An uncoordinated tertiary nitrogen based tricarboxylate calcium network with Lewis acid-base dual catalytic sites for cyanosilylation of aldehydes

Article abstract of DOI:10.1039/d0dt03747h

The design and utilization of dual sites for synergistic catalysts has been recognised as an efficient method towards high-efficiency catalysis in the cyanosilylation of aldehydes, which gives key intermediates for the synthesis of a number of valuable na

Full text of DOI:10.1039/d0dt03747h

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An uncoordinated tertiary nitrogen based
tricarboxylate calcium network with Lewis
acid–base dual catalytic sites for cyanosilylation
of aldehydes†
Cite this: Dalton Trans., 2021, 50,
1740
Ying-Xia Wang,‡ Hui-Min Wang,‡ Pan Meng, Dong-Xia Song, Juan-Juan Hou
and
Xian-Ming Zhang
*
The design and utilization of dual sites for synergistic catalysts has been recognised as an efficient method
towards high-efficiency catalysis in the cyanosilylation of aldehydes, which gives key intermediates for the
synthesis of a number of valuable natural and pharmaceutical compounds. However, most of the reported
dual-site catalysts for this reaction were homogeneous, accompanied by potential deactivation through
internal complexation of the dual sites. Herein, by the rational selection of an uncoordinated tertiary nitro-
gen based tricarboxylic ligand (tris[(4-carboxyl)-phenylduryl]amine, H3TCBPA), a new three-dimensional
calcium-based metal–organic framework (MOF), Ca3(TCBPA)2(DMA)2(H2O)2 (1, where TCBPA = ionized tris
[(4-carboxyl)-phenylduryl]amine and DMA = N,N-dimethylacetamide), possessing accessible dual catalytic
sites, Lewis-basic N and Lewis-acidic Ca, has been designed and constructed by a one-pot solvothermal
reaction. As expected, 1 is capable of dually and heterogeneously catalysing the cyanosilylation of aldehydes
at room temperature, and can be reused for at least 6 runs with a maximum turnover number (TON) of
1301, which is superior to most reported cases. Additionally, 1 shows CO2 adsorption ability and conversion
with epoxides, which is beneficial for the establishment of a sustainable society.
Received 31st October 2020,
Accepted 14th December 2020
DOI: 10.1039/d0dt03747h
rsc.li/dalton
reported for MOF-based catalysts: (1) functionalized ligands
with coordinatively unsaturated metal nodes; (2) incorporated
Introduction
Eco-friendliness and high efficiency are extensively pursued by active species with active sites on structures; (3) bimetallic
chemists in present-day synthetic organic chemistry.1 As a nodes. However, most of them were obtained through compli-
result, catalysts with simple operation, high atom efficiency cated post-synthetic modification (PSM), which may decrease
and pleasant catalytic yields are highly desirable.2–7 Multisite the pore volume of the initial structures or require detailed
catalysts, especially dual catalytic site catalysts, can stimulate confirmation characterization studies.21–23 Moreover, during
multi-step cascading reactions or improve the catalytic the catalytic process, the catalytic sites usually play their roles
efficiency with their synergistic effects, and thus have been in successive separate steps, restricting their applications to
one of the exclusively studied catalytic materials.8–18 Among some extent. Hence, an easy one-pot synthesis of an efficient
the mainly reported catalysts, MOF-based dual catalytic site MOF-based dual-site catalyst, where the two uniformly distrib-
catalysts have attracted the most considerable attention uted catalytic sites work simultaneously, is highly desirable.
because of their convenient modification, easy separation, and
Cyanosilylation of aldehydes is one of the powerful proto-
potential investigation for selectivity and mechanism.19,20 To cols for the formation of cyanohydrin silyl ethers, key inter-
date, three types of dual catalytic sites have been mainly mediates for high-value β-amino alcohols, α-hydroxy esters and
α-amino acids.24–27 Over the past decades, numerous homo-
geneous or heterogeneous catalysts, including Lewis acids,28–30
Lewis bases,31,32 ionic liquids33 and Lewis acid–base bifunc-
Key Laboratory of Magnetic Molecules and Magnetic Information Materials (Ministry
tional catalysts,34,35 have been extensively applied for the
of Education), Institute of Chemistry and Culture, School of Chemistry and Material
Science, Shanxi Normal University, Linfen 041004, China.
cyanosilylation of aldehydes. However, these catalytic systems
have some drawbacks: (i) homogeneous catalysts have high
E-mail: zhangxm@dns.sxnu.edu.cn; Tel: +86 0357 2051402
†Electronic supplementary information (ESI) available. CCDC 2024587. For ESI
efficiency but difficulty in recovery; (ii) heterogeneous catalysts
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
d0dt03747h
are easy to separate but present low catalytic efficiency; (iii)
Lewis acid–base bifunctional catalysts have superior behavior,
‡These authors contributed equally to this work.
1740 | Dalton Trans., 2021, 50, 1740–1745
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but may be diminished through spontaneous internal coordi- ordinated by six coordinated O atoms from four TCBPA and one
nation between flexible Lewis-basic phosphorus, sulfur or from DMA showing a monocapped distorted octahedral geome-
oxygen and Lewis-acidic metal. To properly address these try (Fig. 1b, left). Different from Ca(1), Ca(2) adopts an octa-
issues, we are encouraged to introduce cyanosilylation active hedral geometry, coordinated with six O atoms, in which the
Lewis acid and Lewis base catalysts into heterogeneous struc- equatorial plane comprised of four carboxylic O atoms and the
tures, where the catalytic ability could be maintained, easy axial positions were occupied by two water molecules (Fig. 1b,
recovery could be realized and potential complexation could right). Ca(2) is located at the center of symmetry, which con-
be limited.
nects two Ca(1) atoms by edge-sharing to form a linear tri-
Based on the background hereinbefore and taking the fol- nuclear unit (Ca3). Adjacent Ca3 units are linked by two carboxyl
lowing facts into consideration, H3TCBPA is a tridentate car- groups, resulting in a 1D zigzag chain (Fig. 1c). Furthermore,
boxylate ligand with a central tertiary Lewis-basic N,36,37
a
the 1D chains are extended by TCBPA, resulting in a 3D
potential Lewis base catalyst with steric hindrance for intra- network with two kinds of 1D channels along the a-axis
molecular coordination; calcium is an Earth-abundant (Fig. 1d). The window sizes of the channels are approximately
element with strong Lewis acidity,38,39 high affinity towards 9.15 × 16.22 Å2 and 7.43 × 16.51 Å2. Significantly, the Y-shaped
oxygen-based ligands40,41 and a homogeneous catalytic ability N atoms of TCBPA are exposed to the internal walls, which
for the cyanosilylation of aldehydes.42 In this work, H3TCBPA avoid coordination with the adjacent Ca atom and could act as
and Ca(OAc)2 were chosen as the building units for the con- potential Lewis-basic catalytic sites. Meanwhile, the catalytic
struction of
through a one-pot solvothermal reaction. As we expected, a coordinated DMA. Under the synergy of the above two effects, 1
stable porous Ca-based MOF formulated as could be used as an efficient dual Lewis acid–base catalyst as we
[Ca3(TCBPA)2(DMA)2(H2O)2] (1) with accessible Lewis-basic N expected in the cyanosilylation of aldehydes.
a heterogeneous dual catalytic site catalyst ability of Lewis-acidic Ca could be enhanced after removing the
and Lewis-acidic Ca was obtained and it could catalyze the cya-
The experimental powder X-ray diffraction (PXRD) pattern
nosilylation of aldehydes effectively at room temperature with (Fig. S3†) of 1 matched well with the simulated one, thus
a maximum TON of 1301, which is superior to most reported demonstrating the phase purity of the bulk sample and the
cases. To the best of our knowledge, 1 is the first alkaline- repeatability of the synthesis method. After immersing in
earth element-based MOF with dual catalytic sites for the toluene, DCM or acetone for more than 36 h (Fig. S3†), their
cyanosilylation of aldehydes. Additionally, 1 has the ability for crystalline structure was maintained well with excellent chemi-
CO2 adsorption and further 100% atom-economical cyclo- cal stability, which is essential for its use as a catalyst in organic
addition with epoxides.
synthesis. At the same time, 1 was thermostable (Fig. S4†) with
a weight loss in the range of from 100 to 400 °C attributed to
the gradual removal of free or coordinated solvent molecules
and the collapse temperature was up to 450 °C.
The porosity of 1 was evaluated by N2 adsorption–desorp-
tion isotherms at 77 K. Prior to measurement, fresh samples
were activated by solvent exchange with acetone for 4 days
(exchanged every 12 h) and heating at 120 °C under vacuum
for 12 h. The obtained results (Fig. S5†) showed that 1 exhibi-
Results and discussion
The solvothermal reaction of Ca(OAc)2 with H3TCBPA in DMA
and H2O at 120 °C for 96 h led to the formation of 1 as pale
yellow crystals. Single crystal X-ray diffraction revealed that 1
ˉ
crystallizes in the triclinic space group P1, which contains one
TCBPA, two Ca atoms, one coordinated DMA and one H2O
molecule in the asymmetric unit (Fig. 1a). Ca(1) was hepta-co-
ted
a Type-I isotherm with a maximum adsorption of
104.51 m3 g−1 and a calculated Langmuir surface area of
432.08 m2 g−1. According to the density functional theory
(DFT) pore distribution plot (Fig. S6†), 1 exhibited a micro-
porous structure with the main pore width being less than
1 nm, which was consistent with the single crystal data.
Additionally, 1 showed CO2 adsorption ability and the volu-
metric uptakes were 22.85 and 36.24 m3 g−1 at 298 K and
273 K, respectively (Fig. S7†).
To test our hypothesis, cyanosilylation of benzaldehyde
with (CH3)3SiCN was used as the model reaction to optimize
the reaction conditions. As shown in Fig. 2, when cyanosilyla-
tion took place in air with 1.2 equivalents of (CH3)3SiCN
(column A) in DCM at room temperature, only 20% of 1a was
obtained after 10 h. An inert atmosphere together with a
longer time (column B) could improve the yield to 83% but the
increment of 1 (column C) had a negligible influence on the
Fig. 1 (a) Asymmetric unit in 1. (b) Coordination geometries of Ca(1)
(left) and Ca(2) (right). (c) 1D zigzag chain of a Ca3 unit. (d) 3D network
of 1 along the a-axis.
reaction. When
2 equivalents of (CH3)3SiCN were used
(column D), the yield of 1a reached up to 100% only after 6 h,
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Table 1 Cyanosilylation of a variety of aldehydes catalyzed by 1a
Entry
1
Product
Yield/%
78
1a
2
3
4
5
6
7
8
1b
1c
1d
1e
1f
55
60
94
99
88
92
99
Fig. 2 Optimization of the reaction conditions. A: benzaldehyde
(1 mmol), (CH3)3SiCN (1.2 mmol), DCM (4 mL), 1 (5 mg), under an air
atmosphere, 10 h; B: the same as A, but under an Ar atmosphere, 12 h;
C: the same as B, but 10 mg of 1 was used; D: benzaldehyde (1 mmol),
(CH3)3SiCN (2 mmol), DCM (4 mL), 1 (5 mg), Ar, 6 h; E,: the same as D,
but stirred in toluene for 3 h. All of the yields were determined by 1H
NMR.
1g
1h
9
1i
1j
92
86
indicating that (CH3)3SiCN had a great influence on the reac-
tion outcome. The replacement of DCM with toluene (column
E) could give 1a in 86% yield after 3 h, but the larger initial
reaction rate (Fig. S8†) and easy handling of DCM prompted
us to choose DCM as the optimized solvent. Control experi-
ments in the absence of a catalyst, with Ca(OAc)2, H3TCBPA or
H3BTB (1,3,5-tris(4-carboxyphenyl)benzene), were carried out
(Table S3, entries 6–9 and Fig. S9†) to determine the exact cata-
lytic active sites. The high yields of 1a under the catalysis of Ca
(OAc)2 (99%) and H3TCBPA (50%), but low yields of 1a without
a catalyst or under the catalysis of H3BTB revealed that
10
11
12
1k
1l
55
24
13
14
1m
1n
99
99
15b
1a
85
both Lewis-acidic Ca and Lewis-basic
N contributed to
promoting the reaction, thus confirming the Lewis acid–base
dual-site catalytic ability of 1. Compared to the reported
Lewis acid MOF-based catalysts, such as Zn0.29-STU-2,43
[(Cu4O0.27Cl0.73)3(H0.5BTT)8] (BTT = 1,3,5-benzene tristetrazo-
late),44 [Cd2(NiL1)(CdL2)][Cd2(NiL1)(H2L2)]6DMF. 5MeOH (NiL1
= (R,R)-N,N′-bis(3-tertbutyl-5-(4-pyridyl) salicylidene)-1,2-diphe-
nyldiamine nickel(II), L2 = tetra-(4-carboxy-phenyl)porphyrin),45
a Reaction conditions: Aldehyde (1 mmol), (CH3)3SiCN (2 mmol), 1
(5 mg, 0.003 mmol), DCM (4 mL), under an Ar atmosphere, 3 h.
b Reaction conditions: Benzaldehyde (15 mmol), (CH3)3SiCN
(30 mmol), 1 (5 mg, 0.003 mmol), DCM (60 mL), under an Ar atmo-
sphere, 48 h.
Ce-MDIP1 (H4MDIP
=
methylenediisophthalic acid),46
BINAPDA-Zr-MOF30 and 1·Cd47 (Table S4†), dual Lewis acid– for the cyanosilylation of furfural (Table 1, entry 9), which may
base catalyst 1 showed a lower catalyst loading and a shorter poison the catalyst through coordination of the hetero O atom
reaction time at room temperature.
with active Ca, and afforded 1i with a satisfactory yield of 92%,
With the optimal conditions in hand, the general utility of further proving the existence of dual catalytic sites in 1. The
1 was then explored. As shown in Table 1, a variety of aromatic obtainment of 1j (Table 1, entry 10) with a yield of 86% indi-
aldehydes (Table 1, entries 1–8) bearing electron-donating or cated a negligible impediment in reaction activity due to the
electron-withdrawing groups could be converted successfully presence of an olefin functional group. The significantly
to their corresponding products under the catalysis of 1; decreased yields of 1k (Table 1, entry 11) and 1l (Table 1, entry
specifically, the yields of 1b–1h (Table 1, entries 2–8) were 12) suggested the bigger the substrates, the lower the catalytic
55%, 60%, 94%, 99%, 88%, 92% and 99%, respectively. activity.48 Additionally, the complete conversion of acet-
Further analysis indicated that the electron-withdrawing aldehyde and isobutyraldehyde to 1m (Table 1, entry 13) and
groups were beneficial for this conversion, as explained by the 1n (Table 1, entry 14) proved that 1 was also applicable for the
higher electropositive charge on the carbonyl group. Similar cyanosilylation of aliphatic aldehydes. Finally, for the calcu-
yields of 1g (Table 1, entry 7) and 1h (Table 1, entry 8) revealed lation of maximum TON, 1 was reduced to 0.02 mol%, which
slight steric hindrance effects. In addition, 1 was applicable gave 1a in a yield of 85% with a TON of 1301. All of these
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results demonstrated the broad applicability of 1 in the cyano- in this kind of reaction (Fig. S14†) and could be reused for
silylation of versatile aromatic and aliphatic aldehydes with more than 6 runs with high activity. The only operation
(CH3)3SiCN.
needed before each repeated run was to wash the recovered 1
The ability of 1 for CO2 adsorption and the urgency for the
New portions of reactants were added to the filtrate of the with fresh DCM (5 × 8 mL) and dry it in air.
finished reaction to verify the heterogeneity of 1. After further
stirring for
6
h, the yield of 1a remained unchanged solution of the greenhouse effect inspired us to test the cata-
(Fig. S10†), which confirmed that this reaction was hetero- lytic ability of 1 in the conversion of CO2 with epoxides.49 As
geneous and almost no homogeneous Ca2+ was leached into the attempts indicated, 1 accelerated the reaction only in the
the solution. ICP-OES (inductively coupled plasma optical presence of TBAB (tetrabutyl ammonium bromide), and an
emission spectroscopy) results showed that the leached Ca2+ acceptable yield (91%) of 2a was realized when the reaction
was less than 0.06% of the total Ca content in 1.
took place at 100 °C with a CO2 balloon for 8 h (Table 2,
To test our speculation that cyanosilylation occurred not entries 1–3), comparable to some of the reports from the
only on the surface but also in the channels of 1, we recorded literature50–52 (Table S6†). Higher yields of 2a under the con-
the FT-IR spectra (Fig. S11†) of 1 before and after overnight ditions of 2d and 2e (Table 2, entries 4 and 5) than 2b
immersion in a DCM solution of benzaldehyde or 1-naphth- (Table 2, entry 2) revealed that the main active site in 1 is Ca2+.
aldehyde. Meanwhile, the 1H NMR (Fig. S12†) data of the Under the optimized conditions, the yields of 2b (Table 2,
supernatant were obtained by removing 1 from the suspension entry 6) and 2c (Table 2, entry 7) were 78% and 91%, respect-
of DCM with the same molar ratio of benzaldehyde and ively. Considering the low boiling points of propylene oxide
1-naphthaldehyde. The appearance of the CvO stretching (Table 2, entry 8), 1,2-epoxybutane (Table 2, entry 9) and 1,2-
frequency of aldehyde at 1700 cm−1 for reacquired 1 and the epoxyhexane (Table 2, entry 11), their conversions were per-
higher concentration of 1-naphthaldehyde than benzaldehyde formed at room temperature or 55 °C, and the corresponding
in the solution suggested that free aldehydes were encapsu- yields of 2d, 2e and 2g were 28%, 18% and 24%, respectively,
lated in the channels of 1, meaning that the cyanosilylation which show the crucial role of temperature in this reaction.
also occurred in the channels of 1.
Based on the literature reports that either Lewis base or
Lewis acid can catalyze the cyanosilylation of aldehyde, along
with the coexistence of Lewis-basic N and Lewis-acidic Ca in 1,
Table 2 Conversion of CO2 with epoxides catalyzed by 1a
a dual activation mechanism for this reaction was tentatively
proposed (Fig. 3). In catalytic cycle A, the unsaturated Ca inter-
acted with the oxygen atoms of the aldehydes and polarized
the carbonyl groups first. Next, the nucleophilic cyanide was
allowed to react with the activated aldehyde carbonyl, Entry
Product
Temperature
Yield/%
affording the target product with the regeneration of 1. In cata-
1
2a
2a
100 °C
100 °C
91
30
2b
lytic cycle B, the electron-rich N in the ligand attacked the
vacant 3d orbitals of Si in the (CH3)3SiCN and formed a tight
ion pair intermediate with hypervalent pentacoordinated Si.
After the silyl cation coordination to the aldehyde O and
cyanide addition to the positive C, the target product was
obtained and 1 was released.
3c
4d
5e
6
2a
2a
2a
2b
100 °C
100 °C
100 °C
100 °C
0
81
50
78
The most attractive advantage of heterogeneous catalysis is
easy separation and the reusability of the catalyst. 1 was robust
7
2c
2d
2e
100 °C
r.t.
91
28
18
8
9f
r.t.
10f
11
2f
100 °C
55 °C
17
24
2g
a Reaction conditions: Epoxides (8.75 mmol), 1 (40 mg, 0.026 mmol),
1
TBAB (40 mg, 0.124 mmol), CO2 balloon, 8 h. Yields: based on
H
NMR. b Epoxides (8.75 mmol), TBAB (40 mg, 0.124 mmol), 8 h.
c Epoxides (8.75 mmol), 1 (40 mg, 0.026 mmol), 8 h. d Epoxides
(4.37 mmol), Ca(OAc)2 (6 mg, 0.039 mmol), TBAB (20 mg,
0.062 mmol),
0.039 mmol), TBAB (20 mg, 0.062 mmol), 8 h. f 24 h.
8
h. e Epoxides (4.37 mmol), H3TCBPA (24 mg,
Fig. 3 A plausible reaction mechanism.
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Additionally, the steric effect may also have a great influence (λ = 0.71073 Å). The structure was solved by direct methods and
on this reaction, as indicated by the low yield of 2f of 17% refined by full-matrix least-squares methods with SHELXTL. All
(Table 2, entry 10) even after stirring at 100 °C for 24 h. The non-hydrogen atoms were refined with anisotropic thermal
unchanged PXRD patterns of 1 after catalysis (Fig. S15†) con- parameters.
firmed that 1 is robust and has an acceptable tolerance in the
Typical procedure for cyanosilylation of aldehydes
conversion of CO2 with epoxides.
(CH3)3SiCN (2 mmol) was added to a mixture of aldehyde
(1 mmol) and activated 1 (5 mg, 0.003 mmol) in DCM (4 mL)
in a Schlenk tube under an Ar atmosphere. The resulting sus-
pension was stirred at room temperature for 3 h. Then 1 was
separated by filtration and the filtrate was evaporated to
dryness for 1H NMR to determine the yield of the corres-
ponding O-trimethylsilyl cyanohydrin.
Conclusions
We have designed and synthesized a Ca-based dual catalytic
site catalyst 1 using a one-pot strategy for the effective cyanosi-
lylation of aldehydes. Catalytic results illustrated that 1 was
heterogeneous and the catalytic process occurred both on the
surface and channels of 1. Meanwhile, 1 could be reused for at
least 6 runs without an obvious decrease in catalytic efficiency.
Additionally, 1 had the catalytic ability for the conversion of
CO2 with epoxides. We believe that our work will open an
avenue for the easy preparation of effective and recyclable cata-
lysts for cyanosilylation of aldehydes.
Experimental procedure for the calculation of maximum TON
(CH3)3SiCN (30 mmol) was added to the mixture of benz-
aldehyde (15 mmol) and activated 1 (5 mg, 0.003 mmol) in
DCM (60 mL) in a Schlenk bottle under an Ar atmosphere. The
resulting suspension was stirred at room temperature for 48 h.
Then 1 mL of the reaction mixture was taken out and dried for
1H NMR to determine the yield of 1a.
Experimental
Typical procedure for cycloaddition of CO2 with epoxides
General
Epoxide (8.75 mmol) was added to the Schlenk tube with
All reagents were purchased from Energy Chemical and used
without further purification. 1H NMR and 13C NMR spectra
were recorded using a Bruker Avance III DM 600 MHz system.
The IR spectra on KBr pellets were obtained using a Nicolet
iS50 spectrometer in the region of 4000–400 cm−1. PXRD pat-
terns were recorded using a Rigaku D/Max-2500 diffractometer
with a Cu target tube at 40 kV and 30 mA. Thermogravimetric
analysis (TGA) was performed using a Shanghai yinnuo 1000B
system under an N2 atmosphere at a heating rate of 10 °C
min−1. The N2 (77 K) and CO2 (298 K and 273 K) sorption iso-
therms were measured using an ASPS 2020 gas sorption analy-
zer. Scanning electron microscopy energy-dispersive X-ray
spectroscopy (SEM-EDS) analyses were conducted using a
JSM-7500F SEM equipped with an EDAX CDU leap detector.
ICP-OES analysis was performed using a PerkinElmer Optima
8000 Plasma Emission Spectrometer. GC analysis was per-
formed using an Agilent Technologies 7890B GC system.
activated
1 (40 mg, 0.026 mmol) and TBAB (40 mg,
0.124 mmol) under a CO2 atmosphere. The resulting suspen-
sion was stirred at 100 °C with a CO2 balloon for 8 h. Then,
1 was separated by filtration and the filtrate was used directly
for 1H NMR to determine the yield of the corresponding
carbonate.
Procedure for recycling cyanosilylation of benzaldehyde
The mixture of benzaldehyde (742 mg, 7 mmol) and activated
1 (35 mg, 0.023 mmol) was stirred in DCM (28 mL) at room
temperature under an Ar atmosphere. Then (CH3)3SiCN
(1.4 g, 14 mmol) was added and the suspension was stirred
for a further 12 h. After that, 1 was collected by centrifu-
gation, washed with fresh DCM (5 × 8 mL), and air-dried for
successive runs. The combined supernatant was evaporated
1
to dryness and redissolved in CDCl3 for H NMR analysis.
Preparation of 1
Conflicts of interest
Ca(OAc)2·H2O (12 mg, 0.076 mmol), H3TCBPA (9 mg,
0.015 mmol), dimethylacetamide (DMA, 0.6 mL) and H2O
(0.4 mL) were placed in a 20 mL Teflon-lined stainless steel
reactor and were heated at 120 °C in an oven for 4 days. After
cooling to room temperature, pale yellow plate crystals were
obtained in 73% yield based on the ligand. IR (KBr): 1658 (w),
1600 (s), 1520 (m), 1489 (w), 1405 (s), 1320 (m), 1278 (m), 1183
(m), 1109 (w), 1014 (w), 845 (m), 787 (s), 651 (w), 598 (w), 555 (w).
The authors declare no competing financial interests.
Acknowledgements
This work was supported by the “1331” Project of the Shanxi
Province, the Scientific and Technological Innovation
Programs of the Higher Education Institutions in Shanxi
(2019L0464), the Shanxi Province Science Foundation for
X-ray crystallography
Single crystals of 1 were used for intensity data collection Youths (201901D211391), and the Research Project Supported
using a Bruker SMARTAPEX CCD diffractometer at 298 (2) K by the Shanxi Scholarship Council of China (2020-088).
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27 M. K. Sharma, D. Singh, P. Mahawar, R. Yadav and
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