Synthesis, structure, and magnetic properties of heterometallic {Zn2Ln2} (Ln = Tb, Dy, Ho) compounds with parallelogram-like cores

Article abstract of DOI:10.1016/j.ica.2015.07.026

This work presents the synthesis, structure, and magnetic properties of three tetranuclear heterometallic compounds with the chemical formula [Zn₂Ln₂(L)₄Cl₂]·xCH₃CN·yCH₃OH where Ln = Tb (1), Dy (2), and Ho (3) and the H₂L ligand was 1,2-bis(2-hydroxy-3-methoxybenzylidene) hydrazine. Single-crystal X-ray analyses revealed that compounds 1-3 had similar coordination environments and structures. Direct current susceptibility measurements revealed that the χ_mT product decreased with decreasing temperature due most likely to either the thermal depopulation of the Stark sublevels of the Tb^III, Dy^III, and Ho^III ions or antiferromagnetic coupling within the [Zn₂Ln₂] cores. Furthermore, compound 2 displayed a slow field-induced relaxation of magnetization. An energy barrier of ΔE/k_B = 23.74 K and a pre-exponential factor of τ₀ = 4.33 × 10^-6 s were obtained by fitting the dynamic magnetic data to an Arrhenius rate law.

Full text of DOI:10.1016/j.ica.2015.07.026

Accepted Manuscript
Synthesis, structure, and magnetic properties of heterometallic {Zn2Ln2} (Ln =
Tb, Dy, Ho) compounds with parallelogram-like cores
Wei-Wei Kuang, Yun Xu, Li-Li Zhu, Pei-Pei Yang
PII:
S0020-1693(15)00360-6
http://dx.doi.org/10.1016/j.ica.2015.07.026
ICA 16619
DOI:
Reference:
Inorganica Chimica Acta
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Received Date:
Revised Date:
Accepted Date:
22 May 2015
21 July 2015
22 July 2015
Please cite this article as: W-W. Kuang, Y. Xu, L-L. Zhu, P-P. Yang, Synthesis, structure, and magnetic properties
of heterometallic {Zn2Ln2} (Ln = Tb, Dy, Ho) compounds with parallelogram-like cores, Inorganica Chimica
Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.2015.07.026
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Synthesis, structure, and magnetic properties of heterometallic
{Zn2Ln2} (Ln = Tb, Dy, Ho) compounds with parallelogram-like
cores
Wei-Wei Kuang, Yun Xu, Li-Li Zhu, Pei-Pei Yang*
College of Chemistry and Materials Science, Huaibei Normal University, 100
Dongshan Road, Huaibei, 235000, People’s Republic of China
Keywords: Crystal structure, Magnetic properties, Single-molecule magnet
Abstract
This work presents the synthesis, structure, and magnetic properties of three
tetranuclear
heterometallic
compounds
with
the
chemical
formula
[Zn2Ln2(L)4Cl2]·xCH3CN·yCH3OH where Ln = Tb (1), Dy (2), and Ho (3) and the
H2L ligand was 1,2-bis(2-hydroxy-3-methoxybenzylidene) hydrazine. Single-crystal
X-ray analyses revealed that compounds 1-3 had similar coordination environments
and structures. Direct current susceptibility measurements revealed that the χmT
product decreased with decreasing temperature due most likely to either the thermal
depopulation of the Stark sublevels of the TbIII, DyIII, and HoIII ions or
antiferromagnetic coupling within the [Zn2Ln2] cores. Furthermore, compound 2
displayed a slow field-induced relaxation of magnetization. An energy barrier of
∆E/kB = 23.74 K and a pre-exponential factor of τ0 = 4.33×10-6 s were obtained by
fitting the dynamic magnetic data to an Arrhenius rate law.
1. Introduction
Single-molecule magnets (SMMs) [1], the individual molecules acting as
superparamagnetic entities, have attracted interest as potential components for
ultra-dense data storage and quantum computation [2]. The origin of the behavior of
SMMs is their easy-axis (Ising-type) magnetic anisotropy (D<0), which causes the
formation of an energy barrier due to reorientation of spin and can be defined in terms
of a large-spin ground state and a large magnetic anisotropy [3].
1

To study SMMs, the use of heavy lanthanide ions such as TbIII [4], DyIII [5], HoIII
[6], and ErIII [7] ions has become popular, because of their large spin multiplicity and
large magnetic anisotropies in the ground state. Recently, compounds incorporating
both transition metals and lanthanide ions have shown promise as molecule-based
magnetic materials by virtue of their high number of unpaired electrons and the large
intrinsic magnetic anisotropies of lanthanide ions. Since the first discovery of SMM
behavior in 3d-4f compounds [8], research into heterometallic compounds has been
developed significantly, and a flood of 3d-4f polynuclear clusters have been reported
containing Mn-Ln [9], Cu-Ln [10], Fe-Ln [11], Ni-Ln [12], and Co-Ln [13]. The most
popular species have been Mn-Ln and Cu-Ln. Previous research indicates that the
very weak JM−Ln observed for 3d-4f dinuclear compounds (MII = Cu, Ni, and Co) leads
to small separations in low-lying split sublevels and, consequently, to a smaller energy
barrier for magnetization reversal. Thus, a good strategy to enhance the SMM
properties of 3d-4f aggregates would be to replace the paramagnetic M2+ ions by a
diamagnetic ion (e.g., Zn2+) in order to split the ground sublevels of the LnIII ions [14].
However, the Zn-Ln system has been infrequently studied [15]. [ZnDy0.126Y0.874] [14a]
is one of the few examples of a Dy3+ compound with a high thermal energy barrier
(Ueff = 68 K) and the SMM behavior that is triggered by dilution. In 2011, Kajiwara et
al., developed a single ion SMM, [ZnDy] [14d], with a large magnetic anisotropy.
[Zn3Dy] [16] was the first SMM with a single lanthanide ion bound inside the cavity
of a single organic macrocycle, while [Zn3Er] [14e] was the second.
From a synthetic chemistry perspective, the design of ligands containing
different coordination donors and bonding modes is considered a critical factor for
determining crystal structure [15c]. As was recently demonstrated, organic ligands,
which were formed by the reaction of o-vanillin with hydrazine derivatives, are
necessary for the construction of clusters [17], because (i) two or more oxygen donors
and two or more nitrogen donors in these ligands can coordinate to several metal
centers [18] and (ii) the o-vanillin group displays a variety of bonding geometries
including monodentate, bidentate bridging, and chelate bridging [19].
1,2-Bis(2-hydroxy-3-methoxybenzylidene) hydrazine (H2L, Scheme 1) is a ligand that
2

has been used previously to isolate SMMs in both homometallic systems [17b, 17c]
and 3d-4f heterometallic clusters [17d]. Literature data suggest that a tetranuclear
dysprosium(III) SMM with a large anisotropic barrier [17b] can be synthesized using
this ligand. The H2L ligand is also similar to others with two cresols fused in the
center such as Mn19 [20] and Gd2Mn [21].
To explore the synthesis of 3d-4f heterometallic coordination frameworks, the
1,2-Bis(2-hydroxy-3-methoxybenzylidene) hydrazine ligand was selected for reacting
with lanthanide nitrate and zinc chloride in a methanol/acetonitrile solution by a
"one-pot" self-assembly approach to construct Zn-Ln heterometallic clusters. In this
work, the synthesis, structure, and magnetic properties are reported for three
tetranuclear 3d-4f compounds of [Zn2Ln2(L)4Cl2]·xCH3CN·yCH3OH where Ln = Tb
(1), Dy (2), or Ho (3). Single X-ray diffraction analysis revealed that the [Zn2Ln2O4]
core of compounds 1-3 possessing two LnIII and two ZnII ions are coplanar in an
irregular parallelogram-like shape, connected by four η1 η2 η1:η1:η1:η0:µ3-L2- ligands.
:
:
Moreover, alternating current magnetic studies of these compounds revealed the
SMM behavior of compound 2.
N N
O
O
O
O
Ln
Ln
a) η0 η1 η1:η1:η1:η0:µ2
:
:
N N
O
Ln
O
Ln
M
Ln
O
O
b) η1 η2 η1:η1:η2:η1:µ4
:
:
3

N
N
O
O
O
O
Ln
M
Ln
c) η1 η2 η1:η1:η2:η0:µ3
:
:
N N
O
O
O
O
Ln Ln
d) η0 η1 η1:η0:η1:η0:µ2
:
:
N
N
O
O
O
O
Ln
Ln
Ln
Ln
e) η1 η2 η1:η0:η2:η1:µ4
:
:
Scheme 1. The coordination mode of the H2L ligand.
2. Experimental section
2.1. Starting materials
All starting materials were of A.R. Grade and were used as commercially
obtained without further purification. The Schiff-base ligand H2L was synthesized by
a condensation reaction between hydrazine and o-vanillin in methanol solution [17b].
2.2. Physical measurements
Elemental analyses for C, H, and N were carried out on a PerkinElmer 2400
analyzer. The IR spectra of the compounds were recorded as KBr pellets on a Bruker
Tensor 27 IR spectrophotometer operating at 4000-400 cm-1. Magnetic measurements
on microcrystalline samples were carried out on a Quantum Design SQUID
magnetometer MPMS-XL7. This magnetometer works with an oscillating ac field of
4

2.0 Oe and ac frequencies ranging from 10 to 1000 Hz. Direct current (dc)
susceptibility measurements have been measured between 2 and 300 K in the applied
field of 1000 Oe. All data were corrected for the contribution of the sample holder and
the diamagnetism of the constituent atoms estimated from Pascal’s constant [22].
2.3. X-ray measurements
Suitable single crystals were selected for single-crystal X-ray diffraction analysis
at a temperature of 113 K for compounds 1-3 using a Rigaku Saturn CCD
diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å).
Crystal structures were calculated by direct methods and refined on F2 with a
full-matrix least-squares technique using SHELXS-97 and SHELXL-97 software
packages [23]. The locations of the heaviest atoms (rare earth metal, Zn, and Cl) were
easily determined. O, N, and C atoms were subsequently determined using difference
Fourier maps. Anisotropic refinement was used for all non-hydrogen atoms, while
hydrogen atoms were refined isotropically using the isotropic vibration parameters of
their carrier atoms. Details of crystallographic data collection and structure
refinements of compounds 1-3 are summarized in Table 1.
2.4. Preparation of the compounds
2.4.1. Synthesis of compounds 1-3
[Zn2Ln2(L)4Cl2]·xCH3CN·yCH3OH (1-3): Compounds 1-3 were prepared from
the reaction of H2L (0.2 mmol, 30 mg), triethylamine (0.2 mmol, 20 mg),
Ln(NO3)3·6H2O (0.1 mmol), and ZnCl2·6H2O (0.1 mmol, 13.6 mg) in
CH3OH/CH3CN (10 mL/10 mL) at room temperature, resulting in a bright yellow
solution. After stirring for four hours, the solution was filtered and allowed to stand
without disturbance. Yellow granular single crystals, suitable for X-ray diffraction
analysis, formed after 7 days. The crystals were collected by filtration, washed with a
minimum amount of cold methanol, and dried in air. For 1, Yield: 56.8 mg, 32%.
Elemental analysis (%) calcd for Zn4Tb4C134H121Cl4N19O32: C, 45.36, H, 3.44, N, 7.50;
found: C, 45.33, H, 3.43, N, 7.46. IR (KBr, cm-1): 2987(m), 1607 (vw), 1459 (w),
5

1332 (w), 1277 (vw), 1218 (w), 1082 (vw), 955 (vw), 741 (vw). For 2, yield: 66.8mg,
37%. Elemental analysis (%) calcd for Zn4Dy4C136H123.5Cl4N19.5O33: C, 45.22, H, 3.45,
N, 7.56; found: C, 45.17, H, 3.39, N, 7.61. IR (KBr, cm-1): 2972(m), 1600 (vw), 1447
(w), 1330 (w), 1269 (vw), 1214 (w), 1078 (vw), 952 (vw), 737 (vw). For 3, yield:
59.2 mg, 33%. Elemental analysis (%) calcd for Zn4Ho4C134H123Cl4N19O33: C, 44.82,
H, 3.45, N, 7.41; found: C, 44.90, H, 3.44, N, 7.38. IR (KBr, cm-1): 2980(m), 1604
(vw), 1451 (w), 1327 (w), 1269 (vw), 1215 (w), 1077 (vw), 958 (vw), 741 (vw).
Table 1 Crystal Data and Structure Refinement for compounds 1-3.
1
2
3
formula
C134H121Cl4Tb4N19O32Zn4 C136H123.5Cl4Dy4N19.5O33Zn4
C134H123Cl4Ho4N19O33Zn4
Mr/g·mol −1
crystal system
space group
a / Å
3548.46
Monoclinic
P21/c
3612.32
Monoclinic
P21/c
3590.51
Monoclinic
P21/n
20.729(4)
17.655(3)
20.477(4)
17.622(3)
20.539(4)
17.667(3)
b / Å
c / Å
39.956(13)
90
39.477(12)
90
39.278(12)
90
α / ◦
β / ◦
γ / ◦
105.29(3)
90
105.26(3)
90
105.25(3)
90
V / Å3
14105(6)
4
13743(5)
4
13751(6)
4
Z
µ / mm -1
2.801
2.993
3.119
F(000)
7048
7168
7120
crystal size(mm3)
0.16 x 0.12 x 0.10
-24≤h≤24,
-20≤k≤21,
-47≤l≤45
81463
0.14 x 0.10 x 0.08
-24≤h≤24,
-19≤k≤20,
-46≤l≤46
77303
0.18 x 0.14 x 0.12
-24≤h≤24,
-21≤k≤21,
-46≤l≤46
100328
limiting indices
reflections collected
theta range for data
collection (Å, deg)
GOF on F2
1.27 to 25.02
1.27 to 25.02
1.07 to 25.02
1.062
1.101
1.090
completeness to theta =
25.02
97.7 %
95.5 %
96.7 %
data/restraints/parameters
R1 [I>2σ(I)]
24330 / 0 / 1793
0.0682
23141 / 18 / 1840
0.0547
23485 / 48 / 1805
0.1170
wR2 (all data)
0.1822
0.1433
0.2986
6

3. Result and discussion
3.1. Crystal structures
Single-crystal X-ray diffraction analysis revealed that compounds 1-3 crystallized in the
monoclinic space group P21/c with Z = 4. These three ZnII LnIII compounds are isostructural and
2
2
show similar coordination environments except for slight differences in bond lengths and angles.
For the sake of brevity, only the structure of compound 1 is described in detail as a representative
case. The molecular structure of compound 1 is shown in Figure 1. Selected bond lengths and
angles for the three compounds are given in Table 2. In a typical structure of compound 1, two
TbIII and two ZnII ions are coplanar in an irregular parallelogram, connected by four
η1 η2 η1:η1:η1:η0:µ3-L2- ligands (Scheme 1c), which consists of a [Zn2Tb2N8O4] core arranged by
:
:
four [TbZnN2O] units with a pentagon-like shape. As reported in the literatures [20b, 20c, 20d],
the L2- ligand has several bridging modes. These modes are listed in Scheme 1. In 2009, Murugesu
et al. firstly reported a tetranuclear dysprosium(III) SMM that exhibited a large relaxation barrier.
The two L2- ligands in this compound adopted a η0 η1 η1:η1:η1:η0:µ2 coordination mode.
:
:
Subsequently, Tang’s group synthesized a new alkoxido-bridged, linear tetranuclear DyIII
aggregate showing SMM behavior using H2L. Four deprotonated L2- ligands exhibited two
different bridging modes (η0 η1 η1:η0:η1:η0:µ2 and η1 η2 η1:η0:η2:η1:µ4). In 2011, Tang’s group
:
:
:
:
reported a heterometallic dodecanuclear 3d-4f wheel, exhibiting SMM behavior, synthesized using
the H2L ligand. The wheel-like core of this compound included ten DyIII and two CoII ions
connected by four η1 η2 η1:η1:η2:η1:µ4-L2- ligands and sixteen acetates.
:
:
Figure 1. Molecular structure of the neutral [Zn2Ln2(L)4Cl2] in compound 1 (Hydrogen atoms and
solvent molecules have been omitted for clarity).
7

Table 2 Selected bond lengths (Å) and bond angles (deg) for compounds 1-3.
Ln=Tb
Ln=Dy
Ln=Ho
2.230(6)
Dy(1)-O(2)
2.396(12)
Tb(1)-O(2)
2.209(5)
Ho(1)-O(2)
Dy(1)-O(6)
Dy(1)-O(9)
Tb(1)-O(6)
Tb(1)-O(5)
Tb(1)-O(10)
2.416(6)
2.447(7)
2.219(6)
2.208(5)
2.411(5)
2.397(5)
Ho(1)-O(6)
Ho(1)-O(1)
Ho(1)-O(10)
2.181(14)
2.421(13)
2.241(14)
Dy(1)-O(10)
2.418(7)
2.426(5)
2.368(5)
2.491(6)
2.474(6)
2.384(5)
2.428(5)
2.425(5)
2.409(5)
2.418(15)
2.401(12)
2.495(15)
2.452(15)
2.211(16)
2.418(14)
2.386(12)
Tb(1)-O(13)
Tb(1)-O(14)
Tb(1)-N(1)
Dy(1)-O(13)
Dy(1)-O(14)
Dy(1)-N(1)
Ho(1)-O(13)
Ho(1)-O(14)
Ho(1)-N(3)
2.458(6)
2.526(7)
2.489(7)
2.398(6)
2.444(6)
Tb(1)-N(5)
Dy(1)-N(3)
Ho(1)-N(5)
Tb(2)-O(3)
Dy(2)-O(3)
Ho(2)-O(3)
Tb(2)-O(4)
Dy(2)-O(4)
Ho(2)-O(8)
Tb(2)-O(7)
2.220(6)
2.425(7)
2.410(5)
Dy(2)-O(7)
Ho(2)-O(7)
Tb(2)-O(12)
Tb(2)-O(11)
Tb(2)-O(15)
Tb(2)-N(4)
Dy(2)-O(8)
Ho(2)-O(12)
Ho(2)-O(11)
Ho(2)-O(15)
Ho(2)-N(2)
2.437(14)
2.396(13)
2.184(13)
Dy(2)-O(11)
Dy(2)-O(15)
Dy(2)-N(6)
2.207(5)
2.218(5)
2.459(6)
2.509(6)
2.116(5)
2.121(5)
2.059(5)
2.051(6)
2.133(5)
2.229(7)
2.525(8)
2.508(8)
2.486(18)
2.493(16)
Tb(2)-N(8)
Dy(2)-N(8)
Ho(2)-N(8)
Zn(1)-O(11)
Zn(1)-O(14)
Zn(1)-N(6)
2.143(6)
2.125(6)
2.069(8)
2.050(8)
2.151(7)
Zn(1)-O(7)
Zn(1)-O(11)
Zn(1)-O(14)
Zn(1)-N(6)
2.148(13)
2.137(12)
2.070(15)
Zn(1)-O(10)
Zn(1)-N(4)
Zn(1)-N(7)
Zn(1)-N(5)
Zn(1)-N(7)
2.025(16)
2.147(12)
2.133(12)
2.056(17)
2.050(14)
118.5(5)
118.1(5)
119.5(5)
117.8(5)
Zn(2)-O(3)
Zn(2)-O(3)
Zn(2)-O(2)
Zn(2)-O(6)
2.150(6)
2.058(8)
2.051(8)
117.8(3)
118.8(3)
117.1(3)
117.7(3)
Zn(2)-O(14)
Zn(2)-N(2)
2.134(5)
2.053(6)
Zn(2)-O(7)
Zn(2)-N(2)
Zn(2)-N(1)
2.044(6)
Zn(2)-N(3)
Zn(2)-N(7)
Zn(2)-N(4)
119.41(19)
118.45(19)
118.5(2)
Zn(1)-O(11)-Tb(2)
Zn(1)-O(14)-Tb(1)
Zn(2)-O(3)-Tb(2)
Zn(2)-O(6)-Tb(1)
Zn(1)-O(7)-Dy(2)
Zn(1)-O(10)-Dy(1)
Zn(2)-O(3)-Dy(2)
Zn(2)-O(14)-Dy(1)
Zn(1)-O(11)-Ho(2)
Zn(1)-O(14)-Ho(1)
Zn(2)-O(2)-Ho(1)
Zn(2)-O(7)-Ho(2)
117.57(19)
In this paper, the two central Tb and Zn ions in the core, which were linked by
phenol oxygen atoms (O3, O6, O11, and O14) from the four L2- ligands, were
characterized by Tb-O-Zn angles in the range of 117.1(3)° to 118.8(3)°. The Zn ions
were five-coordinated with Zn-O distances of 2.125(6) - 2.151(7) Å and Zn-N
distances of 2.050(8) - 2.069(8) Å. The coordination sphere of Tb was completed by
8

four phenol oxygen atoms, two methoxy oxygen atoms, and two nitrogen atoms,
forming an eight-coordinate with a square-antiprismatic geometry. The two bases of
the square antiprism of Tb1 consisted of N1, O2, O5, O6 atoms and N5, O10, O13,
O14 atoms. Meanwhile, the two square bases of Tb2 were defined by the N8, O11,
O12, O15 atoms and N4, O3, O4, O7 atoms (Figure 2). The average Tb-O and Tb-N
distances were in the range of 2.219(6)-2.458(6) Å and 2.489(7)-2.526(7) Å,
respectively.
Figure 2. Coordination environment for Tb3+ ion of distorted square-antiprismatic (SAP)
geometry in 1.
Interestingly, π-stacking and abundant hydrogen-bonding interactions (C-H…C1)
organize compound 1 into a two-dimensional sheet (Figure 3, Table 3). The closest
centroid-to-centroid distance of the face-to-face π-stacking interactions between the
L2- ligands from neighboring tetranuclear units was 3.59 Å.
Figure 3. A perspective view on the π…π stacking (green dashed line), and hydrogen-bonding
(red dashed lines) interactions in 2. Hydrogen atoms omitted for clarity except for the hydrogen
bonds of the crystal.
9

Table 3 The hydrogen-bonding lengths (Å) and bond angles (deg) for compounds 1 in
the packing.
H…A (Å)
D-H…A (◦)
D-H (Å)
D…A (Å)
Hydrogen-bonding contacts D-H…A
C(99)-H(99)…Cl(1)
C(77)-H(77)…Cl(2)
C(36)-H(36)…Cl(3)
C(68)-H(68)…Cl(4)
C(51)-H(51)…Cl(4)a
C(108)-H(108)…Cl(4)a
C(109)-H(109)…Cl(4)a
C(51)-H(51)…Cl(4)b
C(52)-H(52)…Cl(4)b
C(68)-H(68)…Cl(4)b
C(45)-H(45)…Cl(1)c
C(77)-H(77)…Cl(2)c
C(36)-H(36)…Cl(3)c
C(28)-H(28)…Cl(4)c
3.1941
2.8819
2.8446
2.9977
2.7638
3.3729
3.2071
2.7638
3.1318
2.9977
3.3825
2.8819
2.8446
2.7175
1616.353
155.627
153.914
169.866
133.292
124.901
132.276
133.292
117.088
169.866
129.931
155.627
153.914
136.553
0.9308
0.9291
0.9306
0.9311
0.9309
0.9328
0.9297
0.9309
0.9282
0.9311
0.9307
0.9291
0.9306
0.9316
4.0870
3.7479
3.7031
3.9177
3.4689
3.9808
3.8938
3.4689
3.6493
3.9177
4.0433
3.7479
3.7031
3.4538
Symmetry transformations used to generate equivalent atoms: a: -x, -0.5+y, 0.5-z; b: 1+x, y, z; c:
1-x, -0.5+y, 0.5-z.
3.2. Magnetic properties
Static susceptibility measurements of the crystalline samples of compounds 1-3
were measured in the temperature range of 2.0 - 300 K under a 1000 Oe direct
current(dc) magnetic field. The temperature dependence of the molar magnetic
susceptibility of compounds 1-3 is illustrated in Figure 4 as plots of χmT versus T
where χm is the molar magnetic susceptibility of each LnIII2 unit. The observed χmT
values at 300 K are 23.32, 28.66, and 28.27 cm3 K mol-1 for compounds 1, 2, and 3,
respectively. These results are in good agreement with the expected values of 23.64,
28.34, and 28.14 cm3 K mol-1 for the two magnetically independent TbIII (4f8, J=8,
7
6
S=3, L=3, g=3/2, F6), DyIII (4f9, J=15/2, S=5/2, L=5, g=4/3, H15/2), and HoIII (4f10,
5
J=8, S=2, L=6, g=4/3, I8) atoms in compounds 1, 2, and 3, respectively. The
temperature dependence of the magnetic susceptibilities of all the compounds follows
a similar trend. Upon cooling to 2.0 K, the χmT value gradually decreased before
10

reaching values of 17.68, 21.63, and 18.03 cm3 K mol-1 for compounds 1, 2, and 3,
respectively. The decrease in χmT resulted from antiferromagnetic interactions of the
metal ions within the tetranuclear unit, the progressive thermal depopulation of the
ground-state LnIII sublevels, and magnetic anisotropy [16,24]. However, the relative
contribution of each of these effects is difficult to distinguish.
29
28
27
Zn Tb
2
2
Zn Dy
26
25
24
23
22
21
20
19
18
17
2
2
Zn Ho
2
2
0
50
100
150
200
250
300
T/K
Figure 4. The plots of χmT versus T under 1kOe for compounds 1-3.
In order to detect the slow relaxations associated with SMM behavior, the
dynamics of the magnetization of compounds 1, 2 and 3 were investigated using
alternating current (ac) susceptibility measurements in the absence of a dc field and
with an ac field of 2.0 Oe at the frequencies indicated in Figures S3, 5, and S4, which
show plots of χm′ vs. T and χm′′ vs. T. As shown in Figure 5, an obvious
temperature-dependent ac signal is observed for compound 2 below 10 K, indicating
the onset of slow magnetization relaxation [25] and, thus, probable SMM behavior.
Unfortunately, the maximum value of the freqency-dependent χm″ signals of the
compound was not detected in the temperature window studied. This phenomenon is
probably due to the fast quantum tunneling of magnetization (QTM). Therefore, a 3.5
11

kOe external magnetic field was employed during the ac susceptibility measurements,
and a clear frequency-dependence was observed for χm′ and χm″ signals in the
temperature range of 2 to 15 K for compound 2 as shown in Figure 6, indicating a
slow field induced relaxation of magnetization. The frequency dependence of the peak
temperature of χm′ was used to estimate Mydosh parameters, which are given by φ =
(∆Tp/Tp)/∆(logf) = 0.406 for compound 2 where Tp is the maximum value of χm′ at
different temperatures and f = 2πν. This Mydosh parameter value excludes the
possibility of compound 2 being a spin glass (0.01 < φ < 0.08) [26]. Plots of ln(τ) vs.
T-1 are shown in Figure 5. A linear regression (R = 0.9989) based on the Arrhenius
rate law (τ = τ0 exp(∆/(kBT))) for a thermally activated mechanism resulted in a
pre-exponential factor of τ0 = 4.33 × 10-6 s and an activation barrier of ∆/kB = 23.74 K,
which are shown in the inset to Figure 5 (solid lines). The calculated value of τ0 is
consistent with literature values (τ0 = 10-6 - 10-11s) for an SMM [27].
10Hz
30Hz
6
100Hz
300Hz
4
600Hz
800Hz
2
0
0.20
0.15
0.10
0.05
0.00
2
4
6
8
10
T/K
Figure 5. Temperature dependence of the in-phase (upper) and out-of-phase (lower) ac
susceptibilities for 2 measured in a 2.0 ac field without a dc field.
12

1.6
1.2
0.8
0.4
100Hz
300Hz
600Hz
800Hz
1000Hz
0.0
0.6
-6.0
-6.5
-7.0
-7.5
-8.0
-8.5
-9.0
0.4
0.2
0.0
0.14 0.16 0.18 0.20 0.22 0.24 0.26 0.28
-1 -1
T /K
2
4
6
8
10
12
14
16
T/K
Figure 6. Temperature dependence of the in-phase (top) and out-of-phase (bottom) ac
susceptibility for 2 under a 3.5kOe dc field. The solid lines represent the best fits to the Arrhenius
law.
4. Conclusion
Three new compounds, [Zn2Tb2], [Zn2Dy2], and [Zn2Ho2], were obtained
successfully through reactions with the H2L ligand, ZnCl2, and Ln(NO3)3 in a 2:1:1
molar ratio in the presence of triethylamine. The structure of the three compounds was
13

that of an irregular parallelogram core containing two Ln3+ and two Zn2+ ions linked
by phenol oxygen atoms from four L2- ligands. A magnetization study of compound 2
at low temperatures clearly revealed that the compound displayed a slow relaxation of
magnetization. An energy barrier of ∆/kB = 23.74K and a pre-exponential factor of τ0
= 4.33×10-6 s were obtained by fitting the dynamic magnetic data to an Arrhenius rate
law. The results described here suggest that the assembly of multinuclear 3d-4f
compounds from suitable multidentate ligands is a promising strategy for the design
of novel molecular magnetic architectures. Further in-depth studies based on this
multidentate ligand, we will use it to react with 3d-4f systems and other auxiliary
ligands to prepare heterometallic 3d-4f compounds with potentially controlled
magnetic properties.
Acknowledgments
This work was supported by the National Science Foundation of China
(21101068), the National Science Foundation of Anhui (1308085MB16), and the
Scientific and technological projects (20140219).
Appendix A. Supplementary data
CCDC 1400642-1400644 (for 1-3), contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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18

Synthesis, structure, and magnetic properties of heterometallic
{Zn2Ln2} (Ln = Tb, Dy, Ho) compounds with parallelogram-like
cores
Wei-Wei Kuang, Yun Xu, Li-Li Zhu, Pei-Pei Yang*
College of Chemistry and Materials Science, Huaibei Normal University, 100
Dongshan Road, Huaibei, 235000, People’s Republic of China
Graphical abstract
Using the 1,2-Bis(2-hydroxy-3-methoxybenzylidene) hydrazine ligand, lanthanide
nitrate and zinc chloride, we obtained and characterized three heterometallic {Zn2Ln2}
compounds. Their crystal structures and magnetic properties were studied.
19

Synthesis, structure, and magnetic properties of heterometallic
{Zn2Ln2} (Ln = Tb, Dy, Ho) compounds with parallelogram-like
cores
Wei-Wei Kuang, Yun Xu, Li-Li Zhu, Pei-Pei Yang*
College of Chemistry and Materials Science, Huaibei Normal University, 100
Dongshan Road, Huaibei, 235000, People’s Republic of China
Highlights
• Three heterometallic parallelogram-like {Zn2Ln2} compounds have been
synthesized.
• Their crystal structures and magnetic properties are studied.
• Dy compound exhibits the properties of single molecule magnet.
20