Lanthanoid pyridyl-β-diketonate 'triangles'. New examples of single molecule toroics

Article abstract of DOI:10.1039/d0dt02855j

Trinuclear lanthanoid clusters have been synthesised and investigated as toroidal spin systems. A pyridyl functionalised β-diketonate, 1,3-bis(pyridin-2-yl)propane-1,3-dione (o-dppdH) has been used to synthesise a family of clusters of the form [Dy3(OH)2(o-dppd)3Cl2(H2O)4]Cl2·7H2O (1), [Tb3(o-dppd)3(μ3-OH)2(CH3CH2OH)3Cl3][Tb3(o-dppd)3(μ3-OH)2(H2O)(CH3CH2OH)2Cl3]Cl2·H2O (2), [Ho3(OH)2(o-dppd)3Cl(H2O)5]Cl3·3H2O (3) and [Er3(OH)2(o-dppd)3Cl2(H2O)3(CH3OH)]Cl2·3H2O·CH3OH (4). Despite the previous occurrence of this structural motif in the literature, these systems have not been widely investigated in terms of torodic behaviour. Magnetic studies were used to further characterise the complexes. DC susceptibility studies support weak antiferromagnetic exchange in the complexes. Slow magnetic relaxation behaviour is observed in the dynamic AC magnetic studies for complex 1. Theoretical studies predict that complex 1 and 3 have a non-magnetic ground state based on a toroidal arrangement of spins. Changes to the coordination environment in 2 do not support a toroic spin state. The prolate nature of the ErIII centres in complex 4 and large transverse anisotropy do not support the toroidal arrangement of lanthanoid spins in the complex.

Full text of DOI:10.1039/d0dt02855j

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DOI: 10.1039/D0DT02855J
ARTICLE
Lanthanoid pyridyl-β-diketonate ‘triangles’. New examples of
single molecule toroics
Chiara Caporale,a Alexandre N. Sobolev,b Wasinee Phonsri,c Keith S. Murray,c Abinash Swain,d
Received 00th January 20xx,
Accepted 00th January 20xx
Gopalan Rajaraman,d Mark I. Ogden, a Massimiliano Massi a and Rebecca O. Fuller a,e
*
DOI: 10.1039/x0xx00000x
Trinuclear lanthanide clusters have been synthesised and investigated as toroidal spin systems. A pyridyl functionalised -
diketonate, 1,3-bis(pyridin-2-yl)propane-1,3-dione(o-dppdH) has been used to synthesise a family of clusters of the form
[Dy3(OH)2(o-dppd)3Cl2(H2O)4]Cl27H2O (1), [Tb3(o-dppd)3(μ3-OH)2(CH3CH2OH)3Cl3][Tb3(o-dppd)3(μ3-OH)2(H2O)(CH3CH2OH)2
Cl3]Cl2H2O (2), [Ho3(OH)2(o-dppd)3Cl(H2O)5]Cl33H2O (3) and [Er3(OH)2(o-dppd)3Cl2(H2O)3(CH3OH)]Cl23H2OCH3OH (4).
Despite the previous occurrence of this structural motif in the literature, these systems have not been widely investigated
in terms of torodic behaviour. Magnetic studies were used to further characterise the complexes. DC susceptiblity studies
support weak antiferromanetic exchange in the complexes. Slow magnetic relaxation behaviour is observed in the dynamic
AC magnetic studies for complex 1. Theoretical studies predict that complex 1 and 3 have a non-magnetic ground state
based on a toroidal arrangement of spins. Changes to the coordination environment in 2 do not support a toroic spin state.
The prolate nature of ErIII centres in complex 4 and large transverse anisotropy do not support the toroidal arrangement of
lanthanoid spins in the complex.
Functionalisation of the diketonate scaffold or the addition of co-
ligands can be used to alter the coordination environment. 11, 13
Introduction
Developing a synthetic methodology to obtain specific lanthanoid
The wealth of functionalities available for the -diketonate family
provides good opportunity to develop structural-magnetic
clusters for applications such as single molecule magnets (SMMs)1, 2
a
4
and luminescence3,
is a
major current area of interest.5
property relationships in a family of structures. This statement may
at first seem counter intuitive, as the development of lanthanoid
SMMs is centred on using the ligand field symmetry to enhance the
inherent anisotropy of the LnIII ions with large magnetic moments.1,
14 15 The best examples of Ln-SMMs involve only a single lanthanoid
Understanding how the structure and coordination environment
impacts on the measured properties is key for the advancement of
these molecules into future applications. -diketones are a versatile
and highly functionalisable ligand class which have been shown to
7
support polynuclear lanthanoid cluster formation.6,
Such
17
ion (e.g. mononuclear complexes).16, Polynuclear Ln complexes
complexes are normally comprised of a hydroxo-bridged polynuclear
usually only display very weak SMM behaviour due to a lack of
lanthanoid cluster core encapsulated by -diketonate ligands.
19
interaction through -bridging between ions.18,
The lack of
9
Examples of mononuclear,8, dinuclear,10 trinuclear11 and larger
exchange and the poor anisotropy does not lead to a stabilisation of
a bistable ground state at notable temperatures (with the exception
of Dy). However, polynuclear clusters comprised of an appropriate
geometry can result in an ideal environment for alternative spin
arrangements.20
clusters12 supported by -diketonate ligands are known.
Coordination with these molecules generally occurs through the
bidentate backbone of the -diketonate ligand together with
additional co-ligands contained within the coordination sphere.
a. School of Molecular and Life Sciences, Curtin University, Bentley WA 6102,
Australia.
Triangular spin arrangements are well known avenues for producing
interesting properties.21 Oxo-bridged transition metal complexes
have long been known to exhibit spin frustration.22, 23 More recently,
triangular Dy3 cluster complexes have been shown to display a
toroidal spin arrangement in these single molecule toroics (SMTs).24
Depending on the type of SMTs, these systems may have a
nonmagnetic ground state which exists based on a toroidal
arrangement of spins.20 This non-magnetic state does not interact
with the applied magnetic field and is observed as a tail in the field
dependent magnetisation measurements. These materials have
unique spin transport properties based on their strongly anisotropic
b. School of Molecular Sciences and CMCA, M310, The University of Western
Australia, Crawley WA 6009, Australia.
c. School of Chemistry, Monash University, Clayton VIC 3800, Australia
d. Department of Chemistry, Indian Institute of Technology BombayPowai, Mumbai,
Maharashtra, 400076, India
e. School of Natural Sciences-Chemistry, University of Tasmania, Hobart TAS 7001,
Australia. E-mail: rebecca.fuller@utas.edu.au
Electronic Supplementary Information (ESI) available: Reaction scheme and
characterisation for o-dppdH (1H NMR; 13C NMR, IR); Structural representations
including packing arrangements and complexes 1-4; Selected interatomic distances
and angles; Polyhedra view complexes 2-4; magnetic measurements complexes 2-
4; Poly_aniso calculated susceptibility; Dynamic calculations for complex 1 and 4;
Magnetic exchange in complexes 2-4; Tabulated energies and ground-state g
tensors. See DOI: 10.1039/x0xx00000x
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nature, resulting in their suitability for a number of potential
applications including quantum computers and spintronic devices. 25,
26 In addition to Dy based SMTs, non-triangular analogues for other
lanthanoids have also been recently reported, Ln = Tb, Ho, Er.27, 28
for the production of these systems. Collection of the product was
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achieved after a series of washing stepsDuOsIi:n1g0.1a0c3e9t/oDn0iDtrTil0e28a5n5dJ
pyridine to remove unreacted o-dppdH and lanthanoid salt from the
target compound. The target clusters were then collected as a
powder and crystals suitable for X-ray diffraction were grown using
slow evaporation or diffusion techniques. If required, the bulk
sample was recrystallised for magnetic measurements as well as
analysis.
Trigonal Dy3 complexes provided the first examples of SMTs.29 In
these complexes the ring-like arrangement of spins is strongly
anisotropic and aligns with the plane of the array. However, as the
SMT field has matured, a wealth of structures has been developed.27,
30, 31
New examples with a range of structural motifs have been
Crystallography
reported, including square,32 wheel,33 cubane34 and 3d-linked pair
of Dy3 heptanuclear clusters.31 In this work we have focused on
developing complexes with a similar structural motif to the trigonal
complexes. 11, 24
Figure 2 shows the structure of the complex cation of [Dy3(OH)2(o-
dppd)3Cl2(H2O)4]Cl27H2O (1). The compound crystallises in the
ퟏ
triclinic space group P . Each of the -diketonate ligands binds to
two of the DyIII centres. One of the oxygens from the -diketone
binds exclusively to one DyIII atom. The other oxygen is shared (2-O)
between the two centres (Dy-O-Dy angles in the 97.96-98.37° range).
The second of the dysprosium centres is also bound to a nitrogen
from the pyridyl group, so that each ligand is bound through 
2(N,O);2(O,O’) to the lanthanoid centres with the other pyridyl
nitrogen atom left unbound. The lanthanoid centres and ligand
bridging oxygen atoms form an essentially planar 6 membered ring
(deviation 0.06 Å). The metal array approximates an equilateral
triangle, with deviation from the ideal Ln-Ln-Ln angle of less than
0.24°. The three eight-coordinate DyIII centres are bridged by two
central 3-OH oxygens which lie above and below the metal plane by
1.211 and 1.175 Å, respectively. Two of the DyIII cations are
coordinated to chloride anions. The final positions in the DyIII
coordination sphere contain H2O molecules. One of the unbound
pyridyl rings is distorted over two positions with occupancies set to
0.6667 and 0.3333. As a result, the neighbouring H2O contained in
the lattice is disordered. Selected bond lengths for all the complexes
are given in Table 1 with additional data contained in the ESI (Table
S1 and S2).
Pyridyl functionalised -diketonates have shown potential as
supporting ligands for SMTs. The pyridin-4-yl analogue has been
used in the synthesis of a cubane-shaped Dy4 complex.27 A HoIII
complex with the bis(pyridin-2-yl) -diketonate has been shown to
consist of a coordination environment similar to o-vanillin DyIII
triangles which exhibited a toroidal spin arrangement.11, 24 Despite
the similarity of the core and bridging atoms, the magnetic behaviour
exhibited by the holmium complex was distinctly different to the
dysprosium system. It was postulated to be likely due to the result of
the difference in the magnetic anisotropy of the holmium and
dysprosium centres. In this vein we have synthesised a family of
triangular molecules based on DyIII, TbIII, HoIII and ErIII with the
deprotonated 1,3-bis(pyridin-2-yl)propane-1,3-dione (Figure 1)
ligand (o-dppdH). This family of lanthanide complexes has been used
to investigate the role of the lanthanoid centre in the spin structure
of the metal core. In this work we aim to further elucidate the impact
of the lanthanoid anisotropy on the ligand field and magnetic
exchange by undertaking a detailed experimental and theoretical
investigation on these systems.
Using continuous SHAPE measurements, the 8-coordinate
environment approximates a triangular dodecahedron (TDD8) with
D2d symmetry and based on the shape distortion parameter given in
Table 1 for all studied complexes, this is valid for all Ln metal
centres.36 The polyhedral representations are given in Figure S3 (ESI)
Figure 1: Structure of the o-dppdH ligand, 1,3-bis(pyridin-2-yl)propane-1,3-dione.
Results and discussion
Synthesis and characterisation of complexes
A series of trinuclear lanthanoid clusters with the formula [Ln3(3-
OH)2(o-dppd)3ClxLy]4-x where Ln= DyIII, TbIII, HoIII or ErIII ; x+y=6; L =
H2O or CH3CH2OH or CH3OH have been prepared. o-dppdH was
synthesised via a Claisen condensation of ethyl-2-picolinate and 2-
35
acetylpyridine using a literature procedure (Scheme S1).11, The
ligand (2 eq.) was treated with a lanthanoid salt of the form
LnCl3.6H2O (where Ln= DyIII, TbIII, HoIII and ErIII) in the presence of
triethylamine. Although a stoichiometry of 1:1 appears to be more
appropriate for the production of a trigonal system, the 2:1 ratio and
complexation proceeding at elevated temperatures was necessary
Figure 2: Molecular structure of complex 1. Dy…Dy distances are 3.54-3.55 Å. Thermal
ellipsoids are set to 30 % probability. For clarity, hydrogen atoms and lattice solvent are
omitted.
2 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/D0DT02855J
Table 1: Selected interatomic distances and SHAPE parameter for [Dy3(OH)2(o-dppd)3Cl2(H2O)4]Cl27H2O 1, {[Tb3(o-dppd)3(OH)2(CH3CH2OH)3Cl3] [Tb3(o-dppd)3(μ3-
OH)2(H2O)(CH3CH2OH)2Cl3]Cl2H2O} 2, [Ho3(OH)2(o-dppd)3Cl(H2O)5]Cl33H2O 3 and [Er3(OH)2(o-dppd)3Cl2(H2O)3(CH3OH)]Cl23H2OCH3OH 4.
1
2
3
4
Dy1
Dy2
Dy3
-
Tb1
Tb2
Tb3
Ho1
Ho2
Ho3
Er1
Er2
Er3
-
distances (Å)
Ln-Cl
Ln-O123 (3-O)
Ln-O321 (3-O)
Ln-N
2.644(2) 2.543(6)
2.672(1) 2.672(1) 2.712(1)
2.390(3) 2.392(3) 2.376(3)
2.386(3) 2.397(3) 2.377(3)
2.530(4) 2.522(4) 2.520(3)
2.645(4)
2.383(8) 2.363(8)
2.356(8) 2.354(7)
2.51(1)
1.213
-
-
2.577(4) 2.642(1)
2.394(5) 2.382(6) 2.359(4)
2.356(5) 2.350(4) 2.374(6)
2.498(7) 2.486(7) 2.486(7)
2.36(1)
2.38(1)
2.511(9)
2.353(3) 2.339(3) 2.357(3)
2.371(3) 2.373(3) 2.331(3)
2.494(4) 2.498(3) 2.498(3)
2.50(1)
0.811
Distortion
SHAPE (D2d)*
1.230
0.854
1.033
1.307
1.296
1.571
0.985
0.814
1.217
0.901
*D2d symmetry for triangular dodecahedral polyhedral
for complexes 2-4. The closer the SHAPE index is to zero the less
distortion from the ideal environment. The geometry of the DyIII
centres in 1 appears to approximate a triangular dodecahedron
(TDD8) with D2d symmetry (Figure 3). The metal bond distances and
angles for 1 are similar to those in the DyIII o-vanillin complexes which
have the form [Dy3(3-OH)2L3Cl2(H2O)4] where L = 2-hydroxy-3-
methoxybenzaldehyde.29 Continuous shape measurements
performed on the DyIII o-vanillin systems found the geometry of the
complexes also approximates a triangular dodecahedron (TDD8)
with D2d symmetry. In complex 1, the lattice contains large voids
which are occupied by non coordinated Cl ions and H2O. The solvent
system used to isolate the complex is also shown to impact on the
solvent contained within the voids of complex 2 and 4.
Figure 3: Polyhedral view of the eight coordinate geometry of
Dy1 in complex the two 3-O(H) are positioned above the LnIII
centre (O321 and O123). This depiction from CrystalMaker®
v9.1.3 supports a TDD-8 coordination environment around the
lanthanoid centre. Purple= DyIII, red=O, green=Cl and blue=N
atom.
A
similar metal array is seen in the {[Tb3(o-dppd)3(μ3-
Cl ][Tb (o-dppd) (μ OH) (H O) Cl ]Cl 
OH)
2(CH3CH2OH)3 (CH3CH2OH)2
3
2
3
3
3
3
2
2
H2O} (2), [Ho3(OH)2(o-dppd)3Cl(H2O)5]Cl33H2O (3) and [Er3(OH)2(o-
dppd)3Cl2(H2O)3(CH3OH)]Cl23H2OCH3OH (4) complexes (ESI Figure
S2). The three lanthanoid centres are in an equilateral arrangement
with similar coordination to the -diketonate ligand and central
hydroxide groups as discussed for 1. Selected bond lengths are given
in Table 1 and in the ESI (Table S1 and S2) Depending on the
lanthanoid atom, the coordination sphere contains between one and
three Cl anions with the other positions consisting of solvent
molecules, dependent on the recrystallisation method (H2O, CH3OH,
CH3CH2OH). Using continuous SHAPE measurements, the 8-
coordinate environment approximates a triangular dodecahedron
(TDD8) with D2d symmetry, the polyhedral representations are
contained in Figure S3 (ESI). The structure of the holmium analogue
(3) is distorted in a similar manner to 1, namely one of the unbound
pyridyl rings occurs in two positions (occupancy 0.5) with
neighbouring lattice solvent also being disordered.
are found to link together through the chloride counter ions and the
pyridyl ring with either a coordinated water and/or hydroxide ligands
(Figure 4). The hydrogen bond is indirect as it does not occur solely
between donor atoms coordinated to the DyIII centres. Rather, it
involves both donor and lattice solvent/counter ions. However, since
it is the triangular arrangement of the spins and the associated
Using CrystalExplorer 3.137 the packing arrangement of molecules is
found to be influenced by - interactions as well as coordinated Cl
anions hydrogen bonding to the pyridyl rings on the adjacent
molecule and lattice solvent (ESI Figure S1a). The metal arrays are
arranged in parallel planes (Figure 4). Intermolecular  stacking
interactions between the delocalised diketonate and pyridyl ring or
between two adjacent pyridyl rings, with a maximum centroid to
centroid distance of 3.9 Å noted in 1 (ESI Figure S1b). The molecules
Figure 4: CrystalExplorer 3.1 is used to depict the hydrogen bonding
network in 1. Purple=DyIII, red=O, green=Cl, light blue=N, grey=C and
white=H.
anisotropy which impact on the stabilisation of a non-magnetic
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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toroidal spin states, the extended network will not significantly affect g[J(J+1)]0.5 values of 10.65 (Dy3+), 9.72(Tb3+), 10.61 (Ho3+) and 9.58
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3+
the occurrence of a toroidal state.24
(Er ) B per Ln centre. As the temperature is decreased from room
temperature to about 100 K we see a slight decrease occurs in MT
that is likely the result of the depopulation of the excited LnIII Stark
DOI: 10.1039/D0DT02855J
Both lattice and coordinated solvents were impacted by conditions
used for crystallisation. When comparing complex 3, to
the previously reported analogue11 an additional water and one less
chloride were refined as co-ligands with further water contained in
the lattice. In complex 2 the co-ligands are disordered, whereby one
of the coordinated H2O molecules is replaced by a CH3CH2OH
molecule. To ensure that the variations between reaction batches
only represented the slight changes mentioned, two structural
analyses for crystals from the erbium system were fully refined.
[Er3(OH)2(o-dppd)3Cl2(H2O)3(CH3OH)]Cl25H2O (4a) highlights the
variable solvation for different crystallisations. Full details of this
complex can be found in the ESI (Table S1) Metal analysis was used
to confirm lanthanide content. These results were consistent with
the proposed formulations as well as values inferred from the room
temperature susceptibility.
The extended structures for complexes 2-4 are dependent on -
interactions and coordinated Cl anions linked to neighbouring pyridyl
rings in the way depicted for complex 1 in Figure S1. The coordination
environments in the lanthanoid triangles is different for TbIII but HoIII
and ErIII are similar to that in DyIII. The linking of the metal arrays for
both 3 and 4 is also similar to that seen for complex 1. In 3, the HoIII
metal array of neighbouring molecules are connected through a
hydrogen bonding network involving the lattice Cl anions being
linked from a pyridyl ring of one molecule to coordinated H2O and
3-O of another. In an analogous manner, the complex 4 metal arrays
are linked through two slightly different lattice Cl anion
environments. The first is identical to that observed in 1 and 3. The
second involves a pyridyl ring and coordinated CH3CH2OH from one
Figure 5:Temperature dependent MT products in a DC field of 1 T for the series of
[Ln3(3-OH)2(o-dppd)3ClxLy]4-x complexes, where Ln = Dy (1) blue; Tb (2) pink; Ho (3) red
and Er (4) green.
levels. At lower temperatures, a more rapid decrease is observed,
which is likely a result of the thermal depopulation of the low-lying
Zeeman levels possibly combined with weak antiferromagnetic
coupling between the centres.
Magnetisation (M) isotherms (2-20 K) for each of the complexes were
determined in DC fields of 0 to 5 T. The results for 1 are shown in
Figure 6 with similar results being observed for 2-4 (ESI Figure S6). In
molecule being linked through the lattice Cl anions to a coordinated each of the complexes, the measurements made at 2 K do not reach
a saturation value at 5 T (i.e. M has a value of 15.60, 13.64, 14.56 and
13.94 N for 1-4, respectively). Similarly, a saturation in the
H2O and central 3-O of the neighbouring molecule. A different
arrangement is seen for the TbIII metal arrays (2). Neighbouring
molecules are still linked through lattice Cl anions. However, in this
case the coordinated CH3CH2OH (or H2O) groups are also linked with
the neighbouring molecule pyridyl, with the central 3-O playing no
role. In the absence of coordinated CH3CH2OH, water in the lattice is
also involved. Figure S4 in the ESI contains representations for each
of the complexes. The alternative environments are not expected to
alter any exchange interaction between the centres as it is the
triangular arrangement of the spins and the associated anisotropy
which governs these processes.
magnetisation is not seen in
5 T fields at 3 K. The non-
superimposability of the curves when plotted as M vs H/T supports
the occurrence of low-lying levels that are energetically close to the
ground state supporting the role of zero field splitting or Zeeman
depopulation effects, arising from magnetic anisotropy. Despite the
coordination environment being reminiscent of reported systems
with a toroidal ground states, the shape of the M vs H plots at low
fields does not have the S-shape that is often, but not always,
associated with toroidal systems.15,18,20-22 However since these
toroidal arrangements are influenced by molecular symmetry and
the moment in addition to interaction one cannot rule out the
possibility that there is a small energy gap between the nonmagnetic
ground state and the first excited state which precludes the S-shape
being observed.34 At present ab initio calculations based on CASSCF
method are best suited to identify such behaviour while
experimental evidence would require methods such as micro-Squid
magnetisation/hysteresis plots31 and NMR to unambiguously detect
and describe such states.
Magnetic Properties
Polycrystalline samples of 1-4 were used for the collection of
magnetic susceptibility data. DC measurements (2-300 K) in fields of
1 T (Figure 5) and 0.1 T (ESI Figure S5) gave similar results. The room
temperature MT values for complexes 1-4 are 40.6, 33.4, 39.6 and
34.0 cm3 mol-1 K, respectively. The value obtained for 3 is consistent
with the previous literature reports for a structural analogue (39.7
cm3 mol-1 K).11 At 300 K the eff per LnIII in complex 1-4 are 10.40,
9.43, 10.27 and 9.53 B. These are consistent with the calculated
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DOI: 10.1039/D0DT02855J
Figure 7: The temperature dependent (2-10 K) out of phase susceptibility, χM”, for
complex 1 in 0 T DC field.
Limitations of the MOLCAS packaged means calculations on the full
complex 1 are not possible. Instead calculations were undertaken in
two stages. Firstly, calculations are performed on each Dy centre by
substitution of the other two DyIII ions by diamagnetic LuIII ions.
Secondly, the single-ion anisotropy of all three DyIII are combined
together to understand the relaxation of the states. All calculations
were performed using the X-ray crystal structure data as input.
Figure 6: Magnetisation isotherms (2-20 K) in applied fields 0 to 5 T for complex 1.
Variable temperature (2-10 K) AC dynamic measurements were also
undertaken for each of the complexes both with and without an
applied bias DC field for a range of frequencies between 20 and 1488
Hz. The bias field applied in experiments was optimised for each
sample by measuring changes M” in a static DC field under an
applied oscillating field (1488 Hz and 498 Hz) at 3 K. The out of phase
component, M” for the [Dy3(OH)2(o-dppd)3Cl2(H2O)4] complex is
shown in Figure 7 in zero applied DC field. The DyIII Kramer’s ion
complex 1 is found to have an out of phase signal below 8 K which
varies with frequency. However, no maxima are observed in M”
plots, even in an applied field (ESI Figure S7). Nevertheless, the
signals are consistent with slow magnetic relaxation occurring for a
multicentred DyIII complex with insufficient anisotropy. The results
for complexes 2-4 are given in the ESI (Figure S7). The DC fields
applied in complexes 2-4 were used in an attempt to obtain efficient
quantum tunnelling and, hopefully, observe frequency dependence
of M”. However, a weak signal to noise (both with and without an
applied DC field) was seen in the M” vs. temperature or vs.
frequency plots for complexes 2-4 (ESI Figure S7), a result similar to
cases involving Ln6 toroics.38 The M” vs. frequency log-plots for 2- 4
showed that the weak, noisy data varied little upon applying the DC
field (Figure S8) with no clear evidence for frequency dependent
maxima. In the case of 1, there is a hint of a maximum at ~1000 Hz,
between 2-3 K, but a Debye analysis to estimate a Ueff value was not
feasible.
The local g tensors for the low-lying Ising doublets in 2 and 3 and the
Kramers doublets (KDs) for 1 and 4 are given in Tables S5-S9 in the
ESI. The local g tensor for complexes 1-3 is Ising in nature with
diminishing contribution towards the transverse anisotropy, as the
combination of six O, one N and one Cl (for one centre seven O and
one N) providing axial approach of ligand field around the oblate LnIII
ions in the eight coordinated square antiprism environment,
whereas for the prolate Er ion, the g tensor is not axial in nature and
they have significant transverse anisotropy.
Since the lanthanide centres are not completely symmetric to one
another, the theoretical analysis confirms that, for the above ligand
field environment when the oblate ion like DyIII is approached by two
different ligand from two different directions (keeping the other six
coordination sites same), the Cl reduces the axiality compare to the
O coordination. This is due to the increase in bond length for the
former (around 2.54 Å) compared to 2.32 Å to the latter, which in
response decreases the interaction of ligand with the metal centre.
For the complexes 1-4 the arrangement of each ground state
anisotropy has been plotted (Figure 8) for all the LnIII centres. In
complex 1 the arrangement is in a circular pattern suggesting
toroidal behaviour for the complex and the same is seen also in
complex 3. Interestingly in 2, two of the TbIII centres have the ground
state anisotropy aligned along the triangular plan similar to 1 and 3,
however the gzz axis of the Tb3 centre is perpendicular to the
triangular plane, destroying the possible toroidal moments in this
complex. This arises from the significant change in the coordination
environment of Tb1 centre where in one water molecule is found
coordinated trans to Cl position compared to ethanol coordination
which is found in the other Tb2 and Tb3 centres. Hence the
arrangement of anisotropic axis around the Tb1 centre is more or less
Theoretical analysis
In the absence of the S-shape in the low temperature magnetisation
isotherms, theoretical studies were undertaken to predict whether
these systems have a toroidal spin arrangement. For a triangular LnIII
complex to display
a toroidal spin arrangement, a planar
arrangement of local anisotropy axes and the polynuclear LnIII
complex requires cyclic symmetry.39
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similar to that of complex 1 (Dy1 in Dy3 complex), whereas the In complex 4, the ligand field is completely reversed to what is
View Article Online
DOI: 10.1039/D0DT02855J
anisotropic axis for the Tb2 and Tb3 centres are parallel to each needed for the prolate ions. It is expected for complex 4 that slow
other. For the prolate ErIII ion, the ligand fields present are not relaxation will not be observed. Indeed this was confirmed from the
suitable as they offer strong axial ligand and weaker equatorial experiments, where
a
large Quantum tunnelling of the
ligation and this leads to significant transverse anisotropy at the magnetisation was found for all the three ErIII centres. For 1 there are
ground state and hence no toroidal behaviour can be expected
(Figure 8). Large transverse anisotropy arises due to significant
mixing of the mJ states as shown in Figure S11 in ESI. The higher
LoProp charge is present at the bridging O of the diketo group and
less for the 3-O and the terminal water O for all the complexes
making the anisotropy axis lying in the direction of the bridging keto
oxo group for the oblate ion complex 1-3 whereas for the prolate Er
for complex 4, the anisotropy axis moves away from above the diketo
oxo group as shown in Figure 8.
The computed energy spectra for the low-lying Ising doublets for 2
and 3 or the KDs for complexes 1 and 4 are given in Tables S3 and S4
of ESI. From the Tables, one can clearly see that the Dy3 centre
possessing two aqua ligands coordinated (and no –Cl) is found to
have the largest ground-state excited state gap of 159 cm-1
compared to other to Dy centres (82 cm-1 and 50 cm-1 respectively
Figure 9: Arrangement of anisotropic axis for the ground state KDs and Ising
doublets for complex 1-4. Violet= Dy, green = Ho, Yellow= Tb, Pink= Er, Red=
O, Grey= C, Blue= N, Green= Cl, H are omitted for clarity.
no clear maximum seen in the out of phase susceptibility plots,
making it not possible to derive any relaxation time for
magnetisation or magnetic blocking barrier. At the individual DyIII
centre, the ground state is not completely pure mj=±15/2 in nature
with significant mixing from the excited mj levels causing fast QTM
between the degenerate ground state KDs. Moving from ground to
first excited state the angle between the anisotropy axes for both
states did not coincide with each other with very large angle of
Figure 8: Dynamics for magnetic blocking relaxation through ab initio
computation for Dy1. The thick blue line represents the Kramers
deviation causing the Raman and Orbach process between ground to
first excited levels. The relaxation diagram for the individual
lanthanide ions for Kramers ion are given in Figure 9 and ESI Figure
S10 - S11.
doublets as a function of computed magnetic moment. The green
dotted arrows show the possible pathway through Orbach/Raman
relaxation, the dotted red lines and blue represent the presence of
QTM/TA-QTM between the connecting pairs. The numbers provided at
each arrow are the mean absolute value for the corresponding matrix
element of transition magnetic moment. The numbers at the KDs
represents the contribution of different states for the corresponding
wave functions.
Toroidal Behaviour and Exchange Coupling:
for Dy1 and Dy2). Moving to complexes 2 and 3, for the Ising
doublets, the tunnel splitting for complexes 2 and 3 occurs and is
found to be in the range of 0.0005 to 0.1 cm-1 for the former and in
the range of 2 to 3 cm-1 for the later which is in agreement with the
previously reported molecule.11 Due to the non-Kramers nature and
high tunnel splitting it is very much expected that these molecules
lack SMM behaviour and hence no significant peak for the out of
phase susceptibility has been observed from the AC magnetic
dynamics measurement.
The inputs from the SINGLE_ANISO calculations have been used in
the POLY_ANISO module to compute the exchange interactions
between the Ln-Ln centre for all the four complexes and the energy
levels for the exchange coupled state have been obtained. For
calculating the exchange interaction, the Lines model has been taken
into account with the Hamiltonian represented in the equations 1-3
(see below in Experimental). Since all the lanthanide centres are in
distinctive ligand environments i.e. they have different terminal
coordination, the exchange interactions between the Ln-Ln centres
are expected to differ. We have considered three different exchange
parameters for the three Ln centres represented in the Figure 10
6 | J. Name., 2012, 00, 1-3
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ground state anisotropy which is responsible for the predicted
View Article Online
toroidal moment. For these two complexes,DtOhIe: 1t0o.1r0o3id9a/Dl 0pDroTp0e28rt5i5eJs
have been exploited using POLY_ANISO module42, 43 to obtain the
toroidal states at the different energy levels. For this the magnetic
interaction has been simulated by considering the magnetic dipole-
dipole interaction and the exchange interaction explicitly within
Lines model approximation. The Hamiltonian used for the approach
is provided in the Experimental section, equations 1-3.
It has been observed that the flipping of spins occurs moving from
the ground to first excited state causing switching to the reversal
arrangement. The ground state vectors in 1 are found to be in almost
perfect triangular arrangement where the angle of deviation of the
gz vector from the Dy3 plane for complex 1 is 2.8°, 3.0 ° and 5.7° for
Dy1, Dy2 and Dy3 respectively. Similarly for complex 3 these values
are 3.9°, 1.5° and 1.9° for Ho1, Ho2 and Ho3 centres. The lack of
toroidal behaviour for complexes 2 and 4 arises from the deviation
of the gz vector from the respective lanthanide Ln3 plane being too
high. These values are 3.5° ,19.7° and 35.4° for complex 2, whereas
Figure 10: Mode of exchange between the Dy-Dy
ions in complex 1.
below (see also ESI Figure S12). For complexes 2-4 all the three
exchange interactions are found to be antiferromagnetic in nature as
obtained by fitting both the experimental susceptibility and
magnetisation data. For complex
1
there are two weak for complex 4, no in plane vectors are found. The gz is out of plane
with respect to the Er3 triangle.27, 30 The energy profile diagram is
ferromagnetic and one weak antiferromagnetic exchange
interactions. A closer look at the structure reveals that there are
some differences in the geometrical parameters apart from the
variation in the terminal ligand. Particularly one of 3-OH, has
significant asymmetry in Dy1-O(H)-Dy angles with one angle being
slightly larger than the other two (98.05 vs. 97.15 and 96.45°). This
large angle which corresponds to the J1 interaction is between two
given in Figure 11.
Dy centres possessing terminal –Cl ions. As shown earlier by us in
41
magneto-structural correlations for several Dy2 dimers,40,
the
angle here is at the border line where even a marginal change
(approximately one degree) could switch the nature of exchange
from weakly ferro to antiferromagnetic. These values are reflected in
the bond angle analysis of the other three complexes as well. The
corresponding Ln-O-Ln for the complex 2 are found to be 96.86,
96.95 and 96.42˚, for complex 3 it was 97.78, 97.13 and 97.60˚, and
for complex 4, 96.49, 96.43 and 97.06˚. In all of these cases the
magnetic interactions are found to be antiferromagnetic in nature.
Moreover the smaller bond angles in complex 4 favours a greater
antiferromagnetic contribution compared to the other complexes.
The experimental and POLY_ANISO calculated temperature
dependent MT for complexes 1-4 are contained in the ESI in Figure
S9.
Table 2 The exchange interactions between the Ln-Ln for complexes
1-4; in cm-1.
J3
J1
J2
J3
J1
J2
J3
J1
J2
dipo
dipo
tot
tot
tot
exch
exch
exch
dipo
-0.65
-0.16
-0.25
-1.95
-0.05
-0.18
-0.23
-1.80
-0.05
-0.18
-0.23
-1.80
-0.25
-0.04
-0.10
-0.45
-0.15
-0.06
-0.10
-0.40
-0.15
-0.06
-0.10
-0.40
-0.40
-0.12
-0.15
-1.50
0.20
0.20
1
2
3
4
-0.12
-0.13
-1.40
-0.12
-0,13
-1.40
Figure 11: Low-lying exchange spectrum for complexes 1 (upper) and 3
(lower). The exchange coupled states (KDs) are placed on the diagram
according to their magnetic moments (bold blue and green lines).
From the SINGLE_ANISO calculations at the individual Ln centres it
was found that in 1 and 3 there is a circular arrangement of the
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The ground toroidal state shows an energy difference of
̴
View Article Online
DOI: 10.1039/D0DT02855J
the first excited state where the flipping of one spin occurs (non-
toroidal state). For complex 2 the anisotropy axes for the ground
Ising doublet are similar to that of toroidal arrangement, (the angle
has been reported above). However slight deviation of the gz axis
from the triangle plane and weaker coupling leads to smaller
toroidal-non-toroidal state gap and hence a smaller barrier ( ̴
0.5 cm-
1) compared to complex 1. In contrast, the axis for the complex 3
shows unusual behaviour due to the significant change in the
terminal coordination for Tb-1 centre which we have already
discussed above, causing two of the ground state axes to be parallel
to each other. Moving to complex 4, as a result of the prolate nature All NMR spectra were calibrated to residual solvent signals. Infrared
of the ErIII ion very large transverse anisotropy in the ground state
was observed, and thus it is expected that there should not be any
toroidal properties. This is confirmed from the theoretical studies.
spectra were recorded using an attenuated total reflectance Perkin
Elmer Spectrum 100 FT-IR with a diamond stage. IR spectra were
recorded from 4000–650 cm-1. Characterisation data (1H NMR; 13C
NMR, IR) for the ligand are contained as figures within the ESI (pp 1-
2). The intensity of the band is reported as strong (s), medium (m),
or weak (w), with broad (br) bands also specified. Melting points
were determined using a BI Barnsted Electrotermal 9100 apparatus.
Elemental analyses were carried out on bulk samples using a Thermo
Finning EA 1112 Series Flash. Inductively coupled plasma atomic
emission spectroscopy (Murdoch-Marine and Freshwater Research
Laboratory) was used to evaluate the lanthanoid content of the
complexes. The metal analysis for the lanthanoid gave results
consistent with the proposed formulations after extensive drying.
Conclusions
Triangular arrangements of lanthanoid spins have been shown to
exhibit a nonmagnetic ground state based on a vortex arrangement
of spins. We have synthesised a family of trinuclear lanthanide
complexes using pyridyl functionalised -diketonate to investigate
this phenomenon. The metal array has the general form [Ln3(3-
OH)2(o-dppd)3ClxLy] where Ln= DyIII, TbIII, HoIII or ErIII. We have
undertaken magnetic studies and theoretical calculations on the
complexes. Despite the inability to observe an S-shape at low
temperatures and fields in the magnetisation isotherms, theoretical
studies have predicted that complexes 1 and 3 support a toroidal spin
arrangement. 1 is found to have a large ground state with Ising
anisotropy, and the spins are arranged toroidally. Complex 3 is also
predicted to show toroidal behaviour which is slightly inferior to 1.
For 2, a large ground state anisotropy is present, but due to
significant change in the coordination environment, it does not
possess any toroidal behaviour. The inability to observe a flattening
in the magnetic isotherms for these complexes is likely due to the
nonmagnetic ground state which is not energetically well separated
from the first excited state. Unsurprisingly, the prolate nature of Er
in 4 and the large transverse anisotropy does not support a toroidal
arrangement.
Crystallographic data for the structure were collected at 100(2) K on
an Oxford Diffraction Gemini diffractometer with Mo Kα or Cu Kα
radiation. Following absorption corrections and solution by direct
methods, the structures were refined against F2 with full-matrix
least-squares using the program SHELXL-2014.44 All hydrogen atoms
were added at calculated positions and refined by use of riding
models with isotropic displacement parameters based on those of
the parent atoms. Anisotropic displacement parameters were
employed throughout for the non-hydrogen atoms. Structure
refinement data are reported in the SI.
1,3-bis(pyridin-2-yl)propane-1,3-dione (o-dppdH):
2-Acetylpyridine (5.60 mL, 0.050 mol) was dissolved in anhydrous
THF (200 mL) and NaH (60% dispersion in paraffin oil, 2.40 g, 0.060
mol) was carefully added. Ethyl-2-picolinate (6.80 mL, 0.050 mol) was
added dropwise and the mixture was vigorously stirred at 60 °C for
12 hours. More portions of THF were added as the mixture thickened
(30 mL x 2). The solvent was removed under reduced pressure and
the red/orange solid was acidified in a 1:5 v/v glacial acetic
acid:water solvent mixture. The solid was filtered out and washed
with multiple portion of 1:5 v/v glacial acetic acid:water solvent
mixture. The solid was then recrystallised from methanol. The target
product was collected as an off-white powder. Yield: 6.16 g (54.5%).
MP: 102 – 103 °C. IR ( / cm-1): 3053 w (C-H asym stretch), 2922 w (C-
H sym stretch), 1603 s (C=O stretch), 1317 m (C-N stretch). 1H NMR
( / ppm, DMSO-d6): 8.77 (d, 2H, J = 4.3 Hz), 8.20 – 7.94 (m, 6H), 7.64
– 7.62 (m, 2H). 13C NMR ( / ppm, DMSO-d6): 196.6, 183.5, 151.9,
151.5, 149.7, 149.1, 137.7, 127.9, 127.2, 121.9, 121.5, 93.7, 48.1.
The Dy-Dy distance in 1 is similar (3.537 Å to 3.553 Å) to the
previously reported Dy3 toroidal molecule by Powell and co-
workers24 (3.514 to 3.540 Å) and is shorter than another Dy3 toroidal
(Dy-Dy distance is 3.73 Å) reported by Murray et al.39 The angle
between the ground state gzz axis for 1 is found to be 6.13°, 10.6° and
2.7° for Dy1, Dy2 and Dy3 respectively and this is also similar to
Powell’s Dy3 system (4.1° , 8.8° and 2.4°) and is significantly smaller
than Dy3 toroidal system report by Murray et al. (~12°). Due to the
striking similarity of 1 to earlier Dy3 system by Powell, we expect that
their toroidal moments are comparable and is expected to be better
than the Dy3 system reported by Murray et al.
The present work confirms that a combination of both theoretical
and experimental studies is essential in the determination of a
toroidal state in triangular (and other) lanthanoid STMs.
8 | J. Name., 2012, 00, 1-3
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Anal. Calcd for o-dppdH C13H10N2O2: C 69.02, H 4.46, N 12.38%.
[Er3(OH)2(o-dppd)3Cl2(H2O)3(CH3OH)]Cl23H2OCH3OHView(4A)r:ticleYOinellinde:
DOI: 10.1039/D0DT02855J
0.155 g (12.3%). Crystals suitable for X-ray analysis were obtained by
Found: C 69.23. H 4.31, N 12.53%.
slow evaporation of a methanol solution of the cluster over a week.
MP: 322 °C (dec). IR ( / cm-1): 3355 w (OH stretch), 3005 w (C-H
asym stretch), 2923 w (C-H sym stretch), 1526 s (C-O stretch), 1312
General synthesis for the lanthanide trinuclear clusters
m
(C-N
stretch).
Anal.
Calcd
for
o-dppdH (0.317 g, 0.0014 mol) was dissolved in dry methanol (40 mL)
[Er3(OH)2(C13H9N2O2)3Cl2(H2O)3(CH3OH)]
and triethylamine (0.2 mL) was added dropwise to deprotonate the
Cl2(H2O)(C5H5N)2(CH3CH2OH)3=C56H73Er3N8O18Cl4: C 37.40; H 4.26; N
6.65 %. Found: 37.49; H 4.30; N 6.86 %; % Er calculated 28.0 % found
27.4 %. eff=9.53 B.M. per Er3+.
.
diketone. LnCl3 6H2O (0.0007 mol) was added to the reaction mixture
and heated at the reflux temperature for 48 hours. The solvent was
evaporated under reduced pressure and the solid was dissolved in 40
mL of acetonitrile (to remove excess of ligand) and centrifuge for 5
minutes at 7500 rpm. The insoluble solid was retained and dissolved
in 40 mL of pyridine, before being centrifuged again (unreacted
lanthanoid salt precipitates out). The solution was collected and
evaporated under reduced pressure and the solid was washed
multiple times with diethyl ether (20 mL x 3). The target complex
used for characterisation and magnetic measurements was either
Crystallography
Experimental data for the structures were measured at 100(2) K on
an Oxford Diffraction Gemini diffractometer or an Oxford Diffraction
Xcalibur X-Ray diffractometers. In complexes 1, 3, 4 and 4a the lattice
Cl are disordered between several positions. During the refinement,
their populations were forced to maintain a balance between the
collected directly as a crystalline powder or recrystallised from positively and negatively charged components of the complexes. The
data were corrected for Lorentz and polarization effects and
absorption. The structures were solved by direct methods and
refined against F2 with full-matrix least-squares using the programs
suit SHELX.45 Anisotropic displacement parameters were employed
for the non-hydrogen atoms. All hydrogen atoms were added at
calculated positions and refined by use of a riding model with
isotropic displacement parameters based on those of the parent
atom. Crystallographic data for the structures reported in this paper
have been deposited at the Cambridge Crystallographic Data Centre.
Copies of the data with CCDC numbers 2022326-2022330 can be
obtained free of charge via https://www.ccdc.cam.ac.uk/structures/,
or from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, U.KCB21EZ, UK (fax +441223336033; email
deposit@ccdc.cam.ac.uk).
methanol, ethanol or ethanol:hexanes mixture. With the exception
of 2, complexes have the general form [Ln3(μ3-OH)2(o-dppd)3ClxL6-x-y
L’y]Cl4-x, where: L and L’ = H2O or CH3CH2OH or CH3OH. Metal analysis
for the lanthanides gave results consistent with the proposed
formulations. Elemental analysis was performed on bulk crystalline
material.
[Dy3(OH)2(o-dppd)3Cl2(H2O)4]Cl27H2O (1): Yield: 0.210 g (19.7 %).
Crystals suitable for X-ray analysis were obtained by slow
evaporation of a methanol solution of the cluster over a week. MP:
323 °C (dec). IR ( / cm-1): 3195 w (OH stretch), 3005 w (C-H asym
stretch), 2923 w (C-H sym stretch), 1521 s (C-O stretch), 1310 m (C-N
stretch). Anal. Calcd for [Dy3(OH)2(C13H9N2O2)3Cl2(H2O)4]
(CH3CH2OH)5=C49H67N6O17Cl2Dy3: C 37.47; H 4.30; N 5.35 %. Found: C
37.56; H 4.66; N 5.83 %. % Dy calculated 31.04 % found 31.9 %.
(1): C39H51Cl4Dy3N6O19, M = 1537.16, colourless needle, 0.192 × 0.048

eff=10.40 B.M. per Dy3+.
3
1
× 0.028 mm , triclinic, space group P (No. 2), a = 10.1440(3), b =
17.5135(4), c = 17.9653(4) Å, α = 62.865(2), β = 73.868(2), γ =
78.120(2)°, V = 2716.81(13) Å3, Z = 2, Dc = 1.879 g cm-3, μ = 4.353 mm-
1. F000 = 1490, MoKα radiation, λ = 0.71073 Å, 2θmax = 64.5°, 58606
reflections collected, 17881 unique (Rint = 0.0847). Final GooF =
1.002, R1 = 0.0613, wR2 = 0.1201, R indices based on 10524
{[Tb (o-dppd) (μ -OH)
Cl ][Tb (o-dppd) (μ -
2(CH3CH2OH)3
3
3
3
3
3
3
3
OH) (H O)
Cl ]Cl H O} (2): Yield: 0.177 g (15.0 %).
(CH3CH2OH)2
2
2
2
2
3
Crystals suitable for X-ray analysis were obtained by slow diffusion of
hexane in an ethanol solution of the cluster over a week. MP: 318 °C
(dec). IR ( / cm-1): 3183 w (OH stretch), 3005 w (C-H asym stretch),
2923 w (C-H sym stretch), 1520 s (C-O stretch), 1306 m (C-N stretch). reflections with I > 2σ(I) (refinement on F2), |Δρ|max= 2.5(2) e Å-3, 745
Anal. Calcd for [Tb (C13H9N2O2) (OH) (H O)
2.5Cl3]
0.5(CH3CH2OH)
parameters, 133 restraints. CCDC-2022326
3
3
2
2
(CH3CH2OH)C5H5N= C51H56N7O12Cl3Tb3 : C 39.72, H 3.66 N 6.35%.
Found: C 39.41, H 3.67, N 6.35%. % Tb calculated 28.3 % found 28.7
%. eff=9.43 B.M. per Tb3+.
(2): C88H92Cl8N12O23Tb6, M = 2922.85, pale yellow blade, 0.291 ×
3
ퟏ
0.119 × 0.030 mm , triclinic, space group P (No. 2), a = 13.3953(3),
b = 14.2766(3), c = 14.9895(4) Å, α = 92.506(2), β = 97.712(2), γ =
95.225(2)°, V = 2824.30(12) Å3, Z = 1, Dc = 1.718 g cm-3, μ = 3.961 mm-
1. F000 = 1414, MoKα radiation, λ = 0.71073 Å, 2θmax = 64.7°, 61139
reflections collected, 18702 unique (Rint = 0.0516). Final GooF =
1.001, R1 = 0.0458, wR2 = 0.0987, R indices based on 13555
reflections with I > 2σ(I) (refinement on F2), |Δρ|max= 0.25(2) e Å-3,
648 parameters, 10 restraints. CCDC-2022327
[Ho3(OH)2(o-dppd)3Cl(H2O)5]Cl33H2O (3): Yield: 0.181 g (16.8 %).
Crystals suitable for X-ray analysis were obtained by slow
evaporation of a methanol solution of the cluster over a week. MP:
314 °C (dec). IR ( / cm-1): 3375 w (OH stretch), 3053 w (C-H asym
stretch), 2922 w (C-H sym stretch), 1521 s (C-O stretch), 1310 m (C-N
stretch).
Anal.
Calcd
for
[Ho3(OH)2(C13H9N2O2)3Cl(H2O)5]
Cl2(CH3CH2OH)2(H2O) = C43H53N6O16Ho3Cl3: C 34.17; H 3.53; N 5.56 %.
Found: C 34.45; H 3.79; N 5.91 %. % Ho calculated 32.7 % found 32.9 (3): C39H45Cl4Ho3N6O16, M = 1490.40, colourless block, 0.161 × 0.126
%. eff=10.27 B.M. per Ho3+.
3
ퟏ
× 0.093 mm , triclinic, space group P (No. 2), a = 10.1060(6), b =
This journal is © The Royal Society of Chemistry 20xx
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8s7p5d3f2g1h.] basis set for LnIII atoms, the [ANO-RCC...3s2p.] basis
DOI: 10.1039/D0DT02855J
set for C atoms, the [ANO-RCC...2s.] basis set for H atoms, the [ANO-
17.3501(9), c = 18.1704(11) Å, α = 110.050(5), β = 105.850(5), γ =
101.302(4)°, V = 2727.2(3) Å3, Z = 2, Dc = 1.815 g cm-3, μ = 10.157 mm-
1. F000 = 1436, CuKα radiation, λ = 1.54178 Å, 2θmax = 134.8°, 25032
reflections collected, 9622 unique (Rint = 0.0769). Final GooF = 1.001,
R1 = 0.0819, wR2 = 0.1944, R indices based on 5808 reflections with
I > 2σ(I) (refinement on F2), |Δρ|max= 1.4(2) e Å-3, 748 parameters,
177 restraints. CCDC-2022328
View Article Online
RCC...3s2p1d.] basis set for N and O the [ANO-RCC...4s3p1d.] basis
set for the Lu atom, [ANO-RCC...5s4p2d1f.] atoms. The Guessorb step
involves for selecting the suitable active space, followed by the spin
averaged CASSCF calculations. The active space taken for the Dy, Tb
, Ho and Er are (9,7), (8,7), (10,7) and (11,7) respectively, indicating
distribution of corresponding number of electrons in the seven 4f
(4): C41H49Cl4Er3N6O16, M = 1525.44, pale brown needle, 0.272 ×
3
ퟏ
0.140 × 0.056 mm , triclinic, space group P (No. 2), a = 10.0875(3), orbitals. For the configuration Interaction procedure 21 sextet roots
has taken for DyIII, for the TbIII ion seven septet, one hundred and
forty quintet excited states and one hundred and ninety-five triplet
excited states for the HoIII ion two hundred and ten triplet excited
states and one hundred and ninety-five singlet excited states, for the
ErIII ion thirty five quartet and one hundred twelve doublet excited
states has been included. After computing all the excited state, all
the low excited states (<50000 cm-1) has been mixed through RASSI-
SO module.48 Finally the SINGLE_ANISO module helps in calculating
the anisotropy factor of the low lying state as well as the nature of
magnetic behaviour at individual Ln centre.
b = 17.5576(4), c = 18.0809(4) Å, α = 110.687(2), β = 105.565(2), γ =
100.854(2)°, V = 2739.91(13) Å3, Z = 2, Dc = 1.849 g cm-3, μ = 4.814
mm-1. F000 = 1474, MoKα radiation, λ = 0.71073 Å, 2θmax = 64.8°,
56013 reflections collected, 18104 unique (Rint = 0.0284). Final GooF
= 1.002, R1 = 0.0390, wR2 = 0.1024, R indices based on 15201
reflections with I > 2σ(I) (refinement on F2), |Δρ|max= 4.3(2) e Å-3, 656
parameters, 40 restraints. CCDC-2022329
(4a): C39H47Cl4Er3N6O17, M = 1515.40, pale brown needle, 0.167 ×
0.111 × 0.082 mm3, triclinic, space group P-1 (No. 2), a = 10.1697(2),
b = 17.4740(3), c = 17.7993(3) Å, α = 62.933(2), β = 74.798(2), γ =
79.589(2)°, V = 2711.1(1) Å3, Z = 2, Dc = 1.856 g cm-3, μ = 4.866 mm-
1. F000 = 1462, MoKα radiation, λ = 0.71073 Å, T = 100(2) K, 2θmax
65.7°, 61314 reflections collected, 18503 unique (Rint = 0.0531).
=
The above results gives the inputs for performing the POLY_ANISO
module for the entire molecule to derive the exchange and dipolar
interaction between the Ln-Ln centres. The Hamiltonian for
calculating the exchange values has been given below.51, 52
Final GooF = 1.003, R1 = 0.0521, wR2 = 0.1165, R indices based on
12677 reflections with I > 2σ(I) (refinement on F2), |Δρ|max= 2.2(2) e
Å-3, 634 parameters, 18 restraints. Lp and absorption corrections
applied. CCDC-2022330
∑
퐻푒푥 = ― 퐽푖푆푖푆푖 + 1
(1)
푖
Magnetism
Here Ji=Jidip+Jiexch; that is, Ji are the total magnetic interaction Ln-Ln,
this describes the interaction between all the neighbouring metal
centres.
Magnetic susceptibility measurements were performed using a
Quantum Design MPMS-XL
7
SQUID magnetometer. DC
measurements were carried out at temperatures between 1.8 and
300 K in fields ranging from 0–5 T. AC susceptibility measurements
were carried out in an oscillating ac field of 3.5 Oe and frequencies
ranging from 0.1 to 1500 Hz. Measurements were made on
polycrystalline samples contained in Vaseline to prevent torqueing
effects.
퐷푦푖 ― 퐷푦푖 + 1
푑푖푝
퐷푦푖 ― 퐷푦푖 + 1
)푠퐷푦 푠퐷푦
푖 + 1 (2)
푖
푒푥푐ℎ
퐻 = ―( ― 퐽
+ 퐽
휇퐵2
퐷푦푖 ― 퐷푦푖 + 1
푑푖푝
퐽
=
푔2퐷푦
(3)
푖 + 1
푅3퐷푦
푖
― 퐷푦
Computational Details
Conflicts of interest
There are no conflicts to declare
Theoretical investigation were performed using ab initio calculations
based on the coordinates from the X-ray crystal structures with the
MOLCAS 8.0 package.46 The calculations involve the stepwise
Acknowledgements
procedure of guessing the active orbitals followed by CASSCF and
48
RASSI calculations.47,
Doughlass Kroll Hamiltonian has been
ROF thanks the ARC for a Discovery Early Career research Award
(DE180100112). The authors acknowledge the CMCA Research
Facility at UWA. KSM thanks the ARC for a Discovery grant. GR would
like to than SERB and DST for funding (CRG/2018/000430;
included to take account of the relativistic effect which is more
pronounced for the heavier lanthanide elements.49 CASSCF
calculations helps in achieving the spin free eigenstate.
SINGLE_ANISO module is used to calculate the magnetic properties
at individual lanthanide centre.50 Using the inputs obtained from the
SINGLE_ANISO module POLY_ANISO calculations has been done to
plot the toroidal states as well the exchange interaction between the
Ln-Ln centre. For the Ln ions TZVP level of basis set has been taken
from the ANO…RCC library where as for the coordinated O and Cl TZV
level of basis set has been used. For the remaining atoms DZV level
basis has been used. We have employed the [ANO-RCC...
DST/SJF/CSA-03/2018-10;
SB/SJF/2019-20/12).
Dr
Thomas
Rodemann of the UTas Central Science Laboratory is thanked for
elemental analysis.
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