Single-Molecule Magnet Behavior Enhanced by Synergic Effect of Single-Ion Anisotropy and Magnetic Interactions

Article abstract of DOI:10.1021/acs.inorgchem.7b00625

As the simplest entity carrying intramolecular magnetic interactions, a dinuclear lanthanide complex serves as a model to investigate the effects of magnetic interactions on relaxation of magnetization, and importantly, it proves to be an efficient method to obtain robust single-molecule magnets via improving the communication between lanthanide centers. Here, three Dy₂ complexes (1, 2, 3) with a similar structural motif, namely, [Dy₂(HL)₂(NO₃)₂(CH₃CN)₂]·2CH₃CN (1), [Dy₂(HL)₂(NO₃)₂(DMF)₂]·2H₂O (2), and Dy₂(HL)₂(NO₃)₂(DMF)₄ (3), were successfully assembled. One critical difference found in this series of complexes is that the Dy center in complex 3 is coordinated by one more solvent molecule. Surprisingly, complex 3 exhibits the best magnet-like behavior, as evidenced by the high effective barrier and butterfly-type hysteresis, although the crystal field effect around Dy ions is weakened heavily. Ab initio calculations revealed the crucial reason is the significant synergic effect between single-ion anisotropy and magnetic interactions, i.e., not only the axiality of the Dy ion is improved efficiently but also the exchange magnetic interactions increased to the same order of magnitude to the dipolar interaction in 3. This effect mainly benefits from the elaborate modification of the local coordinate environment around the Dy ion, which results in a special arrangement of anisotropy axes different from the other two complexes. It demonstrates that the magnetic interactions could be effectively enhanced by means of deliberate local structural modulation.

Full text of DOI:10.1021/acs.inorgchem.7b00625

Article
pubs.acs.org/IC
Single-Molecule Magnet Behavior Enhanced by Synergic Effect of
Single-Ion Anisotropy and Magnetic Interactions
‡
,†
,§
‡
‡
,‡
Li Zhang, Yi-Quan Zhang,* Peng Zhang,* Lang Zhao, Mei Guo, and Jinkui Tang*
†Jiangsu Key Laboratory for NSLSCS, School of Physical Science and Technology, Nanjing Normal University, Nanjing 210023, P. R.
China
‡
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, P. R. China
§
̈
̈
Institut fur Physikalische Chemie, Universitat Stuttgart, Pfaffenwaldring 55, D-70569, Stuttgart, Germany
*
S Supporting Information
ABSTRACT: As the simplest entity carrying intramolecular magnetic
interactions, a dinuclear lanthanide complex serves as a model to investigate
the effects of magnetic interactions on relaxation of magnetization, and
importantly, it proves to be an efficient method to obtain robust single-
molecule magnets via improving the communication between lanthanide
centers. Here, three Dy complexes (1, 2, 3) with a similar structural motif,
2
namely, [Dy (HL) (NO ) (CH CN) ]·2CH CN (1), [Dy (HL) (NO ) -
2
2
3 2
3
2
3
2
2
3 2
(
DMF) ]·2H O (2), and Dy (HL) (NO ) (DMF) (3), were successfully
2 2 2 2 3 2 4
assembled. One critical difference found in this series of complexes is that the
Dy center in complex 3 is coordinated by one more solvent molecule.
Surprisingly, complex 3 exhibits the best magnet-like behavior, as evidenced by
the high effective barrier and butterfly-type hysteresis, although the crystal field
effect around Dy ions is weakened heavily. Ab initio calculations revealed the
crucial reason is the significant synergic effect between single-ion anisotropy
and magnetic interactions, i.e., not only the axiality of the Dy ion is improved efficiently but also the exchange magnetic
interactions increased to the same order of magnitude to the dipolar interaction in 3. This effect mainly benefits from the
elaborate modification of the local coordinate environment around the Dy ion, which results in a special arrangement of
anisotropy axes different from the other two complexes. It demonstrates that the magnetic interactions could be effectively
enhanced by means of deliberate local structural modulation.
INTRODUCTION
representing the typical characteristics of permanent magnets.
Here, a key point is the high sensitivity of QTM in SIMs, where
any slight changes of environment could generate important
perturbation on the axial crystal field, thus accelerating the
QTM tunneling relaxation rate. In contrast, intramolecular
magnetic coupling interactions further impose critical effects on
■
Single-molecule magnets (SMMs) are molecular materials
capable of blocking the magnetization for a relatively long
time at the molecular level, which could make it possible to
1
8
develop the molecule-based information storage and processing
2
technologies. Here, one critical and challenging task is to
achieve the SMMs retaining functionality in an operable
temperature regime, and chemistry, in particular coordination
chemistry, is playing a central role. Given the high perform-
ance in SMM properties of lanthanide complexes, a sustained
QTM in polymetallic lanthanide systems, some of which thus
9
3−
exhibit rather long relaxation times. Typically, the N -radical-
2
3
bridged system still represents the hardest SMM magnet known
to date, as evidenced by larger remanence and coercivity when
compared to any other molecular species at the same
temperature, which mainly benefits from the effective
suppression of QTM by the strong magnetic exchange coupling
interest has been developing in lanthanide coordination
4
chemistry since 2003. Recently, SMMs encapsulating only
one lanthanide ion, usually referred to as single-ion magnets
5
(
SIMs), have been used to achieve remarkable feats in
3−
7d
mediated by the N2 -radical ligand. Naturally, developing
such strongly coupled polymetallic lanthanide systems is
extraordinarily promising for achieving SMMs operating at
higher temperature, and it is essential to obtain an in-depth
understanding of how the nature and strength of interactions
increasing the effective barriers (U ) for reversing magnetic
moments and opening temperature of hysteresis (TB).
eff
6
Especially, the T temperature appears to be closely comparable
B
3
2
−
to, even surmount, the record created by N -radical-bridged
7
Tb SMM. Nevertheless, fast quantum tunneling of magnet-
2
ization (QTM) in SIMs usually triggers the sudden decline of
magnetization at zero field in hysteresis loops, and results in the
decrease and even disappearance of remanence and coercivity
Received: March 9, 2017
©
XXXX American Chemical Society
A
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Article
between lanthanide ions as well as possible alignment of
10
anisotropy axes can affect the SMM behavior.
Dinuclear lanthanide SMMs are the simplest magnetic
entities carrying intramolecular magnetic exchange, which
have greatly contributed to the exploration into relaxation
11
mechanisms influenced by magnetic interactions. The recent
study of electron paramagnetic resonance (EPR) spectroscopy
for a Dy complex provided important experimental validation
2
that parallel alignment of magnetic moments of individual spins
could produce an exchange bias effect within multinuclear
SMMs, which shifts the zero-field quantum tunneling step to a
finite field, thus leading to the possible presence of remanence
1
2
in hysteresis loops. More clearly, ab initio calculations of an
asymmetric Dy SMM from our group revealed the critical
2
effects of single-ion anisotropy and dipolar magnetic
9b
interactions on suppressing zero-field QTM. Herein, single-
ion anisotropy dominates the high-temperature relaxation
process and determines the height of effective barriers, while
strong magnetic interactions between single ions drive an
exchange-blocking regime, thus effectively slowing down the
tunneling relaxation rate. Nevertheless, the ferromagnetic
coupling comes almost entirely from a dipolar interaction,
thus the exchange contribution being negligible, which appears
to be against further enhancement of SMM behavior. Given the
precedent for SMMs in hydrazone-based Dy complexes and
2
high tunability of this ligand platform (hydrazone and terminal
1
3
ligands), we hopefully could tailor chemically those magnetic
molecules to increase the exchange magnetic interactions
between spin centers and further to enhance the blocking
behavior.
Figure 1. Crystal structures of compounds (a) 1, (b) 2, and (c) 3 with
lattice solvent molecules and hydrogen atoms omitted for clarity.
Color code: Dy, purple; O, red; N, blue; C, gray. Symmetry codes: *,
−
x + 1, −y + 2, −z + 1 for 1, −x, −y + 1, −z + 1 for 2, and −x + 1, −y
1, −z + 1 for 3.
Here, we employed a hydrazone ligand (3-hydroxy-N′-(2-
+
hydroxy-3-methoxybenzylidene)picolinohydrazide, H L) to
3
successfully construct three novel Dy complexes (1, 2, 3),
2
which all hold the typical skeleton of this kind of Dy SMMs;
coordinated solvents together with the coordinating direction
of nitrate.
Compounds 1 and 2 are shown to be isomorphous, primarily
2
i.e., two metal centers are bridged by the alkoxido groups of two
“
head-to-tail” hydrazone ligands, but different terminal
1
3
ligands. In particular, the coordination of more solvent
molecules in complex 3 directly changes the local crystal field of
Dy ions and leads to an important distortion of the whole
molecular structure, which can be correlated with a special
arrangement of anisotropy axes different from the other two
complexes. Importantly, the exchange magnetic interaction in 3
is effectively increased to the same order of magnitude to the
dipolar interaction, thus resulting in stronger blocking behavior.
differing in the coordinated solvents with CH
3
CN or DMF
molecule, respectively. In 1, the Dy ion has a N O
5
III
3
coordination environment and exhibits a distorted hula-hoop
(HH-8) geometry with the cyclic ring (hula-hoop) defined by
the atoms N3 and N1* from two ligands, atoms O5 and O6
from a bidentated nitrate, as well as atom N5 from the terminal
III
CH CN molecule (Figure 2a). In contrast, the Dy ion in 2
3
adopts a similar HH-8 geometry with an O N sphere except
6
2
that atom O8 from the DMF molecule replaces N5 in 1 (Figure
b). However, for 3, further coordination of one additional
2
RESULTS AND DISCUSSION
III
■
DMF molecule makes each Dy ion nine-coordinate (O N ) in
7
2
Structure. The reactions of dysprosium nitrate with H L in
3
a distorted muffin (MFF-9) geometry described as a 1:5:3
polyhedron (Figure 2d), concomitant with altering the
coordinating direction of bidentated nitrate. Therefore, the
cyclic set of five vertices is composed of two nitrogen atoms
(N1* and N3) from two ligands, two oxygen atoms (O8 and
O9) from two different DMF molecules, and the only single
atom O6 from the nitrate different from that in 1 and 2 (Figure
2c), leading to lower negative charge present on the equatorial
ring in 3. Here, the definition of the five-membered ring around
the Dy center seems to be different from that in previous
a 1:1 ratio in CH OH/CH CN, treated with Et N (0.1 mmol),
3
3
3
LiOH·H O (0.1 mmol), and Et N (0.2 mmol), respectively,
2
3
using different methods (slow evaporation of solvent or slow
diffusing of diethyl ether) produce yellow crystals of 1−3
(detailed information in the SI). Single-crystal X-ray diffraction
studies reveal that three centrosymmetric dinuclear complexes
crystallize in triclinic space group P1 with Z = 1. As depicted in
Figure 1, all of them possess the similar skeleton of Dy (HL)
̅
2
2
III
in which a pair of Dy ions are doubly bridged by the carbonyl
2−
14
oxygen atoms (O1 and O1*) of two antiparallel HL ligands
reports, where the ring was defined from the coordinating
in the enolate form with the similar Dy1−O1−Dy1* angles of
atoms of two hydrazone ligands. The reason is to correspond to
the anisotropy axis of the Dy ion, as shown in the following
calculation.
The comparison of some important bond distances and
angles of 1−3 shown in Table 1 reveals the shortest bond
approximately 114° and the two centers take up the O N (O1,
2
O2, and N3) and ON (O1 and N1) coordination pockets,
respectively. The crucial difference for these complexes is the
distinct terminal ligands including the number and species of
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Figure 3. Temperature dependence of the χ T values at 1000 Oe for
M
Dy -CH CN (1), Dy -DMF (2), and Dy -2DMF (3). The solid lines
2
3
2
2
correspond to calculated fits to the data.
3
−1
Figure 2. Coordination polyhedra observed in 1−3.
theoretical value of 28.34 cm K mol for two noninteracting
III
6
3
Dy ions ( H , S = 5/2, L = 5, g = 4/3, and C = 14.17 cm K
mol ). For 1 and 2, the temperature dependence of the χMT
15/2
−1
15
Table 1. Selected Bond Lengths [Å] and Angles [deg] for
Compounds 1−3
product exhibits similar thermal evolutions over the whole
temperature range of 300−2 K. Their χ T values gradually
M
compound
decrease with lowering the temperature to a minimum of 25.09
1
2
3
3
−1
and 25.40 cm K mol at ca. 40 K, followed by a rapid increase
3
−1
Dy1−O1
Dy1−O2
Dy1−O1*
Dy1−N1*
Dy1−N3
2.324(3)
2.144(3)
2.346(3)
2.544(3)
2.477(3)
2.436(4)
2.347(4)
2.149(4)
2.341(4)
2.559(5)
2.475(5)
2.443(6)
2.426(6)
2.312(5)
2.330(7)
to reach the values of 35.12 and 36.25 cm K mol at 2 K for 1
2.190(7)
and 2. The decrease in χ T value for both compounds results
M
2.437(7)
from the progressive depopulation of the m sublevels of the
J
2.581(9)
ground-state multiplet, while the sharp increases of χ T values
M
2.513(9)
at low temperature are indicative of the existence of
intramolecular ferromagnetic coupling between the Dy spin
Dy1−Onitrate
2.489(9)
2
.419(4)
2.580(10)
2.329(8) (O9)
carriers. In contrast, for 3, the χ T values do not show a clear
M
Dy1−O(N)solvent
2.501(5)
decline, but remain relatively constant until 30 K, then sharply
3
−1
2
.508(8) (O8)
increase to 41.63 cm K mol at 2.0 K, suggesting possible
stronger intramolecular ferromagnetic interactions in 3.
Magnetization data for 1−3 at fields of 0−70 kOe below 5 K
(Figure S4) reveal a rapid increase in the magnetization at low
magnetic fields, followed by a slow linear increase at high fields
without saturation even at 7 T, most possibly as a result of the
Dy1−Dy1*
Dy1−O1−Dy1*
O1−Dy1−O1*
3.9192(13)
114.11(10)
65.89(10)
3.9422(6)
114.47(16)
65.53(16)
4.0151(8)
114.7(3)
65.3(3)
distance occurring at the axial phenoxo-O atom (d(Dy1−O2) =
.1 Å) showing larger negative charge (Table S2), indicating
III
2
local crystal field effect at the Dy ion and the strong
the strongest electrostatic interaction, which favors an axially
enhanced ligand field. Furthermore, the presence of the second
ferromagnetic interactions between them. Furthermore, M
versus H/T curves (inset of Figure S4) are not superimposed
on a single master curve at varying temperatures, suggesting the
presence of a non-negligible magnetic anisotropy and/or low-
DMF molecule in 3 results in the marked increase of all bond
III
distances associated with the Dy ion, such as the Dy−O
nitrate
7d
distance elongated from 2.419(4) to 2.580(10) Å and the
average Dy−N distances from 2.507 to 2.547 Å, which leads to
an expanded coordination sphere and unexpected weakened
ligand field in 3. Notably, the changes of local coordination
geometry in complex 3 lead to an important distortion of whole
molecular structure relative to complexes 1 and 2, where two
hydrazone ligands are almost parallel.
lying excited states in all systems. Importantly, magnetic
hysteresis measurements were performed on complexes 1−3 on
a sweep rate accessible with a conventional magnetometer, and
thus only complex 3 displays a butterfly-shaped hysteresis loop
(Figure 4). Such a behavior is likely correlated with the stronger
ferromagnetic interaction between Dy centers than those in
9a
complexes 1 and 2. In fact, most of polynuclear lanthanide
SMMs reported to date experience an antiferromagnetic
interaction between metal centers, which is unfavorable to
improve coercivity given the diamagnetic ground state for an
Examination of the packing diagrams of 1−3 (Figures S2 and
S3) reveals that the closest intermolecular Dy···Dy distances are
8.546, 9.257, and 9.864 Å, suggestive of negligible intermo-
9
c,16
lecular exchange interactions.
ideal antiferromagnetic system.
Therefore, such an
Static Magnetic Studies and Theoretical Calculations.
The static magnetic measurements for compounds 1−3 were
carried out under an applied field of 1000 Oe from 300 to 2 K
using a Quantum-Design MPMS magnetometer. As depicted in
exploration into an enhanced ferromagnetic system is of great
interest for future information storage.
Dynamic Susceptibility Studies. In order to gain insight
into the dynamics of magnetization relaxation for complexes
1−3, ac susceptibility data were collected in the absence of an
external magnetic field at frequencies between 0.05 and 1500
Figure 3, the values of χ T product at room temperature are
M
3
−1
2
7.48, 26.90, and 29.50 cm K mol , which are close to the
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to 0.1 Hz in frequency-dependent measurements, the peaks of
χ″ signals were detected below 5 K for complexes 1 and 2
(
Figures S6 and S7), and the extracted relaxation times heavily
deviate from the thermally activated Arrhenius region.
However, such peaks cannot be observed even at 4.5 K in
complex 3. Thus, the limited range of frequencies available to
us prevented further quantitive measurements, but this
evidenced the extremely slow tunneling relaxation rate with
τQTM larger than 1592 ms (υ = 0.1 Hz) at least. Furthermore,
when compared to the asymmetrical Dy SMM reported by
2
9b
some of us (Figure S12), the trend of the ln(τ/s) vs 1/T
curve reveals the possibly longer tunneling relaxation time
present in complex 3 (τQTM > 35 s), which is consistent with
the occurrence of coercive field. Here, the strong suppression of
zero-field QTM is due to the critical synergic effect between
high single-ion anisotropy and strong magnetic interactions in 3
which forces the thermally activated relaxation process over a
much broader temperature range (vide infra), while the diluted
studies and ab initio calculations will give further evidence. For
Figure 4. Magnetic hysteresis loops for Dy -2DMF (3).
2
Hz. As shown in Figure 5 and Figures S6−S11, strong
frequency- and temperature-dependent in-phase (χ′) and out-
of-phase (χ″) magnetic susceptibility signals with peak maxima
were observed at the corresponding frequency and temperature
range for all three complexes, as is characteristic of typical
SMM behavior. A close comparison of the χ″(T) plots between
these complexes reveals the significant difference happening in
the low-temperature region (below 5 K), in which out-of-phase
1
−3, the thermally activated relaxation in high-temperature
domains obeys an Arrhenius-like behavior (τ = τ exp(U /
0
eff
k T)), where the energy barriers to magnetization reversal and
B
−
1
pre-exponential factors are fitted to be 72 K (50 cm , τ = 2.4
0
−
6
−1
−7
×
10 s), 78 K (54 cm , τ = 3.3 × 10 s), and 155 K (108
0
−
1
−8
cm , τ = 3.5 × 10 s), respectively (Figure S13).
0
The Cole−Cole plots of χ″ versus χ′ for 1−3 fitted to a
generalized Debye model are shown in Figures S14−S16. For 1
and 2, nearly symmetric semicircles are observed above 1.9 K
with α parameters below 0.16 and 0.08, respectively, implying a
narrow distribution of relaxation times, and the increasing α
values upon decreasing temperature are most likely due to the
coexistence of fast QTM and thermally induced relaxation
pathways. In contrast, the smaller parameters α in the range of
0.003−0.033 between 8 and 19 K suggest a much narrower
(
χ″) components of 1 and 2 gradually increase upon decreasing
the frequency, indicating the onset of fast tunneling of
magnetization (QTM) at zero dc field; i.e. the magnetic
moments are not frozen completely. It is noted that both χ′ and
χ″ components for 3 vanish completely even at the frequency
as low as 10 Hz, which is rare in lanthanide SMMs, suggesting
the highly efficient suppression of zero-field QTM in complex
3. More obviously, when the ac frequency range was extended
Figure 5. Temperature (top) and frequency (bottom) dependence of the out-of-phase ac susceptibility under zero dc field for 1 (left), 2 (middle),
and 3 (right).
D
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distribution of relaxation times and the presence of a single
relaxation mechanism.
Diluted Studies. The magnetically diluted investigations
into complexes 2 and 3 with 95:5 of Y:Dy percentage ratios
further elucidate the mechanism of the slow relaxation of the
2 to 3 seem to be consistent with the above structural analyses,
where the coordination sphere is expanded due to the second
coordinating DMF molecule, thus weakening the crystal field
splitting of Dy ions in complex 3. Surprisingly, complex 3
functions as the best SMM with the highest effective barrier
among them. The close comparison of transverse g
components (g , g ) of the ground state between them reveals
magnetization in such Dy SMMs, especially the effects of
2
17
exchange interactions on the dynamic magnetic properties. As
shown in Figure S17, ac susceptibility measurements gave
similar out-of-phase signals to those of undiluted samples at the
high-temperature region (>5 K), while the χ″ values obviously
increase with the temperature further decreasing, indicating the
onset of the QTM process concomitant with the disappearance
of magnetic interactions between Dy centers. Furthermore, the
relaxation time can be extracted from the χ″ vs υ plots (Figure
x
y
that the corresponding values for complex 3 are smaller than
those of complexes 1 and 2 by an order of magnitude,
suggesting a higher degree of axiality present in complex 3. As a
result, the tunneling relaxation process is suppressed more
effectively in complex 3, as seen in diluted samples where
quantum tunneling time τQTM of complex 3 is close to 20 times
as long as that of complex 2. Important for the above analysis is
the fact that, instead of attempting to increase crystal field
splitting, the expansion of the coordination sphere in complex 3
leads to the overall decline of crystal field splitting, but
surprisingly decreases the transverse components of the crystal
field efficiently, thus greatly improving its SMM properties. The
main reason is that the values of g and g are far smaller than g
S18) and thus Arrhenius fitting gave their effective barriers, U
eff
−1
=
49 and 96 cm , for the diluted samples of complexes 2 and
3
, respectively, which are comparable to the corresponding
undiluted samples (Figure S19). Critically, the temperature-
independent regime at low temperature reveals the quantum
tunneling time τQTM of complex 3 (763 ms) almost 20 times as
large as that of complex 2 (39 ms), indicating the significant
contribution of enhanced single-ion anisotropy in suppressing
the QTM process in complex 3. The clearer and more
important difference occurs in the M (H) hysteresis measure-
ments for the undiluted and diluted systems. Both diluted
samples exhibit butterfly-shaped hysteresis, similar to what was
observed for some SIMs, and the opening becomes clearer in
complex 3, but the remanence is absent anyway (Figure S20).
When it comes to the undiluted samples, only complex 3
succeeds to the hysteretic nature of magnetization, highlighting
the critical effects of enhanced ferromagnetic interaction on
slowing down under barrier relaxation processes, which are
further elucidated in the following calculations.
x
y
z
in a strongly unaxial system; thus, the expansion of
coordination sphere has a more pronounced impact on
transverse anisotropy of the ground state over axial anisotropy.
In addition, the comparison of calculated energy separations
with the above experimental effective barriers indicates that the
Orbach process is possible only in complex 3, because the
effective barriers in complexes 1 and 2 are far smaller than the
corresponding energy separations between the ground and the
19
first-excited doublets. Therefore, for complexes 1 and 2, the
Orbach process should be negligible. We further plotted the
ln(τ/s) vs ln(T/K) curves, revealing two different linear regions
at low and high temperature, respectively, for both complexes
(
τ
Figure S21). Their linear fitting gave the critical n values for
−1
n
Quantum Chemical Calculations. Ab initio CASSCF/
∼ T (n = 1.62 and 5.40 for 1, n = 1.68 and 5.38 for 2),
RASSI/SINGLE_ANISO calculations have been carried out
indicating the presence of direct and Raman processes at low
and high temperature, respectively. Importantly, we refitted the
ln(τ/s) vs 1/T plots through a sum of two relaxation processes
1
8
III
with MOLCAS 7.8 on individual Dy fragments of
complexes 1−3 on the basis of X-ray determined structures
−1
n
(see the Supporting Information for details). The lowest
(
τ
= AT + BT ) for complexes 1 and 2, and hence a good
Kramers doublets and the g tensors corresponding to the
fitting gave A, B, and n values (Table S5). In comparison, the
ln(τ/s) vs ln(T/K) plots of complex 3 present a single linear
III
pseudo spin S = 1/2 of Dy ions for three complexes are
region with n = 7.13 (τ− ∼ T ), but the plots at high
temperature were not fitted very well, indicating the presence of
Raman and possible Orbach processes. We fitted the ln(τ/s) vs
1/T plots of complex 3 through a sum of Raman and Orbach
1
n
shown in Tables 2 and S4, where the energy separations
−1
Table 2. Energies (cm ) of the Lowest Kramers Doublets
III
and Their g (g , g , g ) Tensors on Individual Dy
x
y
z
processes (τ− = BT + τ exp(−U /k T)) and fixed the U
1
n
−1
Fragments for Complexes 1−3
0
eff
B
eff
−1
to be 200 K (139 cm ) according to the above calculations,
1
2
3
thus giving B = 6.39 × 10− and τ = 1.21 × 10 s, which are
6
−8
0
E
g (S
0.0033
.0062
̃
= 1/2)
E
g (S
̃
= 1/2)
E
g (S = 1/2)
̃
well in the corresponding reasonable region (Figure 6). For the
diluted samples, the data can be fitted well under zero dc field
with the addition of the QTM process, with the parameters
0.00
0.00
0.0071
0.0139
19.6121
0.0774
0.0963
16.9938
0.00
0.0001
0.0024
19.6859
0.0495
0.0665
17.2874
0
4b
1
9.6665
0.0995
shown in Table S5. Here, all ln(τ/s) vs 1/T plots were well
fitted, and the obtained parameters are all in the reasonable
range. In summary, although the energy separations between
the ground and the first-excited doublets in complexes 1 and 2
seem to be rather large, the Orbach process indicating the
critical magnetic bistability has no contribution to relaxation
during the measured range of frequency. In contrast, the
Orbach process gets to function in magnetization relaxation of
complex 3, leading to the stronger SMM behavior, which
greatly benefits from the key modulation of the crystal field in
complex 3.
2
13.11
203.84
139.49
0
.1199
1
7.0032
III
between the ground and the first-excited doublets for the Dy−
1
fragments of 1−3 are 213.1, 203.8, and 139.5 cm ,
respectively. Herein, the calculating g values for all three
z
complexes approach the limiting value of 20 expected for a
ground Kramers doublets with the pure m = 15/2, confirming
J
III
strong unaxial anisotropy of the Dy ion and supporting their
8a
typical SMM behavior. Furthermore, the decreasing energy
The magnetic susceptibilities of complexes 1−3 were
2
0
separations between the ground and excited doublets from 1 or
simulated with the program POLY_ANISO using the
E
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−1
Table 4. Calculated Energies (cm ), the Corresponding
−1
Tunneling Gaps (cm ), and the g Values of the Low-Lying
z
Exchange Doublet States of Complexes 1−3
E
Δtun
gz
07
07
07
06
09
08
1
2
3
0.00
1.4 × 10−
2.6 × 10
6.3 × 10−
39.335
0.000
−
2
.094
0.00
39.226
0.000
−
2
.303
1.0 × 10
0.00
4.3 × 10−
1.9 × 10−
39.226
0.000
4
.474
complexes 1 and 2, suggesting the extremely efficient
22
suppression of the tunneling relaxation process in complex 3.
To gain a deeper understanding into the enhanced exchange
Figure 6. Plots of ln τ versus T−1 for 1−3 and the diluted samples of 2
and 3 under zero dc field. The solid lines correspond to the best fit of
interaction Jexch in complex 3, the easy-axis anisotropic
directions (g ) of Dy centers are given from two different
z
−1
n
−1
directions in Figure 7 for all complexes. Herein, the g direction
the experimental data to equation, τ = AT + BT + τ0 exp(−U /
z
eff
−1
kBT) + τQTM (the right terms correspond to direct, Raman, Orbach,
and tunneling processes).
exchange parameters from Table 3. All parameters were
calculated with respect to the pseudospin S = 1/2 of the Dy
−1
Table 3. Fitted Coupling Parameters (J = Jexch + J ) (cm )
dip
within the Lines Model of Complexes 1−3
Jexch
Jdip
J
1
2
3
−0.75
−0.03
5.00
5.22
5.01
4.69
4.47
4.98
9.69
ions. A great agreement was reached between the calculated
and experimental χ T versus T plots of three complexes, as
M
III
III
Figure 7. Orientations of the local main magnetic axes of the ground
doublets on Dy ions for compounds (a) 1, (b) 2, and (c) 3.
shown in Figure 3. From Table 3, the fitted Dy -Dy
III
21
couplings of three complexes within the Lines model are all
ferromagnetic, and the total coupling parameters J (dipolar and
exchange) were included to fit the magnetic susceptibilities.
of an individual Dy ion in three complexes seems to be similar,
that is, the direction almost parallel to the shortest Dy−O
bonds (Dy−O2), which is also consistent with the structural
analysis of hula-hoop-like geometry (Figure S22) and the
Herein, the ferromagnetic dipolar interactions, J , could be
dip
calculated exactly based on the calculated orientations of local
anisotropy axes and g tensors, while the exchange interactions,
Jexch, were obtained by fitting the static magnetic data.
Therefore, the Jdip of three complexes show the similar values
3c−e
theoretical prediction of electrostatic model.
However, the
molecular structure distortion due to one more coordinating
DMF results in a different arranged mode of anisotropy axes in
complex 3 relative to the other two complexes. As is shown in
Figure 7, the anisotropy axes of Dy centers in complexes 1 and
2 almost completely lie within the Dy O plane with a small
III
given that the main magnetic axes on two Dy ions of 1−3
(Figure S22) are parallel to each other and deviate from the
Dy-Dy vector by a small and similar angle. Critically, the pure
exchange contribution (Jexch) to the interactions is distinct in
complex 3 from that in complexes 1 and 2, where Jexch is almost
negligible. In complex 3, the exchange interactions are
effectively increased to the same order of magnitude and with
the same sign to the dipolar interactions, thus resulting in the
total interaction J being 2 times larger than that in complexes 1
and 2. Furthermore, the spectrum of the lowest exchange
multiplets, the corresponding tunneling gaps (Δ ) and g
2
2
angle with a Dy-Dy link, whereas it is obvious that, in complex
3, the axes deviate out of the Dy O plane. Here, although we
2
2
cannot give a clear relationship between magnetic interactions
and structure details, such a special arrangement most likely
generates a suitable overlap between lanthanide orbitals and
valency orbitals of the bridging atoms to enhance the
superexchange interactions between lanthanide ions in complex
3. In fact, the magnetic interactions between anisotropic
lanthanide ions are proven to be extremely anisotropic and very
sensitive to the arrangement of anisotropy axes in the EPR
tun
z
values are given in Table 4 based on the above interaction
parameters. Naturally, the enhanced magnetic interactions in
complex 3 relative to complexes 1 and 2 generate a larger
energy gap between the two lowest exchange Ising doublets,
which greatly increases the difficulty of spin reversal via excited
doublets at the low-temperature exchange region. As a step
further, all Dy complexes exhibit small tunneling gaps (Δ )
12
studies of the Dy complex from the van Slageren group. The
2
earlier theoretical investigations by Mironov on superexchange
interaction between lanthanide ions also revealed that the
III
III
Ln −L−Ln angles and good overlap between the lantha-
2
tun
for both lowest exchange Ising doublets, but the Δ values in
nide’s and the ligand’s orbitals are even more important than
tun
III
III
complex 3 are 2 orders of magnitude lower than that in
the Ln ···Ln distance in deciding the superexchange
F
DOI: 10.1021/acs.inorgchem.7b00625
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
2
3
mechanism. Therefore, it should be reasonable for the above
analysis that the arranged mode of anisotropy axes in complex 3
plays a decisive role in enhancing the exchange interaction
between Dy ions. As a result, the critical synergic effect between
enhanced single-ion anisotropy and strong magnetic inter-
actions is achieved perfectly on suppressing zero-field QTM in
complex 3.
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
E-mail: tang@ciac.ac.cn (J.T.).
E-mail: zhangyiquan@njnu.edu.cn (Y.-Q.Z.).
E-mail: peng.zhang@ipc.uni-stuttgart.de (P.Z.).
■
*
*
*
CONCLUSION
■
ORCID
The high tunability of hydrazone-based lanthanide complexes
and a careful engineering of experiment conditions allow the
isolations of three typical Dy SMMs (1, 2, 3), which exhibit
similar motifs where two metal centers are bridged by the
alkoxido groups of two “head-to-tail” hydrazone ligands.
Nevertheless, in spite of the seemingly structural similarity,
Yi-Quan Zhang: 0000-0003-1818-0612
Jinkui Tang: 0000-0002-8600-7718
Notes
2
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the National Natural Science Foundation of China
Grants 21525103, 21371166, 21331003, and 21521092) and
■
(
the existing discrepancy in terminal ligands (solvents and
NO ) not only alters the local crystal field around Dy centers
−
3
but also indirectly affects the consistency of whole molecular
structures between them. Specifically, ab initio calculations
reveal that one more coordinating DMF molecule in complex 3
leads to obviously decreasing gx,y values of Dy anisotropy and,
more importantly, the resulting distortion of molecular
structure generates a different arrangement between Dy
anisotropy axes and the Dy O plane when compared with
the Natural Science Foundation of Jiangsu Province of China
Grant BK20151542) for financial support. J.T. gratefully
(
acknowledges support of the Royal Society-Newton Advanced
Fellowship (NA160075).
REFERENCES
■
2
2
(
1) Christou, G.; Gatteschi, D.; Hendrickson, D. N.; Sessoli, R.
Single-Molecule Magnets. MRS Bull. 2000, 25, 66−71.
2) (a) Bogani, L.; Wernsdorfer, W. Molecular spintronics using
complexes 1 and 2. Such a special arrangement most likely
enables a suitable overlap between lanthanide orbitals and
valency orbitals of the bridging atoms to enhance the
superexchange interactions (Jexch) between Dy ions, hence the
overall interaction J = Jexch + Jdip in complex 3 being almost
twice as large as that in complexes 1 and 2. Finally, the
synergistic play of strong single-ion anisotropy and enhanced
magnetic interactions on suppressing QTM drives complex 3 to
be the best SMM. This study demonstrated that the exchange
magnetic interactions (Jexch) between lanthanide ions could be
effectively enhanced by means of the intelligent distortion of
molecular structure based on a deliberate local structural
modulation, which is closely correlated to the alignment of
anisotropy axes and resulting orbital overlap between
lanthanide and bridging atoms. Thus, it is proved to be a
viable means to improve SMM behavior of lanthanide
complexes. Of course, in order to achieve the final target,
extra efforts to increase the blocking temperature are required,
especially the combination with other ideas that are already
being applied with success, such as using radical and large
(
single-molecule magnets. Nat. Mater. 2008, 7, 179−186. (b) Thiele, S.;
Balestro, F.; Ballou, R.; Klyatskaya, S.; Ruben, M.; Wernsdorfer, W.
Electrically driven nuclear spin resonance in single-molecule magnets.
Science 2014, 344, 1135−1138. (c) Jiang, S.; Goß, K.; Cervetti, C.;
Bogani, L. An introduction to molecular spintronics. Sci. China: Chem.
2
(
012, 55, 867−882.
3) (a) Rinehart, J. D.; Long, J. R. Exploiting single-ion anisotropy in
the design of f-element single-molecule magnets. Chem. Sci. 2011, 2,
2
078−2085. (b) Zhang, P.; Guo, Y.-N.; Tang, J. Recent advances in
dysprosium-based single molecule magnets: Structural overview and
synthetic strategies. Coord. Chem. Rev. 2013, 257, 1728−1763.
(c) Chilton, N. F.; Collison, D.; McInnes, E. J. L.; Winpenny, R. E.
P.; Soncini, A. An electrostatic model for the determination of
magnetic anisotropy in dysprosium complexes. Nat. Commun. 2013, 4,
2551. (d) Aravena, D.; Ruiz, E. Shedding Light on the Single-Molecule
III
Magnet Behavior of Mononuclear Dy Complexes. Inorg. Chem. 2013,
́
52, 13770−13778. (e) Gomez-Coca, S.; Aravena, D.; Morales, R.;
Ruiz, E. Large magnetic anisotropy in mononuclear metal complexes.
Coord. Chem. Rev. 2015, 289−290, 379−392.
9
a,c
(4) (a) Woodruff, D. N.; Winpenny, R. E. P.; Layfield, R. A.
Lanthanide Single-Molecule Magnets. Chem. Rev. 2013, 113, 5110−
aromatic bridges.
5
148. (b) Liddle, S. T.; van Slageren, J. Improving f-element single
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b00625.
molecule magnets. Chem. Soc. Rev. 2015, 44, 6655−6669.
5) (a) Jiang, S.-D.; Wang, B.-W.; Sun, H.-L.; Wang, Z.-M.; Gao, S.
An Organometallic Single-Ion Magnet. J. Am. Chem. Soc. 2011, 133,
730−4733. (b) Liu, S.-S.; Xu, L.; Jiang, S.-D.; Zhang, Y.-Q.; Meng, Y.-
■
(
*
S
4
S.; Wang, Z.; Wang, B.-W.; Zhang, W.-X.; Xi, Z.; Gao, S. Half-
Sandwich Complexes of DyIII: A Janus-Motif with Facile Tunability of
Magnetism. Inorg. Chem. 2015, 54, 5162−5168.
Experimental procedures, IR spectra (Figure S1),
crystallography (Figures S2 and S3 and Table S1),
magnetic properties measurements (Figures S4−S21 and
Table S3), and computational details (Tables S2, S4, and
S5 and Figure S22) (PDF)
(6) Feltham, H. L. C.; Brooker, S. Review of purely 4f and mixed-
metal nd-4f single-molecule magnets containing only one lanthanide
ion. Coord. Chem. Rev. 2014, 276, 1−33.
(7) (a) Meihaus, K. R.; Long, J. R. Magnetic Blocking at 10 K and a
Dipolar-Mediated Avalanche in Salts of the Bis(η8-cyclooctatetrae-
nide) Complex [Er(COT)2]−. J. Am. Chem. Soc. 2013, 135, 17952−
Accession Codes
1
7957. (b) Ungur, L.; Le Roy, J. J.; Korobkov, I.; Murugesu, M.;
CCDC 1507443−1507447 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Chibotaru, L. F. Fine-tuning the Local Symmetry to Attain Record
Blocking Temperature and Magnetic Remanence in a Single-Ion
Magnet. Angew. Chem., Int. Ed. 2014, 53, 4413−4417. (c) Jung, J.; da
Cunha, T. T.; Le Guennic, B.; Pointillart, F.; Pereira, C. L. M.; Luzon,
G
DOI: 10.1021/acs.inorgchem.7b00625
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
J.; Golhen, S.; Cador, O.; Maury, O.; Ouahab, L. Magnetic Studies of
Redox-Active Tetrathiafulvalene-Based Complexes: Dysprosium vs.
Ytterbium Analogues. Eur. J. Inorg. Chem. 2014, 2014, 3888−3894.
Thermally Excited Spin States. Angew. Chem., Int. Ed. 2006, 45, 1729−
1733. (b) Tuna, F.; Smith, C. A.; Bodensteiner, M.; Ungur, L.;
Chibotaru, L. F.; McInnes, E. J. L.; Winpenny, R. E. P.; Collison, D.;
Layfield, R. A. A High Anisotropy Barrier in a Sulfur-Bridged
Organodysprosium Single-Molecule Magnet. Angew. Chem., Int. Ed.
2012, 51, 6976−6980. (c) Long, J.; Habib, F.; Lin, P.-H.; Korobkov, I.;
Enright, G.; Ungur, L.; Wernsdorfer, W.; Chibotaru, L. F.; Murugesu,
M. Single-Molecule Magnet Behavior for an Antiferromagnetically
Superexchange-Coupled Dinuclear Dysprosium(III) Complex. J. Am.
Chem. Soc. 2011, 133, 5319−5328.
3
‑
(
d) Rinehart, J. D.; Fang, M.; Evans, W. J.; Long, J. R. A N -Radical-
2
Bridged Terbium Complex Exhibiting Magnetic Hysteresis at 14 K. J.
Am. Chem. Soc. 2011, 133, 14236−14239.
(
8) (a) Ungur, L.; Chibotaru, L. F. Magnetic anisotropy in the excited
states of low symmetry lanthanide complexes. Phys. Chem. Chem. Phys.
011, 13, 20086−20090. (b) Cucinotta, G.; Perfetti, M.; Luzon, J.;
2
Etienne, M.; Car, P.-E.; Caneschi, A.; Calvez, G.; Bernot, K.; Sessoli, R.
Magnetic Anisotropy in a Dysprosium/DOTA Single-Molecule
Magnet: Beyond Simple Magneto-Structural Correlations. Angew.
Chem., Int. Ed. 2012, 51, 1606−1610. (c) Jung, J.; Yi, X.; Huang, G.;
Calvez, G.; Daiguebonne, C.; Guillou, O.; Cador, O.; Caneschi, A.;
Roisnel, T.; Le Guennic, B.; Bernot, K. Analysis of the electrostatics in
DyIII single-molecule magnets: the case study of Dy(Murex)3. Dalton
Trans. 2015, 44, 18270−18275. (d) Qian, K.; Baldovi, J. J.; Jiang, S.-D.;
Gaita-Arino, A.; Zhang, Y.-Q.; Overgaard, J.; Wang, B.-W.; Coronado,
E.; Gao, S. Does the thermal evolution of molecular structures
critically affect the magnetic anisotropy? Chem. Sci. 2015, 6, 4587−
(17) Habib, F.; Lin, P.-H.; Long, J.; Korobkov, I.; Wernsdorfer, W.;
Murugesu, M. The Use of Magnetic Dilution To Elucidate the Slow
Magnetic Relaxation Effects of a Dy2 Single-Molecule Magnet. J. Am.
Chem. Soc. 2011, 133, 8830−8833.
̈
(18) Karlstrom, G.; Lindh, R.; Malmqvist, P.-Å.; Roos, B. O.; Ryde,
U.; Veryazov, V.; Widmark, P.-O.; Cossi, M.; Schimmelpfennig, B.;
Neogrady, P.; Seijo, L. MOLCAS: a program package for computa-
tional chemistry. Comput. Mater. Sci. 2003, 28, 222−239.
(19) Liu, J.-L.; Yuan, K.; Leng, J.-D.; Ungur, L.; Wernsdorfer, W.;
Guo, F.-S.; Chibotaru, L. F.; Tong, M.-L. A Six-Coordinate Ytterbium
Complex Exhibiting Easy-Plane Anisotropy and Field-Induced Single-
Ion Magnet Behavior. Inorg. Chem. 2012, 51, 8538−8544.
4
(
593.
9) (a) Rinehart, J. D.; Fang, M.; Evans, W. J.; Long, J. R. Strong
3
−
(20) (a) Chibotaru, L. F.; Ungur, L.; Soncini, A. The Origin of
Nonmagnetic Kramers Doublets in the Ground State of Dysprosium
Triangles: Evidence for a Toroidal Magnetic Moment. Angew. Chem.,
Int. Ed. 2008, 47, 4126−4129. (b) Ungur, L.; Van den Heuvel, W.;
Chibotaru, L. F. Ab initio investigation of the non-collinear magnetic
structure and the lowest magnetic excitations in dysprosium triangles.
New J. Chem. 2009, 33, 1224−1230. (c) Chibotaru, L. F.; Ungur, L.;
Aronica, C.; Elmoll, H.; Pilet, G.; Luneau, D. Structure, Magnetism,
and Theoretical Study of a Mixed-Valence CoII3CoIII4 Heptanuclear
Wheel: Lack of SMM Behavior despite Negative Magnetic Anisotropy.
J. Am. Chem. Soc. 2008, 130, 12445−12455.
exchange and magnetic blocking in N2 -radical-bridged lanthanide
complexes. Nat. Chem. 2011, 3, 538−542. (b) Guo, Y.-N.; Xu, G.-F.;
Wernsdorfer, W.; Ungur, L.; Guo, Y.; Tang, J.; Zhang, H.-J.;
Chibotaru, L. F.; Powell, A. K. Strong Axiality and Ising Exchange
Interaction Suppress Zero-Field Tunneling of Magnetization of an
Asymmetric Dy2 Single-Molecule Magnet. J. Am. Chem. Soc. 2011,
1
33, 11948−11951. (c) Le Roy, J. J.; Ungur, L.; Korobkov, I.;
Chibotaru, L. F.; Murugesu, M. Coupling Strategies to Enhance Single-
Molecule Magnet Properties of Erbium−Cyclooctatetraenyl Com-
plexes. J. Am. Chem. Soc. 2014, 136, 8003−8010. (d) Fukuda, T.;
Matsumura, K.; Ishikawa, N. Influence of Intramolecular f-f
Interactions on Nuclear Spin Driven Quantum Tunneling of
Magnetizations in Quadruple-Decker Phthalocyanine Complexes
Containing Two Terbium or Dysprosium Magnetic Centers. J. Phys.
Chem. A 2013, 117, 10447−10454. (e) Pugh, T.; Chilton, N. F.;
Layfield, R. A. A Low-Symmetry Dysprosium Metallocene Single-
Molecule Magnet with a High Anisotropy Barrier. Angew. Chem., Int.
Ed. 2016, 55, 11082.
(
21) Lines, M. E. Orbital Angular Momentum in the Theory of
Paramagnetic Clusters. J. Chem. Phys. 1971, 55, 2977−2984.
22) Ungur, L.; Chibotaru, L. F. Strategies toward High-Temperature
Lanthanide-Based Single-Molecule Magnets. Inorg. Chem. 2016, 55,
(
1
(
0043−10056.
1
1
23) Mironov, V. S. Superexchange interaction between lanthanide f
1
ions. Spin-Hamiltonian calculations for the 90° and 180° f -f
superexchange. J. Phys.: Condens. Matter 1996, 8, 10551−10580.
(
10) Blagg, R. J.; Ungur, L.; Tuna, F.; Speak, J.; Comar, P.; Collison,
D.; Wernsdorfer, W.; McInnes, E. J. L.; Chibotaru, L. F.; Winpenny, R.
E. P. Magnetic relaxation pathways in lanthanide single-molecule
magnets. Nat. Chem. 2013, 5, 673−678.
(
11) Habib, F.; Murugesu, M. Lessons learned from dinuclear
lanthanide nano-magnets. Chem. Soc. Rev. 2013, 42, 3278−3288.
(
12) Moreno Pineda, E.; Chilton, N. F.; Marx, R.; Dorfel, M.; Sells,
̈
D. O.; Neugebauer, P.; Jiang, S.-D.; Collison, D.; van Slageren, J.;
McInnes, E. J. L.; Winpenny, R. E. P. Direct measurement of
dysprosium(III)···dysprosium(III) interactions in a single-molecule
magnet. Nat. Commun. 2014, 5, 5243.
(
13) Zhang, P.; Zhang, L.; Tang, J. Hydrazone-based Dysprosium
Single Molecule Magnets. Curr. Inorg. Chem. 2013, 3, 101−111.
14) (a) Guo, Y.-N.; Chen, X.-H.; Xue, S.; Tang, J. Modulating
(
Magnetic Dynamics of Three Dy2 Complexes through Keto−Enol
Tautomerism of the o-Vanillin Picolinoylhydrazone Ligand. Inorg.
Chem. 2011, 50, 9705−9713. (b) Guo, Y.-N.; Chen, X.-H.; Xue, S.;
Tang, J. Molecular Assembly and Magnetic Dynamics of Two Novel
Dy6 and Dy8 Aggregates. Inorg. Chem. 2012, 51, 4035−4042.
(
c) Zhang, P.; Zhang, L.; Lin, S.-Y.; Xue, S.; Tang, J. Modulating
Magnetic Dynamics of Dy2 System through the Coordination
Geometry and Magnetic Interaction. Inorg. Chem. 2013, 52, 4587−
4
592.
(
15) Benelli, C.; Gatteschi, D. Magnetism of Lanthanides in
Molecular Materials with Transition-Metal Ions and Organic Radicals.
Chem. Rev. 2002, 102, 2369−2388.
(
16) (a) Tang, J.; Hewitt, I.; Madhu, N. T.; Chastanet, G.;
Wernsdorfer, W.; Anson, C. E.; Benelli, C.; Sessoli, R.; Powell, A. K.
Dysprosium Triangles Showing Single-Molecule Magnet Behavior of
H
DOI: 10.1021/acs.inorgchem.7b00625
Inorg. Chem. XXXX, XXX, XXX−XXX