Synthesis of heptanuclear Ni4Dy3 coordination aggregate using tridentate ligand: X-ray structure, magnetism and theoretical studies

Article abstract of DOI:10.1016/j.ica.2021.120524

The Schiff base ligand, 2-(((2-hydroxybenzyl)imino)methyl)phenol (H₂L) having ONO donor centres are utilized to synthesize {Ni₄Dy₃} coordination aggregate following the support of six benzoate bridging groups. Sequential a

Full text of DOI:10.1016/j.ica.2021.120524

Inorganica Chimica Acta 526 (2021) 120524
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Synthesis of heptanuclear Ni Dy coordination aggregate using tridentate
4
3
ligand: X-ray structure, magnetism and theoretical studies
a
b
c
d
c
b
Avik Bhanja , Lucy Smythe , Kamil Kotrle , Fabrizio Ortu , Radovan Herchel , Mark Murrie ,
a,*
Debashis Ray
a
Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
School of Chemistry, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK
Department of Inorganic Chemistry, Faculty of Science, Palacky University, Olomouc CZ-77146, Czech Republic
Department of Chemistry, University of Leicester, Leicester LE1 7RH, UK
b
c
d
A R T I C L E I N F O
A B S T R A C T
Keywords:
The Schiff base ligand, 2-(((2-hydroxybenzyl)imino)methyl)phenol (H L) having ONO donor centres are utilized
2
Schiff base
to synthesize {Ni
addition of Dy(NO
aggregation of heptanuclear Na[Ni
4
Dy
3
} coordination aggregate following the support of six benzoate bridging groups. Sequential
⋅6H O and NiCl ⋅6H O to H L followed by PhCO Na completes the coordination driven
Dy (L) -OH) 1,3-PhCO
Dy
3
d-4f complex
3
)
3
2
2
2
2
2
Aggregation
4
3
4
(μ
3
4
(μ
1,1,3,3-PhCO
2
)
2
(
μ
2
)
4
(CH
3
OH)
4
]∙CH
2
Cl
2
⋅9H
2
O (1)
Magnetism
having 2,3,6M7 ꢀ 1 topology. Two adjacent perpendicular inverse Ni
2
2
partial di-cubane units sharing a
CASSCF calculation
III
common vertex through the central Dy ion resulted a new structural arrangement within the Ni ꢀ Dy family of
coordination aggregates. The complex shows no slow magnetic relaxation under zero applied fields and only
shows a very weak field dependent magnetization. The DFT calculations revealed weak ferromagnetic exchange
II
between benzoato-bridged Ni ions, whereas the CASSCF calculations were used to identify magnetic anisotropy
in Ni and Dy ions resulting in low-lying excited states of DyIII ions with significant probability for the quantum
II
III
tunneling of the magnetization, which rationalize the observed fast dynamics in the magnetic properties.
1
. Introduction
Choice and design of multidentate ligand plays a crucial role in co-
important to note that to behave a molecule as SMM, it must have large
ground state spin, high energy barrier and most importantly significant
single ion-anisotropy; [13] choice of suitable lanthanide ions thus come
III
ordination driven multinuclear complex formation. Presence of two
different types of metal ions with different coordination preferences
towards the anionic ligand and co-ligands, lead to a literature unknown
coordination pathway for the formation of novel coordination aggre-
gate. Synthetic endeavour to obtain such agglomerate of metal ions lead
to the identification of new and aesthetically pleasing structures and
properties. The search for such molecules having multiple paramagnetic
metal ions of varying types led to the discovery of unique magnetic
behaviour; potentially suitable for high density information storage
into play. The fast advances of Ln ions involving molecules, especially
III
the Dy incorporating compounds are of huge interest exhibiting
exceptional magnetic properties. [14–19] Use of organic ligand anions,
having borderline and hard donor centres, can thus be appropriate for
the growth of 3dꢀ 4f aggregates with interesting magnetic behaviour.
II
Amongst the 3d ions, choice of Ni ion is advantageous because of its
appreciable contribution towards magnetic anisotropy [20] and for the
III
interesting exchange interactions with the Dy ions within molecular
aggregates. [21,22]
[
1,2], spintronics [3] and quantum computing [4]. Such compounds
also find application in catalysis [5], unique luminescence behaviour
6,7] and quite often function as single molecule magnet (SMM) below a
particular blocking temperature (T ). [8] Following the first report of
Synthetic control for such coordination aggregate is itself highly
challenging as it depends on several factors like nature of ligand anion,
stoichiometric ratio of added metal ions, choice of solvents, pH adjust-
ment from the use of different bases, steric and electronic controls from
ancillary ions etc. [23] Alteration of any of these factors is sufficient to
change the composition and nature of the product along with its
[
B
Mn12 aggregate as SMM [9], several ligand anions bound molecular
aggregates have been reported in search of new SMMs which can be
effective at higher temperature than the reported ones. [10–12] It is
III
preferred shape and topology. The Lewis acidic nature of the Ln ions
*
Corresponding author.
E-mail address: dray@chem.iitkgp.ernet.in (D. Ray).
https://doi.org/10.1016/j.ica.2021.120524
Received 24 March 2021; Received in revised form 1 July 2021; Accepted 7 July 2021
Available online 12 July 2021
0
020-1693/© 2021 Elsevier B.V. All rights reserved.

A. Bhanja et al.
Inorganica Chimica Acta 526 (2021) 120524
also helps in the hydrolysis of the already coordinated water molecules
(1:1, v/v) solvent mixture. A 5 mL of MeOH solution of Dy(NO
(0.033 g, 0.075 mmol) and NEt (0.022 g, 0.20 mmol) was added into
the ligand solution. After 1 h of stirring, a 10 mL of MeOH solution of
NiCl O (0.024 g, 0.10 mmol) was added into that solution and af-
⋅6H
terwards solid sodium benzoate (0.029 g, 0.20 mmol) was added. The
bright green reaction mixture was next stirred for additional 4 h at room
temperature, filtered and kept for slow evaporation at low temperature
(10–15 ◦C) for crystallization. Green block shaped single crystals are
isolated after a week from the mother liquor, which were characterized
by single crystal X-ray structure determination. Yield: 0.024 g, 35%
3
)
3
⋅6H
2
O
[
24] and in situ generation of hydroxido linkers, which again helps in
3
constructing a multinuclear mineral like magnetic cage. [25] Several
II_
III
multinuclear Ni Dy based coordination aggregates has been synthe-
sized in the recent past which includes, Ni Dy [26], Ni Dy [27],
Ni Dy [28], Ni Dy [29], Ni Dy [30], Ni Dy [31] having interesting
2
2
6
4
8
8
5
4
6
6
6
3
5
3
topology such as butterfly, square grid, cube, star etc. Both terminal and
central phenol group bearing Schiff bases have potential in synthesizing
_
many Ni Ln complexes through subtle control of reaction conditions.
[
32–35] However, fine tuning in the nuclearity of the aggregates and the
effect of use of ancillary bridges on the size of the aggregate, still re-
quires extensive synthetic endeavour.
2 4 3 4
(based on Dy). Anal. Calcd for C103H113Cl N NaDy Ni O37 (2815.20): C,
43.94; H, 4.05; N, 1.99. Found: C, 44.12; H, 4.10; N, 2.01. Selected FT-IR
ꢀ 1
Keeping all these factors in mind, we have focused our attention on
data (KBr) cm : 3363 (br), 1650 (w), 1595 (s), 1556 (s), 1478 (s), 1403
(s), 1290 (m), 1160 (w), 1032 (w), 900 (w), 855 (w), 754 (m), 717 (s),
593 (w).
II
synthesizing a flexible phenol-based ligand and its suitability to trap Ni
III
and Dy ions with the support of small ancillary bridges (Scheme 1).
Thus we have chosen, 2-(((2-hydroxybenzyl)imino)methyl)phenol
(
H
2
L) to synthesize Na[Ni
4
Dy
3
(L)
4
(
μ
3
-OH)
4
(
μ
1,1,3,3-PhCO
2
)
2
(
μ
1,3
-
2
.4. Physical measurements
PhCO
2
)
4
(CH
3
OH)
4
]∙CH
2
Cl
2
⋅9H
2
O (1) from bridging action of hydroxido
and benzoate linkers. The present work reports detailed synthetic
endeavour, basic spectroscopic characterization, structure determina-
tion, magnetic measurements and theoretical validation of the observed
properties.
Elemental analysis (C, H, N) of the powder complex were done using
the Perkin ꢀ Elmer model 240C elemental analyzer. BRUKER D2
PHASER diffractrometer (30 kV/10 mA) were used for the powder X-ray
diffraction analysis of the powder sample using Cu ꢀ K
α
radiation (λ =
◦
1
.5418 Å) within 5–50 (2θ) range. For IR spectral measurement, a
2
. Experimental section
Perkin ꢀ Elmer model RX1 FT ꢀ IR spectrometer fitted with KBr disks
has been used. Magnetic measurements were carried out on powdered
crystalline samples restrained in eicosane using a Quantum Design
MPMS 3 SQUID magnetometer. Data were corrected for the diamagnetic
contribution of the sample holder and eicosane by measurements, and
for the diamagnetism of the compound. [38]
2
.1. Starting materials
The chemical and reagents required in this work are of reagent grade
and used as obtained. Salicylamine is prepared following a modified
literature procedure. [36] The following starting materials were used
without further purification: NiCl
Mumbai, India), Dy(NO O (Alfa Aesar, India), salicylaldehyde
Spectrochem Pvt. Ltd. Mumbai).
2
⋅6H
2 3
O and NEt (S. D. Fine Chemicals,
3
)
3
⋅6H
2
2
.5. Theoretical studies
(
The ORCA 4.2 computational software [39–41] was used for the
theoretical calculations, which were based on the experimental X-ray
2
.2. Synthesis of 2-(((2-hydroxybenzyl)imino)methyl)phenol (H
2
L).
structure complex anion of 1, [Ni
4
Dy
3
(L)
4
(
μ
3
-OH)
4
(
μ
1,1,3,3
-
The Schiff base ligand H L has been synthesized by following a
2
-
PhCO
2
)
2
( 1,3-PhCO ) (CH OH) ] , in which only hydrogen atoms posi-
μ
2 4 3 4
modified synthetic protocol (Scheme 2). [37] Salicylamine (0.61 g, 0.50
mmol) was dissolve into 20 mL MeOH solution and added dropwise into
another MeOH solution (10 mL) of salicylaldehyde (0.61 g, 0.50 mmol).
tions were normalized in Mercury software. [42] The Douglas-Kroll-
Hess Hamiltonian was used to treat relativistic effects [43,44]
together with Gaussian finite nucleus model [45] and the increased
radial integration accuracy for metal atoms was also set. We used DKH-
def2-TZVP for Ni, SARC2-DKH-QZVP for Dy, SARC-DKH-TZVP for Lu
and DKH-def2-SVP for all other atoms. [46,47] The auxiliary basis sets
were SARC/J and generated by the AutoAux [48] and the chain-of-
spheres (RIJCOSX) approximation to exact exchange was also used.
◦
After complete addition, the solution was refluxed for 4 h at 80 C. A
yellow solid product was obtained after complete evaporation of solvent
2 4
which was next dried under vacuum over fused CaCl and P O10. Yield:
1
9
6
1
1
2.1% (1.13 g). H NMR (400 MHz, CDCl
3
): 8.4 (s, 1H), 7.3–6.9 (t, 2H),
ꢀ 1
.9–6.8 (d, 4H), 4.8 (s, 2H). Selected FT-IR data (KBr) cm : 3443 (br),
654 (s), 1607 (m), 1534 (m), 1477 (s), 1278 (s), 1236 (m), 1175 (w),
[
49,50] The state average complete active space self-consistent field
144 (m), 1078 (m), 1037 (w), 723 (m). Anal. Calcd. for (%) C14H13NO
2
(
SA-CASSCF) wave functions calculations were done for systems having
(
226.25): C, 73.99; H, 5.77; N, 6.16. Found: C, 74.29; H, 5.71; N, 6.20.
only one paramagnetic ion, thus Ni atoms were replaced with Zn, and Dy
atoms were replaced by Lu. The active space defined by five d-orbitals/
2
.3. Synthesis of Na[Ni
4
Dy
Cl
3
(L)
⋅9H
4
(
μ
3
-OH)
4
(
μ
1,1,3,3-PhCO
2
)
2
(
μ
1,3
-
seven f-orbitals and respective number of electrons for nickel/dyspro-
II
PhCO (CH OH)
2
)
4
3
4
]⋅CH
2
2
2
O (1)
sium ions. The number of the involved multiplets was as follows: Ni
–
III
1
0 triplets and 15 singlets, Dy – 21 sextets. The D-tensors and g-tensors
2 2 2
H L (0.023 g, 0.10 mmol) was dissolved in 10 mL of MeOH:CH Cl
were evaluated with the effective Hamiltonian theory.
2
–
– –
Scheme 1. Different coordination mode of L , PhCO and OH in complex 1.
2
2

A. Bhanja et al.
Inorganica Chimica Acta 526 (2021) 120524
2
Scheme 2. Synthesis of H L.
2
.6. X-ray structural studies
3. Results and discussion
Single crystal X-ray structural study of complex 1 is performed in a
3.1. Ligand design strategy and synthetic aspects
Bruker SMART APEX-II CCD X-ray diffractometer equipped with a
graphite-monochromated Mo-K
α
(λ = 0.71073 Å) radiation by the
ω
Simple tridentate Schiff base ligands with ONO donor atoms are
known for their potential to synthesize spontaneous self-assembled
multinuclear aggregates. Few reports are there for the use of ONO
donor Schiff bases with one or two phenolate moiety showing coordi-
nation trapping of 3d metal ions. [57–60] This type of ligand system is
◦
ꢀ 1
scan (width of 0.3 frame ) at 114 K with a scan rate of 5 s per frame.
SAINT, SMART and XPREP software’s have been used for indexing,
integration and space group determination. [51] Direct method using
SHELXT 2014/5 [52] is used to solve crystal structures and refined by
full-matrix least squares technique using SHELXL (2014/7) programs.
_
also useful in producing 4f [61] and 3d 4f complexes [62]. Usually for
[
53] Empirical absorption corrections (multi-scan) were carried out
coordinating both 3d and 4f ions simultaneously within one frame,
–OMe substituted ligands were used severely. But earlier in 2014, Schiff
base involving salicylaldehyde and 2-aminophenol, has been utilized to
using SADABS program. [54] All non-hydrogen atoms were refined with
anisotropic displacement parameters while hydrogen atoms were
incorporated at geometrical positions and were refined using the riding
model. DIAMOND software was used for presenting the molecular
structures. [55] The structure showed a solvent void filled with a
number of electron density peaks due to disordered/diffuse solvent and
cations; attempts to model this were not possible. Accordingly, the sol-
vent mask routine in OLEX2 [56] was used to account for the contri-
bution of the solvent. The volume and electron density were consistent
with the presence of one sodium ion (for charge balance) and 9 water
molecules (from the thermogravimetric analysis Fig. S1, ESI) per for-
mula unit. Refinement parameters for complex 1 are summarized in
Table 1 and crystallographic data (excluding structure factors) have
been deposited with the Cambridge Crystallographic Data Centre as
supplementary publications CCDC 2072451 (1).
synthesize Ni
4
Dy
3
coordination cluster without any MeO ꢀ backbone
_ _
support. [63] Incorporation of extra CH
2
spacer adjacent to imine ni-
trogen of ONO tridentate span increases the flexibility of the ligand
backbone suitable for coordinating 3d ions without accomplishing its
coordination demand, helps in synthesizing polynuclear complexes.
[64] Previously we have also shown the advantages of the introduction
of such flexible arm within ligand scaffold for synthesizing high nucle-
arity 3d-4f complexes. [65,66]
Herein, we have synthesized 2-(((2-hydroxybenzyl)imino)methyl)
phenol (H
numbers of Ni and Ln ions. Reaction of Dy(NO
NiCl O with H L and PhCO Na in 1:1(v/v) MeOH:CH
⋅6H
followed by crystallization, resulted Na[Ni Dy (L) -OH)
O (Scheme 3) according
2
L) from salicylaldehyde and salicylamine to capture multiple
II
III
3
)
3
⋅6H
2
2
O and
2
2
2
2
2
Cl medium
4
3
4
(
μ
3
4
1,1,3,3
(μ -
PhCO
to eqn. 1.
L + 3Dy(NO
2
)
2
(
μ
1,3-PhCO
2
)
4
(CH
3
OH)
4
]∙CH
2
Cl
2
⋅9H
2
4
H
2
3
)
3
⋅6H
2
O + 4NiCl
2
⋅6H
2
O + 6PhCO
2
Na + 4CH OH +
3
CH
2
Cl
Na[Ni
CH Cl
⋅9H
Infrared spectroscopic analysis was done for complex 1 which dis-
2
→
4
Dy
3
(L)
4
(
μ
3
-OH)
4
(
μ
1,1,3,3-PhCO
2
)
2
(μ
1,3-PhCO
2
)
4
(CH
3 4
OH) ]
Table 1
–
–
+
+
∙
2
2
2
O + 8Cl + 9NO
3
+ 5Na + 12H + 29H
2
O ⋅⋅⋅(eqn. 1)
Crystallographic data and refinement parameter of complex 1.
–
1
Parameters
Complex 1
plays a broad band around 3363 cm for O
–
H stretching frequencies
Formula
C
103
H
113Cl
N
2 4
NaDy
3
Ni O
4 37
originating from lattice H
2
O, coordinated MeOH and bridging hydrox-
ꢀ
1
II
_
_
F.W.(g mol
)
2815.20
ido groups. Ni ion bound imine groups show characteristic C=N
crystal system
space group
Crystal color
a/ Å
monoclinic
C2/c
–1
stretches at 1650 cm , whereas for free ligand H
2
L it appears around
ꢀ 1
1
654 cm (Fig. S2). Bridging benzoato groups of two categories record
Green
22.38(3)
19.13(2)
26.06(3)
90
–
1
sharp asymmetric (
ν
a(COO)) stretching frequencies at 1595 cm and
a(COO)) stretching vibrations are
found at 1290 cm and 1403 cm . The signatory differences (Δ) in
–
1
b/ Å
1556 cm . The associated symmetric (
ν
–
1
–1
c/ Å
ν
a
α
/ deg
–1
–1
(
COO) and
ν
s(COO) frequencies of 305 cm and 153 cm confirms the
β/ deg
γ/ deg
99.256(18)
90
existence of both 1,3 modes of carboxylato couplers within
μ1,1,3,3 and
μ
3
the resulting coordination aggregates. [67] Bulk sample prepared in
different batches are analysed by PXRD method. The experimental
diffraction traces for 1 is in good agreement with the simulated pattern
obtained by single crystal diffraction in favour of phase purity of the
bulk compound (Fig. S3). We have tried to explore the crystallization
V/ Å
11012(24)
4
Z
ꢀ
3
D
c
/g cm
1.698
ꢀ
1
μ
(mm
)
2.815
F(000)
5640
Total reflections
Unique reflections
Observed reflections
R(int)
66,526
10,063
6186
III
protocol involving other Ln ions as well but the reaction pathway
III
found very much metal ion (Dy ) specific.
0.1461
699
Parameters
R
1
; wR
2
2
(I > 2
σ
(I))
0.0786, 0.2154
1.042
3.2. Structural depiction of complex 1
GOF (F )
ꢀ
3
Largest diff peak and hole (e Å
CCDC No.
)
1.391, ꢀ 2.138
2,072,451
The molecular structure of 1 is identified through single crystal X-ray
diffraction studies and the complex crystalizes in monoclinic C2/c space
3

A. Bhanja et al.
Inorganica Chimica Acta 526 (2021) 120524
Scheme 3. Synthetic route for complex 1.
group with Z = 4. The overall formula of the molecular structure after
positioned at the tip of the motif with separations of 5.626 and 5.654 Å.
_
the identification of lattice solvent molecules becomes, Na
Such inverse butterfly topology is rare in Ni Ln family of complexes.
II
[
Ni
CH
Ni
4
Dy
Cl
Dy
3
(L)
⋅9H
(L)
4
(
μ
3
-OH)
O (Fig. 1). The asymmetric unit of 1 is identified as
-OH) )( 1,3-PhCO (CH OH) ] (Fig. 2a).
4
(
μ
1,1,3,3-PhCO
2
)
2
(
μ
1,3-PhCO
2
)
4
(CH
3
OH)
4
]
Among the benzoate linkers, four are
μ
1,3 type connecting one Ni
∙
2
2
2
and one DyIII centres while remaining two are of
μ1,1,3,3 type and
II
III
[
2
3
2
(μ
3
2
(
μ
1,1,3,3-PhCO
2
μ
2
)
2
3
2
responsible for linking two Ni and one Dy centres (Fig. 2c). Within the
two open-dicubane parts of the structure, a total four vertices are
_
The selected bond lengths and bond angles are specified in Table S1 S2
of supporting information.
occupied by the four oxygen donors from two 1,1,3,3-benzoato ligand
μ
_
_
Detailed structural analysis confirms that the mono-anionic
having the longest Ni O distances of 2.157(7) 2.181(7) Å, while the
+
_
{
Ni
4
Dy
3
} aggregate is counterbalanced by a Na ion. The aggregate
shortest distances are coming for Ni Ophenoxido bond within 2.010(7)
contains four Ni and three Dy centres capped by four L2_ supports,
II
III
_
II
5
2.011(7) Å. All four Ni centres stays in distorted NO octahedral
each delivering ONO donor atoms. Characteristically each imine nitro-
environment (Fig. 3a and 3b) fulfilled from tridentate ONO coordination
II
2ꢀ
gen donor binds each Ni centre within ONO pocket and bridges one
of each L in meridional fashion, two O from benzoato site, and one
μ
3
-
III
_
Dy centre via the phenolato oxygen. Interestingly the phenoxido ends
hydroxido group. The average Ni N distances from imine nitrogen do-
2
–
_
at the rigid imine side of L , is utilized for establishing the Niꢀ OPhꢀ Dy
nors are lies within the range of 1.966(9) 1.971(9) Å. SHAPE 2.1
II
bridges and the other phenoxido ends remain mono-coordinated to Ni
analysis also confirms the octahedral coordination geometry around
II
centres. The molecular core was built upon the peripheral supports from
each Ni centre (Table S3). Within the heptanuclear core structure the
ꢀ
III
six benzoate linkers and four
μ
3
-HO bridging groups where two partial
mean plane analysis revealed that all the three Dy centres are nearly
7
+
dicubane cores are remain fused. The [Ni
4
Dy
3
O
12
]
core is generated
co-planar. Within the two butterfly units, all four metal centres of each
◦
from the fusion of two Ni Dy partial dicubane core on the wings over
2
2
unit are coplanar, and two such planar units possess an angle of 70.09
the central Dy3, having no support from ligand anion and act as con-
necting point of two perpendicular dicubanes (Fig. 2b). Both the two
open dicubane units shows an “inverse butterfly” [68] topology where
to each other (Fig. S4).
Terminal bridging from phenoxido groups of ligand anion and
several ancillary oxygen donors provide eight-coordinated environment
III
II
III
two Dy centres occupy the body position and two Ni centres
towards the two terminal Dy centres Dy1 and Dy2. Both centres are
coordinated by eight oxygen donor atoms in a slightly distorted trigonal
dodecahedron environment (TDD-8) (Fig. 3c and 3d); CShM analysis,
using SHAPE 2.1, gives values of 0.990 for Dy1 and 0.907 for Dy2
2
–
(
Table S4). Two of the eight oxygen atoms come from two different L
ligands, two oxygen comes from two 1,3-benzoato groups, there are two
μ
μ
3
-OH groups while the seventh and eighth coordination sites come from
two terminal MeOH donors. The central Dy3 centre remain in a sym-
metric environment occupied by four -hydroxido groups and four
oxygen atoms from two 1,1,3,3-benzoato groups (Fig. 3e). The SHAPE
.1 calculation suggests a distorted cubic geometry (CU 8 = 2.164,
μ
3
μ
_
2
_
_
Table S4). For Dy1 and Dy2, the Dy O bonds lie within 2.308(8) 2.457
8) Å range where the shortest one is from benzoate oxygen (O5) and
(
_
longest one is from MeOH oxygen (O14). Similarly Dy O bond lengths
_
around Dy3 remain within 2.298(7) 2.438(7) Å where the
zoate oxygen (O10) register the longest bond.
μ
1,1,3,3-ben-
Within the molecular core, both the Dy1⋅⋅⋅Dy3 and Dy2⋅⋅⋅Dy3 dis-
tances are close by 3.862(5) and 3.836(5) Å respectively and the Ni⋅⋅⋅Dy
_
separations are in shorter range within 3.402(4) 3.432(4) Å. The core
_
_
_
_
structure gives ∠Dy1 O12 Dy3 and ∠Dy2 O11 Dy3 angles registering
◦ ◦
109.3(3) and 108.1(3) respectively. Three different types of oxygen
Fig. 1. Molecular structure of complex 1 where the ligand backbone is differ-
ently coloured depending upon their metal ion connectivity. Counter-ion, H-
atoms and solvent molecules are removed for clarity.
_
_
_ _
atoms record three different ∠Ni O Dy angles. The ∠Ni O Dy angles from
4

A. Bhanja et al.
Inorganica Chimica Acta 526 (2021) 120524
Fig. 2. (a) Asymmetric unit of complex 1; (b) intermetallic distances (Å) and angles within [Ni
4
3
Dy O
12] core consisting of fused double partial dicubane units; (c)
4 3
Ni Dy aggregate holding by six benzoate linkers of two different types.
Fig. 3. (a and b) Distorted octahedral geometry around Ni1 and Ni2 centres; (c and d) Distorted trigonal dodecahedron geometry around Dy1 and Dy2 centres; and
e) Distorted cubic geometry around Dy3 centre.
(
5

A. Bhanja et al.
Inorganica Chimica Acta 526 (2021) 120524
_
◦
bridging benzoato groups are the smallest at 95.4(3) 98.2(3) range.
3.5. Theoretical CASSCF calculations
_
_
The ∠Ni O Dy angles for phenoxido bridges and for hydroxido bridges
remain within the range of 103.1(3) 103.6(4) and 98.2(3) 104.2(3)
respectively. The Ni Dy aggregate is assembled without any secondary
_
◦
_
◦
The theoretical calculations are performed employing the ORCA 4.2
4
3
computational package for the complex anion [Ni
4
Dy
3
(L)
4
μ
3
( -
ꢀ
H-bonding interactions. Only a weak hydrogen bonding contacts are
present between the coordinated MeOH and lattice water molecules
OH)
4
(
μ
1,1,3,3-PhCO
2
)
2
(
μ
1,3-PhCO
2
)
4
(CH
3 4
OH) ]
of 1. Herein, we
II
focused on the study of the magnetic anisotropy of paramagnetic Ni
III
(
Fig. S5).
and Dy ions. Due to multireference character of such metal complexes,
the state-averaged complete active space self-consistent field (SA-
CASSCF) method was employed. In these calculations, the active space
3
.3. Topological depiction
II
was defined by eight electrons in five d-orbitals for Ni , which results in
The topological description for the key structural features of 1 is
ten triplets and fifteen singlets. There are two crystallographically in-
dependent nickel atoms for which these CASSCF calculations were
performed. First, ab initio ligand field theory (AILFT) [75,76] was used
to analyze the energies of d-orbitals as showed in Fig. 6. The pattern is
identified using methods of Kostakis et al. [69–71] The analysis shown
that the Ni Dy
aggregate can be described by the symbol 2,3,6M7 ꢀ 1.
4
3
The 2,3,6M7 ꢀ 1 motif is comprised of four fused triangles; where each
III
II
triangle consists of two Dy and one Ni node (Fig. 4). With respect to
the central Dy node, the four NiII nodes forms a tetrahedral arrange-
ment. The survey of the database [72] revealed that 2,3,6M7 ꢀ 1 motif is
typical for octahedral complexes (set of t2g and e
g
orbitals), however, the
III
degeneracy of e
ligand field.
g
orbitals is removed due to lower symmetry of the
reported for Cu
Zn
5
Gd
2
[73], Zn
6
Na [74], Zn
7
[74] complexes, where the
The respective ligand field terms and multiplets are showed also in
7
coordination polymer matches well with our topology.
Fig. 6 confirming well separated ground state S = 1 with the zero-field
ꢀ
1
splitting parameters: D = -13.9 cm and E/D = 0.265 for Ni1 and D
ꢀ 1
3
.4. Magnetic properties
= -12.9 cm and E/D = 0.205 for Ni2. Such values are in reasonable
II
h
agreement with other O Ni complexes. [77] Next, the CASSCF calcu-
The temperature dependent magnetic susceptibility data of complex
lations were done for all three crystallographically independent
6
1
, plotted as
χ
T vs. T, is shown in Fig. 5. The data were collected over a
dysprosium atoms focusing on the ligand field induced splitting of H15/
temperature range of 290–2 K in a magnetic field of 0.1 T. The experi-
2
state. The Fig. 7 is showing the splitting of f-orbitals and energies of
3
ꢀ 1
mental value of
expected T value for uncoupled spins (4 Ni ions and 3 Dy ions (gDy
.333 and gNi = 2.3) = 47.8 cm mol K). The
χ
T at 290 K is 47.9 cm mol K, consistent with the
ligand field multiplets. Dy1 and Dy2 ions have similar geometry of the
coordination polyhedra, therefore, the calculated patterns of f-orbitals
and multiplet energy levels are similar. The energies of the eight
Kramers doublets are also listed in Table 2, together with g-tensor values
of each doublet for Seff = 1/2. The positive information deduced from
these calculation is that lowest Kramers possess large axial symmetry (gx,
II
III
χ
=
3
ꢀ 1
1
χT value slowly decreases
3
ꢀ 1
to 47.0 cm mol K at 90 K and then more sharply to a plateau of 44.1
3
ꢀ 1
ꢀ 1
cm mol K at 20 K, before decreasing further to a minimum of 41.3
3
cm mol K. For complex 1, M/Nβ = 23.5 at 2 K and 7 T (Fig. 5) and is
III
not saturated due to the inherent magnetic anisotropy of the Dy and
y
less than 0.5, g
z
≈ 18–19), however, gx,y components are quite large,
II
Ni ions.
thus the quantum tunneling of the magnetization is expected. Moreover,
lowest excited states are rather close and have larger gx,y components
too, which increases also probability of thermally-assisted quantum
tunneling.
The AC susceptibility values are measured over a temperature range
_
of 40 2 K under zero dc field and under a field of 2000 Oe to probe
whether the complex displayed slow relaxation of the magnetisation. No
slow magnetic relaxation is observed under zero dc field (Fig. S7) and
only a very small response below 3 K is seen under the applied dc field
The analysis of the coordination polyhedra with the help of SHAPE
resulted in the best match for TDD-8 and CU-8 shapes and therefore we
have performed also CASSCF calculations for simple model complex
(
Fig. S8), and therefore no further ac measurements were carried out. A
Ni Dy } complex with a different topology and containing one
diamagnetic Ni(II) centre giving an effective {Ni Dy } unit shows
intramolecular ferromagnetic interactions and the onset (no maxima in
5
-
{
4
3
[DyF
8
] having these symmetries of the ligand field - Fig. 8. In case of
3
3
TDD-8 symmetry, the ground state and first excited states are well
energetically separated have significant axial anisotropy: g
= 0.023, g = 19.858 for the first Kramers doublet and g = 0.055, g
0.055, g
x
= 0.023, g
y
′
′
χ
) of slow relaxation of the magnetisation at low temperature. For this
z
x
y
=
reported complex, no supporting theoretical studies were carried out so
the origin of the slow relaxation and hence the difference in properties to
z
= 17.262 for the second Kramers doublet. On contrary, CU-8
symmetry provides three very close lying Kramers doublets separated
ꢀ
1
1
is not clear. [63]
by less than 3 cm having also insufficient axial anisotropy: g
x
= 7.555,
g
y
= 7.611, g
.015, g
= 11.306 for the second Kramers doublet and g
.267, g
z
= 7.659 for the first Kramers doublet, g
x
= 3.333, g
= 1.200, g
y
=
=
5
4
z
x
y
z
= 12.028 for the third Kramers doublet. Thus, it can be
concluded that TDD-8 is superior to CU-8, and the larger deviation from
CU-8 symmetry for Dy3 atom than deviations of Dy1 and Dy2 atoms
from TDD-8 (see section 3.2) is beneficial.
The magnetic properties of 1 is impossible to treat with incorporating
interactions among paramagnetic ions due to very large number of spin
4
3
states, 3 16 = 5308416 and therefore only some aspects of the intra-
cluster interactions can be evaluated. First, we discuss the dipole–dipole
III
interactions between Dy ions. The respective orientations of g
z
axes of
ground Kramers doublets are displayed in Fig. 9. The dipole–dipole in-
III
teractions are evaluated between Dy ions using well-known formula,
(
)(
)
⎡
⎤
→
→
→ →
⋅ r
μ
⋅ r
μ
j
i
μ0
⎢
⎢
⎣
⎥
⎥
⎦
dipolar
→ →
μ ⋅ μ
i j
E
=
ꢀ 3
(2)
ij
r3
2
4π
r
II
Fig. 4. 2,3,6M7 ꢀ 1 topological network for the present work. Green node; Ni
III
and magenta node; Dy ions. (For interpretation of the references to color in
this figure legend, the reader is referred to the web version of this article.)
z
where magnetic moments were calculated based on the orientation of g -
6

A. Bhanja et al.
Inorganica Chimica Acta 526 (2021) 120524
Fig. 5. Left: Temperature dependence of T for complex 1. Right: Magnetization vs. field data for complex 1 at 2, 4 and 6 K.
χ
Fig. 6. The results of the CASSCF calculations with CAS(8,5) for Ni ions in complex anion of 1. The plot of the d-orbitals splitting calculated by ab initio ligand field
theory (AILFT) (left), low-lying ligand-field terms (middle), and ligand-field multiplets showing splitting of ground triplet state (right).
Fig. 7. The results of the CASSCF calculations with CAS(9,7) for Dy ions in complex anion of 1. The plot of the f-orbitals splitting calculated by ab initio ligand field
6
theory (AILFT) (left), and ligand-field multiplets showing splitting of
H
15/2 state (right).
7

A. Bhanja et al.
Inorganica Chimica Acta 526 (2021) 120524
Table 2
III
The CASSCF calculated energies and parameters for Dy centres of 1.
Dy1 Dy2
Dy3
ꢀ
1
◦
ꢀ 1
◦
ꢀ 1
◦
ε(cm
)
g
x
, g
y
, g
z
α
( )
ε(cm
)
g
x
, g
y
, g
z
α
( )
ε
(cm
)
g
x
, g
y
, g
z
α
( )
1
2
3
4
5
6
7
8
0
0.088 0.096 19.440
0.348 0.400 15.513
0.009 0.088 19.719
1.131 3.128 11.484
5.110 6.406 7.542
0.456 0.811 10.349
0.125 0.506 14.575
0.000 0.001 19.668
0
0
0.238
0
0
0.039 0.332 18.216
2.362 4.328 12.664
0.945 5.994 9.672
0.411 6.915 7.513
2.081 5.684 7.133
0.692 5.155 13.577
1.879 2.066 14.589
0.094 0.904 16.368
0
0
1
.329
9.133
59
39.5
37
0.156
117.0
155.6
47.4
67
180.0
180.0
180.0
90.0
0
1
.366
6.406
96
131.8
24.1
67
2.519
138
300
441
555
601
714
8
9
.810
.215
108
150
203
262
542
89
0.112
3
8
.344
.248
90.0
111
131
182
490
0.146
126.2
95.7
0
1
.832
5.579
101.1
110.6
122.9
0.307
90.0
1
1
.675
0.802
0.081
64.7
90.0
0
1
.158
5.350
0.002
127.3
90.0
0
1
.002
9.792
a
th
angle
α
z
is the angle between the g component of the lowest and the n Kramers pairs.
5
-
Fig. 8. The results of the CASSCF calculations with CAS(9,7) for model complex [DyF
8
]
with the ideal symmetry of the coordination polyhedron: triangular
dodecahedron (TDD-8) and cube (CU-8). The plot of the f-orbitals splitting calculated by ab initio ligand field theory (AILFT) (left), and ligand-field multiplets
6
showing splitting of
H15/2 state (right).
→
→
component of respective ground state Kramers doublets and r is the
distance between two magnetic moments. The analysis provided us with
̂
H = ꢀ J( S 1⋅ S 2) and the respective broken-symmetry spin density is
depicted in Fig. 10. Thus, the last unknow interactions in 1 are the ex-
change interactions of the types Dy-Dy and Dy-Ni. They cannot be
theoretically evaluated due to the lack of suitable theoretical approach
for 4f-4f and 4f-3d coupling, in which the lanthanide can not be
described by the spin Hamiltonian model. Moreover, the literature
survey of smaller and therefore theoretically tractable Ni-Dy system
with similar bridging ligands, for which Ni-Dy interactions were deter-
mined, was unsuccessful. This points to the fact that the investigation of
-
5
ꢀ 1
-5
ꢀ 1
these values: E13 = -1.96 × 10 cm , E23 = 2.45 × 10 cm and E12
=
ꢀ
1
0
.35 cm , suggesting a relatively strong ferromagnetic dipole interac-
tion between Dy1 and Dy2, mostly due to very similar orientation of
their magnetic moments, and negligible dipole interactions between
adjacent ions.
II
Next, the isotropic exchange between Ni ions bridged by benzoate
groups (Ni1-Ni2* and Ni1*-Ni2) were calculated by the broken-
symmetry Density Functional Theory (DFT) using PBE0 hybrid func-
tional [79] and the same basis sets as for previous CASSCF calculations.
In this calculation, all other metals were replaced by their diamagnetic
analogues. The the energy difference between high-spin (HS) and
3
d-4f coupling deserves more scientific exploration.
To summarize, the predispositions of 1 to behave as SMM are more
likely enhanced by the ferromagnetic dipolar coupling between Dy1 and
Dy2 ions and also by the ferromagnetic exchange coupling between Ni
ions, but on other hand they are compromised by low lying excited states
broken-symmetry (BS) spin states was calculated as △ = EBS – EHS
=
ꢀ 1
3
.667 cm , thus proposing ferromagnetic coupling. The exchange
III
of Dy ions and significant non-zero values of gx,y of the respective
coupling J-parameter was calculated by Yamaguchi’s approach, [80,81]
II
Kramers doublets, and quite large rhombicity of Ni ions, which all
ꢀ 1
which resulted in J = 1.84 cm for the spin Hamiltonian formulated as
speeds up the QTM process.
8

A. Bhanja et al.
Inorganica Chimica Acta 526 (2021) 120524
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgements
A.B. is thankful to DST-INSPIRE for the research fellowship. R.H. and
K.K. acknowledge the financial support from the institutional sources of
the Department of Inorganic Chemistry, Palacký University Olomouc,
Czech Republic. M.M. thanks the University of Glasgow for financial
support. We acknowledge FIST program of DST, New Delhi for the SC-
XRD facility at the Department of Chemistry, IIT Kharagpur.
Appendix A. Supplementary data
CCDC 2072451 contains the crystallographic data for 1. The elec-
tronic supplementary information (ESI) file contains TGA, FTIR, PXRD
curve, packing diagram, selected bond lengths and angles, SHAPE 2.1
analysis and AC susceptibility plots described in Figure S1ꢀ S7 and
Tables S1ꢀ S4 in the text. Supplementary data to this article can be found
online at https://doi.org/10.1016/j.ica.2021.120524.
Fig. 9. The molecular structure of complex anion of 1 overlaid with violet
z
arrows representing the g -axis of ground state Kramer doublet of respective Dy
atoms determined by CASSCF calculations visualized with VESTA 3 pro-
gram. [78]
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