Crystal transformation in Mn(ii) metal-organic frameworks based on a one-dimensional chain precursor

Article abstract of DOI:10.1039/d1dt00943e

The solvothermal reaction of Mn(ii) salts and 5-((4′-(tetrazol-5′′-yl)benzyl)oxy)isophthalic acid (H₃L) affords an Mn(ii) based coordination polymer Mn(H₂L)₂(H₂O)₂(1), which possesses a one-dimensiona

Full text of DOI:10.1039/d1dt00943e

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Crystal transformation in Mn(II) metal–organic
frameworks based on a one-dimensional chain
precursor†
Cite this: Dalton Trans., 2021, 50,
9540
Yansong Jiang,
Rui Liu, Yiran Gong, Yong Fan,
Li Wang * and Jianing Xu*
The solvothermal reaction of Mn(II) salts and 5-((4’-(tetrazol-5’’-yl)benzyl)oxy)isophthalic acid (H
affords an Mn(II) based coordination polymer Mn(H L) (H O) (1), which possesses a one-dimensional (1D)
chain structure. Using 1 as the precursor, three Mn(II) metal–organic frameworks, Mn (2,2’-bpy) ·5H
2), Mn (H O) (3), and Mn (HL)(H O) ·0.5H O (4), with three-dimensional (3D) networks can be
3
L)
2
2
2
2
3
L
2
2
2
O
(
3
L
2
2
4
4
L
2
2
5
2
obtained by different strategies of crystal transformation. Upon introduction of 2,2’-bipyridine (2,2’-bpy)
as the ligand and 2,2’-biquinoline-4,4’-dicarboxylic acid as the structural-directing agent, 1 undergoes
irreversible crystal transformation into 2 and 3, respectively, and 1 can be transformed into 4 by increasing
the reaction temperature. Interestingly, the irreversible structural transformation of 3 into 2 can be carried
out by adding a 2,2’-bpy ligand. Notably, after the removal of coordinated water molecules, 1 and 3
exhibit good catalytic performance for the cyanosilylation reaction even at 0 °C.
Received 23rd March 2021,
Accepted 28th May 2021
DOI: 10.1039/d1dt00943e
rsc.li/dalton
additional ligands as well as external stimuli such as tempera-
Introduction
1
7,18
ture, solvents, or vapors.
Using a low-dimensional crystal
Over the last two decades, as a class of well-defined inorganic– as a precursor, especially an insolvable precursor, is one of the
organic hybrid crystalline materials, metal–organic frame- effective strategies to alter the structures and properties of
1
9
works (MOFs) have attracted more attention due to their versa- MOFs and to incorporate functionalities of interest. For
tile structures and wide applications in gas adsorption and example, Jiang et al. reported a series of single-crystals of
separation, chemical sensing, catalysis, energy storage, and [Ti
8
Zr
2
O12(COO)16] clusters based on several small acid ligand
1
–10
medicine.
Although many MOFs with interesting topolo- molecules, and these clusters could be used as the precursor
gies have been reported by tuning their metal centers, the in the synthesis of single crystals of PCN-415 (PCN = porous
types of organic ligands, counter-ions, metal-to-ligand ratios coordination network) by introducing the additional ter-
2
0
or solvent systems, the control of the framework dimensional- ephthalic acid ligand. Park et al. reported a Ti-MOF derived
1
1–13
ity and properties of MOFs is still a huge challenge.
from a 0D Ti-oxo cluster precursor which was used to prepare
2
1
Single-crystal transformation is a fantastic approach to con- DGIST-1 with a 3D network by adding a porphyrinic ligand.
4
−
struct versatile MOFs with changes in dimensionality and pro- [Mn
4
(H
precursor, can transform into two 3D solid frameworks upon
Generally, crystal transformation should break the original introduction of additional transition metal ions and solvent
2 2 2 2 9 34 2
O)18WZnMn (H O) (ZnW O ) ] , a 1D anionic chain
1
4–16
perties such as luminescence, magnetism, and catalysis.
2
2
coordination bonds and force the formation of new stable molecules.
coordination bonds, which can strengthen the framework In this work, we selected a flexible N-heterocyclic carboxy-
stability. To date, crystal transformation of MOFs can be late ligand, 5-((4′-(tetrazol-5″-yl)benzyl)oxy)isophthalic acid
1
7
achieved by exchange of metal centers and introduction of (H
3
L), to react with Mn(II) salts for preparing new Mn(II) based
metal–organic frameworks with interesting catalytic perform-
ance. Firstly, Mn(H L) (H O) (1) with a one-dimensional (1D)
chain structure was successfully prepared by the self-assembly
2
2
2
2
State Key Laboratory of Inorganic Synthesis & Preparative Chemistry,
College of Chemistry, Jilin University, Changchun, 130012 Jilin Province, P. R. China. of Mn(II) salts and H L under solvothermal conditions. Then
3
E-mail: lwang99@jlu.edu.cn, xujn@jlu.edu.cn
using 1 as the precursor, three Mn(II) MOFs, Mn
O (2), Mn (H O) (3), and Mn (HL)(H O)
with three-dimensional (3D) networks were obtained through
different routes of crystal transformation. Upon introduction
of 2,2′-bipyridine (2,2′-bpy) as the ligand and 2,2′-biquinoline-
3
L
2
(2,2′-bpy)
2
·
†
Electronic supplementary information (ESI) available: Simplified structures,
5H
2
3
L
2
2
4
4
L
2
2
5
·0.5H O (4),
2
PXRD patterns, FT-IR spectra, TG curves, N adsorption data, crystal data and
2
structure refinement details, selected bond lengths and angles and H-bond
information. CCDC 2062075–2062077. For ESI and crystallographic data in CIF
or other electronic format, see DOI: 10.1039/d1dt00943e
9540 | Dalton Trans., 2021, 50, 9540–9546
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,4′-dicarboxylic acid as the structural-directing agent, 1 under-
Paper
4
For cyanosilylation, the activated 1–3, trimethylcyanosilane
goes irreversible crystal transformation into 2 and 3 respect- (TMSCN, 2 mmol), and aldehydes (1 mmol) were added into a
ively, and 1 can be transformed into 4 by increasing the reac- 4 mL reactor and stirred at room temperature. The reactions
1
tion temperature. Furthermore, 3 can be transformed into 2 by were monitored by H NMR spectroscopy and the yield was cal-
adding a 2,2′-bpy ligand and into 4 by prolonging the reaction culated based on the sum of the integral of product/(product +
2
7
time. In addition to the intriguing structures, the activated 1–3 aldehydic substrates).
can be used as heterogeneous catalysts for the cyanosilylation The recycling studies were performed under the same con-
of different aldehydes under solvent-free conditions at room ditions as mentioned previously, except for using the recycled
temperature and 0 °C. The diverse structures and different catalysts in the last run. After each run of the reaction, the
catalytic active sites of 1–3 result in distinct catalytic activities.
solid-state catalyst was separated from the mixture by centrifu-
gation and washed three times with CHCl , and the recycled
3
catalyst was dried at 80 °C for the next run.
Experimental
Synthesis of 1–4
Mn(H L) (H O) (1). MnCl ·4H O (0.0197 g, 0.10 mmol), Results and discussion
2
2
2
2
2
2
3
H L (0.0240 g, 0.07 mmol), acetonitrile (4 mL) and deionized
Crystal structure description
water (3 mL) were added into a 25 mL Teflon-lined vessel and
sealed in an autoclaved reactor for 2 days at 120 °C. After
cooling to room temperature, colorless crystals were obtained.
The yield was 63% (0.0522 g) based on Mn. Calcd for 1: C,
Single-crystal X-ray diffraction studies revealed that 1 crystal-
lizes in the triclinic system, P ˉ1 space group, and the asym-
metric unit contains one crystallographically independent Mn
atom. As shown in Fig. 1a, Mn1 is coordinated with two car-
4
6.60; H, 3.15; N, 13.59. Found: C, 46.35; H, 3.19; N, 13.34.
−1
boxylate oxygen atoms and two nitrogen atoms from two indi-
FT-IR (KBr, cm ): 3220(m), 1690(s), 1596(s), 1440(m),
−
vidual H
2
L ligands, and the other two oxygen atoms are from
1
9
374(m), 1270(m), 1237(m), 1199(s), 1147(m), 1057(s), 1019(w),
58(w), 882(w), 821(m), 765(m), 685(w), 580(w), 491(w).
the coordinated water molecules, forming a slightly distorted
MnO octahedron. The Mn–O bond lengths and Mn–N
bond lengths are in good agreement with the ranges reported
4 2
N
3 2 2 2
Mn L (2,2′-bpy) ·5H O (2). 2,2′-Bpy (0.0100 g, 0.64 mmol)
was placed in a reactor filled with single-crystals of 1 (10 mg),
acetonitrile (4 mL) and deionized water (3 mL) and sealed in
an autoclaved reactor for 2 days at 140 °C. After cooling to
room temperature, light yellow crystals were collected. The
yield was 83% (8.3 mg) based on 1. Calcd for 2: C, 40.49; H,
2
8–32
for Mn-based MOFs.
Interestingly, eight Mn atoms are
located in the eight vertexes of the unit cell and each Mn atom
occupied 1/8th in one unit cell. The carboxylate groups of the
−
organic ligand are protonated. Each H L ligand links two Mn
2
(
II) cations through one monodentate carboxylate group and
2
.86; N, 10.90. Found: C, 40.05; H, 3.72; N, 11.07. FT-IR (KBr,
−
−
1
2
one tetrazole nitrogen atom. As shown in Fig. 1b, two H L
cm ): 3394(s), 3083(w), 2861(w), 1605(m), 1553(s), 1449(s),
ligands link two MnO N polyhedra forming the infinite one-
4
2
1
8
4
383(s), 1322(w), 1265(m), 1132(w), 1048(m), 1010(m), 935(w),
59(w), 830(w), 770(m), 717(m), 646(w), 580(w), 562(w), 452(w),
24(w).
dimensional rectangle ring chain along the b axis. The free-
carboxylate groups decorate the infinite chain and point to the
outside of the chain. The distance between a tetrazole ring and
a benzene ring is 3.86(3) Å and the distance between two
benzene rings is 3.88(5) Å, indicating that there are continuous
weak π–π interactions in the structure of 1 (Fig. 1c). Extensive
hydrogen bonds also exist among the coordinated water mole-
Mn L (H O) (3). 2,2′-Biquinoline-4,4′-dicarboxylic acid
3
2
2
4
2
(H bqdc) (0.0100 g, 0.31 mmol) was placed in a reactor filled
with single-crystals of 1 (10 mg), acetonitrile (4 mL) and de-
ionized water (3 mL) and sealed in an autoclaved reactor for
2
days at 160 °C. After cooling to room temperature, light
yellow crystals were collected. The yield was 72% (7.2 mg)
based on 1. Calcd for 3: C, 42.15; H, 3.07; N, 12.29. Found: C,
−
1
4
1
1
6
2.05; H, 3.22; N, 12.43. FT-IR (KBr, cm ): 3450(s), 1614(w),
580(s), 1518(s), 1446(s), 1413(m), 1384(s), 1361(s), 1308(w),
265(w), 1146(w), 1041(w), 997(w), 806(w), 773(s), 710(m),
63(w), 634(w), 486(w), 428(w).
4 2 2 5 2
Mn L (HL)(H O) ·0.5H O (4). Single-crystals of 1 (10 mg),
acetonitrile (4 mL) and deionized water (3 mL) were placed in
an oven for 2 days at 140 °C. Single-crystals of 4 were prepared
2
3
according to the reported procedure.
Catalytic experiment
The crystalline samples were immersed in CHCl
3
for one day
Fig. 1 (a) The coordination environment of the Mn center in 1. (b) The
one-dimensional chain in 1. (c) The stacking fashion in the ac plane. (d)
The hydrogen-bond interactions in 1.
and heated at 120 °C under vacuum overnight for
2
4–26
activation.
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cules, carboxylate groups and tetrazole units. The coordinated
water molecules and the free-carboxylate group form two
strong hydrogen bonds with the nitrogen atoms from the tetra-
zole rings of another chain (dO1⋯N3 = 2.81(2) Å; dO5⋯N4
=
2
.70(4) Å) (Fig. 1d). Because of the H-bond interactions and
continuous π–π interactions, the infinite chains of 1 construct
a 3D supramolecular structure.
2
crystallizes in the monoclinic system, C2/c space group.
As illustrated in Fig. 2a, there are two independent Mn atoms
in the asymmetric unit. Both Mn atoms adopt a six-co-
ordinated mode, and Mn1 is coordinated with four carboxylate
3
−
oxygen atoms from four individual L ligands and two tetra-
zole nitrogen atoms, while Mn2 is coordinated with three car-
3
−
boxylate oxygen atoms from two individual L ligands, one
tetrazole nitrogen atom and two other nitrogen atoms from
the 2,2′-bpy unit. The carboxylate groups in the ligand are
Fig. 3 (a) The coordination environment of the Mn centers in 3. (b) The
Mn O N unit. (c) The 3D view of 3 in the ab plane. (d) The schematic
3 12 4
3
−
completely deprotonated. It is noted that one L ligand links representation of the topology for 3.
six Mn(II) cations by its two carboxylate groups and one tetra-
1
1
2
1
1
1
zole motif in a (κ -κ -μ
2
)-(κ -κ -μ
3
)-(κ -κ -μ
2
)-μ
7
coordination
tetrazole nitrogen atom. Moreover, the L − ligand links six Mn
3
fashion. The 2,2′-bpy is coordinated with one Mn(II) cation in a
classic chelating fashion. One Mn1 and two Mn2 atoms form a
trinuclear Mn O N unit, in which the Mn1 atom locates in
3 8 8
(
II) cations by its two carboxylate groups and one tetrazole
1
1
2
1
1
1
moiety in the (κ -κ -μ
fashion. One Mn1 and two Mn2 atoms are connected with
each other forming a Mn O N trinuclear unit, where the
Mn1 atom is located in the center and connects with two Mn2
2
)-(κ -κ -μ
3
)-(κ -κ -μ
2
)-μ
7
coordination
the center and connects with the other two Mn2 atoms by
vertex-sharing mode (Fig. 2b). Each trinuclear unit links six
3
12 4
3
−
L
ligands and extends to a three-dimensional framework
3
−
(
Fig. 2c). From the topology point of view, the trinuclear unit
atoms via sharing vertex oxygen atoms (Fig. 3b). The L
3
−
can be regarded as a six-connected node and the L ligand
can be seen as a three-connected node (Fig. S2†). Thus, the
framework of 2 can be simplified as a 3,6-connected network
with a Schläfli symbol of {4 ·6}
crystallizes in the monoclinic system, P2
As shown in Fig. 3a, there are two crystallography independent
Mn atoms and one L ligand. The two Mn atoms are both in
a six-coordinated fashion and adopt a slightly distorted octa-
hedral coordination geometry. Mn1 coordinates with four car-
boxylate oxygen atoms from L and the other two are nitrogen
atoms from the tetrazole unit, and Mn2 coordinates with three
carboxylate atoms, two coordinated water molecules and one
ligands connect with adjacent trinuclear units to accomplish a
three-dimensional framework. It is noted that the organic
ligand in the structure of 3 is disordered, and the ADPs image
is illustrated in Fig. S3a.† Topologically, the trinuclear unit can
be viewed as a six-connected node and L is regarded as a
three-connected node (Fig. S3b†). Consequently, the frame-
work of 3 can be simplified as a 3,6-connected network with a
2
4
2
8
2
{4 ·6 ·8 ·10} (Fig. 2d).
3
−
3
1
/c space group.
3
−
2
2
10
3
2
Schläfli symbol of {4·6 } {4 ·6 ·8 } (Fig. 3d).
According to our previous work, the two coordination
3
−
modes of the H L ligand mentioned above are two new coordi-
nation modes, noted as IV and V (Fig. 4). Owing to the rotation
of the ether oxygen atom and the –CH – group, the flexible
2
3
H L ligand has variable coordination modes. As shown in
3
Fig. S4,† the angles between the benzene ring planes are
13.73° for IV, 57.51° for V-1, and 28.69° for V-2 while those for
I–III are 23.61°, 40.10°, and 20.93°, respectively. Notably,
3
−
despite the fact that the coordination modes of L in 2 and 3
Fig. 2 (a) The coordination environment of the Mn centers in 2. (b) The
Mn
3 8 8
O N unit. (c) The 3D view of 2 in the ab plane. (d) The schematic
representation of the topology for 2.
Fig. 4 The coordination modes of the organic ligand.
9542 | Dalton Trans., 2021, 50, 9540–9546
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Paper
are both V, their conformations are different due to the flexi- days, the product is still a mixture of 3 and 4. Thus, 3 cannot
3
−
bility of the L ligand. The angles between the benzene ring be completely converted into 4 by prolonging the reaction
planes in 2 and 3 are 57.51° and 28.69°, respectively, and the time. This transformation from 1 to 2–4 may be caused by re-
angles between a benzene ring and a tetrazole ring are 31.75° arrangement or dissociation to its constituent parts under the
and 49.98°, respectively. Therefore, the conformational isomer- pressure and temperature conditions. These results demon-
3
−
ism of the L ligand may directly lead to the difference in strated that 2 and 4 may be thermodynamically very stable
structures of 2 and 3.
compounds because 2 or 4 could not transform into other
compounds. Meanwhile, 1 may be an intermediate state in the
syntheses of 2–4. Thus, external stimuli including additional
Crystal transformation
First, colorless rhomboid block crystals of 1 were synthesized ligand, structural-directing agent and temperature played
through the solvothermal reactions of Mn(II) salts and H
L. important roles in the construction of Mn(II)–MOFs based on
3
3
Then, single-crystals of 1 and the solvent were heated at 140 °C the H L ligand.
for another 2 days (Fig. 5). Subsequently, light yellow rod
single-crystals of 4 were obtained, and the purity of the
Characterization
product was proved by PXRD analysis, indicating that 1 com- The PXRD patterns of 1–3 matched well with the simulated
pletely transformed into 4. Moreover, 10 mg of 2,2′-bpy as an ones calculated using single-crystal X-ray diffraction data, indi-
additional ligand was added to 1 and the solvent. Afterward, cating that the as-synthesized samples of 1–3 are the pure
light yellow cubic single-crystals of 2 were acquired under phase. The differences between the simulated patterns and as-
solvothermal conditions. The purity of the final product was synthesized patterns are due to the different crystal orien-
also confirmed using the PXRD pattern (Fig. S6†). Encouraged tations of the powder samples.
by the successful transition of 1 to 2, we used H
alternative of 2,2′-bpy to synthesize the coordination network. under an air atmosphere (Fig. S12†). For 1, there are two
Notably, H
bqdc did not coordinate to the backbone of the obvious weight loss steps. The first step from 113 to 206 °C is
2
bqdc as the
The thermogravimetric analyses of 1–3 were performed
2
final structure but acted as a structural-directing agent indu- due to the loss of coordinated water molecules (calculated:
cing new coordination networks. Moreover, 1 could not trans- 4.37%, found: 4.39%). The second step of weight loss from 152
form into a pure product of 3 but a mixture of 3 and 4 by to 492 °C can be due to the decomposition of the framework.
crystal transformation (Fig. S7†). The pure product of 3 could For 2, the first step of weight loss before 315 °C corresponds to
be achieved by a one-pot synthesis method (Fig. S8†). In the loss of five free water molecules (calculated: 5.84%, found:
addition, due to the similar building units and topological net- 5.60%), and the second weight loss from 315 to 537 °C is due
works of 2 and 3, the transformation of 3 into 2 was also inves- to the decomposition of the framework. For 3, the first step of
tigated. 10 mg of 2,2′-bpy was added to single-crystals of 3 and weight loss before 300 °C is due to the loss of four coordi-
their mother solution and heated for 2 days at 140 °C.
nation water molecules (calculated: 7.99%, found: 7.81%). The
As a result, single-crystals of 2 could be achieved which second step of weight loss from 300 to 458 °C can be ascribed
suggested that the coordinated water molecules in 3 were to the collapse of the framework (calculated: 26.02%, found:
replaced by the 2,2′-bpy ligand and resulted in the structural 27.27%). The final products of these three MOFs after TGA are
2 3
transformation. Meanwhile, single-crystals of 3 can be partially α-Mn O (PDF#41-1442) which can be verified by PXRD ana-
converted into 4 by prolonging the reaction time (Fig. S10†). lysis (Fig. S13†).
Unfortunately, even if the reaction time is extended to seven
The porosity of these MOFs has been characterized using
adsorption isotherms at 77 K. As shown in Fig. S14,† 3
exhibited a type I adsorption curve and the BET surface area is
N
2
2
−1
1
62 m g and the pore width is about 1.18 nm which agrees
with the single-crystal XRD data; however, 1 and 2 showed no
obvious N uptake.
2
Catalytic properties
As we all know, after removing the coordinated solvent mole-
cules, unsaturated coordinated metal centers can be viewed as
33–36
Lewis acid sites for heterogeneous catalysis.
The cyanosily-
lation of aldehyde is a typical acid-catalyzed condensation reac-
tion and is widely used as a reaction to detect Lewis acidity in
3
7,38
MOFs.
Thus, after activation, 1–3 were used for cyanosilyla-
tion of aldehyde to study their catalytic performances. As illus-
trated in Table 1, when the solvent was CDCl , the yields were
3
86%, 52%, and 61%, and the yields were 90%, 50% and 72%
under solvent-free conditions (entries 1 and 2). Thus, to
Fig. 5 Schematic illustration of crystal transformations between 1–4.
achieve a higher catalytic efficiency at low cost, the catalysis
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a
Table 1 The cyanosilylation reactions catalyzed by 1–3
Yield (%)
Entry
Substrate
Temperature
Solvent
CDCl
1
2
3
1
2
3
4
5
6
7
8
9
Benzaldehyde
Benzaldehyde
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
0 °C
3
86
90
52
50
15
38
50
99
>99
65
49
48
99
>99
68
51
27
37
—
61
72
99
70
71
>99
>99
74
52
50
99
>99
99
90
59
84
62
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
o-Fluorobenzaldehyde
o-Bromobenzaldehyde
o-Methoxybenzaldehyde
o-Cyanobenzaldehyde
p-Cyanobenzaldehyde
m-Cyanobenzaldehyde
1-Naphthaldehyde
9-Anthraldehyde
Pyridine-4-carboxaldehyde
1-Phenylethanone
Acetaldehyde
Propionaldehyde
Valeraldehyde
>99
>99
80
>99
>99
95
54
50
99
>99
>99
>99
99
54
74
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
Cinnamaldehyde
Benzaldehyde
a
Reaction conditions: TMSCN (2 mmol), aldehydes (1 mmol), catalyst (0.5 mol%), solvent. r.t.: room temperature.
experiments were performed under solvent-free conditions. In center, while the Mn center in the structure of 1 and 3 is co-
order to explore the applicability of these three catalysts to ordinated with two water molecules which can be removed by
different substrates, the reactions between aldehydes with activation and then displays Lewis acidic sites. In addition,
different substitute groups and TMSCN under the same con- there is no Lewis acidic site in 2, but the catalytic property
ditions were carried out. When the substitute group is o-F and probably originated from the basic catalytic sites in the
3
9,40
o-Br, the yields of the product are >99% and >99% for 1, 15% ligand.
2 2 3
Additionally, MnCl ·4H O, H L and a physical
and 38% for 2, and >99% and 70% for 3. With the electron- mixture of MnCl
2
·4H O and H L are also employed as homo-
2
3
donating group o-OCH , the yields were 80%, 50% and 71%; geneous catalysts for the cyanosilylation of aldehyde. Their
3
when the electron-withdrawing group o-CN was applied, both yields can reach 99%; however, they are too difficult to separate
the yields were over 99%. Thus, the electronic effects of the from the reaction system to reuse.
substitute groups have an obvious influence on the reaction.
In order to prove the heterogeneous feature of the catalysts,
The position of the substitute group also has an impact on the solid-state catalysts were removed from the reaction system
this reaction. The yields of o-CN and p-CN groups were over by centrifugation after 0.5 h. The reaction process shuts down
9
9%; however, those of m-CN were decreased to 95%, 65%, quickly after removing the catalyst. Even if the reaction system
and 74%, respectively. Moreover, the larger size substrate has a standing for another 1 h, the yield is not increase anymore
low yield (entries 6–8). As for pyridine-4-carboxaldehyde, which indicates that no homogeneous species is present in the
1
-phenylacetaldehyde, acetaldehyde, propionaldehyde and reaction system (Fig. 6a). The recyclability of the hetero-
valeraldehyde, high yield can be obtained, which indicated geneous catalysts is an important feature for the application.
that activated 1–3 have good catalytic activity for the hetero- Thus, the catalysts of 1–3 were separated after catalysis,
cyclic and aliphatic aldehydes. When cinnamaldehyde was washed three times with CHCl , and then dried at 120 °C in a
3
used as the substrate, the yield decreased to 64%, 37%, and vacuum. As illustrated in Fig. 6b, 1–3 can be reused in at least
8
4%, respectively. Furthermore, in order to broaden the range five runs with a slight catalytic activity loss. PXRD patterns
of use of the catalyst, the catalytic experiment was performed of 1–3 after catalysis showed good crystallinity, indicating
at 0 °C. The yields of 1 and 3 were 60% and 57% after 3 h, and that the structures have remained stable (Fig. S15–S17†).
7
4% and 62% after 6 h. It is noted that the catalytic perform- Additionally, the metal leaching experiments of 1–3 after cata-
2
+
ances for 1 and 3 are much higher than that for 2. The reason lysis were measured by ICP-OES. Almost no Mn can be
is that there are no coordinated solvent molecules in the struc- detected, demonstrating that there is no obvious metal leach-
ture of 2, and at the same time, the Mn center is six-co- ing in catalysis (0.11 mg L− , 0.08 mg L , and 0.10 mg L for
1
−1
−1
ordinated and almost no Lewis acidity is observed in the metal 1–3, respectively).
9544 | Dalton Trans., 2021, 50, 9540–9546
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The authors gratefully acknowledge financial support through
the National Natural Science Foundation of China (No.
5
2075218 and 51775232) and the Science and Technology
Development Plan Project of Jilin Province (No.
0190201155JC and 20190201278JC).
2
Notes and references
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9546 | Dalton Trans., 2021, 50, 9540–9546
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