Excess axial electrostatic repulsion as a criterion for pentagonal bipyramidal DyIII single-ion magnets with high: U eff and T B

Article abstract of DOI:10.1039/c8tc00353j

In this work, a large excess of electrostatic repulsion, arising from the axial ligands, over that from the equatorial ligands is taken as the design strategy for high performance pentagonal bipyramidal (PBP) Dy^III single-ion magnets (SIMs). In

Full text of DOI:10.1039/c8tc00353j

View Article Online
View Journal
Journal of
Materials Chemistry C
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Z. Jiang, L. Sun,
Q. Yang, B. Yin, H. Ke, J. Han, Q. Wei, G. Xie and S. Chen, J. Mater. Chem. C, 2018, DOI:
10.1039/C8TC00353J.
This is an Accepted Manuscript, which has been through the
Volume
4 Number 1 7 January 2016 Pages 1–224
Royal Society of Chemistry peer review process and has been
accepted for publication.
Journal of
Materials Chemistry C
Accepted Manuscripts are published online shortly after
Materials for optical, magnetic and electronic devices
www.rsc.org/MaterialsC
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2050-7526
PAPER
~
Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
rsc.li/materials-c

Please do not adjust margins
Journal of Materials Chemistry C
Page 1 of 9
View Article Online
DOI: 10.1039/C8TC00353J
Journal Name
ARTICLE
Excess axial electrostatic repulsion as a criterion for pentagonal
bipyramidal DyIII single-ion magnets with high Ueff and TB
Zhijie Jiang,‡ Lin Sun,‡ Qi Yang, Bing Yin,* Hongshan Ke, Jing Han, Qing Wei, Gang Xie and Sanping
Chen*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
In this work, the large excess of the electrostatic repulsion, arising from the axial ligands, over that from the equatorial
ligands is taken as the designing strategy for high performance pentagonal bipyramidal (PBP) DyIII single-ion magnets
(SIMs). Under this strategy, two PBP DyIII-SIMs (1 and 2) [Dy(bbpen-CH3)X] (X = Cl, 1; Br, 2; H2bbpen = N,N′-bis(2-
hydroxybenzyl)-N,N′-bis(2-methylpyridyl)ethylenediamine) were synthesized and structurally characterized on basis of
highly symmetrical ligand H2bbpen-CH3 where an electron-donating group (-CH3) was installed to favor the conformation
necessary for the axial oxygen atom coordinating to DyIII. Dynamic magnetic measurement verify the value of our design
strategy since complex 2 exhibits high performance with large Ueff (above 1000 K) and high magnetic hysteresis
temperature (15 K). Ab initio calculations further verified the importance of the high excess of axial interaction which
eventually leads to the special electronic structure conceiving desired magnetic properties. The search for excessive axial
repulsion is not controversial to the strategy based on local symmetry around the central ion since various high-
performance PBP DyIII-SIMs of both clearly distorted and nearly ideal geometries successfully acquire such kind of excess.
Apparently this study presents an alternative of designing strategy for promising SIMs.
www.rsc.org/
contributions.5c, 5d, 5e, 5f, 5g The first reports of SIMs that own the
barrier for the reversal of magnetization (Ueff) over 1000 K5c
and the blocking temperatures (TB) around 20 K5d both belong
Introduction
Slow relaxation of magnetization in bistable magnetic
molecules, leading to effective magnetization blocking, is
widely accepted as the origin of single-molecule magnets
(SMMs),1 which have great application potential in various
fields, e.g., quantum computing2 spin-based electronics3 and
high-density storage of information.4 Monometallic SMM,
which is also denoted as single-ion magnet (SIM) in which only
one central metal ion exists, is a concise target suitable for the
studies digging into the fundamental comprehension of the
SMM properties.5 This is because of not only is the
intermolecular interaction is usually negligible in SIM but also
the fact that many recent breakthroughs in this field arise from
SIM systems. Thus, the deep comprehension of SIM systems
will not only increase knowledge of molecular magnet but also
promote the ultimate application of SMM in our real life.
to this group of the complex. Actually, the highest Ueff of PBP
DyIII-SIMs is 1837 K,5e which still keeps the current record
among all the SIMs.
These high-performance PBP DyIII-SIMs are usually deemed
to arise from the possible high local symmetry of the DyIII ion
since the coordination geometries of some of them are
verified to be close to a D5h point group. However, if all the
reported PBP DyIII-SIMs are subjected to the detailed
continuous shape measurements (CShM), their SMM
properties are not monotonously related to their degree of
closeness to the perfect PBP (Figure S23). An even larger
puzzle indeed exists because the coordination geometries of
some high-performance SIMs are actually further away from
perfect PBP when compared with those of similar structures
but inferior SMM property.6
Among this recent progress, DyIII-SIMs of pentagonal
For DyIII-SIMs, the high axiality of all the Kramers doublets
(KDs), especially the ground one, and a high degree of the co-
linearity of the magnetic easy axis of various KDs could
effectively suppress the unwanted fast relaxation, e.g.,
quantum tunneling of magnetization (QTM) and direct
process.7 Under these circumstances, large crystal field
splitting will provide high Ueff that eventually leads to long
relaxation time and high TB for SMMs.7 The KDs of the DyIII-SIM
could be well described as the combinations of the
bipyramidal (PBP) geometry has their important
6
components of the ground H15/2 multiplet of DyIII, i.e., |m>
where
m
ranges from -15/2 to +15/2.7 Under this
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 2 of 9
View Article Online
DOI: 10.1039/C8TC00353J
ARTICLE
Journal Name
approximation, the perfect axiality, i.e., the ideal SIM, would Synthesis
be achieved if each KD consists of only one fixed |m> in a
manner where the larger the absolute value of m, the lower
the energy of the KD.8
Under ideal PBP geometry of D5h symmetry, only axial
components of the crystal field Hamiltonian exist and they will
make KDs the desired composition. Thus, the ensurence of
perfect axiality from high local symmetry should root in its
capability of achieving a special composition of the KDs.
However, when D5h symmetry is actually unavailable for
distorted PBP DyIII complexes, is there any other driving force
toward the special compositions of the KDs?
For DyIII ion, the electron density of the pure |±15/2>
components is of the oblate shape.9 Therefore, the stronger
the stabilization of this aspherical electron density is, the
Scheme 1. Synthesis of the ligand H2bbpen-CH3.
performed using an oscillating ac field of
larger the contribution of |±15/2> component in the ground
KD, i.e., stronger axiality, will be. In order to stabilize such
oblate electron density, the electrostatic repulsion from the
equatorial ligands should be smaller than that of the axial
ligands as much as possible. In this way, distorted PBP DyIII
complexes, which are although apparently different from D5h
symmetry, could still be expected to have good SIM properties
if the large difference between the interactions from axial
ligands and those from equatorial ligands exists. That is to say,
the key is the consistency between the oblate electron density
of DyIII and the electrostatic repulsions from the surrounding
ligands.6a
0
Oe at ac
frequencies ranging from 0.1 or 1.0 to 1000 Hz. The
magnetization was measured in the field range 0-70000 Oe.
Synthesis of the ligand H2bbpen-CH3:
Ethylenediamine (3.85 g, 64 mmol) was added to a solution of
5-methylsalicylaldehyde (16.3 g, 120 mmol) in ethanol (85 mL).
The reaction mixture was stirred at room temperature until
the 5-methylsalicylaldehyde was consumed. The yellow
precipitate was filtered off and dried in vacuo to give (1) as a
yellow powder (16.7 g, 94% yield).
Sodium borohydride (5.1g, 135 mmol) was added to a
stirred suspension of (1) (16.0 g, 54 mmol) in 200 mL ethanol
in three batches. The mixture was stirred for 2 hours, and
hydrochloric acid (150 mL, 1.0 mol·L-1) was added dropwise.
The white precipitate was filtered off and washed with water
(3×10mL), ethanol (3×10mL), then dried in vacuo to give (2) as
a white power (13.9g, 86% yield).
Therefore, for the first time in this current work, the large
difference between axial and equatorial electrostatic repulsion
is taken as the designing strategy, leading to successful
synthesis of two mononuclear DyIII compounds of PBP local
geometry. The magnetic properties of them are promising as
the highest Ueff exceeds 1000 K and the magnetic hysteresis
loop exists up to 15 K.
A suspension of (2) (3.0 g, 10.0 mmol) was treated with
NaOH (20 mL, 1.0 mol·L-1) and stirred until producing the
mixture changed into a clear solution. 2-(chloromethyl)-
Experimental
pyridine hydrochloride (previously neutralized with NaOH (25
mL, 1.0 mol·L-1)) (4.1g, 25 mmol) was added, the reaction
mixture was heated at 85 °C for 3 h. After cooling down the
white precipitate was filtered off and washed with water
(3×5mL), cold ethanol (3×5mL), then dried in vacuo to give (3)
as a white power (1.7g, 35% yield).
1H NMR (400 MHz, CDCl3): δ 10.56 (s, 2H), 8.55 (d, J = 4.3 Hz,
2H), 7.61 (td, J = 7.7, 1.7 Hz, 2H), 7.16 (dd, J = 11.1, 6.4 Hz, 4H),
6.94 (dd, J = 8.1, 1.5 Hz, 2H), 6.7-6.62 (m, 4H), 3.73 (s, 4H), 3.64
(s, 4H), 2.73 (s, 4H), 2.21 (s, 6H).
Materials and measurements
All commercial reagents and solvents were purchased from
1
Aldrich, Adamas and TCI. H-NMR spectra were recorded on a
Bruker AV-400 or AV-100 spectrometer. Chemical shifts (δ)
were reported in parts per million (ppm) are referenced
relative to the residual solvent peak in the NMR solvent (CDCl3:
δ 7.26 (CHCl3)). Data are represented as follows: chemical
shift, multiplicity (s = singlet, d = doublet, t = triplet, q =
quartet, m = multiplet), integration, and coupling constants in
Hertz (Hz). The phase purity of the bulk samples was
confirmed by powder X-ray diffraction (PXRD) measurements
executed on a Rigaku RU200 diffractometer at 60 kV, 300 mA,
and Cu Ka radiation (l = 1.5406 Å), with a scan speed of 51 min-
Syntheses of [Dy(bbpen-CH3)Cl] (1):
A suspension of DyCl3·6H2O (37 mg, 0.1 mmol) and H2bbpen-
CH3 (48.3 mg, 0.1 mmol) in EtOH (5.0 mL) was treated. After
stirring for 15 min, the resulting mixture was immediately
filtrated, and the filtrate left to stand at room temperature for
slow evaporation. Colourless blocky crystals were gathered
after three days in a yield of 68% (based on DyIII salts). Elem
anal. calcd: C, 53.10; H, 4.75; N, 8.26. Found: C, 53.01; H, 4.73;
N, 8.25.
1
and a step size of 0.02° in 2θ. Magnetic measurements were
performed in the temperature range 2.0 K-300 K of 0 Oe, using
a Quantum Design MPMS-XL-7 SQUID magnetometer on
polycrystalline samples. The diamagnetic corrections for the
complexes were estimated using Pascal’s constants.
Alternating current (ac) susceptibility experiments were
Syntheses of [Dy(bbpen-CH3)Br] (2):
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 3 of 9
View Article Online
DOI: 10.1039/C8TC00353J
Journal Name
ARTICLE
To a solution of H2bbpen-CH3 (48.3 mg, 0.1 mmol) in The reaction of the ligand H2bbpen-CH3 with DyX3 (X = Cl,
acetonitrile (6 mL) was added triethylamine (0.2 mmol). After ) in a 1:1 molar ratio gave two target complexes with the
stirring for half an hour, the anhydrous DyBr3 (40 mg, 0.1 general formula [Dy(bbpen-CH3)Cl] ( ) and [Dy(bbpen-CH3)Br]
mmol) solid was added, which was sealed in a 15 mL Teflon- by different reaction routes: slow evaporation and
1; Br,
2
1
(2)
lined stainless container and kept at 75°C for three days, and solvothermal synthesis, respectively.
then cooled to ambient temperature at a rate of 5°C/h. To Crystal structures
form colorless block crystals with a yield of 37% (based on DyIII
Both complexes 1 and 2 crystallize in the monoclinic P21/n space
salts). Elem anal. calcd: C, 49.84; H, 4.46; N, 7.75. Found: C,
49.79; H, 4.42; N, 7.71.
group without any crystallographic solvent molecules (Figures S3,
S4, Table S1). CShM7 results indicate that the {DyO2N4X} cores of 1
and 2 are closest to PBP among all the ideal seven-coordinate
X-ray single-crystal diffraction analysis
Single-crystal X-ray data for complexes
at room temperature on Bruker Smart Apex CCD (1.824) (Table S3). Two negatively charged phenol
diffractometer with
graphite-monochromatized MoKa coordinate to DyIII ions in the axial direction with the Dy-O distance
1
and
2
were measured geometries with the distortion of 2 (2.111) larger than that of 1
a
O
atoms
a
radiation (l=0.71073 Å) by using a ω and φ scan mode. Cell in 2 (2.141 Å) shorter than that in 1 (2.155 Å). The O-Dy-O angles of
determination and data reduction were processed with the 1 (158.070) and 2 (159.400) are close to each other but clearly
SAINT processing program.13a The absorption correction based deviate from 180°. The five equatorial coordination sites are
on multiscan was applied in SADABS.13b By using Olex2,14 the occupied by four N atoms and one Cl for 1 or Br for 2 through the
structures were solved by direct methods with SHELXS and long average Dy-N distances (2.586 Å for 2 and 2.591 Å for 1) and
refined by full-matrix least-squares techniques against F2 by an even longer Dy1-Br1 (Dy1-Cl1) bond length of 2.852 Å in 2 (2.682
using SHELXL-2014 programs.15 All nonhydrogen atoms were Å in 1) (Table S2). The DyIII centers are isolated from each other by
refined anisotropically. All hydrogen atoms were placed in the bulky ligands: the closest distances between DyIII⋯DyIII ions are
calculated positions and refined isotropically. The crystal data 8.479 Å for 1 and 8.470 Å for 2 (Figures S5, S6, Table S5). To foster
and structural refinement parameters are summarized in further learning about intermolecular interactions in our system,
Tables S7 and S8, Supporting Information, whereas selected the two-dimensional (2D)-fingerprint of crystals and the associated
bond lengths and angles for complexes
1 and 2 are listed in Hirshfeld surfaces were employed. Based on the analysis of
Table S9. These data are provided free of charge by the Hirshfeld surfaces, the weak intermolecular interactions of the
Cambridge Crystallographic Data Centre.
neighboring molecules are mainly H···H (1, 63.0%; 2, 62.6%), C···H
(19.9%, 10.6%),·Cl···H (7.4%, 8.0%),·O···H (5.8%, both 1 and 2), C···C
(2.1%, both 1 and 2), and N···H (1.5 %, 1.4%) (Figures S7, S8).
Computational details
Multi-configurational ab initio calculations, including spin-orbit
coupling (SOC), were performed on the experimental Magnetic properties
structures of complexes
1, 1’, 2, 2’ (1’ = [Dy(bbpen)Cl]), 2’ =
At room temperature, the χmT values for 1 and 2 are 13.85 and
13.82 cm3 K mol-1, respectively, lower than the expectation for a
[Dy(bbpen)Br]),2c and 3; [Dy(OtBu)2(py)5][BPh4]2e possessing
3
(
the highest Ueff among the PBP DyIII-SIM) to explore their
magnetic anisotropy. This calculation consists of two steps:16a
(1) a set of SOC-free states, that is, spin eigenstates, are
obtained by the CASSCF17a method; (2) the low-lying SOC
states, that is, Kramers doublets (KD), herein, are obtained by
state interaction,16a that is, diagonalizing the SOC matrix in the
space spanned by the spin eigenstates from the first step. All
calculations were carried out with the MOLCAS 8.0 program.17b
In the CASSCF step, the active space consisted of 9 electrons in
7 orbitals and all the spin eigenstates of 21 sextets, 224
quartets, and 490 doublets were included. In the subsequent
state interaction, due to hardware limitations, only 21 sextets,
128 quartets and 98 doublet states were mixed by the RASSI-
SO module.17c The ANO-RCC basis sets17d, 17e were used. The
extraction procedure according to Chibotaru et al. was
performed to obtain the g-tensors and transition magnetic
moments of low-lying KDs with the SINGLE ANISO module.18
Results and discussion
Synthetic aspects
Figure 1. Molecular structure for complex 2. The equatorial
plane of pentagonal bipyramidal coordination sphere is
highlighted.
The electron-donating group -CH3, at the 4-position of the
phenol rings, is introduced in the H2bbpen ligand2c to increase
the electron density of the axial atoms coordinated to DyIII.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 4 of 9
View Article Online
DOI: 10.1039/C8TC00353J
ARTICLE
Journal Name
6
free DyIII ion (14.17 cm3 K mol-1) due to the splitting of the H15/2
ground multiplet (Figure S9). The non-superposition of the M versus
H/T data on a single master curve suggests the presence of
significant magnetic anisotropy and/or low-lying excited states
(Figure S10). The maximum for χm″ (1000 Hz) appears at 55 K and 62
K for complexes 1 and 2 in zero dc field, respectively, showing the
strong frequency and temperature dependence (Figures 2, 3, S11-
S14). Compared with Tong
higher temperatures with lower ac frequencies (50K/60K with
1488Hz for 1 /2 ), implying the improvement of SMM properties of
our complexes.
’
work,2c the maximum peaks appear at
’
’
For both complexes, the characteristic relaxation times are
extracted using an extended Debye model (Figures S18-S21). The
relaxation times τ extracted from the χm″ peaks for complexes 1 and
2 at selected temperatures under 0 Oe and 2000 Oe. In order to
further verify the domination of the Orbach process at high
temperature, relaxation time vs temperature is plotted in log-log
scale (Figure S22), whose slope indicates the Raman exponent is
respectively n = 12 for complex 1 and n = 18 for complex 2. The
11
anomalously large Raman exponents (n ≫9)10,
exclude the
possibility of the presence of the Raman process in the high-
temperature range, suggesting the Orbach one is dominant. The
relaxation times for complexes 1 and 2 at high temperatures obey
an Arrhenius law (τ = τ0 exp(Ueff/kT)) with an effective energy
barrier for relaxation Ueff/k = 723 K (502 cm−1) and τ0 = 2.36 × 10−10
for complex 1 and Ueff/k = 1162 K (808 cm−1) and τ0 = 1.02 × 10−12
s
s
Figure 3. Temperature dependence of the out-of-phase in zero
dc field (up) and magnetic relaxation (down) for complex 2.
for complex 2.
For the relaxation time products under 0 Oe, the direct process
can be neglected. In the low-temperature range, the Raman process
still plays an important role in the relaxation times. In addition, the
ln(τ) versus 1/T plots for complexes
1 and 2 present some
curvature (Figures 2, 3), indicating that the dynamics cannot
be properly modeled assuming a simple Orbach mechanism.
Therefore, the total relaxation rates mainly remain the Orbach
process, Raman process, and QTM process, using the following
equation (eqn (1)):
−1
QTM
τ ꢀ1
=
τ
+ CT n +τ0−1 exp(−Ueff / kT)
eqn (1)
Where τ is the inverse of the ac frequency, T is the
temperature of the maximum in the ac signal, Ueff is the
effective energy barrier, k is Boltzmann’s constant. τQTM, C, and
τ0 are the fitting parameters of the different relaxation
mechanisms.
In the absence of a static field, the independence of the
relaxation time at low temperatures for complex
of a QTM relaxation process. The fit in the temperature range
T = 2-54 K for complex by eqn (1) resulted in τQTM = 0.11 s, n
1 is indicative
1
= 2.97, C = 4.60 × 10-3 s-1K-2.97, τ0 = 2.36 × 10-10 s, and an
effective energy barrier of Ueff / k = 723 K (502 cm-1) (see SEI
for fitting details). The non-independence of the relaxation
Figure 2. Temperature dependence of the out-of-phase in zero
dc field (up) and magnetic relaxation (down) for complex 1.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 5 of 9
View Article Online
DOI: 10.1039/C8TC00353J
Journal Name
ARTICLE
time at low temperatures for complex 2 indicates the absence electron-donating group in the axial ligands should be an
of a QTM relaxation process. The fit in the temperature range effective route to high-performance DyIII-SIM. Furthermore,
T = 11-65 K for complex 1 by eqn (2) resulted in 3.15, C = 5.35 × the Ueff and TB of complex 2 is higher than that of complex 1 by
10-4 s-1K-3.15, τ0 = 1.02 × 10-12 s, and an effective energy barrier
of Ueff / k = 1162 K (808 cm-1) (see SEI for fitting details).
440 K and 6 K, respectively. These significant improvements
may not be related to the local symmetry of the DyIII ion as the
distortion of complex
that of complex
Theoretical analysis
For the sake of obtaining a deep understanding, ab initio
calculations were performed for complexes as well
as (Table S8). All the gZ values of the ground KDs of the five
2 from ideal PBP is actually larger than
1
.
τ
ꢀ1 = CT n +τ0−1 exp(−Ueff / kT)
eqn (2)
T
IRREV, which is the point where the field-cooled (FC) and
zero-field cooled (ZFC) susceptibilities diverge, is found at 12.1
K for complex (Figure 4), which clearly outweighs the value
of complex (9.5 K). Magnetic hysteresis (Figure 4) loops are
clearly open at zero field up to 15 K for complex (14 K for
complex
) at an average sweep rate of 0.02 T s-1 (time for a
1, 1’, 2, 2’
3
2
SIMs are calculated to be approaching the Ising limit of 20 for
DyIII ion (Table S6) and thus they indicate the strong magnetic
anisotropy of easy-axis type. The gX,Y/gZ ratio, where gXY is the
averaged transversal g values, has been shown to be related to
the axiality of a KD as lower ratio represents higher axiality.12
As shown in Figure 5, the gX,Y/gZ ratios of the five SIMs are
consistent with their SMM properties in the aspects of either
Ueff or TIRREV. The averaged transition magnetic moment within
a given KD, μQTM, could be used to measure the strength of the
corresponding QTM.10, 2a The μQTM of the ground KDs are also
consistent with the SMM properties of the five complexes as
2
’
2
2’
full cycle). For most SMMs TB and TIRREV are very similar, and
observed differences have been assigned to a distribution of
relaxation times.12
Either from the aspect of Ueff or from that of TB/TIRREV, the
SMM properties of complexes
improved when compared with previously reported complexes
and , respectively (Table S8). Thus, the introduction of the
1 and 2 are clearly shown to be
1’
2’
smaller μQTM does relate with higher Ueff or TIRREV
.
Furthermore, theoretical results indicate that the magnetic
relaxation of complex
which the energy
2 occurs via the third excited KD of
Figure 4. Variable-field magnetization data for complex
2,
under field-cooled (FC) and zero-field-cooled (ZFC) conditions
with a field of 2000 Oe (up). Magnetic hysteresis loops were
measured at a sweep rate of 0.02 T s-1 from 2 to 15 K (down).
Figure 5. –log (gxy/gz) vs Ueff, TIRREV (up) and –log μQTM vs Ueff
,
TIRREV (down), for complexes 2 and
1
’
,
1
,
2
’
,
3.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 6 of 9
View Article Online
DOI: 10.1039/C8TC00353J
ARTICLE
Journal Name
Table 1. The results of preliminary ESP (in a.u.) analysis of the complexes 1’, 1, 2’, 2 and 3.
Complex
ESP(equ)/ESP(ax)
ESP(equ_N)/ESP(ax)
ESP(equ_X)/ESP(ax)
ESP(ax)
1′
2′
1
2
3
0.843104
0.513158
0.329950
ꢀ0.8286017
ꢀ0.6985974
ꢀ0.425204
ꢀ0.273394
0.834454
0.503873
0.330581
ꢀ0.8387386
ꢀ0.699889
ꢀ0.422618
ꢀ0.277271
0.806634
0.788671
0.499460
0.2892119
ꢀ0.8473232
ꢀ0.6682597
ꢀ0.423204
ꢀ0.245056
0.560832
0.515078
ꢀ
0.2915556
ꢀ0.8315977
ꢀ0.6707952
ꢀ0.428338
ꢀ0.242457
ꢀ
ꢀ1.0174944
ESP(equ)
ꢀ0.5706429
ESP(equ_N)
ꢀ
ꢀ
ESP(equ_X)
(1179 K) is quite close to the experimental Ueff. (1162 K) monotonic relation exists between this ration and either
(Figures 6, S24). Therefore, the ab initio results here should be Ueff/TIRREV or ab initio parameter (Figures 7, S26-S30). Thus,
reliable and they demonstrate that the difference in the ESP(equ)/ESP(ax) should be a useful parameter for the
electronic structures of the five SIMs should be the reason for prediction of SMM properties of PBP mononuclear DyIII
their different SMM properties.
complex.
The decrease of ESP(equ)/ESP(ax) ratio from complex
arises from the increase of the magnitude of ESP(ax)
as the sum of contributions from two axial O atoms, ESP(ax), (0.83 a.u. for complex vs 0.85 a.u. for complex ) since the
With the calculated atomic charge, the electrostatic
potential (ESP) felt by the central DyIII could be approximated complex
2’ to
2
2
’
2
and those from five equatorial atoms, ESP(equ). The lower the ESP(equ) nearly remains to be 0.67 a.u. Therefore, the ESP
ratio ESP(equ)/ESP(ax) is, the larger the excess of axial results do verify the importance of introducing electron-
electrostatic repulsion over that from the equatorial ligands donating group in the axial ligand. A similar situation also
should be. This ration is calculated to be 0.843, 0.834, 0.807, occurs from complex
0.789 and 0.561 for complexes and , respectively between complex
1
’
to complex
and complex
could be mainly attributed
1
. In the comparison
1,
1’,
2,
2’
3
1
2,
the lower
(Table 1). All these ratios are significantly lower than one, ESP(equ)/ESP(ax) ratio of complex
which means the apparent excess of axial repulsion felt by the to the decrease
central DyIII. This is consistent with the fact that all these five
2
complexes are zero-field SIM of high Ueff. More importantly,
the ESP(equ)/ESP(ax) ratio also accounts for the difference of
the SMM properties among these five complexes as clearly
Figure 6. Magnetization blocking barrier in complex
2.
Exchange states are arranged according to the values of their
magnetic moments (bold horizontal black lines). Arrows show
the transition between the states, while the numbers above
the arrows are the corresponding average matrix element of
the magnetic moment (μ)̅ . Relaxation pathway is outlined by
arrows containing the largest μ̅ (blue arrows).
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 7 of 9
View Article Online
DOI: 10.1039/C8TC00353J
Journal Name
ARTICLE
Ruben and W. Wernsdorfer, Science, 2014, 344, 1135; (e) M.
Atanasov, D. Aravena, E. Suturina, E. Bill, D. Maganas and F.
Neese, Coord. Chem. Rev., 2015, 289-290, 177; (f) J. J.
Baldov&, S. Cardona-Serra, A. Gaita-AriÇo and E. Coronado,
Adv. Inorg. Chem., 2017, 69, 213; (g) S. Demir, J. M. Zadrozny
and J. R. Long, Chem. Eur. J., 2014, 20, 9524; (h) K. S.
Figure 7. ESP(equ)/ESP(ax) vs Ueff, TIRREV (up) and –log A (down)
for complexes 1’, 1, 2’, 2 and 3.
of the equatorial ESP contributions from Cl (0.28 a.u.) to Br
(0.24 a.u.). Although the introduction of equatorial Br instead
of Cl will lead to larger deviation from ideal PBP, the longer Dy-
Br distance, as well as lower magnitude of the negative charge
of Br, will reduce ESP(equ) a lot and then lead to significant
Pedersen, J. Bendix and R. Clérac, Chem. Commun., 2014, 50
,
4396; (i) S. T. Liddle and J. van Slageren, Chem. Soc Rev.,
2015, 44, 6655.
M. N. Leuenberger and D. Loss, Nature, 2001, 410, 789.
L. Bogani and W. Wernsdorfer, Nat. Mater., 2008, 7, 179.
M. Mannini, F. Pineider, P. Sainctavit, C. Danieli, E. Otero, C.
Sciancalepore, A. M. Talarico, M.-A. Arrio, A. Cornia, D.
2
3
4
increase of the axiality as well as SMM properties of
2. Above
all, the excess of axial electrostatic repulsion over the
equatorial one should be a useful guide for the design of high-
performance PBP DyIII-SIMs.
Gatteschi and R. Sessoli, Nat. Mater., 2009,
(a) G. A. Craig and M. Murrie, Chem. Soc. Rev., 2015, 44
2135; (b) J. M. Frost, K. L. M. Harriman and M. Murugesu,
Chem. Sci., 2016, , 2470; (c) J. Liu, Y.-C. Chen, J.-L. Liu, V.
8, 194.
5
,
It is highly worthy of denoting that, both the ab initio
parameters and ESP analysis of
3
are consistent with the
7
Vieru, L. Ungur, J.-H. Jia, L. F. Chibotaru, Y. Lan, W.
Wernsdorfer, S. Gao, X.-M. Chen and M.-L. Tong, J. Am.
Chem. Soc., 2016, 138, 5441; (d) Y.-C. Chen, J.-L. Liu, L. Ungur,
J. Liu, Q.-W. Li, L.-F. Wang, Z.-P. Ni, L. F. Chibotaru, X.-M.
Chen and M.-L. Tong, J. Am. Chem. Soc., 2016, 138, 2829; (e)
Y.-S. Ding, N. F. Chilton, R. E. P. Winpenny and Y.-Z. Zheng,
Angew. Chem. Int. Ed., 2016, 128, 16305; (f) F.-S. Guo, B. M.
Day, Y.-C. Chen, M.-L. Tong, A. Mansikkamäki and R. A.
Layfield, Angew. Chem. Int. Ed., 2017, 56, 11445; (g) C. A. P. G
oodwin, F. Ortu, D. Reta, N. F. Chilton and D. P. Mills, Nature,
2017, 548, 439; (h) S. K. Gupta, T. Rajeshkumar, G. Rajaraman
corresponding experimental observations (Figures 7, S26-S32).
That is to say, a high excess of axial electrostatic repulsion is
also achieved in
3. The local geometry of 3, being clearly
different from the other four DyIII-SIMs, is quite close to the
ideal PBP geometry of D5h (Table S4). Thus, the design strategy
from the aspect of ESP is not controversial to the strategy
based on symmetry and we think these two strategies are
actually consistent with each other.
and R. Murugavel, Chem. Sci., 2016,
(a) M. Li, H.-P. Wu, Q. Yang, H.-S, Ke, B. Yin, Q. Shi, W.-Y.
Wang, Q. Wei, G. Xie and S.-P. Chen, Chem. Eur. J., 2017, 23
1; (b) M. W. Willer, J. R. Long, C. C. McLauchlan and R. H.
Holm, Inorg. Chem., 1998, 37, 328.
L. Ungur and L. F. Chibotaru, Inorg. Chem., 2016, 55, 10043
S. G. McAdams, A.-M. Ariciu, A. K. Kostopoulos, J. P. S. Walsh
and F. Tuna, Coord. Chem. Rev., 2017, 346, 216.
7, 5181.
Conclusions
6
,
In summary, under the strategy of pursuing high excess of axial
electrostatic repulsion, two high-performance PBP DyIII-SIMs
were synthesized and characterized. The importance of this
strategy is further verified by ab initio calculations and ESP
analysis. This strategy is effective for both clearly distorted and
nearly ideal PBP geometries and it should play an important
role in the design of high-performance PBP DyIII-SIMs. Beyond
that, in an effort to emulate the favourable SIM properties
observed in this system, and encouraged by ab initio
predictions, various groups (H2bbpen, containing electron-
donating (-OCH3, -C(CH3)3) in the 4-position of the phenol
rings) have pursued the use of ligands with even more high-
performance PBP DyIII-SIMs is ongoing in our groups.
7
8
9
J. D. Rinehart and J. R. Long, Chem. Sci., 2011, 2, 2078.
10 R. Orbach, Proc. R. Soc. London Ser. A, 1961, 264, 458.
11 K. N. Shrivastava, Phys. Status Solidi B, 1983, 117, 437.
12 D. Casanova, M. Llunell, P. Alemany and S. Alvarez, Chem.
Eur. J., 2005, 11, 1479.
13 (a) Bruker, SMART, SAINT, and XPREP: Area Detector Control
and Data Integration and Reduction Software, Bruker Analy
tical X-ray Instruments Inc., Madison, WI, 1995; (b) G. M.
Sheldrick, SADABS, Program for Empirical Absorption
Correction, Univ ersity of Göttingen, Göttingen, 1996.
14 JG. M. Sheldrick, Acta Crystallogr. Sect. A, 2008, 64, 112.
15 O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard
and H. Puschmann, J. Appl. Crystallogr., 2009, 42, 339.
16 (a) J. Luzon and R. Sessoli, Dalton Trans., 2012, 41, 13556; (b)
L. F. Chibotaru, Struct. Bonding, 2015, 164, 185; (c) A.
Abragam and B. Bleaney, Electron Paramagnetic Resonance
of Transition Ions, Clarendon Press, Oxford, 1970; (d) D. Arav
ena and E. Ruiz, Inorg. Chem., 2013, 52, 13770; (e) J. M. Frost,
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
K. L. M. Harriman and M. Murugesu, Chem. Sci., 2016,
2470; (f) Y. F. Deng, T. Han, B. Yin and Y. Z. Zheng, Inorg.
Chem. Front., 2017, , 1141.
7 ,
We gratefully acknowledge financial support from the National
Natural Science Foundation of China (grant nos. 21673180,
21373162, 21673181, 21727805, 21473135 and 21103137).
4
17 (a) B. O. Roos, P. R. Tay lor and P. E. M. Siegbahn, Chem.
Phys., 1980, 48, 157; (b) F. Aquilante, J. Autschbach, R. K.
Carlson, L. F. Chibotaru, M.G.Delcey , L. De Vico, I. F. Galvan,
N. Ferre, L. M. Frutos, L. Gagliardi, M.Garavelli, A. Giussani, C.
E. Hoyer, G. Li Manni, H. Lischka, D. Ma, P. A. Malmqvist, T.
Muller, A. Nenov , M. Olivucci, T. B. Pedersen, D. Peng, F.
Plasser, B. Pritchard, M. Reiher, I. Rivalta, I. Schapiro, J.
Segarra-Marti, M. Stenrup, D. G. Truhlar, L. Ungur, A.
Valentini, S. Vancoillie, V. Veryazov, V. P. Vysotskiy, O.
Notes and references
1
(a) R. Sessoli, D. Gatteschi, A. Caneschi and M. A. Novak,
Nature, 1993, 365, 141; (b) A. Caneschi, D. Gatteschi, R.
Sessoli, A. L. Barra, L. C. Brunel and M. Guillot, J. Am. Chem.
Soc., 1991, 113, 5873; (c) D. Gateschi, R. Sessoli and J. Villain,
Molecular Nanomagnets, Oxford University Press, Oxford,
2006; (d) S. Thiele, F. Balestro, R. Ballou, S. Klyatskaya, M.
Weingart and F. Zapata, R. Lindh, J. Comput. Chem., 2016, 37,
506; (c) P. A. Malmqv ist, B. O. Roos and B. Schimmelpf ennig,
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry C
Page 8 of 9
View Article Online
DOI: 10.1039/C8TC00353J
ARTICLE
Journal Name
Chem.
Phys.
Lett., 2002, 357, 230; (d) B. O. Roos, R. Lindh, P. A. Malmqvist,
V. Very azov and P. O. Widmark, J. Phys. Chem. A., 2004, 108
2851; (e) B. O. Roos, R. Lindh, P. A. Malmqvist, V. Veryazov
,
and P. O. Widmark, J. Phys. Chem. A., 2005, 109, 6575.
18 (a) L. F. Chibotaru and L. Ungur, J. Chem. Phys., 2012, 137
064112; (b) L. F. Chibotaru, Adv. Chem. Phys., 2013, 153, 397.
,
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 9
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C8TC00353J
44x32mm (300 x 300 DPI)