Reaction of three cyclic thioester ligands with triiron dodecacarbonyl and possible reaction mechanisms

Article abstract of DOI:10.1007/s12039-017-1372-5

Abstract : Three cyclic thioesters of the formula “-SCH2CH2SCO(CH2)n-” (L₁, n = 0 ? L₂, = 1 , L₃, n = 2) and their reactions with Fe ₃(CO) ₁₂ are reported. All the reactions produced a known diiron complex, [Fe ₂(μ - S ₂C ₂H ₄) (CO) ₆] (1), which suggested that in the reactions, cleavage of C-S bond to generate “SCH ₂CH ₂S ” fragment is a common pathway for all the three ligands. In the case of ligand L₂, a new complex 2, [Fe ₂{ μ - SC ₂H ₄(SCH ₂) - κ } (CO) ₆] was isolated and structurally characterized. In the reaction of ligand L₃, an unknown iron carbonyl product was isolated in addition to complex 1. Although its precise structure was not established due to its instability and low yield, its infrared spectrum and decomposing into complex 1 implied that the product may be a cluster with higher nuclearity. The experimental observations suggested that with the increase of the ring size of the cyclic thioester ligands, further bond cleavages were involved in the reaction in addition to that leading to complex 1. GRAPHICAL ABSTRACT: SYNOPSIS Reaction of cyclic thioester ligands with triiron dodecacarbonyl leads to scission of C-S (C) bond which is initiated by the coordination of the S atom to the Fe atom. The larger the ring size of the ligand, the more diverse are the bond cleavages. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-017-1372-5

J. Chem. Sci.
© Indian Academy of Sciences
DOI 10.1007/s12039-017-1372-5
REGULAR ARTICLE
Reaction of three cyclic thioester ligands with triiron
dodecacarbonyl and possible reaction mechanisms
ZHIYIN XIAOa,∗ , YONGLI WANGb, XUEYUAN CHENa, JIAO LONGa and ZHENHONG WEIb
aCollege of Biological, Chemical Sciences and Engineering, Jiaxing University, Jiaxing 314001, China
bDepartment of Chemistry, Nanchang University, Nanchang 330031, China
E-mail: zhiyin.xiao@mail.zjxu.edu.cn
MS received 29 May 2017; revised 28 August 2017; accepted 30 August 2017
Abstract. Three cyclic thioesters of the formula “−SCH2CH2SCO(CH2)n−” (L1, n = 0; L2, = 1, L3, n = 2)
and their reactions with Fe3(CO)12 are reported. All the reactions produced a known diiron complex,
[Fe2(μ-S2C2H4)(CO)6] (1), which suggested that in the reactions, cleavage of C-S bond to generate
“SCH2CH2S” fragment is a common pathway for all the three ligands. In the case of ligand L2, a new complex
κ
2, [Fe2{μ-SC2H4(SCH2)- }(CO)6] was isolated and structurally characterized. In the reaction of ligand L3, an
unknown iron carbonyl product was isolated in addition to complex 1. Although its precise structure was not
established due to its instability and low yield, its infrared spectrum and decomposing into complex 1 implied
that the product may be a cluster with higher nuclearity. The experimental observations suggested that with the
increase of the ring size of the cyclic thioester ligands, further bond cleavages were involved in the reaction in
addition to that leading to complex 1.
Keywords. Iron-sulfur carbonyl complexes; cyclic thioesters; C-S bond cleavage; reaction mechanism.
1. Introduction
could have much more complicated reactions. Break-
ing bonds of the ligands and thus forming new ones
are often encountered.14–22 The latter type of reactions
offers often novel iron-carbonyl complexes.
Diiron carbonyl complexes are a category of classic
organo-iron compounds. Their preparation and further
investigations in reactivity, for example, with nucle-
ophiles, proton, and electron transfer gained fresh atten-
tion in the past decade because of their structural resem-
blance to the diiron subunit of [FeFe]-hydrogenase, a
metalloenzyme with high efficiency and fast reaction
rate in catalyzing both hydrogen evolution and oxida-
tion.1–8 In the research, Fe3(CO)12 has been the main
precursor to synthesize complexes possessing a core of
“Fe2(CO)6−x” (x = 1, 2).9 This triiron precursor reacts
with a variety of ligands of donor atoms S, N, P and C.
Depending on the nature of a ligand employed, reaction
products can be very diverse. In most cases, not all the
productsareisolable. Complexesofdiironcoreareprob-
ably the most common products10–13 and tetrairon or
clusters with higher nuclearity are also not uncommon.
Simple thiolates or bidentate dithiolate lead mostly to
diiron complexes. But ligands with mixed donor atoms
In this study, we report the synthesis of three
cyclic thioester ligands, L1−3 and their reactions with
Fe3(CO)12. All the reactions involved ring-opening
to generate 1,2-ethanedithiolate which was present
in the commonly isolated diiron hexacarbonyl com-
plex, [Fe2(μ-S2C2H4)(CO)6] (1).23,24 In addition to this
known complex, other complexes could also be isolated
depending on the ring-size of the ligands. NMR, infrared
spectroscopies and X-ray single crystal diffraction anal-
ysis were used to identify some of the isolated products.
Possible reaction mechanisms of the cyclic thioester lig-
ands with triiron dodecacarbonyl are proposed.
2. Experimental
2.1 General procedures
All the reactions were carried out under an argon atmosphere
using standard Schlenk techniques. All the solvents were
*
For correspondence
Electronic supplementary material: The online version of this article (doi:10.1007/s12039-017-1372-5) contains supplementary material,
which is available to authorized users.

Zhiyin Xiao et al.
appropriately dried prior to use. The precursor Fe3(CO)12 was anhydrous MgSO4. A pale yellow oily liquid was obtained
prepared using the literature procedure.25 1,3-dithiolane-2- after the evaporation of the solvents.
thione,26 1,3-dithiolan-2-one(L1),27 1,4-dithian-2-one(L2)28
Ligand L1: Yield: 78% (0.39 g). IR (DCM, cm−1):
,
ν
C=O
and 1,4-dithiepan-5-one (L3)29 were synthesized following 1673. 1H NMR ( , ppm in CDCl , 298 K): 3.67 (d, J = 1.8
δ
3
literature methods with slight modifications. 1,2-ethaneditiol Hz, 4H, 2CH2).
was purchased from Alfa Aesar. All operations were manip-
ulated in a fumehood because of the obnoxious odor of
1,2-ethanedithiol. Infraredspectrawererecordedusingasolu- 2.3c 1,4-dithian-2-one (L2) and 1,4-dithiepan-5-one
tion cell with a spacer of 0.1 mm for CH2Cl2 solution on (L3): A solution of 1,2-ethanedithiol (0.5 mL, 6 mmol) and
Scimitar 2000 (Varian). NMR spectral data were collected triethylamine (1.68 mL, 12 mmol) in dichloromethane (80
on Bruker Advance 400/600 MHz or Varian MR-400 with mL) was cooled down to −78 ◦C with an ice–acetone bath
tetramethylsilane as internal standard. Elemental analysis was under Ar. To the pre-cooled mixture was dropwise added a
performed by the Center of analysis and testing at Nanchang solution of 3-chloroacetyl chloride (0.48 mL, 6 mmol) in
University (Vario EL III elemental analyzer).
dichloromethane (40 mL) over 1.5 h. After the addition, a
white precipitate of triethylamine hydrochloride formed. The
reaction mixture was left for stirring at room temperature for
further 2 h. The precipitate was filtered off and the filtrate
was washed with water (3 × 75 mL) and dried over MgSO4.
Removal of the solvent under reduced pressure gave a clear
liquid.
2.2 Crystallographic data collection and structure
determination
InthedatacollectionforX-raysinglecrystaldiffractionanaly-
sis of complex 2, standard procedures were used for mounting
the crystals on a Bruker Smart System CCD at 293(2) K. The
crystals were routinely coated with paraffin oil before being
LigandL2:Yield:60%(0.48g). MicroanalysisforC4H6OS2
(FW = 134.21), calc. (%): C, 35.80; H, 4.51; found (%): C,
ν
35.99, H, 4.32. IR (DCM, cm−1):
, 1674. 1H NMR ( ,
δ
C=O
α
mounted. Intensity data were collected using Mo-K radia-
ppm in CDCl3, 298 K): 3.45 (s, 2H, COCH2), 3.41 (t, J = 4
Hz, 2H, COSCH2), 3.13 (t, J = 4 Hz, 2H, CH2). 13C NMR
( , ppm in CDCl , 298 K): 196.8 (C = O), 35.6 (CH ), 31.4
´
˚
ϕ
ω
tion ( = 0.71073 A) at 293 K using – and –scan mode.
λ
The SAINT and SADABS programs in the APPEX 2 software
package were used for integration and absorption correction.
The structure of complex 2 was solved by direct method using
SHELXS-97 program and refined on F2 with XSHELL6.3.1,
all non-hydrogen atoms being modelled anisotropically.
δ
3
2
(CH2), 26.0 (CH2).
Ligand L3 was analogously prepared by using 3-
chloropropanoyl chloride (0.50 mL, 6 mmol) to replace 3-
chloroacetylchloride. Theligandwasisolatedasawhitesolid.
Ligand L3: Yield: 34% (0.59 g). Microanalysis for
C5H8OS2 (FW = 148.24), calc. (%): C, 40.51; H, 5.44; found
2.3 Synthesis
1
(%): C, 40.06, H, 5.31. IR (DCM, cm−1): C=O, 1671. H
ν
NMR ( , ppm in CDCl , 298 K): 3.58 (m, J = 3.15 Hz,
2.3a Preparation of 1,3-dithiolane-2-thione: A mix-
tureof CS2 (10mL, 0.166mol) andNaOHsolution(5 gNaOH
in 10 mL H2O) were vigorously stirred at room temperature.
A deep red oily liquid started to form at the interface when
n-Bu4NBr (0.2 g, 0.6 mmol) was added. After being stirred
for 10 min, 1,2-dibromoethane (1 mL, 0.012 mol) was intro-
duced in dropwise fashion. The color of the mixture turned
slowly to yellow. A minimum amount of dichloromethane
and H2O were added after reaction for 24 h. The combined
organic phase was extracted with dichloromethane (3 × 15
mL) and dried over anhydrous MgSO4. Removal of the sol-
vents yielded a green-yellow oil product.
δ
3
2H, COCH2), 3.08 (s, 2H, C2 H2), 2.76 (q, J = 4.8 Hz, 2H,
COSCH2), 2.13(m, J =6.6Hz, 2H, C7 H2). 13CNMR( , ppm
δ
in CDCl3, 298 K): 197.5 (C=O), 43.8 (CH2), 40.8 (CH2),
28.7 (CH2), 27.9 (CH2).
2.3d Reaction of ligands L1−3 with Fe3(CO)12
Ligand L1: To a reaction flask containing THF (20 mL)
were added L1 (72 mg, 0.6 mmol) and Fe3(CO)12 (303 mg,
0.6 mmol) under Ar. The reaction was heated to reflux for 2 h
and the color of the reaction mixture turned from dark-green
to brownish red. The reaction was cooled before being con-
centrated for purification using flash chromatography (eluent:
ethyl acetate/petroleum ether = 1/8). The product (complex 1)
was isolated as brownish red solid.
Yield: 70% (0.6 g). Microanalysis for C3H4S3 (FW =
136.25), calc. (%): C, 26.45; H, 2.96; found (%): C, 27.03,
ν
H, 2.82. IR (DCM, cm−1):
, 1074. 1H NMR ( , ppm in
δ
C=S
CDCl3, 298 K): 3.97 (s, 4H, 2CH2). 13C NMR ( , ppm in
Complex 1: Yield: 37% (0.080 g). IR (DCM, cm−1):
,
δ
ν
C=O
CDCl3, 298 K): 228.9 (C=S), 43.9 (CH2).
2076, 2036, 2000, 1995. 1H NMR ( , ppm in CDCl , 298 K):
δ
3
2.37 (s, 4H, 2SCH2). 13C NMR ( , ppm in CDCl , 298 K):
δ
3
2.3b 1,3-dithiolan-2-one (L1): 1,3-dithiolane-2-thione 208.4 (CO), 36.4 (SCH2).
(0.5 g, 3.68 mmol) and Hg(OAc)2 (3.17 g, 9.2 mmol) were
Ligand L2: A solution of L2 (80 mg, 0.6 mmol) and
mixed in CHCl3 / AcOH (3:1, 20 mL) under Ar. The mixture Fe3(CO)12 (303 mg, 0.6 mmol) was dissolved in tetrahydro-
was stirred at room temperature over night. A white precip- furan (THF, 20 mL) under Ar. The mixture was heated under
itate formed in the reaction was filtered off. The filtrate was stirringat65◦Cfor2h. Whenthecolorturnedfromdarkgreen
extracted with NaHCO3 solution (3 × 200 mL) and dried over tored-brown, thesolventwasevaporatedtogivecrudeproduct

Reaction of three cyclic thioester ligands
Scheme 1. Syntheses of ligands L1−3.
which was purified by column chromatography on silica gel under reflux resulted in the formation of complex 1,
with an eluent of a volume mixture of ethyl acetate/petroleum
[Fe2(μ-S2C2H4)(CO)6], a widely reported diiron com-
plex23,24 (Scheme 2). For ligand L1, this complex was
the solely isolable product. But for the other lig-
ands, additional complexes were isolated, Scheme 2.
In the case of ligand L2, a diiron complex (2) was
isolated in good yield (38%). In this complex, the
bridging moiety is associated with a thioether thiol,
2-(methylthio)ethanethiol. The thiolate bridged to the
two iron atoms in μ-manner, as found in many other
diiron complexes, whereas the thioether S and the car-
bene carbon equivalent to deprotonated form (SCH2) of
ether (1/8). Two products, [Fe2(μ-S2C2H4)(CO)6] (1) and
2
κ
[Fe2(μ , -S, C-SC2H4SCH2)(CO)6] (2) were successively
isolated. Recrystallization of complex 2 from a mixed sol-
vent of dichloromethane and hexanes (1/3) afforded yellow
crystals suitable for X-ray single crystal diffraction analysis.
Complex 1: Yield: 16% (0.035 g). Complex 2: Yield: 38%
(0.087 g). Microanalysis for Fe2C9H6S2O6 (FW = 385.8),
calc. (%): C, 28.01, H, 1.57; found (%): C, 28.01, H, 1.25. IR
ν
(DCM, cm−1):
, 2066, 2022, 1994, 1981. 1H NMR ( ,
δ
C=O
ppm in CDCl3, 298 K): 3.5−3.6 (m, 1H, C8 HaHb), 3.3−3.4
(m, 1H, C8Ha Hb), 2.5−2.7 (m, 2H, SC7 Ha Hb), 1.63 (d-d, J
= 11.4 Hz, 1H, C9 HaHb), 0.58 (d, J = 11.4 Hz, 1H, C9Ha Hb) the methylthio group (SCH3) acted as another bridge
(refer to Figure 2 for the labelling of the carbon atom). 13C
κ
in -mode between the two iron atoms. This complex
NMR ( , ppm in CDCl , 298 K): 214.96 (CO), 211.09 (CO),
δ
3
was readily crystallized as yellow crystal blocks from
a mixed solution of dichloromethane and hexanes (1/3)
under Ar atmosphere. The yields for complexes 1 and 2
were approximately at a ratio of 1/2. The decent yield
allowed full characterization of complex 2 by using
FTIR, 1HNMR, 13CNMR, elementalanalysisandX-ray
single crystal structure analysis. For ligand L3, although
an additional claret product was isolated in extremely
smallquantity, itsinstabilitydidnotallowustocomplete
further characterization except infrared spectroscopic
and elemental analysis.
The infrared spectra of all the isolated complexes
are shown in Figure 1. For comparison, the spec-
trum of the known complex 1 in dichloromethane was
also presented (2076, 2036, 2000, and 1995 cm−1).
Compared to the spectrum of complex 1, complex 2
shows a similar spectral profile with absorption bands
at 2066, 2022, 1994 and 1981cm−1. All the absorption
bands undergo “red-shift” by about 10 cm−1. This shift
206.02 (CO), 47.48 (SCH2), 26.60 (SCH2), 2.69 (FeCH2S).
Ligand L3: The reaction of the ligand with the triiron was
analogously performed with L3 (0.089 g, 0.6 mmol). The
reaction produced first complex 1 and then second unknown
product as a claret-colored solid (less than 5 mg). This com-
plex is labile and only its IR spectrum was obtained.
Complex 1: Yield: 32% (0.071 g). Unknown product:
Microanalysis(found%):C, 28.69;H, 3.79. IR(DCM, cm−1):
νC=O
, 2074, 2040, 2008, 1976, 1906.
3. Results and Discussion
3.1 Synthesis
As shown in Scheme 1, cyclic thioester ligands L1−3
with the same fragment, “SCH2CH2SCO”, were pre-
paredbyfollowingtheliteratureproceduresviatwo-step
(L1) or one-step (L2−3) reactions.27–29 Heating a solu-
tion of L1−3 and Fe3(CO)12 (1/1) in tetrahydrofuran

Zhiyin Xiao et al.
Table 1. Crystallographic data and processing parameters
for complex 2.
Formula
C9H6Fe2O6S2
Formula weight (g/mol)
Temperature (K)
Crystal System
Space group
a (Å)
385.98
296(2)
Monoclinic
P 21/n
9.203(2)
b (Å)
c (Å)
13.912(3)
11.055(3)
90
α
(deg)
β(deg)
101.907(2)
90
1384.9(5)
4
γ
(deg)
V (Å3)
Z
Scheme 2. Reaction of cyclic thioester ligands L1−3 with
Fe3(CO)12 and structures of isolated iron carbonyl products.
Crystal size (mm)
0.34 × 0.32 × 0.30
D
calc (g/cm3)
1.851
Absorption coefficient (mm−1
)
2.411
F(0 0 0)
θ
Limiting indices
768.0
(◦)
2.39 to 28.46
−12 <=h<=12,
−18 <=k<=17,
−14 <=l<=14
12481
3464 [R(int)] = 0.0264
99.1%
Reflections collected
Reflections unique
Completeness to
θ
max
Max. and min. transmission
0.485 and 0.58
1.068
R1 = 0.0535, wR2 =
0.1578
GOF on F2
σ
Final R indices [I>2 (I)]
Final R indices [all data]
R1 = 0.0820, wR2 =
0.1847
Largest diff. peak and hole (e/Å3) 1.931 and −0.422
Figure 1. Infrared spectra of the isolated iron carbonyl
complexes in dichloromethane.
R1 = ꢀꢀFo| − |Fcꢀ / ꢀ|Fo| and wR2 = [ꢀ(|Fo2 − Fc2|)2 /
ꢀ (wFo2)2]1/2
is certainly attributed to the strong electron-donating
ability of the carbene group presented in the complex.
For the unknown product, as shown in Figure 1, which
does comprise of the spectral characteristic absorption
bands analogous to diiron complexes such as complex
1 but additional absorption bands indicate that it pos-
sesses more complicated iron-carbonyl unit in addition
to a “Fe2(CO)6” unit. This is confirmed by its slow
decomposition which produced a species with identi-
cal infrared spectrum to that of complex 1. Previously,
we reported clusters of tri-diiron-carbonyl units.13 The
clusters showed also multiplicity in their infrared spec-
tra. Therefore, it is likely that the unknown product is a
cluster containing more than one diiron-carbonyl units.
at −20 ◦C for several days. Its crystallographic details
and selected bond lengths and angles are tabulated in
Tables 1 and 2, respectively. As shown in Figure 2, the
wobbling of the bridging head led to severe disorder
in its crystal structure. Due to the disorder, the bridg-
ing group in complex 2 exhibited disorder over two
positions, S(1)-C(7)-C(8)-C(9)-S(2) and S(1A)-C(7A)-
C(8A)-C(9A)-S(2A). The occupancy between the two
is 0.64/0.36. Nevertheless, in complex 2, in addition to
the μ-thiolato bridging mode, the two iron atoms are
κ
also bridged by “SCH2” in -mode which lowered the
symmetry of the molecule. The entire bridging moiety
is “SCH2CH2SCH2”.
Structurally, the complex is analogous to those with
3.2 Crystallographic analysis of complex 2
bridging moieties of “SCH2S (or CH2)CH2SCH2”14 and
Diffusion of hexanes into a dichloromethane solution of “SeCH2SCH2SeCH2”.16 It is this bridging mode that
complex 2 afforded yellow crystals suitable for X-ray allows the entire moiety more flexibility compared to
single crystal diffraction analysis by storing the mixture those diiron complexes with two μ-thiolato bridges and

Reaction of three cyclic thioester ligands
Table 2. Selected bond lengths (Å) and angles (◦) for com- overallstructurecomparedtootheranalogousdiironcar-
bonyl complexes reported in the literatures.13,30–37
plex 2.
Fe(1)-Fe(2) 2.5996(10)
Fe(2)-S(1)-Fe(1) 71.11(9)
3.3 Possible reaction mechanisms
Fe(1)-S(1)
Fe(1)-S(2)
Fe(2)-S(1)
Fe(2)-C(9)
S(2)-C(9)
Fe(1)-C(1)
Fe(2)-C(2)
2.238(4)
2.261(2)
2.232(3)
2.307(17)
1.522(18)
1.798(7)
1.801(7)
S(2)-C(9)-Fe(2)
C(9)-S(2)-Fe(1)
102.9(5)
104.1(5)
The common product for the three reactions is complex
1 possessing 1,2-dithiolate as bridging linkage. Since
all the three ligands have the motif, “SCH2CH2S”, and
one of the sulfur atoms adjacent to the carbonyl group
(Scheme 1), this suggests strongly that in the three
reactions, the ring opening via two C-S bond cleav-
ages generated complex 1. According to our recent
calculations, such cleavages occur successively upon
the coordination of S atom to one of the iron atoms
of the precursor.30 For ligand L1, the two successive
C-S bond cleavages released one CO. Thus, it is con-
sistent with the observation that complex 1 was the
solely isolable product in the reaction. In the reac-
tion of ligand L2 with Fe3(CO)12, in addition to the
cleavages related to the formation of complex 1, alter-
native bond cleavage occurred. In the second bond
cleavage, it occurred, likely, after the second iron atom
had been assembled. The CH2 group in the fragment
−SCH2CO− involved in bridging (binding) together
with the S atom to the other iron atom in κ-mode and this
binding initiated the decarboxylation to form complex
2. There is, undoubtedly, additional bond(s) cleavages
similar to that occurred in the reaction of ligand L2
with the triiron precursor. But failure to determine
the fine structure of the unknown product generated
from the reaction of ligand L3 with Fe3(CO)12 did not
allow more detailed elucidation of its reaction mecha-
nism.
C(9)-Fe(2)-Fe(1) 75.7(4)
S(1)-Fe(2)-Fe(1) 54.55(12)
S(1)-Fe(1)-Fe(2) 54.34(10)
S(2)-Fe(1)-Fe(2) 76.88(15)
Figure 2. Crystal structure of complex 2 with disorder
(ellipsoids were drawn at a thermal probability of 50% and
hydrogen atoms were omitted for clarity reasons).
thus exhibited the observed disorder. NMR spectra of
the complex echo in accordance with the structure. As 4. Conclusions
seen in Figure S10 (Supplementary Information), 13C
In summary, the synthesis and characterization of
NMR showed cleanly three signals belonging to the
organic bridging linkage (“SC8H2C7H2SC9H2”) in high
field besides three peaks in low field which could be
assigned to the bound CO. However, its 1H NMR spec-
trum (Figure S11 in SI) is more complicated. Due to
cycliceffect, thetwoprotonsoncarbonC(9)weresplitto
a pair of doublet, 1.63 and 0.58 ppm, respectively. While
one of the protons shows a doublet at 0.58 ppm with the
coupling constant of 11.4 Hz, the other proton exhibits
a pseudo-quartet signal at 1.63 ppm. The fine structure
of the signals at 1.63 ppm can be attributed to remote
coupling with the protons on C(7) with a small coupling
constant (1.2 Hz). As being found in other asymmetric
analogues we reported recently,30 its asymmetry leads to
more complicated infrared spectrum compared to com-
three cyclic thioester ligands possessing common
“SCH2CH2S” unit and their reactions with Fe3(CO)12
are reported. The isolation of the same product in all
the reactions, complex 1, asserts how the bond cleav-
ages occurred upon the reaction with the precursor
in the three reactions. The isolation of complex 2 in
the reaction of ligand L2 with Fe3(CO)12 indicated
other pathway(s) of bond cleavage in addition to the
S-C bond cleavage when the ring size of the ligand
increases.
Supplementary Information (SI)
Crystallographic data for the structural analysis of com-
plex 2 which has been deposited with the Cambridge
plex 1. But, noticeably, the variation does not alter its Crystallographic Data Center, with the number of 895034,

Zhiyin Xiao et al.
can be obtained free of charge at http://www.ccdc.cam.ac. 10. Adams R D, Babin J E, Wang J G and Wu W G 1989
Cluster Synthesis .24. Synthesis and Characterization of
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Acknowledgements
We thank the Natural Science Foundation of Zhejiang
Province (Grant No. LQ17B01004) and the Key Project for
Student Research Training of Jiaxing University (851716048)
for supporting this work.
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