In Situ Ligand Formation in the Synthetic Processes from Mononuclear Dy(III) Compounds to Binuclear Dy(III) Compounds: Synthesis, Structure, Magnetic Behavior, and Theoretical Analysis

Article abstract of DOI:10.1021/acs.inorgchem.0c02863

Guided by the self-assembled process and mechanism, the strategy of in situ Schiff base reaction would be capable of bringing a feasible method to construct and synthesize lanthanide compounds with distinct structures and magnetic properties. A mononuclea

Full text of DOI:10.1021/acs.inorgchem.0c02863

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In Situ Ligand Formation in the Synthetic Processes from
Mononuclear Dy(III) Compounds to Binuclear Dy(III) Compounds:
Synthesis, Structure, Magnetic Behavior, and Theoretical Analysis
Sheng Zhang,* Jiamin Tang, Jin Zhang, Fang Xu, Sanping Chen,* Dengwei Hu, Bing Yin,*
and Jiangwei Zhang*
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ABSTRACT: Guided by the self-assembled process and mechanism, the strategy
of in situ Schiff base reaction would be capable of bringing a feasible method to
construct and synthesize lanthanide compounds with distinct structures and
magnetic properties. A mononuclear Dy(III) compound was synthesized through a
multidentate Schiff base ligand and a chelating β-diketonate ligand, which was
named as [Dy(L)(bppd)]·CH3OH [1; H2L = N,N′-bis(2-hydroxy-5-methyl-3-
formylbenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine and bppd = 3-bis-
(pyridin-2-yl)propane-1,3-dione]. Furthermore, a new binuclear Dy(III) com-
pound, [Dy2(H2Lox)(bppd)3]·8CH3OH [2; H4Lox = N,N′-bis[2-hydroxy-5-
methyl-3-(hydroxyiminomethyl)benzyl]-N,N′-bis(pyridin-2-ylmethyl)-
ethylenediamine], was obtained via an in situ synthetic process. Under similar
synthetic conditions, [Dy(L)(ctbd)] [3; ctbd = 1-(4-chlorophenyl)-4,4,4-trifluoro-
1,3-butanedione] and [Dy2(H2Lox)(ctbd)3]·CH3OH·C4H10O (4) were synthe-
sized by modifying the β-diketonate ligand and in situ Schiff base reaction. Compound 3 is a mononuclear configuration, while
compound 4 exhibits a binuclear Dy(III) unit. Therein, formylbenzyl groups of H2L in 1 and 3 were changed to
(hydroxyiminomethyl)benzyl groups in 2 and 4, respectively. In isomorphous 2 and 4, two Dy(III) centers are connected through
two phenol O− atoms of the H2Lox2− ligand to form a binuclear structure. Eight-coordinated Dy(III) ions with different distortions
can be observed in 1−4. The crystals of 1 and 3 suffered dissolution/precipitation to obtain 2 and 4, respectively. The relationship
between the structure and magnetism in compounds 1−4 was discussed through the combination of structural, experimental, and
theoretical investigations. Especially, the rates of quantum tunneling of magnetization of 1−4 were theoretically predicted and are
consistent with the experimental results. For 2 and 4, the theoretically calculated dipolar parameters Jdip are consistent with the
experimental observation of weak ferromagnetic coupling.
barriers of magnetization reversal (Ueff) and blocking temper-
atures (TB). Regulation of SMMs is a big challenge because of
the need to control various conditions, such as the pH, solvent,
temperature, and ratio.2−10
Remarkably, in situ Schiff base reactions have been observed
during the synthesis processes of clusters.11−13 The new Schiff
base ligand has many coordination points. Because of this, the
target would be easily regulated. Especially, in situ Schiff base
reaction can be applied to produce binuclear or cluster systems
based on simpler structures.
INTRODUCTION
■
Researchers in all fields of science constantly seek strategies for
controllable synthesis in order to control as many experimental
variables as possible. This provides a rational synthesis process
and governs the outcome of the experiment. The final
objective is to realize target products and understand the
dominant parameters of the overall behavior. Controllable
syntheses of coordination polymers possessing single-ion
magnets (SIMs) or single-molecule magnets (SMMs) are of
great importance, which is attributed to potential applications
of SIMs or SMMs in high-density information storage and
quantum processing.1−4 Mononuclear or binuclear Ln(III)
compounds are very attractive. The simple systems are very
convenient to study SIMs or SMMs systemically because of
their easy tunability, coordination geometry, crystal field (CF)
around the metal center, magnetic interactions between two
spin carriers, and so on. Knowledge of the structure−
magnetism correlations of Ln(III) SIMs or SMMs would be
helpful for making a breakthrough in the thermal energy
Received: September 26, 2020
Published: January 2, 2021
https://dx.doi.org/10.1021/acs.inorgchem.0c02863
© 2021 American Chemical Society
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Scheme 1. Molecular Structures of the Ligands H2L (a) and H4Lox (b)
(DMF), methanol (CH3OH), ether (C4H10O), dichloromethane,
NH2OH·HCl, and anhydrous Na2CO3 were purchased from Sigma-
Aldrich and used as received without further purification. The
methods for structural characterization, thermal behavior, and
magnetic measurement are given in the Supporting Information.
Synthesis of Compounds 1−4. Synthesis of Compound
[Dy(L)(bppd)]·CH3OH (1). H2L (0.1 mmol, 0.0524 g), bppd (0.1
mmol, 0.0226 g), and Et3N (0.1 mmol, 0.0102 g) were dissolved in 10
mL of a CH3OH solution. The mixed solution was added to a
CH3OH solution (10 mL) of Dy(NO3)3·6H2O (0.1 mmol, 0.0457 g)
with stirring for 6 h. After that, the resultant mixture was filtered. By
slow evaporation of CH3OH into air at room temperature, some pale-
yellow crystals of 1 were observed after several days. Yield: 39%
[0.0137 g, based on the Dy(III) salts]. Anal. Calcd for C46H45DyN6O7
(956.38): C, 57.72; H, 4.71; N, 7.53. Found: C, 57.93; H, 4.79; N,
7.45. IR (KBr, cm−1): 3438 (m), 2854 (m), 1650 (s), 1607 (s), 1535
(m), 1469 (s), 1412 (m), 1388 (m), 1351 (m), 1298 (s), 1263 (s),
1226 (m), 1188 (m), 1141 (m), 1063 (m), 1008 (w), 933 (w), 879
(m), 863 (m), 826 (m), 789 (w), 721 (m), 678 (w), 640 (m), 584
(w), 499 (w).
Synthesis of Compound [Dy2(H2Lox)(bppd)3]·8CH3OH (2). The
crystals of 1 (0.1 mmol) were added to a mixed solution of 4:1
CH3OH/DMF (10 mL). NH2OH·HCl (0.0102 g, 0.1 mmol) and
anhydrous Na2CO3 (0.1 mmol, 0.0102 g) were dissolved in 10 mL of
a CH3OH/dichloromethane solution. The solutions above were
mixed and stirred for 30 h at room temperature. The crystals of 1
were dissolved. After that, the resultant mixture was filtered. By the
slow evaporation of solvent molecules into air at room temperature,
yellow block crystals of 2 were obtained after several weeks. Anal.
Calcd for C79H93Dy2N12O18 (1823.67): C, 54.98; H, 5.10; N, 9.21.
Found: C, 54.94; H, 5.15; N, 9.17. IR (KBr, cm−1): 3438 (m), 2060
(m), 1642 (s), 1550 (s), 1519 (m), 1480 (s), 1458 (m), 1408 (s),
1381 (s), 1306 (m), 1265 (m), 1225 (w), 1157 (w), 1025 (w), 940
(w), 804 (w), 863 (w), 756 (w), 725 (w), 693 (w), 610 (w), 523 (w).
Synthesis of Compound [Dy(L)(ctbd)] (3). The synthetic process
of 3 is similar to that of 1. The bppd ligand (0.1 mmol, 0.0226 g) in 1
was changed to ctbd (0.1 mmol, 0.0251 g). Finally, pale-yellow block
crystals of 3 were obtained after several days. Yield: 45% [0.0207 g,
based on the Dy(III) salts]. Anal. Calcd for C42H37ClDyF3N4O6
(948.71): C, 53.12; H, 3.90; N, 5.90. Found: C, 53.17; H, 3.94; N,
5.87. IR (KBr, cm−1): 3443 (m), 2856 (m), 1650 (s), 1614 (s), 1572
(s), 1516 (w), 1467 (s), 1387 (m), 1351 (w), 1301 (s), 1263 (s),
1226 (m), 1193 (s), 1140 (m), 1095 (m), 1063 (m), 1014 (w), 948
(w), 910 (w), 879 (m), 863 (m), 826 (w), 793 (w), 763 (w), 718
(w), 647 (m), 586 (w), 499 (w).
Herein, a Schiff base ligand, N,N′-bis(2-hydroxy-5-methyl-3-
formylbenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine
(H2L; Scheme 1a and Figures S1−S8),14 and two kinds of β-
diketonate ligands, 1,3-bis(pyridin-2-yl)propane-1,3-dione
(bppd) and 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butane-
dione (ctbd), were selected to construct Dy(III) compounds
for the following reasons: (1) It is highly probable that the
N,O,N,O-based multichelating sites of the H2L ligand would
be inclined to shape a coordinate pocket and enclose one metal
ion.15 (2) Some excellent Dy(III) SIMs with distinct
coordination environments have been synthesized through
these kinds of very similar ligands.16−18 (3) The β-diketonate
ligand with a chelating coordination mode can be instrumental
in constructing a stable mononuclear compound. (4) Dy(III)
ions have been regularly used in building SIMs or SMMs with
diverse polyhedral configurations and symmetries. A Dy(III)
6
ion with a Kramers ground state of H15/2 possesses a large
angular moment, which is good for generating large Ising-type
magnetic anisotropy.4,5,8−10 (5) What is more, the formyl
groups of the H2L ligand can be changed to hydroxyimino-
methyl groups under certain conditions, resulting in the
formation of a new polydentate ligand, N,N′-bis[2-hydroxy-5-
methyl-3-(hydroxyiminomethyl)benzyl]-N,N′-bis(pyridin-2-
ylmethyl)ethylenediamine (H4Lox; Scheme 1b).14 Herein, two
mononuclear compounds were obtained under solution
reactions, namely, [Dy(L)(bppd)]·CH3OH (1) and [Dy(L)-
(ctbd)] (3). Furthermore, the crystals of 1 or 3 were immersed
in a mixed solution of DMF, CH3CH2OH, CH2Cl2, NH2OH·
HCl, and anhydrous Na2CO3. Finally, 1 and 3 were
transformed into [Dy2(H2Lox)(bppd)3]·8CH3OH (2) and
[Dy2(H2Lox)(ctbd)3]·CH3OH·C4H10O (4) through dissolu-
tion/precipitation processes, respectively. Compounds 2 and 4
exhibit binuclear structures. The formylbenzyl groups of H2L
in 1 and 3 were changed into (hydroxyiminomethyl)benzyl
groups in 2 and 4, respectively. In situ ligand formation can be
observed in the synthetic processes from mononuclear Dy(III)
compounds to binuclear Dy(III) compounds. Moreover, the
uniaxial anisotropy, magnetostructural correlation, and relaxa-
tion process were discussed through magnetic research and ab
initio calculation.
Synthesis of Compound [Dy2(H2Lox)(ctbd)3]·CH3OH·C4H10O (4).
A synthetic procedure similar to that for 2 was used to synthesize 4
except that a 4:1 CH3OH/DMF solution (10 mL) was replaced by a
4:1:1 CH3OH/C4H10O/DMF solution (10 mL). Finally, orange-
yellow block crystals of compound 4 were obtained by the slow
evaporation of solvent after several weeks. Anal. Calcd for
EXPERIMENTAL SECTION
■
Materials and Instruction. The H2L ligand was synthesized
following a previous reference.14 3-Bis(pyridin-2-yl)propane-1,3-dione
(bppd), 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione (ctbd),
Dy(NO3)3·6H2O, triethylamine (Et3N), N,N-dimethylformamide
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Table 1. Crystallographic Data and Structural Refinements for Compounds 1−4
1
2
3
4
molecular formula
fw
temperature (K)
cryst syst
space group
a (Å)
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
C46H45DyN6O7
956.38
293(2)
monoclinic
P21/n
15.8427(3)
14.7700(2)
18.9588(3)
90
106.966(2)
90
4243.22(13)
4
C79H93Dy2N12O18
1823.67
293(2)
monoclinic
P21/c
13.2072(12)
34.767(5)
17.250(2)
90
96.645(10)
90
C42H37ClDyF3N4O6
948.71
293(2)
monoclinic
P21/c
10.9905(5)
10.8292(7)
35.578(2)
90
112.713(6)
90
3906.1(4)
4
C65H59Cl3Dy2F9N6O12
1718.53
293(2)
monoclinic
P21/n
13.4189(12)
22.4963(16)
23.249(2)
90
102.999(10)
90
6838.3(11)
4
7867.4(16)
4
1.540
Z
D
calc(g cm−3
)
1.497
1.613
1.669
F(000)
μ (mm−1
1940
9.901
4367
11.107
1900
11.444
3404
13.405
)
θmin−θmax (deg)
reflns collected
GOF on F2
R1 /wR2 [I > 2σ(I)]
R1/wR2 (all data)
CCDC
3.209−67.064
21770
1.043
0.0450/0.1092
0.0558/0.1162
1947756
3.601−64.983
31687
0.942
0.0858/0.1751
0.2218/0.2549
1947757
2.690−67.250
13572
1.004
0.0555/0.0947
0.1039/0.1168
2024916
3.502−65.998
27317
1.063
0.0847/0.1660
0.1870/0.2178
2024917
a
b
a
b
2
2
R1 = ∑|Fo| − |Fc|/∑|Fo|. wR2 = [∑w(Fo − Fc2)2/∑w(Fo )2]1/2
.
Figure 1. Crystal structures of compounds 1 (a) and 2 (b) showing general ligand configurations.
C65H59Cl3Dy2F9N6O12 (1718.53): C, 45.39; H, 3.43; N, 4.89. Found:
RESULTS AND DISCUSSION
■
C, 45.33; H, 3.39; N, 4.95. IR (KBr, cm−1): 3333 (m), 2842 (m),
1619 (s), 11589 (s), 1567 (m), 1521 (w), 1487 (m), 1467 (m), 1382
(m), 1265 (s), 1245 (w), 1191 (m), 1142 (m), 1088 (m), 1072 (m),
1010 (w), 854 (w), 801 (m), 662 (w), 586 (w), 555 (w), 476 (w),
439 (w).
Crystal Structures. The synthetic processes for 1−4 are
shown in Figures 1 and S9. Compounds 2 and 4 were
synthesized by using compounds 1 and 3, respectively. The
crystals of 1 were dissolved in a mixed solution of DMF,
CH3CH2OH, CH2Cl2, NH2OH·HCl, and anhydrous Na2CO3.
The solution above was stirred for about 30 h at room
temperature. Finally, some yellow crystals of 2 were observed
at the bottom of beaker after several weeks. Obviously, the
crystals of 1 were transformed into 2 through a dissolution/
precipitation process. Meanwhile, the crystals of 3 were used to
synthesize compound 4. The 4:1 CH3OH/DMF solution (10
Single-Crystal X-ray Diffraction Analysis. The SADABS19 and
SHELXL-201820 programs were used in data analysis. Crystal data
and structure refinements were displayed in the Supporting
Information. Other details of the crystal data and refinement statistics
are given in Table 1. The selected bond lengths and angles are listed
in Table S1.
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mL) in 2 was replaced by 4:1:1 CH3OH/C4H10O/DMF
solution (10 mL) in the synthetic process of 4. High-quality
crystals of 4 without impurities could be obtained when
C4H10O was introduced into the synthetic process of
compound 4. Compounds 1−4 were fully characterized
through powder X-ray diffraction (Figures S10−S13),
elemental analysis, IR spectroscopy (Figures S14−S17),
thermal analysis (Figures S18−S21) and single-crystal X-ray
diffraction (Tables 1 and S1) techniques. Meanwhile, the
compositions of compounds 1−4 were determined by these
measurements. The results of structural analyses reveal that 1
and 4 crystallize in the monoclinic space group P21/n (Table
1). 2 and 3 crystallize in the monoclinic space group P21/c.
Compounds 1 and 3 exhibit similar mononuclear structures
(Figures 1 and S9). A Dy(III) ion in 1 is coordinated through
one deprotonated L2− ligand and one negative β-diketonate
ligand. Dy(III) ions in 1 and 3 display eight-coordinated
environments. One CH3OH solvent guest is found to reside in
1 (Figure S22). No solvent molecules are observed in 3.
However, compounds 2 and 4 display binuclear structures
(Figures 1 and S9). 2-Dy1 or 4-Dy1 ions locate in a pocket
formed by two benzaldoxime N atoms and two bridged phenol
O atoms of the H2Lox2− ligand as well as four chelated O
atoms of two β-diketonate ligands. Eight-coordinated 2-Dy2 or
4-Dy2 ions are surrounded by two ethylenediamine N atoms,
two pyridine N atoms, and two bridged phenol O atoms of the
H2Lox2− ligand as well as two chelated O atoms of one β-
diketonate ligand, respectively. The formyl groups of H2L in 1
and 3 were changed to the hydroxyiminomethyl groups of
H4Lox in 2 and 4 under certain conditions, respectively. The
lattice solvent molecules are found in the molecular structures
of 2 and 4. The Dy(III)−O bond lengths are in the ranges
2.229(3)−2.322(3) Å for 1, 2.237(10)−2.380(9) Å for 2,
2.230(5)−2.346(5) Å for 3, and 2.247(8)−2.314(10) Å for 4,
respectively (Table S1). The Dy(III)−N bond lengths are in
the ranges 2.590(4)−2.628(3) Å for 1, 2.531(12)−2.601(13)
Å for 2, 2.560(6)−2.632(6) Å for 3, and 2.550(13)−2.566(12)
Å for 4, respectively. The shortest Dy(III)−O distances are
2.229(3) Å [Dy(III)−O2], 2.237(10) Å [Dy(III)−O7],
2.230(5) Å [Dy(III)−O5], and 2.247(8) Å [Dy(III)−O7] in
1−4, respectively. In 1−4, the average distances of the
Dy(III)−O bonds are 2.285, 2.396, 2.292, and 2.297 Å, while
the average Dy(III)−N lengths are 2.614, 2.569, 2.597, and
2.562 Å, respectively. Obviously, the shortest Dy(III)−O bond
length is observed in 1. However, the Dy(III)−N distances for
1 and 2 are longer than those for 3 and 4, respectively. The
units in 1−4 are well-separated, and the nearest intermolecular
Dy(III)···Dy(III) distances are 9.1198(5), 7.9204(17),
9.8662(8), and 9.1732(12) Å, respectively. In compound 1,
formation of the O−H···O hydrogen bond with O7−H7A···O5
lead to bond distances of 0.821 and 2.285 Å (Figure S22),
respectively. The hydrogen bond angle is 117.75°. The metal
centers in the dinuclear cores of 2 and 4 are bridged by two
phenol O atoms (O4 and O9 in 2; O7 and O9 in 2) of one
H2Lox2− ligand (Figures 2 and S23), with the Dy(III)···
Dy(III) distances being 3.8843(14) and 3.8223(12) Å,
respectively. The Dy(III)−O−Dy(III) angles are 115.9(4)°
[Dy(III)−O4−Dy(III)] and 113.5(4)° [Dy(III)−O9−Dy-
(III)] in 2 as well as 113.5(3)° [Dy(III)−O7−Dy(III)] and
113.2(4)° [Dy(III)−O9−Dy(III)] in 4, respectively.
Figure 2. Metal centers in the dinuclear core of 2 are bridged by two
phenol O atoms (O4 and O9) of one H2Lox2− ligand.
dodecahedron (D2d) configurations. The Dy1 and Dy2 centers
in 2 and 4 closely pertain to a square antiprism (D4d)
configuration with a continuous shape measure (CShM)
parameters of 0.714 (2-Dy1) and 0.833 (4-Dy1) as well as
an approximate triangular dodecahedron (D2d) configuration
with CShM parameters of 1.185 (2-Dy2) and 1.182 (4-Dy2),
respectively. The polyhedra of the Dy(III) centers for 1−4 can
be observed in Figures 3 and S24.
Magnetic Properties. Powder X-ray diffraction patterns
were measured (Figures S10−S13). The results indicate that
these experimental patterns are in accordance with the
corresponding calculated ones to verify the phase purity of
1−4. Direct-current (dc) magnetic susceptibility data of 1−4
were carried out from 2 to 300 K under a 1000 Oe dc field
(Figure 4). The χMT values for 1 and 3 are 14.35 and 14.29
cm3 K mol−1 at 300 K, respectively, which are in agreement
with the theoretical value of a noninteracting Dy(III) ion (S =
5/2, L = 5, g = 4/3, and 6H15/2).23 For compounds 2 and 4, the
χMT values are 28.07 and 28.73 cm3 K mol−1 at 300 K,
respectively. The two values are close to the theoretical value
of 28.34 cm3 K mol−1 for two noninteracting Dy(III) ions in
the H15/2 ground state.23 Upon cooling, the χMT values of 1
6
and 3 slightly decrease in the high-temperature range.
Furthermore, the curves degrade rapidly at low temperature.
At 2.0 K, the values in 1 and 3 are 8.55 and 12.07 cm3 K mol−1,
respectively, strongly implying the presence of magnetic
blocking. As the temperature is lowered, the χMT products of
2 and 4 decrease gradually as thermal depopulation of the
Stark sublevels of the Dy(III) ion.23 The minimum values are
22.76 cm3 K mol−1 for 2 at 7.0 K and 22.85 cm3 K mol−1 for 4
at 10.0 K. The χMT values of 2 and 4 then increase sharply to
values of 23.41 and 23.79 cm3 K mol−1 at 2.0 K, respectively.
The process results from the intramolecular ferromagnetic
coupling for 2 and 4.
Field-dependent magnetization of 1−4 was carried out at 2.0
K (Figure 5). The values of 1−4 increase fast at weak fields
and then increase slowly. The magnetization values of 1−4
increase to 6.08, 11.39, 5.00, and 10.68 Nβ at 70 kOe,
respectively. These values at 70 kOe are lower than the
expected saturation values of 10 or 20 Nβ, which are mainly
attributed to strong magnetic anisotropy.23 The magnetic
hysteresis loops were examined for 1−4. Butterfly-shaped
hysteresis loops are obviously open from 2 to 5 K in 1 (Figure
6a). A weak butterfly-shaped hysteresis loop can be observed at
2 K in 3 (Figure 6b). However, magnetic hysteresis loops
cannot be found in compounds 2 and 4.
These configurations of the Dy(III) centers in 1−4 were
analyzed through the SHAPE 2.1 software (Table S2).21,22
Compounds 1 and 3 belong to approximately triangular
The temperature dependence of alternating-current (ac)
susceptibilities for 1−4 was carried out under a 0 Oe dc field
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Figure 3. Local coordination geometries of the Dy(III) ions for 1 (a) and 2 (b).
Figure 4. Temperature dependence of χMT measured at 1 kOe for 1−4 (a−d), respectively.
(Figures S25−S28). For 1, out-of-phase (χ″) susceptibilities
show obvious temperature dependence (Figure S25). Their
peaks are in good shape, indicating typical SMM behaviors. No
peak data can be observed above 2.0 K in compounds 2−4
(Figures S26−S28). The χ′ and χ″ products of 1−4 increase as
the temperature decreases. The χ′ and χ″ values rise again in 1
below 7.5 K, revealing the appearance of quantum tunneling of
magnetization (QTM). The phenomenon is often found in
SMMs. To restrain QTM, the temperature dependence of ac
susceptibilities for 2 was measured with a 1500 Oe dc field
(Figure S29). The significant peaks demonstrate field-induced
slow magnetic relaxation behavior.
Besides, the frequency dependence of ac susceptibilities in
1−4 was measured, as seen in Figures 7−10. Compounds 1
and 3 show frequency dependencies based on observable χ′
and χ″ signals (Figures 7 and 9), respectively. The peaks of the
χ″ susceptibilities for 1 and 3 smoothly shift from the medium-
frequency region to the high-frequency region with rising
temperature. The variable frequencies on the ac susceptibility
measurement of 2 were performed at 2.2 K under a wide range
of applied dc fields (Figure S30). Strikingly, 1200 or 1500 Oe
is the optimal field (Hop), which results in strong relaxation
phase. Therefore, the frequency-dependent ac magnetic
susceptibilities were carried out in the range from 2.0 to 5.5
K under a 1200 Oe dc field (Figure 8) as well as from 2.0 to
7.0 K under a 1500 Oe dc field in 2 (Figure S31). Both the χ′
and χ″ signals of compound 2 exhibit frequency dependencies.
The χ″ peaks present two relaxation processes, attributed to
the fast relaxation (FR) and slow relaxation (SR) processes,
respectively. The FR process in compound 2 may result from
one main reason: QTM is enhanced by dipolar interactions
between the Dy ions, which can be partly suppressed by the
applied field. Additionally, it is also possible that the two
relaxation processes came from the two different Dy(III)
ions.23f Compound 4 shows very weak χ″ signals under a 0 Oe
dc field (Figure S32). The variable frequencies on the ac
susceptibility measurement in 4 were carried out at 2.2 K
under a wide range of applied dc fields (Figure S33).
Obviously, a Hop value of 800 Oe results in a strong relaxation
phase in the high-frequency region. Furthermore, ac magnetic
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Figure 5. M(H) plots for 1−4 (a−d), respectively.
Figure 6. Magnetic hysteresis loops for 1 (a) and 3 (b).
Figure 7. Plots of the χ′ (a) and χ″ (b) ac susceptibilities from 2.0 to 35.0 K for 1 under a 0 Oe dc field.
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Figure 8. Plots of the χ′ (a) and χ″ (b) ac susceptibilities from 2.0 to 7.0 K for 2 under a 1200 Oe dc field.
Figure 9. Plots of the χ′ (a) and χ″ (b) ac susceptibilities from 2.0 to 16.0 K for 3 under a 0 Oe dc field.
Figure 10. Plots of the χ′ (a) and χ″ (b) ac susceptibilities from 2.0 to 5.5 K for 4 under a 800 Oe dc field.
data for 4 were collected in the range from 2.0 to 5.5 K under a
800 Oe dc field (Figure 10). The frequency dependencies were
observed in the χ′ and χ″ components of compound 4.
Meanwhile, the FR and SR processes were also found in 4. A
similar phenomenon can be seen in compound 2.23f
The Cole−Cole plots of 1 and 3 based on the frequency-
dependent ac susceptibilities exhibit good semicircular shapes
(Figures 11 and 12). The Cole−Cole plots of 2 and 4 present
two relaxation phases corresponding to the FR and SR
processes (Figures S34−S36). When the corresponding data of
1 and 3 are fited with a generalized Debye model, the
parameter α can be obtained in the ranges of 0.064−0.173
(Figure S37 and Table S3) and 0.102−0.186 (Figure S38 and
Table S4), respectively, indicating a narrow distribution of
relaxation times for a single relaxation process. This narrow
distribution indicates that magnetic relaxation can be well
described by a single relaxation time parameter τ in 1 or 3. The
relaxation times of 1 and 3 at high temperatures obey an
Arrhenius law [τ = τ0 exp(Ueff/kT)] with effective energy
barriers of Ueff = 171.7 K and τ0 = 1.28 × 10−7 s as well as Ueff
= 22.7 K and τ0 = 9.29 × 10−5 s, respectively (Figures 13 and
14). The ln(τ) versus 1/T plots in 1 and 3 exhibit some
curvature. The overall dynamics cannot be properly modeled
based on the Orbach mechanism. Therefore, the total
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Figure 14. Fitting of the frequency dependence of relaxation times
under a 0 Oe dc field for compound 3.
Figure 11. Cole−Cole plots for 1 from 2.0 to 35.0 K under a 0 Oe
applied dc field.
Theoretical Analysis and Structure−Property Rela-
tionship. In order to interpret the magnetic anisotropy and
relaxation of the systems here, electronic structure calculations,
based on multiconfigurational methods including spin−orbit
coupling, were performed. The ab initio calculations were
conducted via a procedure of CASSCF/RASSI-SO/SINGLE
ANISO.24−32 All of the calculations were carried out with the
code of MOLCAS@UU, a free version of MOLCAS 8.033,34 for
academic users. The details of the computations are included
in the Supporting Information.
For 1 and 3, the crystal structure was used directly. For 2
and 4 of dinuclear geometry, each of the paramagnetic Dy(III)
ions was replaced by one diamagnetic Lu(III) to give
mononuclear models for ab initio calculation. These models
are denoted as 2-Dy1, 2-Dy2, 4-Dy1, and 4-Dy2 hereafter.
In principle, the microscopic states of the Kramers system,
e.g., 1 and 2 here, are grouped into various 2-fold degenerate
Figure 12. Cole−Cole plots for 3 from 2.0 to 16.0 K under a 0 Oe
applied dc field.
states, called as Kramers doublets (KDs). Each KD could be
1
̃
uniquely associated with a pseudospin of /2, i.e., S =
1/2.31,32,35,36 Thus, the principal values of the g matrix of this
pseudospin provide an univocal description on the related
KD.8,9,13 With accurate ab initio results, analysis based on
these g values is reliable and widely accepted in the field of Ln-
based SIM.24,31,32,35,37−44
The dinuclear 2 and 4 are non-Kramers Ln-based systems.
The 4f electrons of Ln ions are strongly localized, and, hence,
the exchange interaction between Ln ions is usually accepted
to be very weak.24,35,41 In comparison, the magnetic dipolar
interaction between Ln ions is usually stronger than the
exchange interaction. However, even the sum of these two
interion interactions is quite weaker than the local CF of an
individual Ln ion.35 Thus, the final electronic structure of
either 2 or 4 is dominated by the sum of the local CF levels of
constituent mononuclear Kramers Ln fragments.35,38,41 Finally,
these local CF levels will be expanded into bands due to the
weak interion interaction.
Figure 13. Fitting of the frequency dependence of relaxation times
under a 0 Oe dc field for compound 1.
The electronic structure of a dinuclear Ln compound
includes groups of energy levels. The intergroup energy
differences are mainly determined by the local CF of various
Ln ions. However, the small intragroup energy difference is
mainly determined by the weak exchange and dipolar
interactions. Thus, the lowest doublets of 2 and 4 are well
separated from other doublets, and they mainly arise from the
relaxation rates were fitted through the Orbach, Raman, and
QTM processes (Figures S39 and S40), resulting in an
effective energy barriers of Ueff = 247.3 K in 1 and Ueff = 78.0 K
in 3. The details can be seen in Table S5.
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Table 2. Ab Initio Computed Relative Energies (cm−1),
Principal Values of the g Tensors, and Theoretical and
Experimental QTM Times (τQTM-theo and τQTM-exp in
Seconds) of the Compounds Studied in This Work
interaction between ground-state KDs of individual Ln
fragments.35
To observe slow magnetic relaxation, the relaxation rate
ought to be slow enough to be monitored by an experimental
apparatus. In Ln-based SMMs, different pathways of relaxation
exist at the same time,35,37−39,45 and, thus, the final relaxation
rate has contributions from all of the existing pathways. The
dominance of one single pathway across a wide temperature
range is rare in Ln-based SMMs.37,38,45 This is one important
reason for the complexity of Ln-based SMMs.
1
2-Dy1
0.000
2-Dy2
0.000
KD0
E
0.000
gZ
gX
gY
gXY
19.9067
18.2784
0.1445
0.3487
0.3774
18.6767
0.2422
0.7407
0.7793
0.1222 × 10−2
0.1861 × 10−2
0.2226 × 10−2
The relaxation pathways could be grouped into spin−lattice
τQTM-theo 0.1435 × 10−1
0.4585 × 10−6 0.1100 × 10−6
pathways43 and QTM.44 Generally, the rate of QTM (τQTM
)
−1
τQTM-exp
E
0.720 × 10−2
207.803 (171.8)
17.0215
0.7760 × 10−1
0.9773 × 10−1
0.1248
within the ground-state doublet dominates in the region of low
a
−1
KD1
KD2
KD3
52.846
14.3378
0.1006 × 101
0.1190 × 101
0.1559 × 101
112.479
78.604
12.8343
0.2788 × 101
0.3625 × 101
0.4573 × 101
118.850
temperature, so that τQTM could be taken as the lower limit
of the total relaxation rate.45 Thus, the necessary condition for
gZ
gX
gY
gXY
E
−1
the zero-field SMM is that τQTM of the ground state is slow
enough.38,45,46 Clearly, the key parameter characterizing QTM
−1
is just τQTM or its reciprocal QTM time τQTM
.
−1
366.407
A general equation for theoretical prediction of τQTM has
been given previously (eq 1a).45 For Kramers system under a 0
Oe dc field, the tunnel splitting (Δtun) and energy bias (εbias),
which are necessary for the prediction of τQTM−1, are provided
by Zeeman interaction, as shown in eqs 1b and 1c. Under the
assumption of an isotropic internal magnetic field, a working
equation to predict τQTM−1 of a Kramers SIM (eq 1d) has been
given, and it shows reliable accuracy.45,47
gZ
gX
gY
gXY
E
11.4018
11.4425
11.2489
0.2283 × 101
0.4975 × 101
0.5474 × 101
413.341
0.2170 × 101
0.3289 × 101
0.3940 × 101
173.646
0.1979 × 101
0.3756 × 101
0.4245 × 101
163.503
gZ
gX
gY
gXY
0.1685
2.5208
12.7454
0.9526 × 101
0.7006 × 101
0.1182 × 102
3
0.8512 × 101
0.6378 × 101
0.1064 × 102
4-Dy1
0.2584 × 101
0.2921 × 101
0.3900 × 101
4-Dy2
2
2Δtun
−1
τQTM
=
2
2 1/2
h(εbias + 4Δtun
)
(1a)
KD0
E
0.000
0.000
0.000
gZ
gX
gY
gXY
τQTM-theo
τQTM-exp
E
gZ
gX
gY
gXY
E
gZ
gX
gY
gXY
E
19.9023
18.1217
19.1034
1
2
2
2
2
2 1/2
0.2228 × 10−2
0.3013 × 10−2
0.3747 × 10−2
0.5064 × 10−2
0.180 × 10−2
209.543 (54.2)
17.0373
0.3377 × 10
0.1016 × 101
0.1071 × 101
0.5654 × 10−7
0.2094 × 10−1
0.4208 × 10−1
0.4701 × 10−1
0.3089 × 10−4
Δtun
=
[β(gX BX + gY BY
)
]
(1b)
(1c)
εbias = βBZgZ
2
gXY
βBave
−1
KD1
KD2
KD3
54.210
11.7906
0.3060 × 101
0.5216 × 101
0.6048 × 101
89.537
89.161
14.6430
0.4965 × 10
0.9371 × 10
0.1060 × 101
139.195
τQTM
=
,
2 1/2
2
h
2(gXY + gZ )
2 1/2
0.5764 × 10−1
0.6593 × 10−1
0.6593 × 10−1
407.609
2
gXY = (gX + gY )
(1d)
It needs to indicate that the dominating pathways in the
high-temperature region are the spin−lattice ones, e.g., the
Orbach and Raman pathways, rather than QTM. The most
popular parameter describing spin−lattice relaxation is the
effective magnetic reversal barrier (Ueff).44,48,49 Thus, good
SMMs could be concisely described as the ones of
simultaneous achievement of both long τQTM and high Ueff.45
However, the original definition of Ueff comes from the
Arrhenius rule between the relaxation rate and temperature.50
Among the various pathways of magnetic relaxation, this rule is
only obeyed by the Orbach one. Thus, the importance of Ueff
should not be overestimated because it is actually phenom-
enological.
13.7086
10.0937
12.0463
0.7278 × 10
0.9439 × 10
0.1192 × 101
511.923
0.3410 × 10
0.3704 × 101
0.3720 × 101
120.607
0.1168 × 10
0.1196 × 101
0.1202 × 101
202.428
gZ
gX
gY
gXY
12.6118
13.2062
9.2971
0.3513 × 101
0.5596 × 101
0.6607 × 101
0.2580 × 101
0.4044 × 101
0.4797 × 101
0.1133 × 101
0.3369 × 101
0.3554 × 101
a
The values of experimentally fitted Ueff are shown in parentheses.
With the principal g values obtained from ab initio
calculations (Table 2), τQTM is predicted for the compounds
In principle, the τQTM-theo values of 2 and 4 in Table 2 are
theoretical predictions for their constituent mononuclear
fragments rather than the true dinuclear compounds. As
shown above, the electronic structures of 2 and 4 are mainly
determined by these mononuclear fragments. Thus, we assume
that the properties of the constituent fragments could
represent the essential part of the properties of their parent
dinuclear compounds. For 2 and 4, τQTM is theoretically
predicted to be within the range 10−8−10−5 s (Table 2). These
are quite short QTM times (or fast QTM rates equally), which
here. In the cases of SIMs 1 and 3, theoretical τQTM (τQTM
-
theo) is consistent with the experimental values (τQTM-exp)
because they are within the same order of magnitude, i.e.,
0.1435 × 10−1 s versus 0.720 × 10−2 s for 1 and 0.5064 × 10−2
s versus 0.180 × 10−2 s for 3. Theoretical predictions are also
consistent with the experimental observation in that τQTM of 1
is longer than that of 3. In other words, QTM of 1 is weaker
than that of 3.
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Figure 15. Directions of the ab initio magnetic easy axes of the ground-state KDs of the compounds here.
are hard to catch based on the current experimental apparatus.
As shown above, under a 0 Oe dc field, neither 2 nor 4
demonstrates a peak in their ac susceptibility signals. These
experimental observations mean that magnetic relaxation of 2
and 4 is very fast. Thus, our theoretical prediction is also
consistent with the experiments in 2 and 4. According to the
results of the constituent fragments, the dipolar parameters Jdip
are calculated to be 3.02 and 2.56 cm−1 for 2 and 4,
respectively. These theoretical results are consistent with the
experimental observation of weak ferromagnetic (FM)
coupling in both 2 and 4.
Furthermore, 1 is theoretically predicted to have the weakest
QTM among the compounds here, and this prediction is also
in line with the observation that the SMM properties of 1 are
the best here because it is the only one that clearly shows a
peak in the imaginary part of the ac signal under a 0 Oe dc field
and its opening in the magnetic hysteresis loop is wider.
Under the dominance of the Orbach pathway, Ueff could be
close to the energy of a given excited state. As shown in Figure
S41, the spin−lattice relaxation here proceeds via the first
excited-state KD, i.e., KD1. However, the residual ground-state
QTM, represented by the red arrow connecting the ground-
state KD (Figure S41), as well as the Raman pathway exclude
the ideal domiance of Orbach one. Therefore, Ueff, fitted from
the experimental data, is clearly lower than the ab initio energy
of KD1 (Table 2). 1 is the one for which the experimentally
fitted Ueff is closest to the energy of KD1 among the
compounds here. This might be due to the fact that the
ground-state QTM of 1 is the weakest.
Because of the oblate electron density of the ground-state
multiplet of the Dy(III) ion,51−57 a suitable electronic structure
for a promising Dy SIM could be analyzed via an electrostatic
route.39,51−54 This means that the electrostatic repulsion (ESP)
along the easy axis should be as strong as possible. The ab
initio magnetic easy axes are shown in Figure 15. Therefore,
the axial atoms could be defined as the ones lying closest to the
easy axis within the first sphere (Table 3).
With the atomic charges and lengths to the central Dy(III)
ion (Table 3), we could estimate the ESP along the axial
direction at a semiquantitative level.39,52−54 As shown in Table
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Table 3. Atomic Charges (|e|) from Ab Initio Calculations, Related Dy−O/N Bond Lengths (Å), and Angles θ (deg) with
Respect to the Magnetic Easy Axes of the Ground-State KDs of the Atoms in the First Sphere
Compound 1
a
O3-a
O4-a
O2
O5
N6
N7
N8
N9
charge
−0.887
2.228
10.1
−0.880
2.267
18.7
−0.760
2.322
−0.742
2.320
−0.288
2.628
−0.329
2.616
−0.330
2.590
−0.301
2.621
Dy−O/N
b
θ
c
ESP(ax)
0.750
Compound 2-Dy1
O3-a
O5-a
O4
O6
O9
O10
N11
N16
charge
Dy−O/N
θ
−0.8171
2.262
17.8
−0.737
2.311
33.1
−0.766
2.376
−0.769
2.276
−0.722
2.243
−0.759
2.340
−0.130
2.574
−0.192
2.555
ESP(ax)
0.640
Compound 2-Dy2
O3-a
O8-a
O4
O7
N12
N13
N14
N15
charge
Dy−O/N
θ
−0.806
2.342
35.9
−0.738
2.280
21.7
−0.802
2.280
−0.773
2.288
−0.305
2.601
−0.360
2.562
−0.356
2.592
−0.299
2.547
ESP(ax)
0.623
Compound 3
O4-a
O5-a
O2
O3
N6
N7
N8
N9
charge
Dy−O/N
θ
−0.871
2.247
11.3
−0.868
2.230
17.1
−0.689
2.342
−0.679
2.345
−0.340
2.560
−0.305
2.632
−0.293
2.629
−0.344
2.565
ESP(ax)
0.743
Compound 4-Dy1
O3-a
O9-a
O4
O10
N12
N13
N14
N15
charge
Dy−O/N
θ
−0.768
2.324
38.1
−0.709
2.313
20.5
−0.788
2.282
−0.734
2.279
−0.370
2.531
−0.301
2.576
−0.354
2.567
−0.306
2.562
ESP(ax)
0.593
Compound 4-Dy2
O4-a
O6-a
O3
O5
O7
O8
N11
N16
charge
Dy−O/N
θ
−0.776
2.295
21.0
−0.680
2.279
17.8
−0.781
2.248
−0.695
2.327
−0.677
2.304
−0.737
2.315
−0.179
2.585
−0.170
2.550
b
ESP(ax)
0.598
a
b
“-a” indicates the two axial atoms that lie closest to the magnetic easy axis within the first sphere. Only the θ values of the two axial atoms are
c
shown. ESP(ax) is the semiquantitative estimate of the axial electrostatic repulsion in atomic units (au).
3, 1 has the largest value of ESP(ax), suggesting that the ESP
from the axial atoms of 1 is the strongest among all of the
systems here. Thus, our semiquantitative analysis does support
that 1 has the best SMM properties because of its best
fulfillment of the electrostatic route. In comparison, the
ESP(ax) values of the mononuclear fragments of dinuclear 2
(∼0.63 au) and 4 (∼0.60 au) are clearly smaller than those of
mononuclear 1 (0.75 au) and 3 (0.74 au). These results are
also consistent with the theoretical prediction of τQTM above.
In our previous work, two new Dy(III) compounds,
[Dy(L)(Dppd)]·solvent and [Dy(L)(Dppd)],5b were obtained
through the same multidentate Schiff base ligand and a similar
β-diketonate ligand. The two compounds also exhibit
mononuclear structures, belonging to an approximate trigonal
dodecahedron (D2d) configuration. However, different average
distances of the Dy(III)−O and Dy(III)−N bond lengths are
observed. Magnetic studies reveal that these compounds
display slow magnetic relaxation behavior under a 0 Oe dc
field with Ueff of 221.38, 278.56, 247.3, and 78.0 K for
[Dy(L)(Dppd)]·solvent, [Dy(L)(Dppd)], 1, and 3, respec-
tively. On the basis of theoretical analysis, the calculated
ground-state gZ values are 19.837 (gXY = 0.003), 19.841 (gXY
=
0.001), 19.9067 (gXY = 0.002), and 19.9023 (gXY = 0.004) for
[Dy(L)(Dppd)]·solvent, [Dy(L)(Dppd)], 1, and 3, respec-
tively. The gZ values are very similar. The gX and gY values are
slightly different, corresponding to the different zero-field
SMM properties. The large gXY value could cause more obvious
QTM (eq 1d). Obviously, [Dy(L)(Dppd)] would present a
more significant axial anisotropy compared to [Dy(L)-
(Dppd)]·solvent, 1, and 3 based on the gXY values.
Experimentally, [Dy(L)(Dppd)] exhibits the highest Ueff value.
[Dy(L)(Dppd)3]·solvent,5b 2, and 4 show dinuclear cores in
which the metal centers are bridged by two phenol O atoms of
one L2− ligand or one H2Lox2− ligand. The Dy(III)···Dy(III)
distances are 3.9031, 3.8840, and 3.8223(12) Å in [Dy(L)-
(Dppd)2]·solvent, 2, and 4, respectively. The Dy(III)−O−
Dy(III) angles of [Dy(L)(Dppd)2]·solvent are 113.2(3) and
115.8(3)°. The Dy(III)−O−Dy(III) angles of 2 are 113.5(4)
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and 115.9(4)°. The Dy(III)−O−Dy(III) angles of 4 are
113.5(3) and 113.2(4)°. The minimum distances and average
bond angles can be observed in compound 4. [Dy(L)-
(Dppd)2]·solvent and 2 show similar Dy(III)−O−Dy(III)
angles and Dy(III)···Dy(III) distances. These different
distances and angles would provide different magnetic coupling
pathways between Dy(III) ions.58−60 The Dy(III)···Dy(III)
interactions in [Dy(L)(Dppd)2]·solvent, 2, and 4 are very
weak FM. The dipolar parameters Jdip are calculated to be 1.66
cm−1 in [Dy(L)(Dppd)2]·solvent, 3.02 cm−1 in 2, and 2.56
cm−1 in 4, which are consistent with the experimental results of
weak FM coupling in them. The Jdip value in 2 is stronger than
those of [Dy(L)(Dppd)2]·solvent and 4. However, the
calculated orientations of the local main magnetic axes on
the Dy(III) ions in the ground-state KDs of [Dy(L)(Dppd)2]·
solvent exhibit a smaller angle (56.1°) than those of
compounds 2 (112.3°) and 4 (128.8°) (Figure 15). Obviously,
the easy axes of 2 and 4 are not parallel to the vector
connecting the Dy(III) ions. This deviation would lead to
transversal components of the dipolar field, which significantly
increase the efficiency of the tunneling mechanism.59,61
Additionally, the calculated ground-state gZ values are 18.933
(gX, gY = 0.147, 0.346) and 19.286 (gX, gY = 0.010, 0.014) for
[Dy(L)(Dppd)2]·solvent, 18.278 (gX, gY = 0.145, 0.349) and
18.677 (gX, gY = 0.242, 0.741) for 2, and 18.122 (gX, gY = 0.338,
0.102) and 19.103 (gX, gY = 0.209, 0.420) for 4, respectively.
Obviously, the high values of gX and gY in 2 and 4 would lead
to strong QTM. Finally, [Dy(L)(Dppd)2]·solvent displays
SMM behavior under a 0 Oe dc field with Ueff of 162.92 K.
The unparallel easy axis and high values of gX and gY are
responsible for field-induced SMM behavior in 2 and 4. It is
well-known that the Dy(III)−O−Dy(III) angles have a
significant impact on the magnetic exchange. The overlap
between the magnetic orbitals of the Dy(III) ions would be
modified through the Dy(III)−O−Dy(III) angles.61−64 For
compound [Dy2ovph2Cl2(MeOH)3]·MeCN (H2ovph = pyr-
idine-2-carboxylic acid [(2-hydroxy-3-methoxyphenyl)-
methylene]hydrazide),64 the two eight-coordinated metal
ions are linked through the alkoxido groups (O1 and O4) of
two antiparallel, or “head-to-tail”, ovph2− ligands to generate a
binuclear unit. The Dy(III)···Dy(III) distance is 3.8644(5) Å.
The two Dy(III)−O−Dy(III) angles are 112.3(2) and
111.5(2)°. The corresponding local anisotropy axes of the
two Dy(III) ions are almost parallel to each other. The
compound presents stronger intramolecular ferromagnetic
interactions. Meanwhile, excellent SMM behavior can be
observed in [Dy2ovph2Cl2(MeOH)3]·MeCN. Additionally, ab
initio calculations of magnetic interactions and magnetic axis
inclination in [Dy2(L)(NO3)3(CH3O)] and [Dy2(L)-
(NO3)3(CH3CH2O)] reveal the significance of the Dy(III)−
O−Dy(III) angles and the direction of the easy axis. The two
important criteria above would regulate f−f interactions and
further impact the magnetic performances of binuclear
SMMs.65−68
structures, while compounds 2 and 4 are binuclear cores.
The metal centers in 2 or 4 are bridged by two phenol O−
atoms of one H2Lox2− ligand. 1 and 3 show slow magnetic
relaxation behavior under a 0 Oe dc field with Ueff of 247.3 and
78.0 K, respectively. The obvious butterfly-shaped hysteresis
loops can be observed from 2 to 5 K in 1. However, 3 shows
weak butterfly-shaped hysteresis loop at 2 K. Interestingly, two
relaxation processes are presented under a 1200 or 1500 Oe dc
field, corresponding to the FR and SR phases in 2, respectively.
The FR process in compound 2 may result from QTM. It can
be enhanced by dipolar interactions between the Dy(III) ions
or the presence of an applied field. A similar phenomenon can
be seen in 4. The KD0 of 1 is of a high degree of axiality, which
leads to weak QTM. Additionally, theoretical τQTM values are
also consistent with the experimental values in that τQTM of 1 is
longer than those of 2−4. In other words, QTM of 1 is weaker
than that of 2−4. This is consistent with the experimental
observations of apparent SMM behavior in 1 under a 0 Oe dc
field, while 2−4 show weak slow magnetic relaxation behavior.
According to the results of the constituent mononuclear
Dy(III) fragments, the dipolar parameters Jdip in 2 and 4 were
calculated to be 3.02 and 2.56 cm−1, respectively. They are
consistent with the experimental results of weak FM coupling.
This work presents an efficient approach to designing and
synthesizing Ln compounds with different structures for in situ
Schiff base reaction and provides a new method for magnetic
regulation.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c02863.
■
sı
Structural and magnetic characterization and theoretical
calculation (PDF)
Accession Codes
CCDC 1947756,1947757, 2024916, and2024917 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
Sheng Zhang − Faculty of Chemistry and Chemical
Engineering, Engineering Research Center of Advanced
Ferroelectric Functional Materials, Key Laboratory of
Phytochemistry of Shaanxi Province, Baoji University of Arts
and Sciences, Baoji, Shaanxi 721013, China; orcid.org/
0000-0001-9370-0548; Email: zhangsheng19890501@
163.com
Sanping Chen − Key Laboratory of Synthetic and Natural
Functional Molecule of the Ministry of Education, College of
Chemistry and Materials Science, Northwest University,
Xi’an, Shaanxi 710127, China; orcid.org/0000-0002-
6851-7386; Email: sanpingchen@126.com
Bing Yin − Key Laboratory of Synthetic and Natural
Functional Molecule of the Ministry of Education, College of
Chemistry and Materials Science, Northwest University,
Xi’an, Shaanxi 710127, China; orcid.org/0000-0001-
8668-9504; Email: rayinyin@nwu.edu.cn
CONCLUSIONS
■
In situ ligand formation was exhibited in the synthetic
processes from mononuclear to binuclear Dy(III) compounds.
The crystals of 1 and 3 underwent dissolution/precipitation
processes and changed into 2 and 4, respectively. The
formylbenzyl groups of H2L in 1 and 3 were changed to the
(hydroxyiminomethyl)benzyl groups of H4Lox in 2 and 4,
respectively. Compounds 1 and 3 exhibit mononuclear
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Inorg. Chem. 2021, 60, 816−830

Inorganic Chemistry
pubs.acs.org/IC
Article
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Dalian 116023, P. R. China; orcid.org/0000-0002-1221-
3033; Email: jwzhang@dicp.ac.cn
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Authors
Jiamin Tang − Faculty of Chemistry and Chemical
Engineering, Engineering Research Center of Advanced
Ferroelectric Functional Materials, Key Laboratory of
Phytochemistry of Shaanxi Province, Baoji University of Arts
and Sciences, Baoji, Shaanxi 721013, China
Jin Zhang − Faculty of Chemistry and Chemical Engineering,
Engineering Research Center of Advanced Ferroelectric
Functional Materials, Key Laboratory of Phytochemistry of
Shaanxi Province, Baoji University of Arts and Sciences,
Baoji, Shaanxi 721013, China
Fang Xu − Faculty of Chemistry and Chemical Engineering,
Engineering Research Center of Advanced Ferroelectric
Functional Materials, Key Laboratory of Phytochemistry of
Shaanxi Province, Baoji University of Arts and Sciences,
Baoji, Shaanxi 721013, China
Dengwei Hu − Faculty of Chemistry and Chemical
Engineering, Engineering Research Center of Advanced
Ferroelectric Functional Materials, Key Laboratory of
Phytochemistry of Shaanxi Province, Baoji University of Arts
and Sciences, Baoji, Shaanxi 721013, China; orcid.org/
0000-0001-7961-7115
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c02863
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript. B.Y. is responsible for the theoretical part of
this work including ab initio calculation and theoretical
interpretation of magnetic anisotropy and dynamics.
4
6
clusters constructed by a polydentate Schiff base ligand and a β-
diketone co-ligand: structures, fluorescence properties, magnetic
refrigeration and single-molecule magnet behavior. Dalton Trans.
2019, 48, 16744−16755.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(6) Liu, K.; Zhang, X.; Meng, X.; Shi, W.; Cheng, P.; Powell, A. K.
Constraining the coordination geometries of lanthanide centers and
magnetic building blocks in frameworks: a new strategy for molecular
nanomagnets. Chem. Soc. Rev. 2016, 45, 2423−2439.
(7) Meng, Y. S.; Jiang, S. D.; Wang, B. W.; Gao, S. Understanding
the magnetic anisotropy toward single-ion magnets. Acc. Chem. Res.
2016, 49, 2381−2389.
■
We gratefully acknowledge financial support from the National
Natural Science Foundation of China (Grants 21703002,
21727805, and 21673180), the Young Talent Fund of
University Association for Science and Technology in Shaanxi,
China (Grant 20200610), the Special Scientific Research
Project of Education Department of Shaanxi Provincial
Government (Grant 20JK0484), the Natural Science Basic
Research Plan in Shaanxi Province of China (Grant 2019JQ-
180), the Open Foundation of Key Laboratory of Synthetic
and Natural Functional Molecule Chemistry of Ministry of
Education [Grant 338050067(2018-008)], the National
Undergraduate Training Programs for Innovation and
Entrepreneurship (Grant S202010721006), and the Doctoral
Scientific Research Starting Foundation of Baoji University of
Arts and Science (Grant ZK2017024).
(8) Pointillart, F.; Cador, O.; Le Guennic, B.; Ouahab, L.
Uncommon lanthanide ions in purely 4f single molecule magnets.
Coord. Chem. Rev. 2017, 346, 150−175.
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performance lanthanide-based single-molecule magnets. Chem. Soc.
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