Controllable preparation of magnetic carbon nanocomposites by pyrolysis of organometallic precursors, similar molecular structure but very different morphology, composition and properties

Article abstract of DOI:10.1039/d0nj05699e

Four cobalt-containing organometallic compounds were synthesized for solid-state pyrolysis (SSP) to study the structure-property relationship between the precursors and the as-synthesized magnetic carbon nanocomposites (MCNs). In this research, the only s

Full text of DOI:10.1039/d0nj05699e

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Controllable preparation of magnetic carbon
nanocomposites by pyrolysis of organometallic
precursors, similar molecular structure but
Cite this: New J. Chem., 2021,
45, 2044
very different morphology, composition and
properties†
a
Zhijun Ruan,
Jingwen Ran,a Shanshan Liu,a Yanmei Chen,*a Xichao Wang,a
Jie Shi,*b Lihong Zhu,a Shengfang Zhaoa and Junqi Lin*a
Four cobalt-containing organometallic compounds were synthesized for solid-state pyrolysis (SSP) to
study the structure–property relationship between the precursors and the as-synthesized magnetic
carbon nanocomposites (MCNs). In this research, the only saturated carbon atom in MC was replaced by
a N, O or S atom, to produce precursors MN, MO and MS, respectively. It was found that the crystal
phase of cobalt generated upon pyrolysis is dependent on the kind of heteroatom introduced into the
precursor: fcc-Co for MC/MN, while the fcc/hcp-Co hybrid for MO/MS. Metal cobalt with different crystal
phases has its special catalytic and magnetic properties. Thus, MCNs with very different morphologies,
compositions and properties could be prepared by just altering one heteroatom in the precursors upon
SSP. Uniform nanotubes were generated from pyrolysis of MC/MN, while nanospheres were generated
from MO/MS. The obtained MCNs all show good magnetic properties with Ms ranging from 47.6 to
54.5 emu gꢀ1. Due to the magnetic difference between fcc-Co and hcp-Co, the Ms values of MCNs
obtained from MO/MS are slightly lower than those of MC/MN, but the Mr and Hc values of the former
are 2 to 5 times higher than those of the latter.
Received 23rd November 2020,
Accepted 23rd December 2020
DOI: 10.1039/d0nj05699e
rsc.li/njc
nanocomposites with different morphologies and compositions
have their specific properties and application fields.9 Recently,
Introduction
Carbon-based nanomaterials, including carbon nanotubes great achievements of Sahoo et al. demonstrated that pyrolysis of
(CNTs), graphene, carbon dots, fullerene, etc. have attracted cheaper and commercially available precursors is a very powerful
much attention due to their novel structure and unique and economical method to produce functional magnetic nano-
properties.1 Among them, magnetic carbon nanocomposites materials for a wide range of applications, such as optical limiting,
(MCNs) are important functional materials for a wide range of photodetection, magnetorheological and electromagnetic inter-
applications, such as catalysis,2 information storage,3 micro- ference shielding. Furthermore, the morphology, composition,
wave absorption,4 environmental treatment,5 and biomedical crystal phase and properties of the nanomaterials can be tuned
science.6 In MCNs, the magnetic nanoparticles well wrapped in by changing the synthesis parameters, i.e., reaction temperatures,
carbonaceous species can possess excellent stability, dispersibility heating rate, carbon source, concentration of precursors etc.10
and biocompatibility.7 Various approaches such as chemical vapor Despite the many fabrication methods, the controllable preparation
deposition, electric arc discharge, hydrothermal/solvothermal treat- of MCNs with a desired morphology and properties is still a
ment and the pyrolysis procedure have been successfully applied challenge. More importantly, the growth mechanism of these
for the fabrication of functional MCNs.8 And the prepared nanocomposites is still ambiguous.
Organometallic complexes including both metal and carbon
a Hubei Key Laboratory of Processing and Application of Catalytic Materials,
College of Chemistry and Chemical Engineering, Huanggang Normal University,
Huanggang 438000, China. E-mail: cingym@163.com, linjq19@126.com
b School of Food and Biological Engineering, Hefei University of Technology,
Hefei 230009, China. E-mail: shijie@hfut.edu.cn
sources are excellent raw materials for the preparation of
MCNs.11 The metal-containing moieties could be transformed
into metal nanoparticles under pyrolysis. Then, the generated
metal catalyst could catalyze the formation of carbon nano-
particles (CNPs).12 Meanwhile, the magnetic metal NPs formed
in the pyrolysis process could be well wrapped by the
† Electronic supplementary information (ESI) available: Experimental details and
spectral data. See DOI: 10.1039/d0nj05699e
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carbonaceous materials, which could hinder the oxidation and atom, MN, MO and MS were obtained, respectively. Scheme S1
agglomeration of metal NPs.13 Recently, Vollhardt and Mu¨llen (ESI†) illustrates the synthetic routes to the intermediates and
et al. demonstrated that solid-state pyrolysis (SSP) of organo- final products. Firstly, alkynyl-functionalized compounds 1–4
metallic complexes is promising for the preparation of MCNs.14 were synthesized by the palladium-catalyzed Sonogashira
In SSP, powders of organometallic precursors were sealed in coupling reaction. Then, organometallic compounds MC, MN,
quartz tubes under high vacuum. Placed in a furnace, the MO and MS were all prepared via the reaction between the
precursors underwent stepwise thermolysis without the need alkynyl-functionalized 1–4 and an excess of Co2(CO)8, affording
of feedstock gases, an inert atmosphere, extra catalysts, and [CCCo2(CO)6] moieties with satisfactory yield.16 All the com-
expensive equipment. Especially, the well-defined organo- pounds were well characterized by nuclear magnetic resonance
metallic compounds played a vital role in regulating the properties (NMR), elemental analysis (EA), mass spectroscopy, and Fourier
and structure of the corresponding CNPs formed in SSP.15 In the transform infrared (FTIR) spectroscopy, which well confirmed
process, the molecular structure of organic precursors could their explicit molecular structures (Fig. S7–S22, ESI†).
be subtly modified to control the morphology and properties of
Fig. 2 shows the IR spectra of 1, 2, MC and MN. The
the obtained CNPs. Thus, it is urgent to know more about stretching vibration of the CRC of 1 and 2 appears at about
the structure–property relationship between the organometallic 2210 cmꢀ1, which completely disappears in the spectra of MC
precursors and the pyrolysis products.
and MN. However, in the spectra of MC and MN, three strong
In the present work, four organometallic compounds (i.e., absorption bands appear in the range of 2010 to 2090 cmꢀ1
,
MC, MN, MO and MS) precise in the molecular structure were which are the typical absorptions of [CCCo2(CO)6], confirming
synthesized to study the structure–property relationship that alkynyl group has been completely reacted with
between the precursors and the as-synthesized MCNs as well Co2(CO)8.17 Meanwhile, due to the presence of the N–H bond
as the inherent mechanism. Surprisingly, just changing one in 2 and MN, they also show an absorption peak at about
heteroatom in the precursors could lead to a completely 3400 cmꢀ1. The IR spectra of the four organometallic com-
different morphology, composition and properties of the as- pounds and their intermediates are given in Fig. S1 (ESI†), and
1
synthesized MCNs (Fig. 1). After pyrolysis, the Co-containing similar results are obtained. Fig. 3 shows the H NMR and 13C
moieties in MC/MN were transformed into fcc-Co, but it was NMR spectra of 3 and MO. After the incorporation of the
converted to the fcc-Co/hcp-Co hybrid in MO/MS. Subsequently, [Co2(CO)6] unit, the 13C NMR spectra demonstrate an obvious
the morphology of the MCNs could be well controlled as signal shift for the carbons of the alkynyl group. The signals
nanotubes (for MC/MN) or nanospheres (for MO/MS) with assigned to CRC (Ca) shift from 89.4/89.9 to 91.9/92.3 ppm
adjustable sizes and magnetic properties. The experimental (Ca0). In addition, a strong singlet assigned to the carbonyl
results indicate that the heteroatom in the precursor could carbon (Cb) of [CCCo2(CO)6] appears at about 199.4 ppm.18
regulate the crystal phase of metal Co (possesses different Moreover, in both the 1H NMR and 13C NMR spectra, great
catalytic activities and magnetic properties), thereby controlling changes have also been observed in the aromatic areas close to
the morphology and magnetic properties of the resulting MCNs the [CCCo2(CO)6] unit.
upon SSP. The results confirm the power of the concept of
precursor-controlled pyrolysis towards defined MCNs, and
provide a possible route for the partially controllable preparation
of MCNs.
Thermal properties and pyrolysis process
In SSP, samples would generally undergo a program of stepwise
pyrolysis. The precursors were first heated to the decomposition
temperature of metal carbonyl groups and held at this
Results and discussion
Synthesis and characterization
MC was synthesized using fluorene as the basic unit. Then,
replacing the only saturated carbon atom in MC with a N, O or S
Fig. 1 Chemical structure of compounds MC, MN, MO and MS, and the as-
synthesized magnetic carbon nanocomposites with different morpholo-
gies, compositions and properties.
Fig. 2 IR spectra of compounds 1, 2 and organometallic precursors
MC, MN.
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the diameter size. The wall of the CNTs is comprised of ca. 40
graphene layers with d002 = 3.47 Å (Fig. 4f). As shown in Fig. 5b
and Fig. S3d (ESI†), the top of the CNT precisely demonstrates its
multilayer tubular structure.
Surprisingly, unlike the cases of MC and MN, as just chan-
ging one heteroatom in the precursors (from N to O or S), MCNs
totally different in the morphology are obtained from MO and
MS, both giving nanospheres with a Co@C core–shell structure.
For MO, the TEM and SEM images showed that the diameters of
the obtained nanospheres are mainly about 10–15 nm (Fig. 4g–i).
And Co NPs are well embedded in amorphous and graphitized
carbon with a thickness of 5–10 nm. As shown in Fig. 5c and
Fig. S4 (ESI†), the Co NPs embedded in graphitized carbon (d002
=
3.43 Å) display a clear lattice structure. The spacing between the
lattice planes is, respectively, 0.174 nm and 0.216 nm corres-
ponding to the (111) planes of face centered cubic (fcc) and (100)
planes of hexagonal-closed-packed (hcp) phases of cobalt.20 The
results illustrate the coexistence of the fcc (area circled by blue
dashed line, Fig. 5c) and the hcp (in green dashed line) structures.
Moreover, the fcc phase locating at the center was surrounded by
the hcp phase.
As to precursor MS, the TEM and SEM analysis showed that
the diameters of the nanospheres mainly range from 35 to
55 nm, and the Co NPs are well encapsulated in carbonaceous
materials (Fig. 4j–l). And the lattice fringes of Co could be
clearly observed in the HRTEM image (Fig. 4l). Interestingly, a
special phenomenon was observed in the case of precursor MS:
in addition to nanospheres (the main products), a few cobalt
core/carbon sheath nanocables with a diameter of about
200 nm and a length of 7 mm are obtained (Fig. 5d and Fig.
S5, ESI†). The TEM-EDX technique was applied to analyze the
element distribution of the nanocable (Fig. 5e). When the
electron beam passed through the core (label 1–1 in Fig. 5d)
and the sheath (label 1–2) of the nanocable, Co and C are the
main elements detected (Cu was from the copper grid), con-
firming its cobalt core/carbon sheath architecture.
Fig. 3 1H NMR and 13C NMR spectra of 3 and MO (in CDCl3), the solvent
peaks are marked with asterisks.
temperature for several hours to ensure complete decomposition
of the cobalt complexes before further heating at a higher
temperature for a longer period. We investigated the thermal
properties of the organometallic compounds (MC–MS) by TGA.
The temperatures (Td) for thermal decomposition of the com-
pounds were about 170 1C (corresponding to a weight loss of 5%)
(Fig. S2, ESI†). Thus, the pyrolysis procedure was as follows:
powder of an organometallic compound was vacuum sealed in a
quartz tube, and then placed in a furnace. The other three
compounds were handled similarly, and all four underwent
the same heating program in one furnace at the same time.
The samples were first slowly heated to 170 1C at a rate of 1.9 1C
minꢀ1 and held for two hours. Then they were heated to 700 1C
at a rate of 5.2 1C minꢀ1 and held for eight hours. After natural
cooling to room temperature, the produced products were well
characterized by powder X-ray diffraction (XRD), transmission
electron microscopy (TEM), scanning electron microscopy
(SEM), vibrating sample magnetometry (VSM), and energy-
dispersive spectroscopy (EDX).
It is interesting to find out how the change of just one atom
could lead to the formation of MCNs that have a completely
different morphology. Generally, fcc and hcp are the two main
Morphological characterization of the MCNs
As discussed above, the precursor-controlled pyrolysis method crystalline structures of metallic cobalt. Among them, the
is an effective way to produce defined CNPs. Following the same hcp-Co is stable at room temperature, while the fcc-Co is a
pyrolysis procedure, the prepared organometallic precursors metastable phase formed at temperature above 450 1C.21 In
could be well converted to two completely different types of pyrolysis, cobalt mainly existed in the fcc phase at high
MCNs, viz. nanotubes and nanospheres, with high yield. Upon temperature, especially for the production of CNTs.22 Despite
SSP, MC and MN produced multiwalled CNTs (Fig. 4a–f). TEM cobalt being a common catalyst for the synthesis of CNTs, and
analysis showed that the average inner and outer diameters of the that its morphology, density and size effect extensively
CNTs are about 20 and 40 nm for MC, respectively (Fig. 4b), and studied,23 the impact of the crystal phase on catalytic perfor-
the length of these CNTs is 410 mm. From the high-resolution mance was rarely considered, mainly because of the absence of
TEM (HRTEM) images, the nanotubes are well graphitized, made the hcp phase during pyrolysis. Although hcp-Co could exist
up of B25 layers, and the space between the layers is 3.51 Å under specific conditions in pyrolysis, the main pyrolysis
(Fig. 4c and Fig. S3a, ESI†), consistent with the range reported for products were carbon-encapsulated cobalt NPs.10g,24 The result
the interplanar spacings of graphite (d002 = 0.34–0.39 Å).19 As for imply that fcc-Co is a phase catalytically active for the fabrication
the CNTs produced from MN, they are with length o1 mm, and of CNTs, while hcp-Co is conducive to the generation of carbon-
with inner and outer diameters of about 30 nm and 60 nm, encapsulated cobalt NPs.
respectively (Fig. 4d and e). Compared with the CNTs obtained
Importantly, in classic cobalt-catalyzed Fischer–Tropsch
from MC, there is a reduction of the length and enlargement of reactions, it was demonstrated that hcp-Co has higher catalytic
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Fig. 4 SEM (a, d, g and j), TEM (b, e, h and k) and HRTEM (c, f, i and l) images of the materials obtained through pyrolysis of MC (a–c), MN (d–f), MO (g–i)
and MS (j–l).
activity than fcc-Co.25 This is mainly due to the special surface composites), rather than nucleation and growth of CNTs. In
structure of the hcp crystal phase, which has higher intrinsic contrast, the moderate catalytic activity of fcc-Co favors the
activity and density of active sites. So it is more beneficial to the gradual nucleation and growth of CNTs.
decomposition, diffusion and recombination of carbon sources
On the other hand, according to previous reports, stacking
on its surface.26 Likewise, during catalytic pyrolysis, hydro- fault is an important aspect for the production of hcp-Co. Thus,
carbons were adsorbed and underwent decomposition on the the presence of oxygen or sulfur in precursors perhaps could
metal catalyst, and then the carbon species diffused and restruc- reduce the activation energy for the formation of stacking
tured to carbon NPs.27 In the present work, based on the faults, thus facilitating the formation of the hcp-phase at high
experimental results and inspired by the above information, it temperature.10g,24 Overall, in this work, for the first time, we
is envisioned that there is fast diffusion and deposition of the found that a heteroatom (even just changing one atom) in the
carbon source on hcp-Co, leading to complete encapsulation of organometallic precursors could regulate the crystal phase of
cobalt NPs by carbon (i.e., formation of cobalt core–carbon shell metal Co, thereby controlling the morphology and properties of
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Fig. 5 HRTEM images of the materials obtained through pyrolysis of MC (a) and MN (b) and MO (c). TEM images of the cobalt core/carbon sheath
nanocable obtained through pyrolysis of MS (d), and its corresponding TEM-EDX spectra (e).
the resulting MCNs upon SSP, providing an effective approach the (111), (200) and (220) planes of the fcc-Co.28 Due to the
to prepare MCNs controllably.
presence of the broad signal of the amorphous matrix and
impurities covering on the as-synthesized CNTs, the peak at
about 261 corresponding to the (002) planes of graphite struc-
ture is weak.29 In agreement with the HRTEM results, fcc and
hcp phases coexist in MO-S and MS-S, because in addition to the
peaks of the fcc phase, there are peaks at 41.61 and 47.51 that
correspond to the (100) and (101) planes of the hcp phase
observed over the two samples.30 Meanwhile, in comparison
with those of MO-S, the intensity of the diffraction peaks for the
hcp phase in MS-S became much narrower and sharper, indi-
cating an improvement in crystallinity and enlargement of the
cobalt size.31 XRD results showed that cobalt mainly exists in
elemental Co without forming a complex with the heteroatom.
Actually, heteroatoms in the organometallic precursors are
almost not present in the pyrolysis products due to their low
content and easy conversion into gaseous substances at high
temperatures.15,22 According to the results of SEM-EDX analy-
sis, except the presence of a small amount of sulfur in MS-S, the
main compositions of all the MCNs are Co and C elements, and
the cobalt contents are around 30% (Fig. S6, ESI†).
Composition of the MCNs
Powder XRD was used to further study the crystal phase of the
produced MCNs (Fig. 6). To differentiate the pyrolysis products
from their organometallic precursors, the MCNs obtained from
MC, MN, MO and MS are hereinafter named as MC-S, MN-S, MO-S
and MS-S, respectively. MC-S and MN-S exhibited Bragg reflec-
tions at 2y of 44.3, 51.6 and 75.91, which could be assigned to
Magnetism of the MCNs
All the Co enriched carbon nanocomposites are magnetizable
and could be attracted to a magnet at room temperature
quickly. Thus, to study the magnetism of the obtained MCNs,
especially highlight the impact of hcp-Co on the magnetic
anisotropy, VSM was utilized to quantitatively investigate their
Fig. 6 XRD diffractograms of MC-S, MN-S, MO-S and MS-S.
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heteroatom into the precursor molecule, leading to MCNs that
are different in the morphology, composition, and magnetic
properties upon SSP. Using such an approach, uniform nano-
tubes and nanospheres with an adjustable size and magnetic
properties could be efficiently fabricated with high selectivity.
The obtained MCNs all show good and differentiated magnetic
properties, their magnetic properties display a good accordance
with their structure, and they could be promising candidates
for practical magnetic and catalytic applications. Thus, the
results demonstrate the power and workability of precursor-
controlled SSP, and could provide useful information for the
partially controllable preparation of MCNs.
Experimental
Materials and instrumentation
Fig. 7 Plots of magnetization (M) versus applied magnetic field (H) at
300 K for MC-S, MN-S, MO-S and MS-S. Inset is the enlarged portion of the
M–H plot close to the origin.
Compounds 1–4 were synthesized according to the literature.33
Octacarbonyldicobalt (Co2(CO)8) was purchased from Alfa
Aesar. Dichloromethane (DCM) was dried over and distilled
from calcium hydride. Tetrahydrofuran (THF) was dried over
and distilled from the K–Na alloy under an atmosphere of dry
nitrogen. All other reagents were purchased from commercial
suppliers and used as received without further purification.
1H NMR and 13C NMR spectroscopy studies were conducted
with a Varian Mercury-300 spectrometer and Bruker Avance-400
NMR spectrometer using tetramethylsilane (TMS; d = 0 ppm) as
the internal standard. MS spectra were acquired with a ZAB 3F-
HF mass spectrometer. The Fourier transform infrared (FTIR)
spectra were recorded on a Nicolet NEXUS-6700 FTIR spectro-
photometer in the region of 400–4000 cmꢀ1. Elemental analyses
of hydrogen, carbon and nitrogen were performed over a
CARLOERBA-1106 micro-elemental analyzer. Thermogravi-
metric analysis (TGA) was performed on a SQT Q600 TA thermal
analyzer at a heating rate of 10 1C minꢀ1 in N2 with a flow rate
of 20 cm3 minꢀ1. The X-ray diffraction (XRD) analyses were
performed on a SHIMADZU XRD-6100 diffractometer with
CuKa radiation (l = 1.5418 Å). Scanning electron microscopy
(SEM) was conducted with a ZEISS-SIGMA scanning electron
microscope. Transmission electron microscopy (TEM) was
measured with JEM-2010HT and JEM-2010FEF microscopes at
an accelerating voltage of 200 kV. TEM samples were prepared
by drying a droplet of the suspension on a TEM copper
micrograte mounted with a carbon film. Energy-dispersive X-
ray spectra (EDX) were recorded using the TEM or SEM.
Magnetization curves were recorded on a physical property
measurement system (PPMS-9T) with the vibrating sample
magnetometer (VSM) option at 300 K.
Table 1 Magnetization data for various samples measured at 300 K
Sample
Ms (emu gꢀ1
)
Mr (emu gꢀ1
)
Mr/Ms
Hc (Oe)
MC-S
MN-S
MO-S
MS-S
54.5
51.7
50.6
47.6
6.8
5.9
12.6
14.2
0.12
0.11
0.25
0.30
150
190
760
610
magnetic properties at 300 K. Fig. 7 shows the magnetization
curves of the MCNs, all the samples exhibited a soft ferromag-
netic behavior with high magnetizability. The magnetization
rapidly increased with an increase in the strength of the applied
field before 5 kOe, with relatively low magnetic remanence (Mr)
and coercivity (Hc). The magnetization data are summarized in
Table 1. With saturation magnetization (Ms) ranging from 47.6
to 54.5 emu gꢀ1, the produced MCNs are endowed with good
magnetic properties. Analyzing carefully, the Ms values of MO-S/
MS-S are slightly lower than those of MC-S/MN-S, but, their Mr
and Hc values were 2 to 5 times higher than those of the latter.
The Ms and Hc values of MC-S/MN-S are 6.8/5.9 emu gꢀ1 and
150/190 Oe, respectively. However, as to MO-S/MS-S, these
values significantly increased to 12.6/14.2 emu gꢀ1 and 760/
610 Oe, respectively. Considering the presence of hcp-Co in MO-
S and MS-S, those results are understandable: compared with
fcc-Co, hcp-Co has a slightly lower Ms value but much stronger
Mr and Hc values.32 Therefore, the hcp-Co generated in MO-S
and MS-S leads to the unique magnetism across the
prepared MCNs.
Conclusions
Synthesis of the organometallic compounds
Through rational molecular design, four organometallic pre- General method for the synthesis of organometallic compounds
cursors were synthesized for solid-state pyrolysis (SSP) to study MC, MN, MO and MS: Co2(CO)8 (6.0 equiv.) and compound 1, 2, 3
the structure–property relationship between the precursors and or 4 (1.0 equiv.) were dissolved in dry THF under a nitrogen
the as-synthesized MCNs. It was found that the crystal phase of atmosphere. The mixture was stirred overnight at 25 1C and then
the cobalt catalyst could be regulated by the introduction of a the solvent was removed under vacuum. The residue was
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purified by column chromatography on neutral Al2O3 using Hubei Province (2017CFB223), and Research Foundation of
petroleum ether–DCM mixture as an eluent. Huanggang Normal University (201721703 and 201721903) for
Compound MC: black solid was obtained in 68% yield. financial support. The authors thank Prof. C. T. Au for helpful
1H NMR (300 MHz, CDCl3) d (ppm): 7.78 (m, 4H, ArH), 7.65 suggestions.
(m, 6H, ArH), 7.39 (m, 6H, ArH), and 3.98 (s, 2H, –CH2–). 13C
NMR (100 MHz, CDCl3) d (ppm): 199.5, 144.5, 141.4, 138.6,
137.3, 129.4, 129.2, 128.7, 128.1, 125.8, 120.6, 92.5, 92.4, and
Notes and references
36.9. FTIR (thin film), n (cmꢀ1): 2016.2, 2052.4, and 2088.6
(Co2(CO)6). Anal. calcd for C41H18Co4O12: C 52.48, H 1.93;
found: C 52.93, H 2.11.
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Compound MN: black solid was obtained in 80% yield.
1H NMR (300 MHz, CDCl3) d (ppm): 8.32 (br, 3H, ArH), 7.64
(br, 6H, ArH), and 7.39 (br, 8H, ArH). 13C NMR (100 MHz,
CDCl3) d (ppm): 199.6, 139.8, 138.9, 129.8, 129.4, 129.1, 128.3,
127.9, 123.6, 121.2, 93.5, and 92.3. FTIR (thin film), n (cmꢀ1):
2018.0, 2050.6, 2088.6 (Co2(CO)6), and 3409.5 (N–H). Anal. calcd
for C40H17Co4NO12: C 51.15, H 1.82, and N 1.49; found: C 52.03,
H 1.74, and N 1.57.
Compound MO: black solid was obtained in 76% yield.
1H NMR (300 MHz, CDCl3) d (ppm): 8.15 (s, 2H, ArH), 7.54 (d,
J = 8.4 Hz, 2H, ArH), 7.63 (m, 6H, ArH), and 7.38 (m, 6H, ArH).
13C NMR (100 MHz, CDCl3) d (ppm): 199.6, 156.6, 138.5, 133.6,
129.5, 129.4, 129.2, 128.2, 124.6, 121.1, 92.3, and 91.9. FTIR
(thin film), n (cmꢀ1): 2019.8, 2051.1, and 2089.5 (Co2(CO)6).
Anal. calcd for C40H16Co4O13: C 51.09, H 1.72; found: C 51.69,
H 1.61.
Compound MS: black solid was obtained in 65% yield.
1H NMR (300 MHz, CDCl3) d (ppm): 8.36 (s, 2H, ArH), 7.85 (d,
J = 8.1 Hz, 2H, ArH), 7.65 (m, 6H, ArH), and 7.36 (m, 6H, ArH).
13C NMR (75 MHz, CDCl3) d (ppm): 199.4, 139.8, 138.5, 136.0,
135.5, 129.3, 128.7, 128.2, 128.0, 123.6, 122.6, 92.5, and 91.8.
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n
(cmꢀ1): 2019.6, 2051.5, and 2088.5
(Co2(CO)6). Anal. calcd for C40H16Co4O12S: C 50.24, H 1.69;
found: C 50.86, H 1.51.
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Z. R. contributed in conceptualization, formal analysis, writing –
original draft, and writing – review & editing. J. R. contributed in
formal analysis. S. L. contributed in formal analysis and
resources. Y. C.: contributed in funding acquisition and super-
vision. X. W. contributed in formal analysis. J. S. contributed in
conceptualization, investigation, and writing – review & editing.
L. Z. contributed in formal analysis. S. Z. contributed in formal
analysis and resources. J. L.: contributed in conceptualization and
project administration.
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Acknowledgements
We are grateful to the National Natural Science Foundation of
China (21704032 and 21501061), Natural Science Foundation of
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