Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Dalton
Transactions
View Article Online
PAPER
Cite this: Dalton Trans., 2023, 52,
2804
View Journal | View Issue
Slow magnetic relaxation in a homoaxially
phosphine oxide coordinated pentagonal
bipyramidal Dy(III) complex†
Pankaj Kalita, a Naushad Ahmed, ‡a Shruti Moorthy, ‡b Virginie Béreau, c,d
Arun Kumar Bar, e Pawan Kumar,f Prakash Nayak, g Jean-Pascal Sutter, *c
Saurabh Kumar Singh *b and Vadapalli Chandrasekhar *a,f
We report the synthesis of [(L)DyIII(Cy3PO)2]·[BPh4] (1-Dy) (where H2L = 2,6-diacetylpyridine bis-benzoylhydrazone and Cy = cyclohexyl) which crystallized in the triclinic, P1̄ space group. The local geometry
around Dy(III) in 1-Dy was found to be pentagonal bipyramidal ( pseudo-D5h). The AC magnetic susceptibility measurements performed on 1-Dy and on its diluted 1-Y(Dy) samples showed a typical single-molecule magnet signature revealed by the appearance of AC-frequency dependent out-of-phase susceptibility signals in the absence of a static magnetic field. The out-of-phase AC susceptibility signals were well
resolved on the application of a small magnetic field (HDC = 500 Oe) and yielded an energy barrier for
Received 24th November 2022,
Accepted 23rd January 2023
magnetization flipping of Ueff/kB = 50 K for the diluted derivative. The magnetic studies on 1-Dy and
DOI: 10.1039/d2dt03789k
1-Y(Dy) and data analysis further confirm that Raman and QTM under-barrier magnetic relaxations play a
crucial role in lowering Ueff despite the almost axial nature of the Dy(III) ion in 1-Dy. We have rationalized
rsc.li/dalton
these observations through detailed ab initio calculations performed on the X-ray crystal structure of 1-Dy.
Introduction
In recent years coordination and organometallic complexes
containing lanthanide ions have been the focus of research
with a view to discovering new single-molecule and single-ion
magnets.1–3 Since the pioneering discovery by Ishikawa and
co-workers that the [Tb(Pc)2]− complex showed slow relaxation
of magnetization,4 exploration of lanthanide complexes in this
area continues unabated.5–9 Ln(III) ions are particularly suited
a
Tata Institute of Fundamental Research, 36/P, Gopanpally Village, Serilingampally
Mandal, Ranga Reddy District, Hyderabad 500046, India. E-mail: vc@tifr.res.in,
vc@iitk.ac.in
b
Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi,
Sangareddy, 502284 Telangana, India. E-mail: sksingh@chy.iith.ac.in
c
Laboratoire de Chimie de Coordination du CNRS, Université de Toulouse, CNRS,
Toulouse, France. E-mail: jean-pascal.sutter@lcc-toulouse.fr
d
Université de Toulouse, Institut Universitaire de Technologie Paul SabatierDépartement de Chimie, Av. Georges Pompidou, F-81104 Castres, France
e
Department of Chemistry, Indian Institute of Science Education and Research
(IISER) Tirupati, Tirupati, Andhra Pradesh 501507, India
f
Department of Chemistry, IIT Kanpur, Kanpur 208016, India
g
School of Chemical Sciences, National Institute of Science Education and Research,
HBNI, Bhubaneswar 752050, India
† Electronic supplementary information (ESI) available. CCDC 2191768. For ESI
and crystallographic data in CIF or other electronic format see DOI: https://doi.
org/10.1039/d2dt03789k
‡ These authors contributed equally.
2804 | Dalton Trans., 2023, 52, 2804–2815
in this arena because of their large magnetic moment and
inherent magnetic anisotropy arising from the spin–orbit
coupling, the latter as a result of unquenched orbital angular
momentum.10–12 Complexes containing Dy(III), Tb(III), Er(III),
and Ho(III) have been most investigated, although there have
been reports of SMM/SIM behavior in complexes of Nd(III),
Tm(III), and Yb(III) also.13–17 In contrast to polynuclear Ln(III)
complexes, mononuclear complexes are currently of significant
interest as they serve as the simplest model system to understand magnetic anisotropy and establish a strong magnetostructural correlation by investigating their relaxation
dynamics.5,18,19
The key parameter to obtain optimal SMM behavior in
monometallic complexes is the nature of the crystal field
around the Ln(III) ion.20–22 Though the crystal field effects in
lanthanide complexes are small compared to the spin–orbit
interactions, they, nevertheless, play a crucial role in generating a highly anisotropic ground state by lifting the degeneracy
of the (2J + 1) fold ground state.23,24 For a given crystal field
environment, magnetic bistability with the highest mJ state
will result only when the repulsive interaction between the 4f
electron cloud and the ligand electrons attain a minimum
energy configuration.25 For example, in order to harness the
anisotropy of an oblate-shaped 4f-electron cloud such as Dy(III),
an axially compressed geometry would be preferred due to
the minimization of the repulsive electronic interactions.
This journal is © The Royal Society of Chemistry 2023
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Dalton Transactions
Utilizing this qualitative approach introduced by Long and coworkers, numerous high-performance SMMs/SIMs were
synthesized.26–28 Furthermore, it was realized that certain CF
symmetries such as C∞v, D∞h, S8, D5h, and D6d around the
Ln(III) center enhance the SMM properties by reducing the
quantum tunneling of magnetization (QTM).29,30 It is worth
mentioning that QTM is prevalent in many mononuclear SMMs
which is fundamentally driven by a dynamic crystal field.31
Theoretical investigations reveal that for the Dy(III) ion, a
perfect axiality up to the highest Kramers Doublets (KDs)
could be achieved in linear geometries of coordination
numbers 1 and 2 which potentially results in very high energy
barrier SMMs.32–35 In practice, such coordination geometries
are synthetically challenging. Nevertheless, the recent discoveries of very high magnetization blockade barriers and open
magnetic hysteresis loop temperatures in pseudo linear sandwiched Dy-metallocenes have validated this idea.36–39
Significantly, another class of mononuclear air/moisture-stable
pseudo linear complexes of the pentagonal bipyramidal (D5h)
and hexagonal bipyramidal (D6h) coordination geometries has
grabbed attention owing to their highly effective energy barriers and open magnetic hysteresis temperatures up to
20 K.40–46 In particular, the oblate shaped Dy(III) ion has
shown promising SMM properties in these coordination geometries, provided the strength of the axial field is stronger
than that of the equatorial crystal field.47–49
We have been involved in the synthesis of mononuclear
pentagonal bipyramidal (PBP) Ln(III) complexes utilizing pentadentate chelating ligands.7,50,51 In our previous work, we synthesized homoaxially Cl− coordinated PBP complexes and the
latter emphasized the synthesis of strong axially coordinated
PBP Dy(III) complexes (Fig. 1). In all the cases, the pentagonal
chelating ligands provided a rigid pentagonal equatorial
plane. In these two series, we have observed a significant
enhancement in the energy barrier of Dy(III) derivatives when
one of the axial Cl− ligands is substituted by phosphine oxide
ligands. To confirm that we have attained the axial limit in
these series of complexes, we have synthesized a cationic
mononuclear PBP Dy(III) complex, [(L)Dy(Cy3PO)2][BPh4] [(1-Dy
and its diluted derivative 1-Y(Dy))] where both the axial coordi-
Fig. 1 Schematic representation of the mononuclear pentagonal bipyramidal Dy(III) complexes 1-Dy–4-Dy.
This journal is © The Royal Society of Chemistry 2023
Paper
nation sites are occupied by two cyclohexyl phosphine oxide
ligands. The magnetic properties of this complex and its
diluted derivative are measured and compared with ab initio
calculations. These results are discussed herein.
Results and discussion
Synthetic aspects
Appropriately designed multi-dentate chelating ligands are
becoming important in the assembly of mononuclear Ln(III)
complexes of appropriate geometry. The latter are being vigorously investigated as single-ion magnets. In this regard,
lanthanide complexes possessing a pentagonal bipyramidal
geometry with weak equatorial and strong axial donors are of
interest. We have previously reported the synthesis, structural
characterization and magnetic studies of two series of mononuclear pentagonal bipyramidal (PBP) Ln(III) complexes. The
assembly of such complexes was accomplished using a pentadentate chelating ligand which effectively provided a rigid pentagonal equatorial plane. The effectiveness of this paradigm
lies in the fact that axial ligands can be varied. In our search to
find the axial limit of the crystal field, we were interested in
examining if we can place two phosphine oxide ligands in the
axial positions while keeping the equatorial coordination
environment the same. Accordingly, we utilized the same
ligand that was used by us earlier and succeeded in assembling a homoaxially tri-cyclohexyl phosphine oxide coordinated mononuclear PBP cationic Dy(III) complex, [(L)Dy
(Cy3PO)2]+ stabilized by a bulky [BPh4]− anion (Scheme 1). The
equatorial plane in this complex was provided by the rigid
pentadentate coordinating platform of the ligand. In addition,
an isostructural diluted complex [Dy@Y(L)(Cy3PO)2][BPh4] (1-Y
(Dy)) was synthesized for the magnetic dilution experiments.
X-ray crystallography
The molecular structure of 1-Dy was confirmed by a single
crystal X-ray diffraction study. The mononuclear complex 1-Dy
ˉ space group
crystallized in the triclinic crystal system in the P1
(Z = 2). The asymmetric unit of 1-Dy contains a complete molecule comprising a Dy(III) ion encapsulated by the pentadentate
ligand [L]2− in the equatorial coordination sites. The two cyclohexyl phosphine oxide (Cy3PO) ligands occupy the axial coordination sites leading to an overall pentagonal bipyramidal geometry around Dy(III) (Fig. 2).
The pentadentate ligand [L]2− coordinates to the Dy(III)
center in a κ5-ONNNO chelating interaction leading to four
five-membered rings as observed in the previously reported
complexes. Thus, the pentagonal bipyramidal 3N,4O coordination environment is fulfilled by three imino N atoms and
two enolized hydroxy O atoms in the equatorial sites and two
oxo O atoms in the axial sites. Continuous-shape measurement
calculations were performed using the SHAPE software to
ascertain the actual geometry of the hepta-coordinate environment around the Dy(III) ion.52,53 The computed results reveal
the least deviation from the pentagonal bipyramidal geometry
Dalton Trans., 2023, 52, 2804–2815 | 2805
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Paper
Scheme 1
Dalton Transactions
Reaction scheme for the synthesis of 1-Dy.
Fig. 2 (left) Molecular structure of 1-Dy (color codes: B = purple; C = grey; N = blue; O = red; Dy = olive green; the H-atoms have been omitted for
clarity); (right) pentagonal bipyramidal polyhedron of the Dy(III) ion in 1-Dy.
(ChSM = 1.396) with a pseudo-D5h symmetry for the [DyN3O4]
core (Table S1† and Fig. 2). A comparison of the C–N and C–O
bond lengths of the pentadentate ligand [L]2− in 1-Dy reveals a
close resemblance with the previously reported complexes and
suggests the involvement of a partially enolized form of the
ligand (see Table S2†).
The equatorial Dy–N bond distances are in the range of
2.444(4)–2.467(3) Å and Dy–O bond distances are in the range
of 2.262(3)–2.282(3) Å while the axial Dy–O distances are in the
range of 2.223(3)–2.241(3) Å. The axial Dy–O bond distances
are comparatively shorter than the equatorial Dy–O and Dy–N
bond distances leading to a compressed pentagonal bipyramidal geometry consistent with the strong-field nature of the
phosphine oxide ligands (Table S2†). The Dy–Ophos bond distances in the axial sites are comparable to the previously
reported complexes (see Table 2). The Ophos–Dy–Ophos bond
angle of 175.33(10)° in 1-Dy suggests an approximate linear
disposition of the two phosphine oxide ligands in the axial
sites. The solid-state packing diagram revealed a shortest intermolecular Dy(III)⋯Dy(III) separation of ∼9.425 Å (Fig. S1 and
S2†). The solid-state phase purity of 1-Dy and 1-Y(Dy) was confirmed by powder X-ray diffraction studies (see Fig. S3†). The
bond lengths and bond angles of 1-Dy are presented in
Table S2 (see the ESI†).
2806 | Dalton Trans., 2023, 52, 2804–2815
Table 1
Crystallographic data and refinement parameters
1-Dy
Empirical formula
Formula weight
Temperature
Crystal system
Space group
Unit cell lengths (Å)
Unit cell angles (°)
Volume (Å3)
Z
Density (calculated), g cm−3
Absorption coefficient, μ/mm−1
F(000)
Crystal size (mm)
2θ (°) range for data collection
Reflections collected
Index ranges
Independent reflections
Data/restraint/parameter
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak/hole (e Å−3)
CCDC number
C83H105B1Dy1N5O4P2
1471.96
297.26(10)
Triclinic
ˉ
P1
a = 13.8161(2)
b = 15.6888(2)
c = 19.0034(3)
α = 89.3110(10)
β = 71.1960(10)
γ = 89.0170(10)
3898.62(10)
2
1.254
1.050
1542.0
0.56 × 0.38 × 0.32
4.402 to 51
61 931
−16 ≤ h ≤ 16
−18 ≤ k ≤ 19
−23 ≤ l ≤ 22
14 453 [Rint = 0.1065]
14 453/208/945
1.030
R1 = 0.0482, wR2 = 0.1261
R1 = 0.0552, wR2 = 0.1331
0.88/−0.59
2191768
This journal is © The Royal Society of Chemistry 2023
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Dalton Transactions
Table 2
Paper
Comparison of bond distances and angle parameters of 1-Dy and previously reported complexes
Complex
Dy–Clax (Å)
Dy–Ophos (Å)
Shortest Dy–Oeq (Å)
Lax–Dy–Lax (°)
Ref.
[(L)Dy(Cy3PO)2][BPh4]
[(L)Dy(Cy3PO)Cl]
[(L)Dy(Ph3PO)Cl]
(L′)DyCl2
[Dy(Cy3PO)2(H2O)5]Cl3
—
2.6253(8)
2.6226(7)
2.6067(17) & 2.6798(17)
—
2.223(3) & 2.241(3)
2.237(2)
2.2755(16)
—
2.218(4) & 2.221(4)
2.262(3)
2.2586(18)
2.2818(18)
2.264(3)
2.326(5)
175.33(10)
169.62(6)
174.07(5)
166.33(5)
175.79(14)
This work
51
51
50
40
Magnetic properties
The variation of χMT with temperature for 1-Dy (Fig. 3) shows a
smooth and steady increase from 11.1 cm3 mol−1 K at 2 K to
13.8 cm3 mol−1 K for 298 K. Such a behavior is in agreement
with the behavior anticipated for a Dy(III) ion. The value
obtained at 298 K is close to the 14.17 cm3 mol−1 K calculated
in the high temperature limit for Dy(III) (gDy = 4/3, 6H15/2). The
field dependence of the magnetization has been recorded for
different temperatures between 2 and 6 K (Fig. S4†). At 2 K, the
magnetization increases rapidly for fields below 10 kOe and
only very less for larger fields, reaching 4.8µB for 50 kOe
(Fig. 3). The weak augmentation for larger fields is indicative
of higher energy levels well separated from the ground state.
The diluted 1-Y(Dy), which contained 5 mol% of the Dy
complex, exhibited magnetization versus field behavior at 2 K
that perfectly superposed that of 1-Dy (Fig. S4b†)
AC susceptibility studies showed the emergence of an out of
phase component (χ″M) below 25 K, a clear signature for slow
relaxation of the magnetization. However, the continuous
increase of χ″M as T decreases indicated the occurrence of a
fast relaxation due to QTM, which was quenched by the appli-
cation of a static field (Fig. S4c and d†). The slowest relaxation
time at 5 K was found for a field of 750 Oe that was subsequently applied for the complete AC studies. The temperature and frequency dependencies of χ′M and χ″M are plotted in
Fig. 4 and S5.†
The analysis of the Cole–Cole plots (i.e. χ″M = f (χ′M),
Fig. S6†) indicated a very narrow distribution width of the
relaxation times over the whole temperature domain with an αparameter spanning from 0.07 at 16 K to 0.09 at 4 K. The relaxation time, τ, between 3.6 and 17 K was assessed by the analysis of χ″M = f (frq) with the extended Debye model
(Table S3†). The best modeling of the temperature dependence
of τ between 5 and 17 K (Fig. 4b) was obtained when Raman
and Orbach processes (eqn (1)) were considered; yielding
Ueff/kB = 51 K, τ0 = 3 × 10−7 s, A = 0.05 K−n s−1, and n = 4.3.
However, the behavior below 5 K was poorly reproduced
suggesting possibly some contribution of QTM; the latter
being favored by intermolecular dipolar interactions.
τ 1 ¼ AT n þ τ0 1 expðU eff =kB TÞ
ð1Þ
The AC susceptibility behavior of the diluted Dy complex, 1Y(Dy), showed a well-defined maximum for χ″M already in the
absence of a static field (Fig. S7†) but with an up-turn, at the
lowest T. Application of a field of just 100 Oe was already
sufficient to cancel this upturn but the longest relaxation time
at 5 K was found with 500 Oe (Fig. S7†), which was considered
as the optimal field. The temperature and frequency dependencies of χ′M and χ″M obtained in the optimal DC field are
plotted in Fig. 4c and S8.† The temperature dependence of τ is
very similar to that of the pure Dy complex but now it could be
analyzed down to 4 K when considering Raman and Orbach
processes (Fig. 4d). Best fit parameters were Ueff/kB = 50 K, τ0 =
1.4 × 10−7 s, A = 0.01 K−n s−1, and n = 5.0; the values are consistent with those obtained for 1-Dy.
Computational studies
Fig. 3 Direct current magnetic susceptibility and magnetization data
(insight) for complex 1-Dy. The hollow square represents the experimental data, and the solid lines represent the CASSCF/NEVPT2 computed data.
This journal is © The Royal Society of Chemistry 2023
To shed light on the origin of magnetic anisotropy and slow
relaxation associated with 1-Dy, we have carried out CASSCF/
NEVPT2 calculations on the X-ray crystal structure. The details
of the calculations are provided in the computational methodology section. The low-lying energy spectrum corresponding to
the 6H15/2 term of Dy(III) ion spans over the energy range of
∼746 cm−1, with the first excited Kramers doublet (KD) being
placed at ∼198 cm−1. The inclusion of dynamic correlations by
means of NEVPT2 calculations further expands the energy
spectrum of eight low-lying Kramers doublets marginally by
Dalton Trans., 2023, 52, 2804–2815 | 2807
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Paper
Fig. 4
Dalton Transactions
Frequency dependence of χ’’M = f (T ) and temperature dependence of τ for 1-Dy (a and b) and 1-Y(Dy) (c and d).
∼60 cm−1, with the first excited KD being placed at ∼194 cm−1
(see Table S10 of the ESI†). The effects of dynamic correlations
are minimal on the computed f–f multiplets of the Dy(III) ion
as 4f-orbitals are deeply buried, and bonding is predominantly
ionic in nature. The computed g-value of the ground state KD
is gxx = 0.0088 (0.0188), gyy = 0.0230 (0.0458) and gzz = 19.6418
(19.6246) at the NEVPT2(CASSCF) level of theory. The computed g-values are highly axial, indicating the stabilization of
6
H15/2 as the ground state KD; however, it lacks the pure Ising
type (gxx = gyy = 0) ground state. A wavefunction decomposition
analysis indicates 96.5% |±15/2⟩ as the ground state with small
admixing from other excited KDs. The NEVPT2(CASSCF) computed ground state gzz axis is oriented towards one of the –O
atoms ∼6.8° (24°) present in the equatorial plane (see Fig. 5a).
The computed orientation is in line with the previous report,
where the g-tensor orients perpendicular to the disk-shaped
beta-spin density aligned towards the Dy–Lax bond.51 The first
2808 | Dalton Trans., 2023, 52, 2804–2815
excited KD is placed at ∼194 cm−1 away from the ground state
KD, with the gzz orientation deviating ∼70 degrees from the
ground state gzz orientation. As per wavefunction decomposition analysis, the first excited KD has a major contribution
from |±13/2⟩ KD: 49.2% |±13/2⟩ + 27% |±9/2⟩ + 11.7% |±5/2⟩
along with significant mixing from the other excited KDs. This
agrees with the computed g-values (gxx = 0.8582, gyy = 2.2911,
and gzz = 13.722) of the first excited KD possessing a significant amount of transverse anisotropy. The large θ value (angle
between the ground and first excited KD gzz orientations) and
the transverse component in the g-values indicate that the
magnetic relaxation is likely to occur via thermal assisted
quantum tunneling (TA-QTM) through the first excited KD.
Additionally, our calculations witnessed the presence of nonnegligible transverse anisotropy in the ground state g-values,
indicative of the QTM mechanism as another competing
pathway for magnetic relaxation. The computed experimental
This journal is © The Royal Society of Chemistry 2023
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Dalton Transactions
Paper
Fig. 5 (a) NEVPT2 computed orientation of the main magnetization axes of 1-Dy; (b) NEVPT2 computed ab initio blockade barrier of 1-Dy. The red,
green, and blue lines represent the possible QTM, thermal and Orbach relaxations. The grey line on the x-axis represents the KDs as a function of
magnetic moments. Color code: pink (Dy), red (O), blue (N), brown (P), grey (C), and white (H).
static DC properties (magnetic susceptibility and magnetization data) agree with the experimental data, highlighting the
goodness of the computed SH parameters (see Fig. 3).
To further understand the mechanism of the magnetic
relaxation of the Dy(III) ion in 1-Dy, we have constructed an
ab initio blockade barrier by computing the transverse magnetic moment between the KDs (see Fig. 5b). The calculated
transverse magnetic moment between the ground state KDs is
very large, ∼1 × 10−2μB (usually <10−6μB for complete quenching of QTM), indicating QTM to be one of the dominant pathways for magnetic relaxation. The large transverse anisotropy
in these complexes is due to the competitive ligand
field
environment
in
a
pentagonal
bipyramidal
environment.7,50,51,54 On the other hand, the computed transverse magnetic moment between the ground and first excited
KDs is significantly larger than the number connecting the
ground state doublet, indicative of magnetic relaxation via the
first excited KD. The matrix element joining the first excited
KD (green color in Fig. 5b) represents TA-QTM via this KD. The
non-collinearity between the ground and excited KDs sets
the theoretical barrier height at ∼194 cm−1, in line with the
previously studied Dy(III) SIMs with similar ligand
scaffolds.7,42,43,51,54–56 The large discrepancy between the computed and experimental barrier height arises due to the intermolecular interactions, spin–vibronic coupling57,58 and hyperfine interactions59,60 which are formally absent in our model
calculations. Although the barrier height is quite high, the
large transverse magnetic moment between the ground state
KDs enables the QTM within the ground state, likely to suppress the SMM behaviour at zero field. The proposed mechanism agrees with the experimental observation where the χ″M
signal constantly increases with a decrease in the temperature
due to the presence of QTM within the ground state KD.
Contrarily, the application of a small static DC field is likely to
perturb the energy levels, which helps in quenching the QTM
within the ground state and leads to the observation of slow
relaxation for magnetization in 1-Dy.
This journal is © The Royal Society of Chemistry 2023
In our previous reports, we have isolated several Dy(III)
based SIMs in the PBP environment where the pentadentate
ligand
(2,6-diacetylpyridine
bis-benzoyl/salicylhydrazone)
occupies the equatorial plane while Cl−/Cy3PO/Ph3PO occupies
the axial position. Previous studies indicate that the presence
of the Cy3PO/Ph3PO ligands in the axial position in [LeqDyCl
(Cy3PO/Ph3PO)] complexes led to a substantial increase in the
computed barrier height compared to the Cl− analogue in the
[L′eqDyCl2]− complex.7,50,51 This observation is further supported by our calculations where 1-Dy (both axial positions are
occupied by Cy3PO ligands) shows a relatively higher barrier
height than previously reported Dy(III) complexes in a similar
equatorial ligand field environment.7,49,51 For 1-Dy, we have
noticed that the average axial/equatorial bond length ratio is
<1, generating a preferable condition for stabilizing the |±15/2⟩
as the ground state. Moreover, a marginally higher average
axial/equatorial Mulliken charges ratio (i.e., >1) further
leverages the axiality, which results in the large energy gap of
∼194 cm−1 between the ground and excited KD (see Tables S5
and S6†). Despite having a significant barrier height for 1-Dy,
the experimental observations do not show any remarkable
improvement in the SMM character compared to other
reported Dy(III) complexes.7,51 To further understand the differences in the observed magnetic properties of other Dy(III) PBP
complexes with similar ligand scaffolds, here we have performed calculations on a series of complexes [(Leq)Dy(Lax)2]+/−
complexes (where Lax = Cl, Cy3PO, Ph3PO); while Leq = 2,6-diacetylpyridine bis-(salicylhydrazone). First, we recalculated the
magnetic anisotropy of the previously reported [LeqDyCl2]−
complex (2-Dy) using our computational methodology.51 Our
calculations yield a highly axial g-value (gxx = 0.0023, gyy =
0.0078 and gzz = 19.6887) with the first excited KD located at
∼149 cm−1, and most importantly, the computed SH parameters nicely match with previous theoretical values.51
Calculations on the [(Leq)DyCl(Cy3PO)] (3-Dy) complex51 (one
–Cl and one Cy3PO ligand in the axial position) show an
increase in the barrier height compared to 2-Dy. The ligand
Dalton Trans., 2023, 52, 2804–2815 | 2809
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Paper
field stabilizes the mJ |±15/2⟩ as the ground state with highly
axial g-values (gxx = 0.0149, gyy = 0.0301, and gzz = 19.6617). A
very similar result was obtained for the [(Leq)DyCl(Ph3PO)]
(4-Dy) complex,51 which led to a barrier height of ∼176 cm−1,
highlighting the similarity in the donor strength of the axial
ligand field for both the complexes (see Table S7†). Among all
the studied complexes, the orientation of the ground state gzz
passes nearly through one of the shortest Dy–Oeq bonds to
minimize the repulsion. The close resemblance of the computed energy spectrum for all these complexes was rationalized
earlier based on the similar rigid equatorial ligand field framework for all the complexes.51
Our calculations show that the ground and first excited KD
gap increases in the following manner, 2-Dy < 3-Dy ∼ 4-Dy
< 1-Dy. Among the studied complexes, the calculated barrier
height is the highest for 1-Dy, indicating a strong ligand field
imposed by the Cy3PO axial ligands.51,61 CASSCF computed
charge analysis (ratio of avg. axial and equatorial charges)
shows a nearly similar trend for all the complexes. The only
noticeable difference is in the structural aspect, where the
ratio of the avg. axial/equatorial bond length is smaller (<1) for
1, while it is always large (>1) for other complexes. To correlate
the observed trend in the barrier height with the nature of the
Dy–Lax bonding (as the equatorial ligand field is the same),
Dalton Transactions
here we have analyzed the AILFT computed f-orbital ordering.
Since the equatorial ligand field is the same, the splitting of
the f-orbital manifold is directly related to the axial ligand
field strength. The AILFT computed f-orbital manifold is the
largest for 1-Dy (∼1197 cm−1), highlighting a higher degree of
lanthanide–ligand covalency, which explains why the gap
between the ground and first excited KDs is the largest for
1-Dy. The computed AILFT f-orbital splitting pattern follows
the same trend as the observed gap between the ground and
first excited KDs for all the complexes. A closer inspection of
the AILFT computed f-orbital manifold in Fig. 6 shows that the
fx(x2−3y2) orbital is the most destabilized orbital compared to
the other 4f-orbitals in all the studied complexes. The lobes of
the highly destabilized fx(x2−3y2) orbital are mainly located in
the equatorial plane, indicating a stronger interaction from the
equatorial ligand (five donor atoms). This highlights that the
equatorial ligand field in these series of complexes is reasonably large and competes with the axial ligand field.
Additionally, the π-donor capability of –Cl and –Cy3PO/Ph3PO
ligands prefers to destabilize those f-orbitals which are off the
z-axis and hence generate an equatorial ligand field, despite
being present in the axial position (see Fig. 6). Moreover, the
transverse component in the g-value increases with an increase
in the f-orbital splitting pattern, which is directly related to the
Fig. 6 AILFT computed the splitting pattern of 4f orbitals along with the ground state g values for complexes 1-Dy to 4-Dy. Ligand field energies
are calculated using CASSCF with an active space of CAS(9,7). Color code: pink (Dy), red (O), blue (N), brown (P), green (Cl), grey (C), and white (H).
2810 | Dalton Trans., 2023, 52, 2804–2815
This journal is © The Royal Society of Chemistry 2023
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Dalton Transactions
π-donor strength of the axial ligands (as the equatorial ligands
are the same). From the electrostatic (CASSCF computed
Mulliken charges) perspective, the Cy3PO ligand favours the
axiality and increases the barrier height, nonetheless, the
π-type lanthanide–ligand covalency from the axial direction
penalizes the electrostatic axiality. As a result, we notice that
the transverse component in the ground state g-values
increases despite having a large gap between the KDs, which
in turn fastens the ground state QTM and quenches the zerofield SMM behaviour in 1-Dy. Most importantly, the sizable
equatorial ligand field followed by the π-donating ligand on
the axial positions diminishes the axiality and kills the zerofield SMM behavior in all these studied complexes.
It is well known in the literature that the nature of metal–
ligand covalency and the nature of ligands (σ vs. π) play a
crucial role in determining the magnetic anisotropy in transition metal/actinide complexes.62–67 Due to deeply buried 4forbitals, the lanthanide ligand covalency is often neglected or
less explored in designing SMMs as the design criteria are
mainly driven based on electrostatic consideration.25,35,51,68,69
To prove our hypothesis of ligand field effects on magnetic anisotropy, we have prepared a model complex [L(CH3)2Dy]−
Paper
(5-Dy) where both the –Cy3PO ligands were replaced by the
typical σ-donor –CH3 ligands. The position of –CH3 was optimized, and the ∠CH3–Dy–CH3 angle was kept linear throughout the calculations to achieve the axiality. CASSCF calculations
on the 5-Dy yield highly anisotropic g-values (gxx = 0.0039, gyy =
0.0046 and gzz = 19.9550), with the first excited state being
placed at ∼471 cm−1 higher in energy from the ground state.
For 5-Dy, the first excited KD is ∼four times higher in energy
than 1-Dy, indicating maximum repulsion through the axial
ligands. The energy window of the eight low-lying KDs spans in
the range of ∼1623 cm−1, which is nearly two times larger than
1-Dy. The computed g-values are highly axial in nature for 5-Dy
compared to 1-Dy. Here, we have noticed the preferential destabilization of the fz3 orbital oriented on the −z-axis due to the
pure σ-bonding interaction from the axial direction (see Fig. 7).
This indicates that apart from the ligand placed on the z-axis
(i.e., linear ∠Lax–Dy–Lax angle), the σ-bonding ligand is preferred over π-bonding ligands for maximizing the gap between
the KDs. Moreover, our computed ab initio blockade barrier
shows that the extent of QTM is an order smaller for 5-Dy compared to the 1-Dy complex. It is gratifying to see that the nature
of lanthanide ligand covalency (σ vs. π) has a significant impact
Fig. 7 (a) CASSCF computed AILFT f-orbital for 1-Dy and 5-Dy using CAS(9,7); (b) ab initio computed plausible magnetic relaxation for 5-Dy;
(c) ab initio computed plausible magnetic relaxation for 1-Dy, respectively. The red, green, and blue arrows shown in (b) and (c) represent the
QTM/TA-QTM, Orbach, and Raman relaxation possibilities. Color code: Pink (Dy), red (O), blue (N), brown (P), grey (C), white (H).
This journal is © The Royal Society of Chemistry 2023
Dalton Trans., 2023, 52, 2804–2815 | 2811
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Paper
on magnetic anisotropy. Our analysis suggests replacing
π-donor axial ligands with σ-donor ligands bring a new recipe
for achieving a large barrier height for the Dy(III) ion in the PBP
(pseudo-D5h) environment.
Summary
In conclusion, we have synthesized a cationic mononuclear
PBP Dy(III) complex, [(L)Dy(Cy3PO)2]+ (1-Dy), using a flexible
pentadentate chelating ligand that provides a rigid equatorial
plane. Both the axial coordination sites of this complex are
occupied by two cyclohexyl phosphine oxide ligands. The cationic complex is stabilized by the bulky tetraphenylborate
anion which further positioned the Dy(III) centers mutually far
apart in the solid-state. The magnetization dynamics of this
complex and its diluted derivative (1-Y(Dy)) revealed out-ofphase magnetic susceptibility signals, which are well resolved
for 1-Y(Dy) on the application of a very small static magnetic
field. The lower effective energy barrier for magnetization
reversal (Ueff/kB = 50 K) in these complexes is attributed to fast
under-barrier magnetic relaxations such as Raman and QTM
(triggered by the dipolar interactions) despite the axial nature
of the Dy(III) ion in the PBP ( pseudo-D5h) ligand environment.
Furthermore, detailed theoretical investigations on 1-Dy
yielded the SH parameters, which support the experimentally
observed dynamic magnetic behaviour. CASSCF/NEVPT2 calculations, in conjunction with ab initio ligand field theory analysis, highlight that magnetic anisotropy is highly sensitive to
the nature of lanthanide–ligand covalency (σ vs. π) and the
presence of σ-donor ligands in the axial position further leverage the axiality of the Dy(III) ion in the PBP environment.
Experimental section
Reagents and general procedures
Solvents and other general reagents used in this work were
procured from commercial sources. Acetonitrile was purified
according to standard procedures.70 Dy(OTf )3 and Y(OTf )3
were obtained from Sigma Aldrich, India. Diacetyl pyridine
(TCI Chemicals, India) and benzoic hydrazide (Spectrochem,
India) were used as received. The pentadentate organic ligand
2,6-diacetylpyridine bis-benzohydrazone (H2L) was synthesized
following a reported procedure.71 FT-IR spectroscopy was performed with pressed KBr pellets using a Bruker FT-IR spectrometer. Elemental analyses of the compounds were performed
using a Euro Vector EA instrument (CHNS-O, model
EuroEA3000). A powder X-ray diffraction study was performed
on a finely ground polycrystalline material with a Bruker D8
Advance powder X-ray diffractometer.
Synthesis of 1-Dy and 1-Y(Dy). A mixture of H2L (1 eq.),
Cy3PO (2 eq.) and NEt3 (2 eq.) was dissolved in 20 mL of hot
acetonitrile. To this solution, [NHEt3][BPh4] (1 eq.) and Dy
(CF3SO3)3 (1 eq.) were added in a stepwise manner which
resulted in a cloudy yellow solution. The reaction mixture was
2812 | Dalton Trans., 2023, 52, 2804–2815
Dalton Transactions
then heated under reflux conditions at 80 °C for 1 h and
allowed to cool to room temperature. The volume of this solution was reduced to 10 mL. Vapor diffusion of this solution
with diethyl ether afforded block-shaped crystals suitable for
X-ray crystallography after one week. The stoichiometry of the
reactants involved in each reaction, the yield of the products,
and their characterization data are provided below.
[(L)Dy(Cy3PO)2][BPh4] (1-Dy). H2L (0.08 g, 0.200 mmol),
Cy3PO (0.119 g, 0.401 mmol), [NHEt3][BPh4] (0.084 g,
0.200 mmol), Dy(CF3SO3)3 (0.122 g, 0.200 mmol), and NEt3
(56 μL, 0.400 mmol) were used. Yield: 0.174 g, 59% (based on
Dy). M.P.: >250 °C. IR (KBr ν/cm−1): 3484(br), 3055(m),
3035(m), 3001(m), 2984(m), 2928(s), 2852(s), 1586(m),
1554(m), 1502(s), 1447(m), 1425(m), 1409(m), 1370(s),
1324(m), 1292(m), 1257(m), 1227(m), 1172(m), 1150(m),
1099(s), 1067(m), 1032(s), 1001(m), 914(w), 895(m), 852(m),
809(m), 763(w), 746(m), 732(m), 707(s), 690(m), 679(m),
640(m), 612(m), 566(w), 547(m), 533(m). Anal. calcd for
C83H105B1Dy1N5O4P2 (1472.04): C, 67.72; H, 7.19; N, 4.76.
Found: C, 67.47; H, 6.96; N, 4.61.
[(L)Y0.95Dy0.05(Cy3PO)2][BPh4] (1-Y(Dy)). H2L (0.08 g,
0.200 mmol), Cy3PO (0.119 g, 0.401 mmol), [NHEt3][BPh4]
(0.084 g, 0.200 mmol), Y(CF3SO3)3 (0.102 g, 0.190 mmol) Dy
(CF3SO3)3 (0.007 g, 0.011 mmol), and NEt3 (56 μL,
0.400 mmol) were used. Yield: 0.184 g, 67% (based on Y).
Anal. calcd for C83H105B1Y0.95Dy0.05N5O4P2·CH3CN (1443.18):
C, 70.74; H, 7.54; N, 5.82. Found: C, 70.76; H, 7.36; N, 5.63.
Magnetic measurements
The magnetic measurements of all the samples were carried
out with a Quantum Design MPMS 5S SQUID magnetometer
in the temperature range of 2–300 K. The measurements were
performed on polycrystalline samples in gelatin capsules. The
crystalline powder of 1-Dy was mixed with grease. The temperature dependences of the magnetization were measured in
an applied field of 1 kOe and the isothermal field dependence
of the magnetizations was collected up to 5 T. The molar susceptibility (χM) was corrected for the sample holder and for the
diamagnetic contribution of all the atoms using Pascal’s
tables. AC susceptibility has been collected in zero field and
with applied fields in the frequency range of 1–1500 Hz.
X-ray crystallographic studies
The single-crystal X-ray diffraction data of 1-Dy were collected
on a Rigaku Xtal LAB X-ray diffractometer system equipped
with a CCD area detector and operated at 30 W power (50 kV,
0.6 mA) to generate MoKα radiation (λ = 0.71073 Å) at 297 K.
Data were integrated using CrysAlisPro software with a narrow
frame algorithm.72 Subsequently empirical absorption correction of the data was performed using the SCALE3 ABSPACK
scaling algorithm program.72 The structure was solved by the
intrinsic phasing method in SHELXTL73 and refined by the
full-matrix least-squares method on F2 (SHELXL-2014)74 using
Olex-2 software.75 The non-hydrogen atoms were refined with
anisotropic displacement parameters. All the hydrogen atoms
were included in idealized positions and refined considering
This journal is © The Royal Society of Chemistry 2023
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Dalton Transactions
the riding model. All the mean plane analyses and crystallographic figures have been generated using DIAMOND software
(version 3.2k).76 The crystal data, data collection, and refinement parameters for 1-Dy are summarized in Table 1. More
details on the crystallographic data can be found in the X-ray
crystallographic files in the CIF format.
Computational methodology
All the calculations were carried out using the ORCA 5.0.2
code.77,78 All the calculations were performed on the X-ray
crystal structure, where the position of the hydrogen atoms
was optimized at the BP86 level of theory79 and def2-SVP basis
sets.80 For the calculation of spin-Hamiltonian (SH) parameters, we performed a complete active space self-consistent
field (CASSCF)81 followed by the N-electron valence perturbation theory (NEVPT2) method.82–84 All these calculations
were carried out with the SARC basis set for Dy,85 the DKHdef2-TZVP basis set for Cl and P, the DKH-def2-TZVP(-f ) basis
set for O and N, and the DKH-def2-SVP basis set86 for all other
atoms as implemented in the ORCA code. The relativistic
effects were modeled by the Doughlas–Kroll–Hess (DKH)
approximation as implemented in ORCA. For Dy(III) complexes,
the active space is comprised of Dy(III) based nine electrons in
seven 4f-active orbitals i.e. CAS(9,7). The starting orbitals for
CASSCF calculations were taken from the restricted Open-shell
Hartree–Fock calculations. We have computed all the 21
sextets and 224 quartet states in a state-average fashion with
an equal weightage. The spin–orbit coupling (SOC) effects
were incorporated by using quasi-degenerate perturbation
theory (QDPT)87 as implemented in ORCA to compute spin–
orbit states. Here we used spin–orbit mean-field Hamiltonian
(SOMF-1X)88 to calculate one-electron integrals. To understand
the role of the ligand field in the magnetic anisotropy of Dy(III)
complexes, we have performed ab initio-based ligand field
theory (AILFT)89 and computed the f-orbital splitting pattern,
spin–orbit coupling constants, and interelectronic repulsion
parameters. Ab initio blockade barriers were constructed using
SINGLE_ANISO90 as the stand-alone program, which is inbuilt
with the ORCA 5.0.2 code.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
V. C. is thankful to the Dept. of Science and Technology, New
Delhi, India, for a National J. C. Bose Fellowship. P. K. and
N. A. are thankful to the Tata Institute of Fundamental
Research,
Hyderabad,
for
postdoctoral
fellowships.
S. K. S. acknowledges the Department of Science and
Technology for the Start-up Research Grant SRG/2020/01323
and IIT Hyderabad for generous funding. SM thanks PMRF for
the PhD fellowship. The support and resources provided by
This journal is © The Royal Society of Chemistry 2023
Paper
PARAM Shivay Facility under the National Supercomputing
Mission, Government of India, at the Indian Institute of
Technology, Varanasi, are gratefully acknowledged.
References
1 J. H. O. María, C. H. M. Lewis and A. L. Richard, in
Organometallic Magnets, Topics in Organometallic
Chemistry, ed. V. Chandrasekhar and F. Pointillart,
Springer, Cham, 2019, vol. 64, pp. 253–280.
2 Z. Zhu, X.-L. Li, S. Liu and J. Tang, Inorg. Chem. Front.,
2020, 7, 3315–3326.
3 R. Marin, G. Brunet and M. Murugesu, Angew. Chem., Int.
Ed., 2021, 60, 1728–1746.
4 N. Ishikawa, M. Sugita, T. Ishikawa, S.-y. Koshihara and
Y. Kaizu, J. Am. Chem. Soc., 2003, 125, 8694–8695.
5 Y.-S. Meng, S.-D. Jiang, B.-W. Wang and S. Gao, Acc. Chem.
Res., 2016, 49, 2381–2389.
6 K. S. Pedersen, A.-M. Ariciu, S. McAdams, H. Weihe,
J. Bendix, F. Tuna and S. Piligkos, J. Am. Chem. Soc., 2016,
138, 5801–5804.
7 A. K. Bar, P. Kalita, M. K. Singh, G. Rajaraman and
V. Chandrasekhar, Coord. Chem. Rev., 2018, 367, 163–216.
8 B. M. Day, F.-S. Guo and R. A. Layfield, Acc. Chem. Res.,
2018, 51, 1880–1889.
9 A. Dey, P. Kalita and V. Chandrasekhar, ACS Omega, 2018,
3, 9462–9475.
10 R. Sessoli and A. K. Powell, Coord. Chem. Rev., 2009, 253,
2328–2341.
11 L. Sorace, C. Benelli and D. Gatteschi, Chem. Soc. Rev.,
2011, 40, 3092–3104.
12 D. N. Woodruff, R. E. P. Winpenny and R. A. Layfield,
Chem. Rev., 2013, 113, 5110–5148.
13 J. D. Rinehart, M. Fang, W. J. Evans and J. R. Long, J. Am.
Chem. Soc., 2011, 133, 14236–14239.
14 R. J. Blagg, L. Ungur, F. Tuna, J. Speak, P. Comar,
D. Collison, W. Wernsdorfer, E. J. L. McInnes,
L. F. Chibotaru and R. E. P. Winpenny, Nat. Chem., 2013, 5,
673–678.
15 J. J. Le Roy, L. Ungur, I. Korobkov, L. F. Chibotaru and
M. Murugesu, J. Am. Chem. Soc., 2014, 136, 8003–8010.
16 Y.-C. Chen, J.-L. Liu, W. Wernsdorfer, D. Liu,
L. F. Chibotaru, X.-M. Chen and M.-L. Tong, Angew. Chem.,
Int. Ed., 2017, 56, 4996–5000.
17 O. Y. Mariichak, S. Kaabel, Y. A. Karpichev,
G. M. Rozantsev, S. V. Radio, C. Pichon, H. Bolvin and
J.-P. Sutter, Magnetochemistry, 2020, 6, 53.
18 S.-D. Jiang, B.-W. Wang and S. Gao, in Molecular
Nanomagnets and Related Phenomena, ed. S. Gao, Springer
Berlin Heidelberg, Berlin, Heidelberg, 2015.
19 A. Chiesa, F. Cugini, R. Hussain, E. Macaluso, G. Allodi,
E. Garlatti, M. Giansiracusa, C. A. P. Goodwin, F. Ortu,
D. Reta, J. M. Skelton, T. Guidi, P. Santini, M. Solzi, R. De
Renzi, D. P. Mills, N. F. Chilton and S. Carretta, Phys. Rev.
B, 2020, 101, 174402.
Dalton Trans., 2023, 52, 2804–2815 | 2813
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Paper
20 R. A. Layfield and M. Murugesu, Lanthanides and Actinides
in Molecular Magnetism, Wiley-VCH Verlag GmbH & Co.
KgaA, 2015.
21 C. A. P. Goodwin, Dalton Trans., 2020, 49, 14320–14337.
22 L. Zhu, B. Yin, P. Ma and D. Li, Inorg. Chem., 2020, 59,
16117–16121.
23 J. Tang and P. Zhang, Lanthanide Single Molecule Magnets,
Springer-Verlag, Berlin, Heidelberg, 2015.
24 J. T. Coutinho, B. Monteiro and L. C. J. Pereira, in
Lanthanide-Based Multifunctional Materials, ed. M.-R. Pablo
and R. S. Manuela, Elsevier, 2018, pp. 195–231.
25 J. D. Rinehart and J. R. Long, Chem. Sci., 2011, 2, 2078.
26 J. Lu, M. Guo and J. Tang, Chem. – Asian J., 2017, 12, 2772–
2779.
27 S. G. McAdams, A.-M. Ariciu, A. K. Kostopoulos, J. P. S. Walsh
and F. Tuna, Coord. Chem. Rev., 2017, 346, 216–239.
28 D. Shao and X.-Y. Wang, Chin. J. Chem., 2020, 38, 1005–
1018.
29 S. K. Gupta and R. Murugavel, Chem. Commun., 2018, 54,
3685–3696.
30 J.-L. Liu, Y.-C. Chen and M.-L. Tong, Chem. Soc. Rev., 2018,
47, 2431–2453.
31 Y.-S. Ding, K.-X. Yu, D. Reta, F. Ortu, R. E. P. Winpenny,
Y.-Z. Zheng and N. F. Chilton, Nat. Commun., 2018, 9, 3134.
32 L. Ungur and L. F. Chibotaru, Phys. Chem. Chem. Phys.,
2011, 13, 20086–20090.
33 N. F. Chilton, C. A. P. Goodwin, D. P. Mills and
R. E. P. Winpenny, Chem. Commun., 2015, 51, 101–103.
34 L. Ungur and L. F. Chibotaru, Inorg. Chem., 2016, 55,
10043–10056.
35 S. K. Singh, T. Gupta and G. Rajaraman, Inorg. Chem.,
2014, 53, 10835–10845.
36 C. A. P. Goodwin, F. Ortu, D. Reta, N. F. Chilton and
D. P. Mills, Nature, 2017, 548, 439–442.
37 F.-S. Guo, B. M. Day, Y.-C. Chen, M.-L. Tong,
A. Mansikkamäki and R. A. Layfield, Angew. Chem., Int. Ed.,
2020, 59, 18844–18844.
38 F.-S. Guo, B. M. Day, Y.-C. Chen, M.-L. Tong,
A. Mansikkamäki and R. A. Layfield, Science, 2018, 362,
1400–1403.
39 K. Randall McClain, C. A. Gould, K. Chakarawet, S. J. Teat,
T. J. Groshens, J. R. Long and B. G. Harvey, Chem. Sci.,
2018, 9, 8492–8503.
40 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, 2829–2837.
41 Y.-S. Ding, N. F. Chilton, R. E. P. Winpenny and
Y.-Z. Zheng, Angew. Chem., Int. Ed., 2016, 55, 16071–16074.
42 S. K. Gupta, T. Rajeshkumar, G. Rajaraman and
R. Murugavel, Chem. Sci., 2016, 7, 5181–5191.
43 J. Liu, Y.-C. Chen, J.-L. Liu, V. 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,
5441–5450.
44 A. B. Canaj, S. Dey, E. R. Martí, C. Wilson, G. Rajaraman and
M. Murrie, Angew. Chem., Int. Ed., 2019, 58, 14146–14151.
2814 | Dalton Trans., 2023, 52, 2804–2815
Dalton Transactions
45 Z.-H. Li, Y.-Q. Zhai, W.-P. Chen, Y.-S. Ding and Y.-Z. Zheng,
Chem. – Eur. J., 2019, 25, 16219–16224.
46 J.-P. Sutter, V. Béreau, V. Jubault, K. Bretosh, C. Pichon and
C. Duhayon, Chem. Soc. Rev., 2022, 51, 3280–
3313.
47 G.-Z. Huang, Z.-Y. Ruan, J.-Y. Zheng, Y.-C. Chen, S.-G. Wu,
J.-L. Liu and M.-L. Tong, Sci. China: Chem., 2020, 63, 1066–
1074.
48 P. Kalita, J. Acharya and V. Chandrasekhar, J. Magn. Magn.
Mater., 2020, 498, 166098.
49 T. G. Ashebr, H. Li, X. Ying, X.-L. Li, C. Zhao, S. Liu and
J. Tang, ACS Mater. Lett., 2022, 4, 307–319.
50 A. K. Bar, P. Kalita, J.-P. Sutter and V. Chandrasekhar,
Inorg. Chem., 2018, 57, 2398–2401.
51 P. Kalita, N. Ahmed, A. K. Bar, S. Dey, A. Jana,
G. Rajaraman, J.-P. Sutter and V. Chandrasekhar, Inorg.
Chem., 2020, 59, 6603–6612.
52 J. Cirera, E. Ruiz and S. Alvarez, Organometallics, 2005, 24,
1556–1562.
53 E. S. Group, SHAPE: Continuous Shape Measures calculation,
version 2.1, Universitat de Barcelona, Spain, 2013.
54 J. Acharya, N. Ahmed, J. Flores Gonzalez, P. Kumar,
O. Cador, S. K. Singh, F. Pointillart and V. Chandrasekhar,
Dalton Trans., 2020, 49, 13110–13122.
55 X.-C. Huang, M. Zhang, D. Wu, D. Shao, X.-H. Zhao,
W. Huang and X.-Y. Wang, Dalton Trans., 2015, 44, 20834–
20838.
56 J.-L. Liu, Y.-C. Chen, Y.-Z. Zheng, W.-Q. Lin, L. Ungur,
W. Wernsdorfer, L. F. Chibotaru and M.-L. Tong, Chem.
Sci., 2013, 4, 3310–3316.
57 F. Ortu, D. Reta, Y.-S. Ding, C. A. P. Goodwin,
M. P. Gregson, E. J. L. McInnes, R. E. P. Winpenny,
Y.-Z. Zheng, S. T. Liddle, D. P. Mills and N. F. Chilton,
Dalton Trans., 2019, 48, 8541–8545.
58 L. Escalera-Moreno, J. J. Baldoví, A. Gaita-Ariño and
E. Coronado, Chem. Sci., 2020, 11, 1593–1598.
59 G. Huang, X. Yi, J. Jung, O. Guillou, O. Cador, F. Pointillart,
B. Le Guennic and K. Bernot, Eur. J. Inorg. Chem., 2018,
2018, 326–332.
60 J. Flores Gonzalez, F. Pointillart and O. Cador, Inorg. Chem.
Front., 2019, 6, 1081–1086.
61 C. J. Windorff, M. J. Beltran-Leiva, T. E. Albrecht-Schönzart,
Z. Bai, C. Celis-Barros, C. A. P. Goodwin, Z. Huffman,
N. C. McKinnon and J. M. Sperling, Dalton Trans., 2021, 50,
14537–14541.
62 V. A. Kopotkov, D. V. Korchagin, V. D. Sasnovskaya,
I. F. Gilmutdinov and E. B. Yagubskii, Magnetochemistry,
2019, 5, 58.
63 S. K. Singh, C. J. Cramer and L. Gagliardi, Inorg. Chem.,
2020, 59, 6815–6825.
64 A. B. Canaj, S. Dey, O. Céspedes, C. Wilson, G. Rajaraman
and M. Murrie, Chem. Commun., 2020, 56, 1533–1536.
65 X.-Q. Zhu, W.-H. Cao, S.-D. Su, X.-T. Wu and T.-L. Sheng,
Dalton Trans., 2020, 49, 6738–6743.
66 J. Acharya, A. Sarkar, P. Kumar, V. Kumar, J. Flores
Gonzalez, O. Cador, F. Pointillart, G. Rajaraman and
This journal is © The Royal Society of Chemistry 2023
View Article Online
Published on 24 January 2023. Downloaded by Birla Institute of Technology and Science - Hyderabad Campus on 4/19/2025 4:47:30 AM.
Dalton Transactions
V. Chandrasekhar, Dalton Trans., 2020, 49, 4785–
4796.
67 L. R. Thomas-Hargreaves, M. J. Giansiracusa, M. Gregson,
E. Zanda, F. O’Donnell, A. J. Wooles, N. F. Chilton and
S. T. Liddle, Chem. Sci., 2021, 12, 3911–3920.
68 J. D. Rinehart and J. R. Long, Dalton Trans., 2012, 41,
13572–13574.
69 N. F. Chilton, D. Collison, E. J. L. McInnes,
R. E. P. Winpenny and A. Soncini, Nat. Commun., 2013, 4,
2551.
70 W. L. F. Armarego and C. Chai, Purification of laboratory
chemicals, Butterworth-Heinemann, 2003.
71 C. Pelizzi and G. Pelizzi, J. Chem. Soc., Dalton Trans., 1980,
1970–1973.
72 CrysAlisPRO, Oxford Diffraction UK Ltd, Yarnton, England.
73 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Adv., 2015,
71, 3.
74 G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem.,
2015, 71, 3–8.
75 O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard
and H. Puschmann, J. Appl. Crystallogr., 2009, 42, 339–341.
76 K. Brandenburg and H. Putz, DIAMOND, Crystal Impact
GbR, version 3.2, Bonn, Germany, 1997–2014.
77 F. Neese, F. Wennmohs, U. Becker and C. Riplinger,
J. Chem. Phys., 2020, 152, 224108.
This journal is © The Royal Society of Chemistry 2023
Paper
78 F. Neese, Wiley Interdiscip. Rev.: Comput. Mol. Sci., 2022, 12,
e1606.
79 A. D. Becke, Phys. Rev. A, 1988, 38, 3098–3100.
80 F. Weigend and R. Ahlrichs, Phys. Chem. Chem. Phys., 2005,
7, 3297–3305.
81 C. Angeli, R. Cimiraglia, S. Evangelisti, T. Leininger and
J. P. Malrieu, J. Chem. Phys., 2001, 114, 10252–10264.
82 C. Angeli, R. Cimiraglia and J.-P. Malrieu, Chem. Phys. Lett.,
2001, 350, 297–305.
83 C. Angeli, R. Cimiraglia and J.-P. Malrieu, J. Chem. Phys.,
2002, 117, 9138–9153.
84 C. Angeli, B. Bories, A. Cavallini and R. Cimiraglia, J. Chem.
Phys., 2006, 124, 054108.
85 D. A. Pantazis, X.-Y. Chen, C. R. Landis and F. Neese,
J. Chem. Theory Comput., 2008, 4, 908–919.
86 B. A. Hess, Phys. Rev. A, 1986, 33, 3742–3748.
87 D. Ganyushin and F. Neese, J. Chem. Phys., 2013, 138, 104113.
88 F. Neese, J. Chem. Phys., 2005, 122, 034107.
89 M. Atanasov, D. Ganyushin, K. Sivalingam and N. Frank, in
Molecular Electronic Structures of Transition Metal Complexes
II, Structure and Bonding, ed. D. M. P. Mingos, P. Day and
J. P. Dahl, Springer, Berlin, Heidelberg, 2011, vol. 143, pp.
149–220.
90 L. F. Chibotaru and L. Ungur, J. Chem. Phys., 2012, 137,
064112.
Dalton Trans., 2023, 52, 2804–2815 | 2815