Tunable morphology and the changeable catalytic property of layered scandium coordination polymer

Article abstract of DOI:10.1016/j.jssc.2019.121151

Sc-CP 1, 1A, 1B and 1C with controllable morphologies were successfully synthesized by the conventional hydrothermal method and microwave (MW) assisted hydrothermal method. 1 was macroscopic, 1A was nano sized, while 1B and 1C were micron sized. Sc-CP 1 s

Full text of DOI:10.1016/j.jssc.2019.121151

Journal Pre-proof
Tunable morphology and the changeable catalytic property of layered scandium
coordination polymer
Ziqian Zhu, Chengxia Tong, Pengcheng Wang, Wei Wang, Jing Sun, Jingjing Xue, Li
Wang, Yong Fan, Jianing Xu
PII:
S0022-4596(19)30656-5
DOI:
https://doi.org/10.1016/j.jssc.2019.121151
YJSSC 121151
Reference:
To appear in: Journal of Solid State Chemistry
Received Date: 25 October 2019
Revised Date: 14 December 2019
Accepted Date: 20 December 2019
Please cite this article as: Z. Zhu, C. Tong, P. Wang, W. Wang, J. Sun, J. Xue, L. Wang, Y. Fan, J. Xu,
Tunable morphology and the changeable catalytic property of layered scandium coordination polymer,
Journal of Solid State Chemistry (2020), doi: https://doi.org/10.1016/j.jssc.2019.121151.
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Graphical abstract
Tunable morphology and the changeable catalytic property of
layered scandium coordination polymer
a
a
a
a
a
Ziqian Zhu, Chengxia Tong, Pengcheng Wang, Wei Wang, Jing Sun, Jingjing
a
a
a
a
Xue, Li Wang, Yong Fan and Jianing Xu *
a
College of Chemistry, Jilin University, Changchun 130012, Jilin, P. R. China.
e-mail: xujn@jlu.edu.cn.
©
2D layered Sc-CPs with tunable morphologies were synthesized by conventional
and MW-assisted hydrothermal methods and their catalytic performance for
cyanosilylation reaction of aromatic aldehydes was dependent on the morphology
and size of the particles.

Tunable morphology and the changeable catalytic property of
layered scandium coordination polymer
a
a
a
a
a
Ziqian Zhu, Chengxia Tong, Pengcheng Wang, Wei Wang, Jing Sun, Jingjing
a
a
a
a
Xue, Li Wang, Yong Fan and Jianing Xu *
a
College of Chemistry, Jilin University, Changchun 130012, Jilin, P. R. China.
e-mail: xujn@jlu.edu.cn.
Abstract
Sc-CP 1, 1A, 1B and 1C with controllable morphologies were successfully
synthesized by the conventional hydrothermal method and microwave (MW) assisted
hydrothermal method. 1 was macroscopic, 1A was nano sized, while 1B and 1C were
micron sized. Sc-CP 1 showed two-dimensional (2D) layered structure which was
constructed from the connections of left- and right-hand helical chains. Catalytic
experiments showed the catalytic performances of Sc-CP 1, 1A, 1B and 1C for the
cyanosilylation reaction of aromatic aldehydes were dependent on the morphologies
of the particles. Flower-ball-like 1C featuring a high concentration of Lewis acidic
Sc(III) sites on its exposed external surfaces showed better catalytic activity than
-3
-1
others, the best constant rate of which was 6.4 × 10 min .
Keywords: Scandium CPs; Tunable morphology; Changeable catalytic property
1

1
. Introduction
Coordination polymers (CPs) have attracted an extensive attention not only due
to their diverse compositions and intriguing structures but also owing to their potential
1
-2
applications in the field of the luminescence, sensing, magnetism, gas storage, drug
3
-11
delivery, ion exchange, and catalysis, etc.
In particular, CPs as heterogeneous
catalysts have many good advantages, such as allowing the simple filtration,
1
2-16
facilitating product separation and catalyst reusing.
Moreover, the structures and
active sites of CPs can be flexibly designed by tuning different metal centers and
1
7
organic linkers. To date, a lot of CPs as heterogeneous catalysts exhibit the high
1
8-22
activity and selectivity in various reactions
, among them, Sc-CPs as Lewis acid
catalysts are of particular interest. The main reason is that Sc(III) usually adopts a
lower six coordination number, which can provide effective Lewis acid sites for the
catalysis of various organic reactions. For example, [Sc (C O ) ] presented
2
4
4 3
1
9
particularly good activity for cyanosilylation with 90% yield after 12 h. MIL-100(Sc)
could be used as a multifunctional catalyst for a series of reactions, such as the imine
2
0-22
formation, Michael reaction, indole reaction and carbonyl-ene reaction.
[
Sc (C H S O )(OH) ] exhibited excellent activity for the oxidation of sulfides and
2
10
6
2
6
4 n
could be recycled in several consecutive reactions without any loss of the activity or
2
3
selectivity.
Recently, a new research trend has been focused on tuning the morphology
24-28
and crystal size
of nanoparticles (NPs) because the chemical and physical
2

24-28, 29-35
properties of NPs are greatly influenced by their size and shape.
For
example, the catalytic properties could be greatly enhanced by changing the
components, particle sizes, morphologies or generators of gold nanoparticles.
24-28
For instance, compared with the normal CPs, nano-sized CPs exhibited
31-32
33-34
unique or enhanced properties in the absorption,
drug delivery
and
35
heterogeneous catalysis for the easier transportation of guest molecules, short
31-35
diffusion pathways and exposed active sites.
The synthesis of the
size/morphology-controlled CPs usually depends on the control over the
36-40
nucleation and growth of CPs.
Currently, due to the rapid/homogeneous
heating and fast kinetics, the microwave (MW)-assisted hydrothermal method
41-43
has been applied successfully for the fabrication of CPs
with complex
morphologies even in seconds with the high phase purity and high
29-30,44-48
yield.
For example, straw-sheaf-like CP architectures were synthesized
through MW heating in 15 min, which presented the surface area of 152.51
2
-1
m ·g and the highly sensitive and selective luminescent probes for heavy
29
ions. With the aid of MW heating, cubic-shaped, well-tuned sizes of
30
nano-Zn O(C H O ) had been produced by Feng etc, the nano-sized particles
4
8
4
4 3
possessed hierarchical pores from 1.4 to 5 nm, that was beneficial for the
molecule diffusion and the loading of large molecules.
Our group has been devoted to the design and synthesis of Sc-CPs. Based
on various multicarboxylic acids, many Sc-CPs with novel structures were
49-53
synthesized and exhibited good catalytic properties.
Some nanoparticles
3

were synthesized through adjusting the synthetic components in order to control
24-25, 28
the morphologies and sizes.
Instead, the same component of the synthetic
materials were used to obtain different nanoparticles with various morphologies
and sizes by changing the conditions of synthetic procedure in this work. Using
pyridine-2,5-dicarboxylic acid (H L) as bridging linker, we synthesized a new
2
Sc-CP [Sc L (HL) (H O) ]·H O (1) via conventional hydrothermal method,
2
2
2
2
2
2
showing two dimensional (2D) layered structure formed by the connection of
left- and right-hand helical chains. Then we tried to tune the morphologies of
Sc-CP
morphologies of Sc-CP
flower-like balls (1C) were successfully obtained. Further catalytic experiments
indicated that the morphology and size of the particles of Sc-CP series played
1
by using MW-assisted hydrothermal heating method and three distinct
1
including nanoribbons (1A), nanosheets (1B) and
1
a significant role on their catalytic performance for the cyanosilylation reaction
of aromatic aldehydes. Herein, the synthetic condition, crystal morphologies
and catalytic properties of Sc-CP
1 were discussed in detail.
2
2
. Experimental
.1 Chemicals and materials
All the reagents of analytical grade were obtained from commercial sources and
used without further purification. MW heating was performed on a MDS-6
microwave digestion system. The size and morphology of the produced structures
were determined using a scanning electron microscope (SEM, SU8020, Hitachi, Japan)
and a transmission electron microscope (TEM, JEM-2200FS, JEOL, Japan). Powder
4

X-ray diffraction (PXRD) data were collected on a Rigaku D/max-2550
diffractometer with Cu-Kα radiation (λ = 1.5418 Å). The elemental analyses (C, H
and N) were performed on an Elemental Vario EL cube CHNOS elemental analyzer.
−
1
The infrared (IR) spectra were recorded over 400−4000 cm region on a Nicolet
Impact 410 FTIR spectrometer using KBr pellets. The thermal gravimetric analyses
(TG) were performed on a Perkin-Elmer TGA 7 thermogravimetric analyzer
-1
instrument in an atmospheric environment with a heating rate of 10 °C min . The
1
H-NMR spectra were recorded on a Bruker 400 MHz spectrometer, with chemical
1
shifts (δ) being given in ppm. The percent conversion was determined by H-NMR.
2
.2 Hydrothermal synthesis of [Sc L (HL) (H O) ]·H O (1)
2 2 2 2 2 2
Sc(NO ) ·6H O (0.0339 g, 0.1 mmol), H L (0.0167 g, 0.1 mmol), H O (4
3
3
2
2
2
mL) and HNO (0.2 mL, 1 M) were placed in a 20 mL glass bottle which was
3
then sealed and heated at 80 °C for 24 h. The system was allowed to cool to the
room temperature naturally. Colorless crystals were obtained with 30.16%
based on the scandium and the pure crystals were washed with distilled water.
They can be dried in air without the appearance changing.
2
.3 MW-assisted hydrothermal synthesis of [Sc L (HL) (H O) ]·H O (1A),
2 2 2 2 2 2
[
Sc L (HL) (H O) ]·H O (1B) and [Sc L (HL) (H O) ]·H O (1C)
2 2 2 2 2 2 2 2 2 2 2 2
Sc(NO ) ·6H O (0.339 g, 1 mmol), H L (0.167 g, 1 mmol), H O (40 mL)
3
3
2
2
2
and HNO (2 mL, 1 M)were mixed in a 60 mL Teflon reactor. The mixture was
3
stirred for 10 min, which was then closed in polyether-ether-ketone (PEK).
5

Keep the pressure at 200 Kpa for 6 min by microwave irradiation (P = 400 W).
The system was allowed to cool to the room temperature. 1A was obtained with
the yield of 80.15% and the products can be dried in the air without the
appearance changing.
For the same component, raise the pressure from 200 to 1200 KPa at 200
KPa/min by microwave irradiation (P = 400 W). The system was allowed to
cool to the room temperature. 1B was obtained with the yield of 70.69% and
the products can be dried in the air without the appearance changing.
For the same component, raise the pressure from 200 to 1200 KPa every
2
00 KPa per 3 minutes by microwave irradiation (P = 400 W). The system was
allowed to cool to the room temperature. 1C was obtained with the yield of
5.42% and the products can be dried in the air without the appearance
changing.
6
2
.4 X-ray structure determinations
Suitable single crystals of
1
were selected for single-crystal X-ray
were collected on a Rigaku
diffraction analyses. Crystal data for
1
RAXIS-RAPID diffractometer using Mo Kα radiation (λ = 0.71073 Å).
Crystallographic structures were solved by direct methods and refined by
2
full-matrix least-squares on F using the SHELXTL-2014 software package. All
the metal atoms were located first, and then O, N, and C atoms of the
compounds were subsequently found in difference Fourier maps. H atoms of
the ligands were placed geometrically, and H atoms of the water molecules
6

could not be located but were included in the formula. All non-hydrogen atoms
were refined anisotropically. The crystallographic data for (CCDC 1935656)
have been deposited at the Cambridge Crystallographic Data Centre. The
detailed crystallographic data and structure refinement parameters for are
summarized in Table S1, and selected bond length and angle data are presented
in Table S2. Hydrogen bonds for are shown in Table S3.
1
1
1
2
.5 Catalytic experiments
For the experiments of cyanosilylation catalysis, catalyst (0.05 mmol),
CH ) SiCN (1.2 mmol), -nitrobenzaldehyde (0.5 mmol) were sequentially
(
p
3
3
added to a standard 5 mL vial in the solvent free condition. The reaction
mixtures were stirred at the room temperature. The reactions were monitored by
1
HNMR spectroscopy and the conversion yield was determined to the integrals
of all the signals (the aldehydes and products).
2
.6 Recycling catalysis experiments
For the recyclability tests, the reactions were performed under the same
conditions as described above, except for using the recycled catalyst. After the
catalytic reaction, the catalyst was separated from the reaction mixture by
filtration, during which washed with 10 mL CH OH for 5 times, then dried at
3
8
0 °C for 12 h.
3
. Results and discussion
3
.1 Description of crystal structure
7

Single-crystal X-ray diffraction analysis revealed that 1 crystallized in
3
+
2-
monoclinic space group P2 /c. There were two different Sc ions, two L ligands,
1
-
two HL ligands, two coordinate water molecules and one free molecule of water in
the asymmetric unit (Fig. 1c). The coordination geometries around Sc1 and Sc2
adopted two different distorted pentagonal bi-pyramidal geometries (Fig. 1a-b). Sc1
was seven-coordinated and bonded to four oxygen atoms, two nitrogen atoms from
2
-
-
three L and one HL ligands, one oxygen atom from one coordinated water molecule.
Sc2 was also seven-coordinated by four oxygen atoms and two nitrogen atoms from
2
-
-
two L and two HL ligands, one oxygen atom from one coordinated water molecule.
The bond lengths of Sc-O varied from 2.048(4) to 2.195(3) Å while the Sc-N bond
lengths varied from 2.318(4) to 2.362(4) Å. The bond angles of O-Sc-O ranged from
7
4.15(14) to 173.72(16) °, the O-Sc-N ranged from 69.28(13) to 140.33(13) ° and the
N-Sc-N ranged from 145.72(15) to 146.15(14) °. All of the bond lengths and angles
54-56
2-
were comparable to those reported in other scandium compounds.
Two L and
-
two HL ligands presented four kinds of coordination modes in 1 (Fig. 2). Using one
2
-
nitrogen atom and two oxygen atoms of L ligands to bridge Sc1 atoms (Fig.2,
2
-
mode-b), N5 and O5 of L ligands acted as a µ -didentate spacer, while O6 linked
2
another Sc1, which generated a 1D left-hand chiral chain (Fig. 1e). The µ -bridging
4
2
-
mode of L ligands (Fig. 2, mode-a) was firstly observed in Sc-CPs, in which N2 and
O2 acted as the chelate bridging coordination fashion to link a Sc2 atom, O10
coordinated with Sc2 and O8 bridged Sc1 respectively. Herein, a right-hand 1D chiral
2
-
chain was formed by Sc2 and L ligands (Fig. 1d). Moreover, using µ -bridging mode
2
8

-
-
of HL ligands (N3 and O9) to link Sc1 and using µ -bridging mode of HL ligands
1
-
(
O12) to link Sc2, HL ligands also joined the two different 1D chains to form the 2D
layer structures and performed as the µ -tridentate bridging mode in all (Fig. 2,
3
-
mode-d). Interestingly, HL ligands also adopted as a chelate bridging mode (Fig. 2,
mode-c) to occupy two coordinative nodes of Sc2 atoms.
The Sc1 and Sc2 atoms featured the two infinite right- and left-hand
helices, as shown in Fig. 1d-e. The helical chain grew around a crystallographic
2-
21
lengths of 6.8149(25) Å for the infinite right- hand chain and 8.4940(23) Å for
the infinite left- hand chain, respectively. These helical chains along axis with
screw axis formed by adjacent Sc atoms and L ligands with the pitch
c
opposite chirality are connected alternately together to form a 2D waved sheet
structure (Fig. 1f). Furthermore, 2D waved structures were stacked in parallel
without interpenetration and extended into 3D super-molecular architecture
through hydrogen bond interactions among wave-like layers and free water
Fig. 1 (a) The polyhedron of Sc2; (b) Polyhedron of Sc1; (c) Coordination environment of
3
+
Sc ions in 1; (d) The Sc2 chiral chain; (e) The Sc1 chiral chain; (f) The 2D layer of 1.
9

molecules. (Fig. S1)
2-
-
Fig. 2 (a), (b) Coordination modes of L ligands; (c), (d) Coordination modes of HL ligands.
3
.2 Synthesis and morphology
As well known, the size, morphology, yield of crystal product can be
significantly influenced by the change of synthesis condition and method.
Much bigger crystals that can be seen clearly by our naked eyes are usually
harvested through conventional method, such as hydrothermal synthesis.
Conventional hydrothermal synthesis usually takes several hours to days and
49, 50-53
the products yields were not stable.
In contrast, MW-assisted
hydrothermal method exhibits rapid/homogeneous heating and fast kinetics for
the fabrication of CPs even in seconds with high phase purity and high yield. In
this study, we firstly prepare rhombic crystals of
1 with 0.5 mm (Fig. 3a) under
conventional hydrothermal conditions with the reaction time of 24 h and the
yield of 30.16%. Then by changing the pressure or temperature, we attempt to
1
0

prepare different sizes and morphologies of
hydrothermal method.
1 through MW-assisted
Fig. 3 (a) 1: The fluorescence microscope image of rhombic crystal strips through hydrothermal synthesis and the
XRD pattern of 1; (b) 1A: The SEM image of nanoribbons through MW heating and the XRD pattern of 1A; (c)
1
B: The TEM image of nanosheets through MW heating and the XRD pattern of 1B; (d) 1C: The TEM image of
flower balls through MW heating and the XRD pattern of 1C.
1
1

When keeping the pressure at 200 Kpa for 6 min, nano-crystals of
1 with
the size of 10 nm x 50 nm, named 1A, were obtained. As shown in Fig.3b, 1A
shows nanoribbon-like morphology. Increasing the pressure from 200 to 1200
-1
KPa with the rate of 200 KPa·min , semicircle nanosheets of
1 with the
thickness of 10 nm (1B) were obtained as shown in Fig.3c, while
flower-ball-like crystals (1C) could be got by improving the pressure from 200
to 1200 KPa in 18 min. Fig. 3d illustrated the well-defined microstructure of
1
C
, which presented several flower balls with broad interface spaces. A
magnified TEM image (Fig. S2) disclosed that the flower ball was composed of
0 nm thickness semicircle nanosheets which were sporadically and arbitrarily
1
arranged. An organization status of crystallites was revealed in scheme S1. As
showed in scheme S1-(1), 1 was self-assembled by oriented aggregation with
1
A
. Scheme S1-(2) demonstrated that one piece of nanosheet of 1B was in fact
built from smaller rhombic crystals that contained even smaller 1A. The phases
of 1A 1B and 1C were confirmed by XRD measurements and each XRD
pattern of the as-synthesized sample was consistent with the simulated one. (Fig.
a-d) The differences in intensity might be owing to the preferred orientation of
the powder samples. The XRD patterns demonstrated that 1A 1B and 1C
were isomorphic but four kinds of morphologies were observed (Fig. 3a-d),
which were first reported in Sc-CPs. The yields of 1A 1B and 1C were 80.15%,
0.69% and 65.42%, respectively, through which we could find that MW
1
,
,
3
1
,
,
,
7
1
2

heating products obtained higher yields. No matter we did the synthesis
experiments in any season, it did no influence.
MW heating was a beneficial and responsible method which was seldom
used in the synthesis of Sc-CPs. Firstly, MW heating method took much shorter
time than conventional heating in synthesis. 1A
,
1B and 1C took several
1B or 18 min for 1C
minutes, spent 24 hours by contract. Either 6 min for 1A
1
/
was rather more efficient than 24 hours. Secondly, the size of crystals could be
shrunk by controlling the synthesis conditions through MW heating and even
the morphologies were different from normal crystals. The longer time of the
raising pressure lasted, the higher concentration status of the crystals presented.
1B and 1C were more applicable in catalysis, due to these kinds of nanosheets
and flower-balls concentrated higher density of functional sites of Sc-CPs
which could present higher conversion yield in organic reactions. Last, MW
heating showed high reproducibility and product yields, which made the
synthesis procedure more efficient. Reproducibility and product yields of the
catalyst also played an important role in the catalytic properties.
3
.3 Characterization
Anal. Calc. for 1: C, 41.68; H, 2.48; N, 6.95. Found: C, 41.40; H, 2.52; N,
-
1
7
1
.05. IR data (KBr pellet cm ): 3506(m), 1720(m), 1614(s), 1484(w), 1385(s),
349(m), 1278(m), 1185(s), 1131(w), 955(w), 691(m) (Fig. 4). A middle broad
-1
peak at 3506 cm indicated the presence of the water molecules (including one
free water molecule and two coordination water molecules). There was a
1
3

-
1
middle peak in the range of 1690 to 1730 cm , which indicated not all carboxyl
groups of L ligands were completely deprotonated. The bands from 1500 to
-1
-1
1
700 cm and 1300 to 1500 cm correspond to asymmetric stretching and
symmetric stretching of the carboxylate groups, respectively, which indicated
two kinds of coordination modes of carboxyl groups (µ -unidentate and
1
-1
µ -didentate). The peaks in the range of 703 and 1159 cm were associated
2
with the stretching vibrations of pyridine rings. The Anal. Calc. and IR data of
1A, 1B and 1C were the same as 1.
Fig. 4 IR spectrum for 1 (The spectrums of 1A, 1B and 1C are the same as 1).
Thermal stability of
1, 1A, 1B and 1C had been investigated by TG
analysis experiments of mass loss (Fig. S3). For all, the weight loss of 6.7%
corresponded to the departure of one free water molecule and two coordination
water molecules, and then the structure decomposed. The expulsion of the
-
organic component of one HL ligand molecule occurred with the weight loss of
1
4

2
0.6%. The weight loss after that is attributed to the collapse of the framework
of . Both and 1A displayed the continuous weight loss. The TG plot trend of
and 1C were similar, which demonstrated a slowly weight loss platform
from 185 to 417 °C. The TG data showed that 1B and 1C were more stable than
and 1A, which might be attributed to the different aggregation status of the
crystals.
BET data were 0.7443 m /g, 1.0866 m /g, 6.4433 m /g and 16.5573 m /g
1A 1B and 1C, respectively.
1
1
1
B
1
2
2
2
2
for
1
,
,
3
.4 Catalytic Studies
The catalytic properties of
1, 1A, 1B and 1C were investigated as
heterogeneous Lewis acid catalysts for the cyanosilylation of
-nitrobenzaldehyde (Table 1). Aldehydic substrates and the trimethylsilyl
p
cyanide (1:2 molar ratio) were running for the catalytic reaction at the room
1
temperature. Conversions of the reactions were determined by H-NMR
spectroscopy. For hydrothermal synthetic compound:
in 42 h with a conversion of 99%. For MW heating compounds: 1A reached a
9% conversion rate within 36 h, 1B catalyzed the reaction in 17.5 h with a
conversion of 99%, 1C catalyzed the reaction in 15 h with a conversion of 99%
Table 1). The results suggested that acted as good catalysts for
cyanosilylation under room temperature, especially obtained from MW
heating exhibited better catalytic property. Different morphologies of made an
influence towards the results of the catalytic reaction. In our previous work, we
1 catalyzed the reaction
9
(
1
1
1
1
5

had already demonstrated that the smaller sized CPs showed better catalytic
abilities under the condition of the same structure. Through this study, the
aggregation status of CP catalysts also played an important role in the catalytic
experiments. 1C displayed the best properties, due to the flower ball status
featuring a high concentration of Lewis acidic Sc(III) sites.
Table 1 Results for the heterogeneous cyanosilylation of carbonyl substrates in the presence of 1, 1A, 1B and 1C.
-
3
-1
Entry
Cat.
1
Time (h)
42
Conversion yield (%)
K
×
10 (min )
1
2
3
4
99
99
99
99
1.8
2.1
4.4
5.1
1A
1B
1C
36
17.5
15
Reactions conditions: room temperatures under the air; solvent free; (CH ) SiCN, 1.2 mmol;
3
3
p
-nitrobenzaldehyde, 0.5 mmol; catalysts: 0.05 mmol (10 mol %); Cat. represented for 1, 1A, 1B and 1C.
1
57
The conversion yield was determined by H-NMR; K was fitted to first-order model.
As 1C showed better catalytic ability than others, we further studied the
substrate generality of 1C. As summarized in table 2, -Nitrobenzaldehyde and
-Trifluoromethylbenzaldehyde reached 99% conversion yield in 15 hours and
2.5 hours, respectively. -Fluorobenzaldehyde showed 99% conversion yield
p
p
1
P
after 18 hours that was monitored in Fig. 5. The conversion yield of
p
p
-Methylbenzaldehyde was 99%, which took 20 hours. For
-Methoxybenzaldehyde, the convertion yield was 99% and the reaction time
was 22 hours. Heterocyclic substrates, such as pyridine-4-carboxaldehyde, it
displayed 99% conversion yield after 12 hours. When the large substrates were
utilized, not as good as small substrates conversion yields were observed.
Valeraldehyde achieved 99% conversion yield in 48 hours. Cinnamaldehyde,
1
6

p
-phenoxybenzaldehyde and 1-naphthaldehyde were tested in the
cyanosilylation, 99% conversion yield were obtained after 56 hours, 72 hours
and 56 hours, respectively. 1C could be utilized in 5 runs (Fig. S4). For other
types of morphologies,
1 and 1B also could be cycled in 5 runs while 1A could
be reused in 3 runs. Higher aggregation status of the nano-crystals or the large
crystals showed better property of recycling.
To investigate whether an excess of homogeneous catalyst from
1 had
some influence on the catalytic activity, we separated the organic matter by
filtration after 2 hours. Then the filtrate was stirred for further several hours. As
presented in Fig. S5, no conversion of products was observed. The result
demonstrated that the catalysis was actually heterogeneous.
Compared to other types of nanostructures that utilized in catalytic
24-28
reactions,
our Sc-CP catalysts also showed the effect of morphological
shape and size distribution on their activity. The catalytic reactivity was
1
monitored through testing the H-NMR picks of reactants (R-CHO) and
1
products (CN-RCH-OSiMe ). As demonstrated in Fig. 5, H-NMR pick of
3
1
P
-Fluorobenzaldehyde was disappeared at 10.0 ppm, while a new H-NMR
pick of 2-(4-fluorophenyl)-2-((trimethylsilyl)oxy)acetonitrile at 5.7 ppm
subsequently formed during the reaction hours. Moreover, kinetics of the
57
catalytic reactions were studied to the first order model. As tabulated in table
-3
-1
1
, the rate constant (K) of the cyanosilylation was 5.1
×
10 (min ) by using
catalyst 1C, which was three times higher than using catalyst
1
. Due to the
1
7

flower balls like 1C showed better catalytic property, we did the substrate
expansion experiments which were presented in table 2.
Pyridine-4-carboxaldehyde expressed the highest rate constant (K) of all the
substrates catalysed by 1C
.
Table 2 Different aldehydic substrates for the cyanosilylation catalysed by 1C.
-3
-1
Entry
1
Substrate
Time (h)
15
Conversion yield (%)
K × 10 (min )
99
99
99
99
99
99
99
99
99
5.1
4.3
6.1
3.8
3.5
1.6
1.4
1.1
6.4
2
18
3
12.5
20
4
5
22
6
48
7
56
8
72
9
12
1
0
56
99
1.4
Reactions conditions: room temperatures under the air; solvent free; (CH ) SiCN, 1.2 mmol;
3
3
p
-nitrobenzaldehyde, 0.5 mmol; catalysts: 0.05 mmol (10 mol %); Cat. represented for 1C. The
1
57
conversion yield was determined by H-NMR; K was fitted to first-order model.
1
8

Fig 5 P-Fluorobenzaldehyde: 1H NMR spectra of cyanosilylation.
4
. Conclusions
In summary, a new Sc-CP was synthesized by pyridine-2, 5-dicarboxylic
acid under conventional and MW-assisted hydrothermal conditions. By
controlling the synthesis conditions, the Sc-CP demonstrated four different
kinds of morphologies including normal crystals-1, nanoribbons-1A,
nanosheets-1B and flower balls-1C. The Sc-CPs prepared by MW heating
exhibited much smaller sizes and interesting morphologies, which displayed
better catalytic properties than that prepared by hydrothermal method. 1C
showed the best catalytic property of all. Further work will be focus on the
synthesis of nano-CPs with various morphologies and utilize them in more
applications.
Acknowledgments
1
9

The authors gratefully acknowledge the financial support through the National
Natural Science Foundation of China (Grant Nos. 21171065, 21201077,
2
1401005)
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5

Highlights
►
A Sc-CP were synthesized through conventional hydrothermal method and
Microwave-assisted method.
►
Microwave-assisted method is environmental friendly and energy saving. Notably,
it could reduce the synthesis time obviously.
Four morphologies of the Sc-CP-1 were obtained by controlling the conditions of
synthesis procedures.
Catalytic performance of the Sc-CP-1 for cyanosilylation reaction was dependent
on the morphology and size of the particles.
►
►

Guarantor of integrity of entire study: Ziqian Zhu; Jianing Xu
Study concepts: Li Wang; Yong Fan
Study design: Ziqian Zhu
Literature research: Pengcheng Wang; Wei Wang; Jing Sun
Experimental studies: Ziqian Zhu; Chengxia Tong
Data acquisition: Ziqian Zhu; Jingjing Xue
Data analysis/interpretation: Ziqian Zhu; Li Wang
Statistical analysis: Ziqian Zhu; Yong Fan
Manuscript preparation: Ziqian Zhu; Li Wang; Yong Fan
Manuscript definition of intellectual content: Ziqian Zhu; Li Wang; Yong Fan; Jianing
Xu
Manuscript editing: Ziqian Zhu
Manuscript revision/review: Ziqian Zhu; Li Wang
Manuscript final version approval: Ziqian Zhu; Li Wang; Yong Fan; Jianing Xu

Conflicts of interest
There are no conflicts to declare.