Wheel-like Ln18 Cluster Organic Frameworks for Magnetic Refrigeration and Conversion of CO2

Article abstract of DOI:10.1021/acs.inorgchem.7b03142

Two isostructural 2D MOFs ([Ln₇(CDA)₆(HCOO)₃(μ₃-OH)₆(H₂O)₈]_n, abbreviated as 1-Gd and 2-Dy) were successfully synthesized under solvothermal conditions. The self-assem

Full text of DOI:10.1021/acs.inorgchem.7b03142

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Wheel-like Ln Cluster Organic Frameworks for Magnetic
18
Refrigeration and Conversion of CO
2
†
‡
‡
‡
†
,†,§
Tian-Qun Song, Jie Dong, An-Fei Yang, Xue-Jing Che, Hong-Ling Gao, Jian-Zhong Cui,*
,‡,§
and Bin Zhao*
†Department of Chemistry, National Demonstration Center for Experimental Chemistry & Chemical Engineering Education,
National Virtual Simulation Experimental Teaching Center for Chemistry & Chemical Engineering Education, Tianjin University,
Tianjin 300072, P. R. China
‡
Department of Chemistry, Nankai University, Tianjin 300071, P. R. China
§
Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai University, Tianjin 300071, P. R. China
*
S Supporting Information
ABSTRACT: Two isostructural 2D MOFs ([Ln (CDA) (HCOO) (μ -
7
6
3
3
OH) (H O) ] , abbreviated as 1-Gd and 2-Dy) were successfully synthesized
6
2
8 n
under solvothermal conditions. The self-assembly of lanthanide(III) nitrate and
,1′-cyclopropane-dicarboxylic acid (H CDA) resulted in wheel-like Ln
1
2
18
cluster second building units (SBU), which are further linked to six neighboring
wheels to generate a 2D ordered honeycomb array. Both 1-Gd and 2-Dy
exhibit high thermal stability and decompose above 330 °C. Moreover, they
have good solvent stability in ten common solvents and pH stability with pH
values from 1 to 13. Magnetic studies reveal that 1-Gd exhibits weak
3+
antiferromagnetic coupling between adjacent Gd ions and has a large
−
1
−1
magnetocaloric effect of 47.30 J kg
K
(ΔH = 7.0 T at 2 K), while 2-Dy
3+
shows ferromagnetic interaction between adjacent Dy ions. Interestingly, 1-
Gd and 2-Dy can catalyze the cycloaddition of CO to epoxides under mild
2
conditions and can be reused at least five rounds with negligible loss of catalytic
performance.
n the past few decades, great interest in the construction and
study of high nuclearity clusters has emerged due to not only
applied magnetic field. However, only a few cases have the large
22
I
changes necessary for application for refrigerant materials. To
obtain a large MCE, weak superexchange interactions and large
magnetic density are of great importance. Gd3+ is an excellent
choice to construct refrigerant materials due to its low lying
excited spin states, large spin ground state (S = 7/2), and
their structural diversity but also their potential applications in
1
−8
electricity, optics, magnetism, and catalysis.
As we all know,
the assembly of high nuclearity clusters can generate cluster-
9
10
11
based MOFs, such as [Ln ], [Cu30], [Cd Cu ] , and
2
4
4
6 n
1
2
1
8,23,24
[
Gd Cu ]. An especially fascinating type within this class is
3 12
negligible magnetic anisotropy (D).
Besides, small
the molecular wheel. Although numerous molecular wheels
have been reported, the design and construction of molecular
wheels are still formidable challenges owing to the uncontroll-
ability of the nuclearity and size of the wheel. Up to now, only a
15
ligands can impove the magnetic density, which is apt to get
a large MCE. Recently, many studies show that the
dimensionality seems to play a negligible role in the MCE
and a compact structure with large spin density is beneficial for
1
3
14
few lanthanide wheel clusters like [Ln ], [Ln10], [Ln12],
25
8
a large MCE.
1
5
16
[
Ln ], and [Ln18] have been synthesized. However, as
15
It is worth mentioning that various small ligands are
employed to achieve high nuclear wheels. By this method, it
is easy for them to capture closely situated metallic ions to
generate curved building units, which contributes to the
construction of wheel-like structures. Here, we selected the
lanthanide ions have not only diversified and high coordination
17,18
numbers but also poor directionality,
the 2D or 3D
lanthanide MOFs based on wheel-like clusters are very rare; so
9
far, only two examples of such 3D MOFs ([Ln ] and
24
1
9
[
Ln ] ) have been reported, and there have been almost no
12
lightweight 1,1′-cyclopropane-dicarboxylic acid (H CDA) as
2
reports for 2D.
the ligand, which is expected to yield fascinating structure and a
large magnetic density, and successfully synthesized two 2D
frameworks based on wheel-like Ln18 second building units
On the other hand, MOFs with metal clusters as magneto-
caloric materials have been greatly developed due to their high
magnetic density and are expected to replace the rare and
3
20,21
expensive He.
Magnetocaloric effect (MCE) has attracted
increasing attention, as it is related to the magnetic entropy
change and the adiabatic temperature change with a varying
Received: December 14, 2017
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b03142
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
SBU), [Gd (CDA) (HCOO) (μ -OH) (H O) ] (1-Gd) and
Article
(
7
6
3
3
6
2
8 n
[
Dy (CDA) (HCOO) (μ -OH) (H O) ] (2-Dy). Then, we
7 6 3 3 6 2 8 n
structurally and magnetically characterized the frameworks.
Magnetic study shows that 1-Gd has a larger magnetic entropy
max
−1 −1
change with −ΔS
= 47.30 J kg
K
(ΔH = 7 T at 2 K).
m
Furthermore, considering the high stability and Lewis acidic
sites of 1-Gd and 2-Dy, they can act as heterogeneous catalysts
to be employed in CO conversion with epoxides and can be
2
reused at least five times with negligible loss of catalytic ability.
Therefore, 1-Gd and 2-Dy are potential magnetic and catalytic
materials.
EXPERIMENTAL SECTION
■
Preparation of [Gd (CDA) (HCOO) (μ -OH) (H O) ] (1-Gd).
7
6
3
3
6
2
8 n
H CDA (0.2 mmol), Gd(NO ) ·6H O (0.15 mmol), and NaOH (0.2
2
3
3
2
mmol) were mixed in H O (7 mL) and DMF (3 mL). The mixture
2
was sealed in a Teflon-lined stainless-steel vessel and heated at 120 °C
for 3 days. After the reaction temperature was slowly decreased to 30
3+
Figure 1. (a) The coordinated environments of Gd . (b) The
hexagonal prism structure of a Gd18 wheel second building unit (SBU)
along the c axis. (c) The Gd18 wheel second building unit (SBU) and
the 2D honeycomb array of 1-Gd. All hydrogen atoms were omitted
for clarity. Cyan: Gd. Red: O. Gray: C.
°
C, colorless block single crystals were obtained. The yield was 79%
(
based on Gd(NO ) ·6H O). Elemental analysis (%) calcd: C 17.60,
3
3
2
−1
H 2.18. Found: C 17.22, H 2.13. IR (cm ) (Figure S1 in the
Supporting Information): 3395 (s), 2799 (w), 1569 (vw), 1544 (vs),
1
451 (s), 1420 (vw), 1352 (w), 1255 (m), 1209 (m), 1044 (w), 972
(
m), 931 (m), 874 (m), 787 (s), 731 (vs), 571 (s), 509 (w), 478 (s).
Preparation of [Dy (CDA) (HCOO) (μ -OH) (H O) ] (2-Dy).
7
6
3
3
6
2
8 n
The synthesis of 2-Dy was similar to that of 1-Gd, only using
Dy(NO ) ·6H O instead of Gd(NO ) ·6H O. Colorless block single
are two identical planes composed of three Gd1 and three Gd3,
which are parallel to the plane of Gd2 (Figure S4). The ligand
has a cyclopropane ring alternately above or below the plane of
3
3
2
3
3
2
crystals were obtained, and the yield was 68% (based on Dy(NO ) ·
3
3
6
1
1
H O). Elemental analysis (%) calcd: C 17.32, H 2.14. Found: C
6.76, H 2.17. IR (cm ): 3370 (s), 2804 (w), 1564 (vw), 1544 (vs),
456 (s), 1410 (s), 1342 (w), 1255 (m), 1219 (m), 1044 (w), 977
−
2
the wheel due to steric hindrance. Three HCOO anions are
−1
trapped in the inside of the wheel, which play a significant role
32
in stabilizing the lanthanide wheel. Each Gd18 wheel can be
(
m), 937 (m), 880 (m), 797 (s), 735 (vs), 571 (s), 509 (w), 478 (s).
viewed as a centrosymmetrical second building unit (SBU)
which is surrounded by six neighboring, as well as equivalent,
wheels by sharing −(Gd1) −(μ -OH)−Gd2−(μ -OH)−
RESULTS AND DISCUSSION
■
2
3
3
Structure Description. Crystallographic analysis reveals
that 1-Gd and 2-Dy are isomorphous in the hexagonal space
(Gd3) − bridges, generating a 2D ordered honeycomb array
2
9
(Figure 1c). In addition, these honeycomb layers are further
group P6 /m, and the structure of 1-Gd is described as an
stacked along the c axis to generate a 3D supramolecular
structure (Figure S5). Comparatively, to the best of our
knowledge, there are a few wheel-like Ln cluster or cluster-
based MOFs with larger nuclei, and they are listed in Table S3.
Therefore, 1-Gd is a rare example of a 2D wheel-like Ln18
organic framework.
3
example. The asymmetric unit of 1-Gd contains three
independent Gd ions, Gd1, Gd2, and Gd3, with different
occupancies of 1/3, 1/2, and 1/2, respectively. As shown in
Figure 1a, Gd1 is coordinated by ten oxygen atoms: three
oxygen atoms (O1, O1a, O1b) from μ -OH groups, one oxygen
3
atom (O2) from a terminal H O molecule, and six oxygen
atoms (O3, O4, O3a, O4a, O3b, O4b) from three CDA
ligands. The coordination mode of Gd3 is similar to that of
Powder X-ray Diffraction (PXRD) and Thermogravi-
metric Analysis (TGA). The PXRD analyses of 1-Gd and 2-
Dy were carried out, and corresponding patterns are shown in
Figure S6. The peaks of as-synthesized samples matched well
with simulated ones, showing that 1-Gd and 2-Dy were
presented as pure phases. To study the pH stability and solvent
stability of 1-Gd and 2-Dy, the as-synthesized samples were
immersed in ten common solvents for about 14 h and a series
of solutions with pH values from 1 to 14 for about 5 h,
respectively. The PXRD analyses reveal that both samples were
stable in ten solvents and solutions with pH values between 1
and 13 (Figure S7). The peaks disappeared partly under pH =
14, indicating that the samples became amorphous. The
thermal stability of 1-Gd and 2-Dy was studied by TGA
2
2−
Gd1, except for a lack of a coordinated H O molecule. Gd2 is
2
nine-coordinated, surrounded by two oxygen atoms (O1b,
O6b) from μ -OH groups, one oxygen atom (O9) of a
3
−
HCOO anion derived from the decomposition of DMF under
solvothermal conditions,
26−29
two oxygen atoms (O5, O5a)
from terminal H O molecules, and four oxygen atoms (O4, O7,
2
2−
O4c, O7c) from two CDA ligands. The Gd···Gd separations
range from 3.472 to 4.041 Å (Figure S2). The Gd−O bond
lengths fall in the range of 2.387−2.777 Å, and the Gd−O−Gd
angles are in the range of 92.6(2)−115.6(2)° (Table S2).
Besides, Gd−O bond distances are slightly longer than that of
Dy−O, which can be attributed to the effect of the lanthanide
under a N atmosphere (Figure S8). The TGA plots have
2
3
0,31
contraction.
Interestingly, Gd ions are interlinked by μ -
similar curves since 1-Gd and 2-Dy are isomorphous. A weight
loss of 6.50% for 1-Gd and 6.22% for 2-Dy could be seen from
3
2
−
OH groups and stabilized by CDA ligands (coordination
mode: μ -κO3, O4: κO4, O7: κO7, O8) to assemble into a
nanosize Gd18 wheel structure with a diameter of 18.17 Å
110 to 210 °C, owing to the loss of coordinated H O molecules
(calcd: 6.40% (1-Gd) and 6.30% (2-Dy)). Then, 1-Gd and 2-
Dy were decomposed gradually above 330 °C.
3
2
(Figure S3). Along the c axis, 18 Gd ions form a hexagonal
prism whose plane is composed of five Gd ions (Figure 1b). In
the ac plane, six Gd2 are in the same plane. Meanwhile, there
Magnetic Properties. Magnetic properties of 1-Gd and 2-
Dy were studied in order to understand magnetic interactions.
B
DOI: 10.1021/acs.inorgchem.7b03142
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
The magnetic susceptibility measurements were performed
from 2.0 to 300 K in an applied field of 1 kOe. As shown in
3
−1
Figure 2, the χ T value is 55.26 cm K mol at 300 K for 1-
M
Figure 3. Field-dependent experimental magnetization plots for (a) 1-
Gd and (b) 2-Dy at 0−8 T between 2 and 10 K.
Figure 2. Plots of temperature-dependent χ T (■) under an applied
M
field of 1 kOe between 2.0 and 300 K for (a) 1-Gd and (b) 2-Dy.
3
+
anisotropy and/or the depopulation of the Dy Stark
sublevels.
36
Gd, which is in good agreement with the expected value (55.16
3
−1
3+
8
Dynamic Magnetic Property. To explore the magnetic
dynamics of 2-Dy, the temperature dependence of the
alternating current (ac) susceptibility data was collected at a
Oe ac magnetic field with a zero direct current (dc) field
(Figure S10). Unfortunately, no out-of-phase ac signal is
observed, indicating that there is no slow magnetic behavior for
cm K mol ) for seven free Gd ions ( S , g = 2). The χ T
7
/2
M
value stays almost constant from 300 to 55 K and then
3
−1
decreases rapidly to reach a minimum of 42.93 cm K mol at
K, indicating antiferromagnetic interactions between adjacent
3
2
3+
−1
Gd ions. The curve of χ
versus T from 2.0 to 300 K can be
M
well fitted according to the Curie−Weiss law, giving C = 55.34
2-Dy.
3
−1
cm K mol and θ = −0.123 K (Figure S9). The negative value
of θ further indicates a weak antiferromagnetic coupling
Magnetocaloric Effect. Considering the low M /N (Mw
w
Gd
3+
is molecular mass and NGd is the number of Gd ions per mole
of 1-Gd) ratio of 321, 1-Gd is a good candidate for
magnetocaloric materials. In order to estimate the MCE,
magnetic entropy changes ΔSm are obtained from the
3
+
33,34
interaction between adjacent Gd ions.
As for 2-Dy, the
3
−1
−1
χ T value of 98.75 cm K mol at 300 K is close to the
expected value (99.19 cm K mol ) for seven isolated Dy
ions ( H15/2, g = 4/3). When the temperature decreases, the
M
3
3+
6
magnetization data according to the Maxwell equation
3
37−39
χ T value gradually reduces to a minimum value of 83.47 cm
ΔS (T) = ∫ [∂M(T, H)/∂T] dH.
As shown in Figure
M
m
H
−1
K mol at 12 K. Then, below 12 K, the χ T value increases
4a, the −ΔS value increases when the magnetic field increases
m
and temperature decreases. Under a mild field change with ΔH
of 3.0 T at 2 K for 1-Gd, the maximum magnetic entropy
(94.45 mJ cm K ). With ΔH =
7.0 T at 2 K, the maximum magnetic entropy change is 47.30 J
M
3
−1
rapidly to a maximum value of 99.17 cm K mol at 2.0 K. The
phenomenon indicates the coexistence of ferromagnetic
interaction and thermal depopulation of the Stark sublevels of
change is 34.57 J kg−
1
K
−1
−3 −1
3
+
35
Dy ions in the system. When the temperature is above 12 K,
−1
−1
−3
−1
3+
kg
theoretical value of 53.80 J kg
weak antiferromagnetic interactions between Gd ions.
K
(129.2 mJ cm K ), which is smaller than the
the thermal depopulation of the Stark sublevels of Dy ions is
−1
−1
K
due to the existence of
dominant, leading to the slight decrease of the χ T value. On
M
3+
40,41
the contrary, ferromagnetic interaction plays a crucial role
However, 1-Gd still has a large magnetic entropy change
compared with the recently reported wheel clusters, 2D MOFs,
and 3D macrocycle frameworks as magnetocaloric materials
below 12 K, which results in the sharp rise of the χ T value.
M
The magnetization data of 1-Gd and 2-Dy were measured at
0
−8 T between 2 and 10 K (Figure 3). The M increases with H
(
Table 1). Therefore, 1-Gd is a possible magnetic refrigerant to
and reaches the maximum value (48.52 Nβ) for 1-Gd at 2.0 K
and 8 T, which is approximate to the theoretical value (49 Nβ)
for seven isolated Gd ions, while the M value of 47.68 Nβ at 8
T for 2-Dy does not reach the saturation value for seven
be used in practice.
By comparison, the −ΔS value rises gradually from 10.0 to
m
3
+
5.0 K and then slowly drops with cooling above 1.0 T for 2-Dy
(Figure 4b). With ΔH = 3.0 T at 5.0 K, the maximum value of
3+
−1 −1
−3 −1
isolated Dy ions (70 Nβ), indicating the presence of magnetic
−ΔS is 13.31 J kg
K
(37.65 mJ cm K ). When ΔH =
m
C
DOI: 10.1021/acs.inorgchem.7b03142
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
kg− K , which is mainly attributed to the significant magnetic
1
−1
2
anisotropy in 2-Dy. The large difference in the −ΔS value
m
between 1-Gd and 2-Dy results from negligible magnetic
anisotropy in 1-Gd and the significant one in 2-Dy, the large
ground-state spin (Gd , S = 7/2 and g = 2.0), as well as a large
3+
3+
number of low lying excited spin states of Gd .
Catalytic Properties. Considering the high stability and
Lewis acidic sites of 1-Gd and 2-Dy, we focused catalytic
experiments on the conversion of CO with epoxides, and the
2
initial substrate was styrene oxide (Table 2). The yield of the
desired epoxide was 99% (TON 32.1) when using 2 mmol of
styrene oxide, about 3 mol % 1-Gd (based on Gd), 2.5 mol %
cocatalyst TBAB (tetrabutylammonium bromide) under
solvent-free condition, and a CO pressure of 0.1 MPa at 80
2
°
C for 12 h (Table 2, entry 3), which is higher than the yields
achieved at 60 and 70 °C (Table 2, entries 1 and 2), showing
that higher temperatures contribute to the cycloaddition
reaction of CO . Comparably, the yield was 98% (TON
2
3
3.3) using 3 mol % 2-Dy (based on Dy), 2.5 mol % cocatalyst
TBAB, and a CO pressure of 0.1 MPa at 80 °C for 12 h, which
2
shows catalytic ability similar to that of 1-Gd (Table 2, entry 4).
Here, 1-Gd was chosen for further investigation. When the
reaction time was reduced to 9 h, the yield became 68% (TON
2
1.9) (Table 2, entry 5). Therefore, the optimized condition
was 20 mg of 1-Gd and 2.5 mol % TBAB at 80 °C for 12 h.
Additionally, under the optimized reaction conditions, the yield
was only 67% when 1-Gd was absent (Table 2, entry 6),
indicating that 1-Gd can largely improve the yield of
cycloaddition reactions and will be an effective catalyst.
Figure 4. Calculated magnetic entropy changes for (a) 1-Gd and (b)
2
-Dy at 0−7 T between 2 and 10 K.
The cycloaddition of CO and other epoxide substrates was
2
studied to evaluate the generality of 1-Gd. As shown in Table 3,
1-Gd showed excellent catalytic ability for the transformation of
.0 T at 5.0 K, the maximum value of −ΔS is 13.92 J kg K−1
−
1
7
(
m
39.4 mJ cm− K ), far from the theoretical value of 52.93 J
3 −1
CO with various epoxides in high yields (81−99%), and
2
max
Table 1. Comparison of −ΔSm Values among 1-Gd, Wheel Cluster, and 2D and 3D Gd-Based Complexes That Are Potential
Magnetic Coolers
−ΔSm (J kg− K−1
1
)
−ΔS
m
3
magnetic
interaction
M /N
w
metal
ratio
(ΔH)
(mJ cm− K−1
)
ref
0
D wheel clusters
{
{
{
{
{
{
Gd Zn }
AF
AF
AF
AF
AF
AF
436
582
592
476
727
755
30.0 (7 T)
26.6 (7 T)
26.0 (7 T)
25.9 (7 T)
21.0 (7 T)
14.0 (7 T)
44.8
45.8
55.3
40.0
32.4
25.5
42
43
44
16
45
46
24
6
Gd }
10
Gd Co }
24
16
Gd }
18
Gd Cu }
24
36
Gd Cu }
6
12
2
D frameworks
Gd(HCOO)3
AF
AF
AF
AF
292
231
335
321
56.0 (7 T)
51.9 (7 T)
48.0 (7 T)
47.3 (7 T)
215.7
−
144.0
47
48
49
Gd (OH) Cl·1.5H O
2
5
2
[
Gd(C O )(H O) Cl]
2
4
2
3
n
1-Gd
129.2
this
work
[
[
[
[
[
[
Gd(oxa)(H PO )(H O) ]
AF
346
348
356
339
350
363
347
46.6 (7 T)
46.6 (7 T)
45.9 (7 T)
45.0 (7 T)
43.8 (7 T)
43.6 (7 T)
39.7 (7 T)
134.3
75.9
50
51
25
52
23
53
17
2
2
2
2
Gd (C O ) (H O) ·0.6H O]
ferro
AF
2
2
4
3
2
6
2
Gd(HCOO)(OAc) (H O) ]
2 n
110.0
128.1
104.5
115.2
91.4
2
2
Gd(pda)(ox)0.5(H O)]n
ferro
AF
2
Gd(C O )(OH)(H O) ]
4 n
4
4
2
Gd(cit)(H O)]
ferro
AF
2
n
{
[Gd (NA) (OH) (O) (NO ) (N ) (H O) ]Cl ·28H O}
36 36 49 6 3 6 3 3 2 20 2 2 n
3
D macrocycle frameworks
{
{
[Gd (IDA) ]·2H O}
n
AF
315
387
414
40.6 (7 T)
37.1 (7 T)
34.1 (7 T)
100.6
93.4
74.5
54
55
56
2
3
2
[Gd(fum)(ox)0.5(H O) ]·2H O}
n
ferro
AF
2
2
2
[Ln (DPA) (NA) (μ -OH) (H O) ]·2.5H O
7 5 3 3 8 2 3 2
D
DOI: 10.1021/acs.inorgchem.7b03142
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
,57
8
Table 2. Cycloaddition Reaction of CO with Styrene Oxide
under Various Reaction Conditions
electron-donating group in the structure of the substrate.
Hence, 1-Gd has great generality to various epoxides.
2
a
Here, we evaluated the recyclability of 1-Gd. As shown in
Figure 5, 1-Gd can be used at least five times with negligible
c
TBAB
T
t
TOF
yield
d
b
−1
entry
catalyst
1-Gd
(mol %) (°C) (h) TON
(h
)
(%)
1
2
3
4
5
6
7
8
2.5
2.5
2.5
2.5
2.5
2.5
0
60
70
80
80
80
80
80
80
12
12
12
12
9
16.1
21.9
32.1
33.3
21.9
−
1.3
50
68
>99
98
68
67
<1
24
1-Gd
1-Gd
2-Dy
1-Gd
0
1.8
2.7
2.8
2.4
12
12
12
−
−
0.7
1-Gd
Gd(NO3)3
−
8
2.5
a
Reaction conditions: styrene oxide (240 mg, 2.0 mmol), catalyst 1-
Gd (20 mg, about 3 mol % based on Gd), catalyst 2-Dy (20 mg, about
mol % based on Dy), catalyst Gd(NO ) (26 mg, about 3 mol %
3
Figure 5. Recycle tests of 1-Gd for the transformation reaction of CO2
3
3
based on Gd), TBAB (16 mg, 2.5 mol %), solvent-free, and CO (0.1
with styrene oxide.
2
b
MPa). Turnover number (TON) = moles of yielded cyclic
c
carbonates/mole of catalyst (based on Gd/Dy). Turnover frequency
loss for the cycloaddition of CO2 with styrene epoxides.
Further, the PXRD analyses of the reused catalyst were carried
out and matched well with the simulated one from 1-Gd
(
TOF) = moles of yielded cyclic carbonates/mole of catalyst (based
d
1
on Gd/Dy)/reaction time (h). Determined by H NMR spectros-
copy using 1,3,5-trimethoxybenzene as an internal standard.
(
Figure S11), revealing that the framework of 1-Gd keeps its
Table 3. Cycloaddition Reaction of CO with Various
integrity. The filtrate of the last recycling cycle was measured by
2
3
+
Epoxides under Optimized Reaction Conditions with
inductively coupled plasma (ICP), and only 0.3 ppm Gd of
leakage from the framework 1-Gd was detected (Table S4).
Therefore, 1-Gd is a promising heterogeneous catalyst with
high recyclability.
a
Catalyst 1-Gd
In order to explore the possible mechanism of this process,
only 20 mg of catalyst 1-Gd in the absence of TBAB was used
for the cycloaddition of CO to styrene epoxides, and the yield
2
was negligible (Table 2, entry 7), suggesting that TBAB plays a
vital role in the system. When Gd(NO ) instead of 1-Gd
3
3
conducted the reaction, the yield was just 24% (TON 8) (Table
2
, entry 8), indicating that salt cannot effectively catalyze the
reaction. Therefore, the synergistic catalysis of catalyst 1-Gd
and TBAB is the main reason for the high catalytic activity, and
the plausible mechanism was proposed as follows (Figure
5
8−61
S12):
First, epoxides were activated by the Lewis acidic
−
sites in 1-Gd, and Br acting as the nucleophile attacked the C
atom of methylene on the less sterically hindered side of the
epoxides. As a result, selective ring opening occurred. Then,
CO was simultaneously inserted in the opened epoxides to
2
form alkylcarbonate salts (CO adsorption/desorption of 1-Gd,
2
as shown in Figure S13). Finally, the corresponding products
were obtained through ring closure along with regeneration of
the catalyst. 1-Gd and 2-Dy have good catalytic ability, which
may be attributed to the 2D nature facilitating the diffusion of
62
substrates and products near the active sites.
a
Reaction conditions: epoxides (2.0 mmol), catalyst 1-Gd (20 mg,
about 3 mol % based on Gd), TBAB (16 mg, 2.5 mol %), solvent-free,
CONCLUSION
b
■
and CO (0.1 MPa). Turnover number (TON) = moles of yielded
2
c
In summary, two isomorphous 2D frameworks based on wheel-
like Ln cluster second building units (SBU) were successfully
cyclic carbonates/mole of catalyst (based on Gd/Dy). Turnover
frequency (TOF) = moles of yielded cyclic carbonates/mole of
18
d
1
catalyst (based on Gd/Dy)/reaction time (h). Determined by H
NMR spectroscopy using 1,3,5-trimethoxybenzene as an internal
standard.
synthesized under solvothermal conditions. 1-Gd exhibits weak
antiferromagnetic coupling between adjacent Gd ions and has
a large magnetic density with −ΔS
7 T at 2 K), indicating that 1-Gd is a potential magnetic
3
+
max
−1 −1
= 47.30 J kg
K
(ΔH
m
=
corresponding TON and TOF are also listed in Table 3.
refrigerant. 2-Dy shows ferromagnetic interaction between
adjacent Dy3+ ions. In addition, 1-Gd and 2-Dy, acting as
efficiently heterogeneous catalysts, exhibit excellent catalytic
Besides, the cycloaddition of CO to 1,2-epoxyhexane (Table 3,
2
entry 5) had a slightly lower yield owing to the presence of an
E
DOI: 10.1021/acs.inorgchem.7b03142
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b03142.
■
*
S
Serving as Recyclable Catalysts for CO Fixation with Aziridines. Adv.
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Sci. 2016, 3, 1600048.
X-ray crystallographic data in CIF format; IR, TGA,
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Accession Codes
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CCDC 1559634−1559635 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing 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.
based MOFs with Accelerated Chemical Conversion of CO through
2
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AUTHOR INFORMATION
Corresponding Authors
E-mail: cuijianzhong@tju.edu.cn.
E-mail: zhaobin@nankai.edu.cn.
Complex, Dy10(OC24OCH
3
)30. Chem. Commun. 2003, 1012−1013.
■
(15) Wang, R.; Selby, H. D.; Liu, H.; Carducci, M. D.; Jin, T.; Zheng,
Z.; Staples, R. J.; Anthis, J. W. Halide-templated Assembly of
Polynuclear Lanthanide-hydroxo Complexes. Inorg. Chem. 2002, 41,
*
*
2
78−286.
ORCID
(16) Wang, K.; Chen, Z. L.; Zou, H. H.; Hu, K.; Li, H. Y.; Zhang, Z.;
Liang, F. P.; Sun, W.-Y. A Single-stranded {Gd } Nanowheel with a
Symmetric Polydentate Diacylhydrazone Ligand. Chem. Commun.
Jian-Zhong Cui: 0000-0002-9762-0243
Bin Zhao: 0000-0001-9003-9731
Notes
18
2
(
016, 52, 8297−8300.
17) Wu, M.; Jiang, F.; Kong, X.; Yuan, D.; Long, L.; Althabaiti, S. A.;
The authors declare no competing financial interest.
Hong, M. Two Polymeric 36-metal Pure Lanthanide Nanosize
Clusters. Chem. Sci. 2013, 4, 3104−3109.
ACKNOWLEDGMENTS
(18) Peng, G.; Qiu, Y. C.; Liu, Z. H.; Liu, B.; Deng, H. Spontaneous
Assembly of d-f Coordination Frameworks: Syntheses, Structures, and
Photoluminescence. Cryst. Growth Des. 2010, 10, 114−121.
■
This work was supported by the NSFC (21625103, 21571138,
and 21473121), the Key Laboratory of Advanced Energy
Materials Chemistry (Ministry of Education, Nankai University,
Opening Foundation), and the 111 Plan project (B12015).
(19) Ren, Y. X.; Zheng, X. J.; Li, L. C.; Yuan, D. Q.; An, M.; Jin, L. P.
Three-dimensional Frameworks Based on Dodecanuclear Dy-hydroxo
Wheel Cluster with Slow Relaxation of Magnetization. Inorg. Chem.
2
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