM) relaxation mechanisms.
Luminescent properties at room temperature for this com-
pound are also reported.
Since the pioneering works on [Mn12O12(CH3CO2)16(H2O)4],[1]
different synthetic strategies have been elaborated to obtain
compounds with efficient Single Molecule Magnet (SMM)
behaviours, i.e. usable as ultra-small magnetic bit for high-
density data storage, integrated component for spintronics or
Qbits for quantum applications.[2–11] The use of SMM for such
applications is strongly hampered by the low temperature
necessary for stabilizing the SMM state[7] as well as low chemical
stability, especially when integrated onto surfaces,[12–15] or dis-
entanglement/decoherence problem.[16–19] Many efforts have
initially concerned the elaboration of molecular compounds of
high nuclearity to maximize the total spin moment of the
system, combined with high anisotropy barrier. Despite many
interesting achievements,[20–24] the approach was much limited
due to the difficulty for maintaining the local anisotropy of
each magnetic centre in a particular direction and fully
controlling the magnetic exchange pathways within the
polynuclear entities. More recently, the possibility to build
SMMs involving only one magnetic ion exhibiting high
[a] Dr. N. Benamara, Dr. M. Diop, C. Leuvrey, Dr. M. Lenertz, Dr. P. Gilliot,
Dr. M. Gallart, Dr. G. Rogez, Dr. P. Rabu, Dr. E. Delahaye
Institut de Physique et Chimie des Matériaux de Strasbourg – UMR 7504
Université de Strasbourg and CNRS
67034 Strasbourg, France
E-mail: emilie.delahaye@lcc-toulouse.fr
[b] Dr. N. Benamara, Dr. F. Setifi
Laboratoire de Chimie, Ingénierie Moléculaire et Nanostructures
Université Ferhat Abbas Sétif 1
Sétif 19000, Algeria
[c] Dr. H. Bolvin
Laboratoire de Chimie et de Physique Quantiques
Université de Toulouse and CNRS
31062 Toulouse, France
[d] Dr. E. Delahaye
Laboratoire de Chimie de Coordination
Université de Toulouse and CNRS
31077 Toulouse, France
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Nesrine Benamara earned her master
1
of environmental
Hélène Bolvin earned her M.Sc. degree in Chemistry from ENS
Saint-Cloud-Lyon (France) and received her Ph.D. degree in 1993
from Université Paris-Sud (France), under the supervision of Prof.
Olivier Kahn. She is senior CNRS researcher in Toulouse (France)
with subsequent positions in Tromsö (Norway) and Strasbourg
(France). Her research interests focus on the quantum chemistry
description of magnetic properties of f complexes.
chemistry in 2014 from the University of Setif (Algeria) and her
master 2 of analytical chemistry in 2015 from the University of
Strasbourg (France). In 2020, she obtained her PhD from the
University of Strasbourg (at the Institute of Physics and Chemistry
of Materials of Strasbourg) and the University of Setif (at the
Laboratoire de Chimie, Ingénierie Moléculaire et Nanostructure)
under the supervision of Dr. P. Rabu, Prof. F. Setifi and Dr. E.
Delahaye. During her PhD, she worked on the synthesis of new
magnetic and luminescent networks using functional ligands
based on imidazolium salts or triazole derivatives.
Guillaume Rogez graduated from Ecole Normale Supérieure de
Cachan in 1999. He obtained his PhD in 2002 from the University
of Paris-Sud Orsay (now Paris Saclay) under the supervision of Pr.
Talal Mallah, working in coordination chemistry and molecular
magnetism. He was then a post-doctoral fellow in the Departe-
ment of Chemistry of the University of Bologna, under the
supervision of Pr. Vincenzo Balzani, Pr. Alberto Credi and Pr. Maria-
Teresa Gandolfi, working on the photochemical properties of
supramolecular assemblies. He entered the CNRS in the Institute
of Physics and Chemistry of Materials of Strasbourg, working on
layered hybrid materials (hydroxides and oxides) and on their
controlled exfoliation for magnetic and optical applications, and
more recently for CO2 electroreduction.
Mayoro DIOP is titular Professor of Coordination, Analytical and
Environmental Chemistry at the University Cheikh Anta Diop of
Dakar (Senegal), General Inspector of Education and Training in
Physical Sciences and member of Division II Inorganic Chemistry
of the International Union of Pure and Applied Chemistry (IUPAC).
Fatima SETIFI graduated from the university of Constantine 1 in
Algeria and received her PhD from the university of Rennes1 in
France. Then, she held a Postdoctoral position at the University of
Brest in the field of switchable materials. She works currently as a
Professor at the university of Ferhat Abbas-Setif 1 in Algeria. Her
research work is mainly located in the field of molecular chemistry
including design and synthesis. It covers certain aspects of
material sciences, such as magnetic, switchable and luminescent
materials. She published more than 70 papers. Her h-index is 21
with more than 1061 citations.
Cédric Leuvrey has
a position of engineer on the MEB-Cro
plateform of the Institute of Physique and Chemistry of Materials
of Strasbourg since 2001 and works on the characterization of
materials by Scanning Electron Microscopy and EDX analysis.
Marc LENERTZ did his PhD at the Institute of Physique and
Chemistry of materials (IPCMS: University of Strasbourg – CNRS)
under the supervision of Silviu COLIS in the field of the structural
Pierre Rabu was born in Nantes, France, in 1964. He obtained his
PhD in solid state chemistry from the University of Nantes, France,
in 1990. He then became CNRS researcher at the Institute of
Physics and chemistry of Strasbourg, IPCMS, France, to work on
low-dimensional (LD) magnetic materials. He works in the Depart-
and magnetic properties of oxides thin films. Then he got
a
Postdoctoral position at the Laboratoire Léon Brillouin (LLB: CEA)
and was working on neutron diffraction. Since 2015, he got a
position as engineer and head of the X-Ray diffraction platform of
the IPCMS back in Strasbourg.
ment of Chemistry of Inorganic Materials, which is
a joint
department with the European School of Chemistry, Polymers and
Materials of Strasbourg (ECPM). He was short term research fellow
at Institute for Fundamental Organic Chemistry, Kyushu University,
Fukuoka, Japan, in 1996 and visiting fellow of Advanced Materials
Research Institute, University of New Orleans, USA, in 2001. He
received the 1998 prize of the Solid State Chemistry division of
the French Chemical Society. Since 2005, Pierre Rabu is director of
research and focuses his activities on the design of molecular,
inorganic or hybrid organic-inorganic solids, with
a special
Pierre Gilliot is “Research Director” at the CNRS. He was born in
1964. He obtained his Ph.D. at the Louis Pasteur University of
Strasbourg in 1989. From 1990 to 1991, he worked as a post-doc
in the group of Prof. Hartmut Haug at the Institut für Theoretische
Physik of the Frankfurt-am-Main University, in Germany. He
received his habilitation in 2003. Since 1992, he has been CNRS
researcher. He is the head of the team “Ultrafast spectroscopy of
semiconductors” at the “Institut de Physique et Chimie des
Matériaux de Strasbourg” UMR 7504 CNRS.
emphasis on synthesis, structure-properties relationships, model-
ling and analysis of the magnetic behaviour of LD systems. His
current activities involve especially layered materials, multifunc-
tional hybrid materials and magnetic, photo active, or chiral 3d or
4f metal-based inorganic structures. In 2005–2008, he was director
of the CNRS national group of research on Multifunctional Hybrid
Materials. Pierre Rabu was head of the Department of Chemistry
of Inorganic Materials (2014–2017) and is director of IPCMS since
2018.
Emilie Delahaye obtained her PhD in 2007 from the University of
Paris-Sud Orsay under the supervision of Pr. René Clément
working of the synthesis of nanoparticles exhibiting nonlinear
optical properties. From 2007 to 2012, she held various post-
doctoral fellows working first on the synthesis of multifunctional
lamellar compounds (at the Institute of Physics and Chemistry of
Materials of Strasbourg with Dr. G. Rogez and Dr. P. Rabu and
then to the Max Planck Institute of Mainz with Dr. A. Taubert and
Pr. J. Gütmann) and then on the synthesis of magnetic and
photomagnetic nanoparticles (at the University of Paris-Sud Orsay
with Pr. A. Bleuzen). In 2012, she obtained a CNRS position at
IPCMS and moved in 2018 to the Laboratory of Coordination
Chemistry in Toulouse. Since 2012, she works on the synthesis of
multiferroic coordination compounds (coordination networks and
molecular magnets).
Mathieu GALLART – 47 years old – UDS assistant professor. After a
Phd (1998–2001) dedicated to time resolved spectroscopy of
nitride quantum wells (Université Montpellier 2), M. Gallart worked
as postdoctoral researcher in Laboratoire de Photonique et
nanostructures (Marcoussis, UPR 20) where he studied single
photon sources. In 2002, he was appointed to the Université de
Strasbourg as an assistant professor. His field of expertise
addresses semiconductor ultra-fast spectroscopy including spin
and phase relaxation dynamics. The publications co-authored by
M. Gallart have been cited more than 1400 times; 21 of them have
been cited more than 21 time (h factor of 21 according to web of
science).
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Results and Discussion
The Continuous Shape Measures performed with the
software SHAPE[50] showed that the coordination sphere around
the Dy3+ ion is a quasi-regular octahedron (Table S2). The
DyÀ Cl distances range between 2.630(1) Å and 2.645(1) Å
(Figure 2 and Table S3). These values are similar to those
reported in related hexachloro compounds.[48] The four cis
angles Cl1À DyÀ Cl1i, Cl1iÀ DyÀ Cl3, Cl3À DyÀ Cl3i and Cl3iÀ DyÀ Cl1
Synthesis
[BiCNIm]3[DyCl6] has been synthesized in solvothermal con-
ditions by reacting one equivalent of DyCl3 ·6H2O with two
equivalents of the nitrile-functionalized IL [BiCNIm][Cl] in
acetonitrile at 363 K for 2 days. After cooling down to room
temperature, colorless crystals has been obtained.
It is worth to underline here that despite the final IL/Dy
stoichiometry of 3/1, only the use of 50% excess of Dy
(stoichiometry 2/1) provides the crystallization of [BiC-
NIm]3[DyCl6]. Several attempts to use other solvents (water or
ethanol for instance) or to change the stoichiometry of the
starting mixture did not lead to the title compound. In
particular, starting with a 3/1 stoichiometry as observed in the
title compound, or with a larger excess of Dy (200% excess,
stoichiometry 1/1) resulted only in solutions, with no formation
of any crystalline compound upon further crystallization
attempts.
°
°
are comprised between 89.19(4) and 93.08(6) while the trans
°
angle Cl2À DyÀ Cl2i is equal to 179.95(5) (Figure 2 and Table S3).
The shortest distance between two adjacent Dy3+ ions is 8.9 Å.
Short interactions between chloride anions and hydrogens
of the imidazolium moieties are responsible of the cohesion of
the crystal (see Figure S2 and Table S4).
The phase purity of the compound obtained as crystalline
powder has been investigated performing a Rietveld refinement
on the powder X-ray diffraction (PXRD) pattern with the Fullprof
software.[51] It was observed that the crystal structure deter-
mined from the single crystal analysis is in agreement with the
PXRD pattern (Figure S3). This study also revealed some addi-
tional peaks with low intensity (see purple arrows on Figure S3).
These peaks have been attributed to the presence of a second
phase likely stemming from the partial hydrolysis of the
[DyCl6]3À entities as already observed in related compounds.[49]
However, as confirmed by elemental analysis and thermogravi-
metric analysis (Figure S4 and Figure S5), this second phase is a
very minority phase and does not hamper the analysis of
physical properties reported below since the decomposition
product does not contribute to any of these properties.
Actually, when it is left in air for few days, the compound turns
to an amorphous powder (Figure S6) which is no longer
luminescent and does not exhibit slow magnetic relaxation
properties.
Crystal structure of [BiCNIm]3[DyCl6]
[BiCNIm]3[DyCl6] crystallizes in the orthorhombic space group
Pbcn. Selected crystallographic data for this compound are
collected in Table S1.
The asymmetric unit consists in one Dy3+ ions positioned
on 2-fold axis, three chloride anions coordinated to the Dy3+
ions and one and a half independent cations [BiCNIm]+
(Figure S1). The repetition of this unit in the periodic structure,
gives rise to [DyCl6]3À entities aligned along the a axis and
surrounded by [BiCNIm]+ cations (Figure 1).
Analysis of the luminescent properties
The luminescent properties of the title compound [BiC-
NIm]3[DyCl6] have been investigated in the solid state at room
temperature (Figure 3, Figure S7 and Figure S8). Under excita-
Figure 1. View showing the alternation of the cationic and anionic entities in
[BiCNIm]3[DyCl6] along the a axis (Dy in cyan, Cl in green, C in grey, N in
blue, H are omitted for clarity).
Figure 2. View in ellipsoid mode showing some selected DyÀ Cl distances
and ClÀ DyÀ Cl angles in the octahedral [DyCl6]3À entities contained in
[BiCNIm]3[DyCl6]. Symmetry code: (i) 1À x, y, 1/2À z.
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Figure 4. χT vs. T (black squares) and χ vs. T (red circles) for [BiCNIm]3[DyCl6]
under a static dc field of 5000 Oe.
Figure 3. Photoluminescence spectrum (red line) and photoluminescence
excitation spectrum (blue line) at room temperature and in solid state for
[BiCNIm]3[DyCl6].
field value to reduce QTM was chosen as the one that provides
the slowest magnetic relaxation (Figure S12a and Figure S12b),
i.e. 500 Oe. It can be seen on Figure S12a, there are (at least)
two relaxations modes, one at high frequency in low fields
(between 100 and 1000 Oe), and another one at low frequen-
cies, which appears when the applied dc field increases.
Finally, ac susceptibility measurements were performed as a
function of the ac field frequency between 1.8 K and 3.86 K
under this optimized dc field of 500 Oe determined above
(Figure S13 and Figure 5).
Figure S14 shows the corresponding Cole-Cole plot. It
appears clearly on this plot, but also on the χ’=f(ν) and χ”=
f(ν), that the distribution of the relaxation times for this
compound is non-symmetrical. Therefore, a generalized Debye
model is unable to fit properly the ac data (Figure S15).[54,55] This
asymmetry of the relaxation time distribution at 500 Oe can be
due to the vicinity of different relaxation modes, difficult to
discriminate or to some structural disorder.
tion at 350 nm, the emission spectrum displays a very broad
band centered at 550 nm corresponding to the luminescence of
the ligand (Figure S9) superimposed with two peaks centered at
574 nm and 668 nm. These two peaks are assigned to the
6
4
6
4F9/2! H13/2 and F9/2! H11/2 transitions of Dy3+ ion,
respectively.[52] The intense band at 574 nm is responsible of the
yellow emission color of the compound. The peak expected for
4
6
the F9/2! H15/2 transition of Dy3+ ion, which is responsible for
blue emission color (around 480 nm), is not observed here.
Actually, this feature is merely masked by the relatively intense
signal of the ligand in comparison with the one coming from
the lanthanide it-self.
In the excitation spectrum, monitoring the most intense
transition at 574 nm, we observe five bands at 350, 363, 385,
451 and 471 nm which can be ascribed to the transitions
6
4
between the ground state H15/2 and excited states M15/2 +6P7/2
,
The relaxation times were determined from the maxima of
the χ”=f(ν) curves (Table S5). These τ values are consistent with
those usually encountered for other SIMs.[56–58] The plot of the
4
4I11/2
,
4M21/2 +4I13/2 +4K17/2 +4F7/2
,
4I15/2, and F9/2 of Dy3+ ion,
respectively.[41] These bands are also in keeping with the
absorption spectra (Figure S10).
Magnetic study
The static susceptibility measurement was performed in the
1.8–300 K temperature range with an applied field of 5000 Oe
(Figure 4).
The
χT
value
at
room
temperature
(13.2 emu·K·molÀ 1) is in good agreement with the expected
value of 14.17 emu·K·molÀ 1 for mononuclear DyIII ion (S=5/2,
6
L=5, H15/2, g=4/3).[53] Upon cooling, the χT product decreases,
because of a combination of thermal depopulation of excited
MJ sublevels and significant magnetic anisotropy. Magnetization
is not saturated even at 7 T because of strong magnetic
anisotropy (Figure S11).
Under zero dc field and at 1.8 K, no out-of-phase signal is
observed in the ac frequency range investigated, merely due to
Quantum Tunneling of Magnetization (QTM).[11] Further meas-
urements were carried out under a small dc field. The optimum
Figure 5. Out-of-phase susceptibility curves for [BiCNIm]3[DyCl6] measured
with an ac field of 10 Oe for 10 Hz<ν<120 Hz and 2 Oe for
120 Hz<ν<1000 Hz under a static dc field of 500 Oe at various temper-
atures.
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relaxation time as a function of temperature can be equally well
fitted by a Raman+QTM process (τÀ 1 =τQTMÀ 1 +C×Tn with
QTM =1.8(4).10À 3 s, C=3(2) sÀ 1.KÀ n and n=7.9(6)) or by an
Orbach+QTM process (τ-1 =τQTMÀ 1 +τ0À 1e(À Ueff/T) with τQTM
which is also suggested by the asymmetric distribution of the
relaxation rates.
τ
In order to have further insight in the magnetic behaviour,
we have examined the structures of compounds showing Dy3+
ions in different octahedral environments (Figure 7 and
Table S6) and some characteristic values describing their
magnetic behaviours are given in Table 1.[35–43] Since the local
geometry influences the magnetic properties, we have limited
this research to compounds containing Dy3+ ions surrounded
by six ligands in an octahedral geometry (see CShM values in
Table 1). As one can observe, the majority of these compounds
showing SIM properties tends to exhibit the shorter distances
along the axial direction and angle values comprised between
=
1.4(2).10À 3 s, τ0 =9(5).10À 8 s and Ueff =20(2) KÀ 1) (Figure 6). The
values of the parameters are within the range of values
determined for other Dy3+ SIMS in octahedral environment
(Table 1). Even though n should be equal to 9 for a Kramers ion,
it can take lower values, down to n=4.[59–62]
Distinction between Raman and Orbach mechanisms is here
rather difficult as the fits are equally good. Due to the very
limited temperature range, a fit considering both Orbach and
Raman mechanisms is clearly overparametrized. Therefore, the
fits were performed considering the two mechanisms sepa-
rately, along with remaining QTM mechanism, which is not
totally suppressed by application of a dc field. Nevertheless, the
three mechanisms likely coexist in this temperature range,
°
°
170 and 180 . When the compounds exhibit an equatorial
crystal field with the four shortest distances in the equatorial
plane (see for example third line in Figure 7), almost no
compound exhibits SIM behaviour. Beyond consideration of the
local symmetry, it seems that coordination of halides with
decreasing electronegativity in the equatorial plane generates
increasing values of Ueff (i.e. longer bond length and weaker
ligand field, see for example first line in Figure 7). These
observations are in agreement with the assumption that oblate
electron densities would be more efficient for SIM properties
with axial ligand fields.[5,4,63]
Concerning the nature of the mechanisms involved in the
relaxation of the magnetization for these compounds, it can be
noticed that QTM mechanism is not suppressed and that
Orbach and Raman processes are both suggested in numerous
cases.
Theoretical study
Figure 6. Inverse of the relaxation time as a function of T (black squares:
experimental points, full red line: best fit using Raman+QTM process, full
green line: best fit using Orbach+QTM process).
To probe the electronic structure and the magnetic anisotropy
of the title compound [BiCNIm]3[DyCl6], ab initio calculations
Table 1. Nature of atoms constituting the first coordination sphere, values of the deviation from an ideal octahedron, relaxation time for QTM (τQTM),
effective energy barrier (Ueff), relaxation rate (τ0), values of n and C for Raman process, additional dc field used for the ac measurements of different
mononuclear compounds containing Dy3+ ions in octahedral environment.
Compound
Sphere
CShM[a]
τQTM [s]
Ueff [K]
τ0 [s]
n
C [sÀ 1.KÀ n
]
Hdc [Oe]
Ref
[DyI3(Cy3PO)2(CH3CN)]
[DyI3(Cy3PO)3] ·2THF
[DyBr3(OPPh3)2(THF)] ·THF
[DyCl3(OPPh3)2(THF)] ·THF
[DyCl3(OPPh3)3] ·0.5((CH3)2CO)
[DyCl2(ImDippN)(THF)3]
[DyCl2(OAr*)(THF)3]
[DyR2(THF)4][BPh4]
[DyR2(py)4][BPh4] ·2py
[Dy(TpMe2)2]I
DyO2N1I3
DyO3I3
2.57
2.85
1.40
0.85
0.63
0.96
0.97
0.16
0.11
1.57
1.16
0.87
0.60
2.50
0.25
0.25
1.70
1.70
4.7×10À 3
1002
–
70.9
49.1
35.1
803
52
57.6
72.0
13.5
22.9
–
–
–
–
20
–
–
5.0×10À 12
–
2.95
3.67
4.3
6.4
8.0
4.0
4.64
5[b]
5[b]
6
2.7
–
–
–
7.9
–
0.017
0.11
0.0002
0.003
0.058
0.00086
0.018
0.00005
0.0000083
0.1
3.2
–
–
–
3
–
–
–
0
0
400
400
1000
0
0
0
0
800
1200
–
–
–
500
500
–
41
41
39
39
37
38
38
42
42
35
40
43
37
39
This work
This work
36
0.44×10À 3
DyO3Br3
DyO3Cl3
DyO3Cl3
DyO3N1Cl2
DyO4Cl2
DyO4N2
DyN6
0.02
0.05
0.045
1.6×10À 6
2.0×10À 6
1.31×10À 5
1.4×10À 12
8.0×10À 6
2.0×10À 5
7×10À 5
1.6×10À 6
2.9×10À 6
–
–
3.19×10À 4
0.76×10À 3
4.6×10À 3
DyN6
–
[DyCl2(H3NAP)2]Cl·EtOH
[DyCl2(Ph3AsO)4]Cl·Solv
[DyCl2(OPPh3)4]Cl·solv
[DyI2(OPPh3)4]I·4THF·0.3H2O
[BiCNIm]3[DyCl6][c]
DyO4Cl2
DyO4Cl2
DyO4Cl2
DyO4I2
DyCl6
DyCl6
24×10À 3
–
–
–
–
–
–
1.8×10À 3
[BiCNIm]3[DyCl6][d]
1.4×10À 3
9×10À 8
–
[Dy(L2)2]
DyO2N4
DyO3Cl3
–
–
–
–
(NMe4)[DyCl3(TpMe2)]
–
–
35
[a] Minimal value determined for OC-6 or Oh geometry from the CShM calculation. [b] Fixed value during the fit of the data. [c] Values determined from the fit
using Raman+QTM process. [d] Values determined from the fit using Orbach+QTM process.
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Figure 7. Representation of different octahedral environments observed in mononuclear Dy3+ based compounds (dysprosium in cyan, carbon in grey, oxygen
in red, nitrogen in blue, phosphorus in orange, chloride in green, bromide in brown, iodide in violet, boron in pink). Values of shorter and longer distances as
well as axial angle have been indicated on this figure (for more details, see Table S6). Coloured frames indicate the compounds for which the SIM behaviour
has been observed and their colour is related to the values of Ueff: red for large values of Ueff, yellow for small Ueff and orange for intermediate Ueff. Grey boxe
corresponds to the title compound exhibiting equivalent Raman+QTM mechanisms and Orbach+QTM mechanisms (see Table 1).
have been performed using the SO-CASSCF method. It has
been shown for octahedral f complexes that the ligand field can
be written as following:[64]
symmetrized [DyCl6]3À octahedral structure and then the X-ray
structure. Details for these calculations are reported in
computational details and in SI part. Figure 8 gives the
calculated ab initio energies and the corresponding g factors for
the symmetrized and crystal structures. The splitting of the
ground J manifold is about 300 cmÀ 1. In the symmetrized
structure, the ground state is an isotropic Kramers doublet with
a g factor of 6.62 (Figure 8). The first excited quartet lies at
21 cmÀ 1 and then a Kramers doublet at 98 cmÀ 1. This ordering
of the states corresponds to Eq. 1 with negative W and x. Only
the crystal field parameters B40, B44, B06 and B46 do not vanish
(Table S7). The parameter S allows to evaluate the strength of
the ligand field with only one parameter. The 4th order
parameter S4 is larger than the 6th order one S6 (Table S7), in
accordance with the ordering states which implies that jxj
>0.5. In the crystal structure, the presence of the [BiImCN]+
"
#
^
^
O4
O6
^
VCF ¼ W x
þ ð1 À jxjÞ
(1)
Fð4Þ
Fð6Þ
0
4
0
4
q
^
^
^
^
^
^
^
with O4 ¼ O4ðJÞ þ 5O4ðJÞ and O6 ¼ O6ðJÞ À 215O6ðJÞ; Ok ðJÞare
the Stevens operators for the J manifold, F(4) and F(6) are
factors dependent of the J value, x and W are two adjustable
parameters, W defining the energy scale and x the ratio
between the fourth and the sixth orders. To understand the
influence of the symmetry, the SO-CASSCF calculations have
been realized considering first an idealized case formed by a
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Figure 8. SO-CASSCF energies of the low-lying states and corresponding g-tensor values (in bracket) calculated (a) for the symmetrized [DyCl6]3À structure and
(b) for the X-ray structure of [BiCNIm]3[DyCl6].
cation leads to a deformation of the coordination sphere.
Consequently, the quartets split into two Kramers doublets by
10 cmÀ 1 and the g tensors are anisotropic. As an example, g
values of the ground Kramers doublet range from 5 to 8.6
possibility to vary the imidazolium ILs that can be modified
with different substitutions of the cationic or the anionic part.
(Figure 8). With the lowering of the symmetry, all crystal field Experimental Section
parameters are non-zero (Table S8), but this barely affects the
strength parameters and the response to the magnetic field
(magnetic susceptibility). Consequently, the departure from the
ideal octahedral symmetry leads to a small anisotropy in the g
tensor of the ground state which can be at the origin of the SIM
behaviour. This slight deviation from the ideal octahedral
symmetry can also explain the absence of zero-field SIM
behaviour and the probability of QTM process.
Materials and general methods
Chloroacetonitrile, trimethylsilylimidazole and DyCl3 ·6H2O were
purchased from Alfa Aesar. They were used as received. Elemental
analyses for C, H, N were performed at the Service de Microanalyses
of the Institut de Chimie de Strasbourg. NMR spectra in solution
were recorded using a Bruker AVANCE 300 spectrometer. FTIR
spectra were performed on a Perkin Elmer Spectrum Two UATR-
FTIR spectrometer. The powder XRD patterns were collected with a
These observations tend also to indicate that existence of
axiality within these octahedral Dy3+ based compounds is not
necessary to promote SIM properties since the Dy3+ based
compound with a more regular octehadral environment give
rise to these properties. From this point of view, the possibility
to access to new other compounds with more regular geometry
and to explore their magnetic behaviour is particularly appeal-
ing.
Bruker D8 diffractometer using
a copper Kα1 radiation (λ=
1.540598 Å). The SEM images were obtained with a JEOL 6700F
scanning electron microscope (SEM) equipped with a field emission
gun (FEG), operating at 15 kV in the composition mode of the
instrument. TGA-TDA experiments were performed using a TA
instrument SDT Q600 (heating rates of 5 C·minÀ 1 under air stream).
°
Synthesis of the 1,3-bis((cyanomethyl)imidazolium) chloride
[BiCNIm][Cl]
The imidazolium salt was synthesized according to protocol
adapted from the literature.[65,66] Chloroacetonitrile (1.38 mL,
22 mmol) and trimethylsilylimidazole (1.46 mL, 10 mmol) were
mixed in a round bottom flask. The mixture was stirred and heated
at 333 K for 24 hours. After cooling at room temperature, the brown
mixture is washed with diethyl ether (3×10 mL). The white solid is
dried under vacuum. The yield of the reaction is around 75%.
Conclusion
We have reported the synthesis and the characterization of a
new compound containing Dy3+ ions in an unusual octahedral
hexachloride environment. Despite its sensitivity to air, we have
been able to investigate its photoluminescent and magnetic
properties. The analysis of the experimental magnetic features
indicates that [BiCNIm]3[DyCl6] exhibits SIM properties for
which the relaxation mechanism involves Raman, Orbach and
QTM mechanisms. In contrast with previous examples where
sophisticated ligands are employed to generate an octahedral
environment, this work illustrates the possibility offered by
imidazolium ionic liquid to stabilize octahedral [DyCl6]3À units.
This result paves the way to the synthesis of new series of
lanthanide based SIMs involving other lanthanide salts with the
Elemental analysis for C7H7N4Cl.0.25H2O (M=187.0 g.molÀ 1) Found
1
(Calc) (%): C 45.36 (44.92), H 4.01 (4.01), N 30.30 (29.95). H NMR
(D2O): δ (ppm)=7.75 (s, 2), 5.45 (s, 4). 13C NMR (D2O): δ (ppm)=
138.2, 123.5, 113.4, 37.5. IR (reflectance, cmÀ 1) : 3187 (m), 3136 (w),
3097 (w), 3008 (s), 2969 (m), 2899 (w), 2260 (w), 1806 (w), 1761 (w),
1684 (m), 1563 (s), 1428 (m), 1390 (s), 1345 (m), 1294 (m), 1256 (m),
1180 (s), 1110 (m), 1033 (w), 931 (m), 873 (s), 796 (s), 719 (m), 611
(s), 521 (m), 463 (w).
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Deposition Number 2045435 (for [BiCNIm]3[DyCl6]) contains the
Synthesis of [BiCNIm]3[DyCl6]
supplementary crystallographic data for this paper. These data are
provided free of charge by the joint Cambridge Crystallographic
Data Centre and Fachinformationszentrum Karlsruhe Access Struc-
tures service www.ccdc.cam.ac.uk/structures.
[BiCNIm][Cl] (90 mg, 0.50 mmol) and DyCl3 ·6H2O (94 mg,
0.25 mmol) were introduced in 6 mL of acetonitrile. The mixture
was sealed in a Teflon-lined stainless steel bomb (23 mL) and
heated at 363 K for 2 days. After cooling at room temperature,
colorless crystals were obtained. They were filtered and washed
with ethanol. The yield of the reaction is around 33%.
Elemental analysis for C21H21N12Cl6Dy1 (M=816.5 g.molÀ 1) Found
(Calc) (%): C 33.69 (33.94), H 3.01 (2.83), N 22.38 (22.63). IR
(reflectance, cmÀ 1): 3365 (sh), 3129 (w), 3104 (w), 3065 (m), 2969
(m), 2924 (w), 1622 (w), 1544 (s), 1435 (w), 1396 (w), 1345 (w), 1313
(w), 1256 (w), 1212 (w), 1174 (s),1110 (m), 1020 (w), 918 (m), 876
(w), 835 (m), 745 (s), 617 (s), 484 (sh).
Acknowledgements
The authors thank the Centre National de la Recherche
Scientifique (CNRS), the Université de Strasbourg (Idex), the Labex
NIE (ANR-11-LABX-0058-NIE within the Investissement d’Avenir
program ANR-10-IDEX-0002-02) for funding. Nesrine Benamara
thanks the program Profas B+ of Campus France for the grant of
her PhD and the Direction Générale de la Recherche Scientifique
et du Développement Technologique (DGRSDT). The authors are
grateful to Didier Burger for technical assistance.
Physical measurements
X-ray measurements. Single crystal X-ray diffraction measurement
was carried out at room temperature using a Kappa Nonius CCD
diffractometer. The diffraction intensities were collected with
graphite-monochromatized Mo Kα radiation (λ=0.71073 Å). Inten-
sity data were corrected for Lorenz-polarization and absorption
factors. The structure was solved by direct methods using SIR92,[67]
and refined against F2 by full-matrix least-squares methods using
SHELXL-2018/3[68] with anisotropic displacement parameters for all
non-hydrogen atoms. All calculations were performed by using the
Crystal Structure crystallographic software package WINGX.[69] The
structures were represented with Mercury.[70] All hydrogen atoms
were introduced into the calculations as a riding model with
isotropic thermal parameters.
Conflict of Interest
The authors declare no conflict of interest.
Keywords: Ionic liquid · Imidazolium salt · Lanthanide · Single
ion magnet · Luminescence
Magnetic measurements. The magnetic measurements were
conducted using a Quantum Design MPMS-3 magnetometer. The
static susceptibility measurements were performed in the 1.8 K–
300 K temperature range with an applied field of 0.5 T. Samples
were blocked in eicosane to avoid orientation under magnetic field.
Magnetization measurements at different fields and at given
temperature confirm the absence of ferromagnetic impurities. Data
were corrected for the sample holder and eicosane and diamagnet-
ism was estimated from Pascal constants.
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Manuscript received: February 16, 2021
Revised manuscript received: April 16, 2021
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