Syntheses, structures and characterizations of two organoimido derivatives of POMs containing sulfide groups

Article abstract of DOI:10.1016/j.poly.2015.02.010

Two remote methylthio group functionalized organoimido derivatives of hexamolybdate, (Bu₄N)₂[Mo₆O₁₈(NC₆H₄-SCH₃-p)] (1) and (Bu₄N)₂[Mo₆O₁₈

Full text of DOI:10.1016/j.poly.2015.02.010

Polyhedron 92 (2015) 1–6
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Syntheses, structures and characterizations of two organoimido
derivatives of POMs containing sulfide groups
Hui Guo a,1, Shang-Ze Li a,1, Xin-Xing Xiong a, Di Li a, Zi-Yang Liu a, Long-Sheng Wang a,b,
,
⇑
Ping-Fan Wu a,b,
⇑
a Institute of POM-based Materials, School of Chemistry and Chemical Engineering, Hubei University of Technology, Wuhan City, Hubei Province 430068, China
b The Synergistic Innovation Center of Catalysis Materials of Hubei Province, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two remote methylthio group functionalized organoimido derivatives of hexamolybdate,
(Bu4N)2[Mo6O18(NC6H4-SCH3-p)] (1) and (Bu4N)2[Mo6O18(NC6H4-SCH3-m)] (2), were synthesized through
the refluxing reaction of octamolybdates, the hydrochloride salts of corresponding organic amines in
anhydrous acetonitrile with dicyclohexylcarbodiimide (DCC) as dehydration agent. They are character-
ized by single crystal X-ray diffraction, FT-IR spectra, UV–Vis spectra, elemental analysis, 1H NMR and
cyclic voltammetry. X-ray structural study reveals that anion clusters of both compounds possess some
typical structural features of mono-substituted hexamolybdate, and their anion clusters are connected
into two dimensional network via intermolecular multiple C–Hꢀ ꢀ ꢀO hydrogen bonds.
Received 16 December 2014
Accepted 7 February 2015
Available online 17 March 2015
Keywords:
Hydrogen bond
Polyoxometalates
(Methylthio)aniline
Organoimido
Ó 2015 Elsevier Ltd. All rights reserved.
Molybdenum
1. Introduction
Up to now, many functional groups, e.g. hydroxyl [10], amido
[11], halogen atom [12,13], alkyl [14], vinyl [15], acetenyl [12],
Polyoxometalates (POMs) are a class of discrete anion clusters
which are made up of early transition metal ions (i.e. Mo, W, V,
Nb and Ta) and oxo ligands [1,2]. They have drawn increasing
attention on account of their diverse structures and potential
applications in diverse fields including electrochemistry, catalysis,
magnetism, medicine, photochemistry and semiconductor materi-
als [3–5]. One notable virtue of POMs is that the structures and
properties of POMs can be tuned via the surface modification of
POMs, for example, terminal oxo atoms or bridged oxo atoms of
POMs can be replaced by organic ligands [6,7]. Typical example
of the hybrid compounds, the arylimido derivatives of POMs con-
taining Mo–N multiple bond have drawn particular research inter-
ests owing to the so-called ‘‘synergistic interaction’’, which is
ferrocene [16], carboxyl [17] and terpyridyl [18], have been
introduced into the arylimido derivatives of hexamolybdates,
which afford them the ability for further coordination or post-
modification. However, the organoimido derivatives of hexamolyb-
dates containing soft base (i.e. S or P) are still not reported.
Organosulfur compounds are widely distributed within the
natural world and play an important role in the life process. They
have important potentials and applications in the fields of materi-
als, medicine, catalysts and organic transformations [19]. For
example, m-methylthiobenzylamine is one kind of important
intermediates to prepare thioridazine and mesoridazine, it can be
used in the synthesis of organic compounds with antivirus activity
[20], antitumoral activity [21], and anti-inflammatory activity [22].
Additionally, sulfur atom in thioether is a typical soft base with the
affinity to soft acid (such as Ag(I), Cu(I)), therefore, thioether can be
used to construct coordination compounds or polymers [23].
To explore the organoimido derivatives of POMs containing
sulfide groups, 4-(methylthio)aniline and 3-(methylthio)aniline
are chosen as sulfide ligands and successfully attached to
hexamolybdates via Mo–N triple bond. We herein report the
syntheses, characterizations, structures and electrochemical
studies of (Bu4N)2[Mo6O18(NC6H4SCH3-p)] (1) and (Bu4N)2
[Mo6O18(NC6H4SCH3-m)] (2).
resulted from the d–p conjugated interaction between the inor-
ganic POM cluster and organic ligand [8,9]. Additionally, the
attachment of organoimido ligands on POMs allows the introduc-
tion of different functional groups into POMs.
⇑
Corresponding authors at: Institute of POM-based Materials, School of Chem-
istry and Chemical Engineering, Hubei University of Technology, Wuhan City, Hubei
Province 430068, China. Tel./fax: +86 27 59750482.
E-mail addresses: wls@mail.tsinghua.edu.cn (L.-S. Wang), pingfanwu-111@163.
com (P.-F. Wu).
1
Both authors have the same contributions in this paper.
http://dx.doi.org/10.1016/j.poly.2015.02.010
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

2
H. Guo et al. / Polyhedron 92 (2015) 1–6
3460(m, br), 2960(m), 2933(shoulder), 2873(m), 1564(s), 1479(s),
2. Experimental details
1379(m), 1325(m), 1151(w), 1098(w), 1025(w), 975(m, shoulder),
955(vs), 784(vs), 595(w). UV–Vis(MeCN): kmax = 228.5, 256,
336.5 nm. Elemental Anal. Calc. for C46H88Mo6N4O20: C, 34.69; H,
5.57; N, 3.52. Found: C, 35.26; H, 5.80; N, 3.50%. E1/2 (DCE):
ꢁ0.386 V.
2.1. Materials and physical measurements
[Bu4N]4[a-Mo8O26] was synthesized according to literature pro-
cedure [24] and confirmed by IR. The hydrochloride salts of
corresponding amines were prepared by adding concentrated HCl
into an ethanol solution of corresponding amines. Lots of colorless
crystals were obtained after evaporation of solvent under vacuum
pressure. Anhydrous acetonitrile was refluxed in the presence of
CaH2 and distilled prior to use. All other chemical reagents were
of analytical grade and used as received without further purifica-
tion. Elemental analyses were performed on Vario EL (Elementar
An alysensysteme GmbH). FT-IR spectra were measured using
KBr pellets and recorded on FT-IR spectrometer (PERKINELMER)
spectrophotometer. UV–Vis spectra were measured in acetonitrile
solution with UV-2700 spectrophotometer (Shimadzu). 1H NMR
spectra for both compounds were taken on a JEOL JNM-ECA300
NMR spectrometer at 300 K using DMSO-d6 as solvent. Cyclic vol-
tammetry were performed in DMF solutions at 25 °C in a high pure
N2 filled electrolytic cell using CHI750 electrochemical worksta-
tion. A Pt electrode was employing as the working electrode, dou-
ble salt bridged saturated calomel electrode (SCE) as the reference
electrode, and a Pt platelet electrode as the counter electrode.
[Bu4N]PF6 was used as the supporting electrolyte with a scan rate
2.4. X-ray crystallography
Suitable crystals were mounted on glass fibers and rapidly
transferred onto the diffractometer. X-ray diffraction data of com-
pounds 1 and 2 were collected on a Rigaku RAXIS-SPIDER IP
diffractometer using graphite-monochromatized Mo K
a radiation
(k = 0.71073 Å) at room temperature (293 2 K). Data collection,
data reduction, cell refinement and experiential absorption correc-
tion for compounds 1 and 2 were performed with the software
package of Rigaku RAPID AUTO (Rigaku, 1998, Ver2.30).
Structures of all compounds were solved by direct methods and
refined against F2 by full matrix least squares. All non-hydrogen
atoms, except disordered atoms, were refined anisotropically.
Hydrogen atoms of ligands were generated geometrically. All
calculations were performed using the program package of
SHELXS-97 and SHELXL-97 [25,26]. A summary of X-ray crystal data
of compounds 1–2 is presented in Table 1. ORTEP diagrams of anionic
clusters of both compounds are shown in Fig. 1. The selected bond
lengths and angles are listed in Table 2, the hydrogen bond data of
compounds 1–2 are summarized in Table 3.
of 50 mV sꢁ1
. Epa values were measured versus SCE, and
[Bu4N]2[Mo6O19] was employed as the internal standard
2.2. Synthesis of (Bu4N)2[Mo6O18(NC6H4SCH3-p)] (1)
3. Results and discussion
A mixture of 2.15 g (Bu4N)4[a-Mo8O26], 0.23 g hydrochloride
3.1. Synthesis
salt of 4-(methylthio)aniline and 0.43 g N,N0-dicyclohexylcarbodi-
imide (DCC) were refluxed at 100–110 °C in 20 mL dry acetonitrile.
After 12 h, the resulting black-red solution was cooled to room
temperature, and filtrated to remove the resulting white precipi-
tates. The brown-red filtrate was left to evaporate the solvent
without disturbance. Crude products were obtained after the
volatilization of solvent. Lots of red block crystals were obtained
in a yield of 70–80% through twice recrystallization from the mixed
solvent of acetone/ethanol (1:1). 1H NMR (300 MHz, DMSO-d6):
7.29(d, J = 8.6 Hz, 2H, ArH), 7.15(d, J = 8.6 Hz, 2H, ArH), 3.17(t,
J = 8.4 Hz 16H, NCH2–, [Bu4N]+), 2.37(s, 3H, –SCH3), 1.57(m,
J = 7.8 Hz, 16H, –CH2–), 1.32(m, J = 7.2 Hz, 16H, –CH2–), 0.94, (t,
J = 7.3 Hz 24H, CH3–, [Bu4N]+). IR(KBr pellet, cmꢁ1): 3146(broad,
m), 2961(m), 2933(w), 2873(m), 1627(w), 1573(w),1479(m),
1400(m), 1380(w), 1093(m), 975(m, shoulder), 955(vs), 793(vs),
592(m). UV–Vis (MeCN): kmax = 377 nm. Elemental Anal. Calc. for
In the last three decades, phosphinimines, isocyanates, and aro-
matic amines had been used to make organoimido derivatives of
POMs. Especially, DCC-assisted dehydration protocol developed
by Peng and Wei is a facile and high-yield method to make mono-
substituted and bifunctionalized organoimido derivatives of POMs
[27]. 4-(Methylthio)aniline and 3-(methylthio)aniline are chosen
as imido-releasing reagents because they are of easy access. Title
compounds are prepared via a one-pot reaction of octamolybdate,
hydrochloride salts of corresponding organic amines and DCC with
molecular ratio of 3:4:6 in dry acetonitrile.
3.2. Crystal structure
Single crystal X-ray diffraction structural research reveals that
compound 1 crystallizes in monoclinic system, P2(1)/c space
group, and there is one crystallographically independent anion of
[Mo6O18(NC6H4SCH3-p)]2ꢁ and two cations of (Bu4N)+ in the asym-
metric unit. As shown in Fig. 1, the six molybdenum atoms in the
anion cluster of [Mo6O18(NC6H4SCH3-p)]2ꢁ are connected to one
central oxygen atom O(1) to form a distorted octahedron with
the Moꢀ ꢀ ꢀMo separation ranging from 3.231(1) to 3.295(1) Å.
Mo(1) is six-coordinated with one nitrogen atom (Nt) from 4-
methylthio-aniline, four bridged oxygen atoms (Ob) and one cen-
C39H79Mo6N3O19: C, 31.87; N, 2.86; H, 5.42. Found: C, 31.91; N,
2.90; H, 5.38%. E1/2 (DCE): ꢁ0.390 V.
2.3. Synthesis of (Bu4N)2[Mo6O18(NC6H4SCH3-m)] (2)
A mixture of 2.15 g (Bu4N)4[a-Mo8O26], 0.23 g hydrochloride
salt of 3-(methylthio)aniline and 0.43 g N,N0-dicyclohexylcarbodi-
imide (DCC) was refluxed at 100–110 °C in 20 mL of anhydrous
acetonitrile. After 12 h, the resulting red solution was cooled to
room temperature and filtrated to remove resulting white precipi-
tates. The red filtrate was left alone without disturbance. Lots of
red block crystals were obtained in a yield of 50–60% through
twice recrystallization from the mixed solvent of acetone/
EtOH(1:1). 1H NMR (300 MHz, DMSO-d6): d = 7.37(d, J = 8.1 Hz,
1H, ArH), 7.09(d, J = 6.9 Hz, 1H, ArH), 6.98(d, J = 6.9 Hz, 2H, ArH),
3.17(t, J = 8.1 Hz, 16H, NCH2–, [Bu4N]+), 2.50(s, 3H, –SCH3),
1.55(m, J = 7.7 Hz, 16H, –CH2–), 1.32(m, J = 7.7 Hz, 16H, –CH2–),
0.94, (t, J = 7.2 Hz, 24H, CH3–, [Bu4N]+). IR (KBr pellet, cmꢁ1):
tered
l6-O(1) (Oc) to form a distorted octahedron. The other
molybdenum atoms are six-coordinated with one terminal oxygen
atom (Ot), four bridged oxygen atoms (Ob) and one centered
l6-O(1) (Oc) to form a distorted octahedron. The Mo–N bond in
compound demonstrates substantial triple bond character
1
considering the short bond length (1.726(3) Å) and nearly liner
Mo–N–C angle (173.13°). Thus, an organic-inorganic hybrid conju-
gated system is constructed between 4-methylthio-aniline and the
hexamolybdates cluster through the Mo„N triple bond. The bond
length of Mo(1)„N(1) (1.723(5) Å) is longer than that of Mo„Ot

H. Guo et al. / Polyhedron 92 (2015) 1–6
3
Table 1
Table 3
Crystallographic data of compounds 1–2.
Summary of hydrogen bonds in compounds 1–2.
Compound
1
2
D–Hꢀ ꢀ ꢀA
d(Hꢀ ꢀ ꢀA)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
<(DHA)
Formula
Formula weight
Crystal system
Space group
a (Å)
C
39H79Mo6N3O18
S
C39H79Mo6N3O18
1485.75
monoclinic
P2(1)/n
18.164(4)
15.485(3)
20.980(4)
105.97(3)
5673(2)
4
S
Compound 1
1485.75
monoclinic
P2(1)/n
17.571(4)
15.785(3)
21.031(4)
104.61(3)
5644(2)
4
C(7)–H(7A)ꢀ ꢀ ꢀO(11)#1
0.96
0.93
0.93
2.41
2.77
2.72
3.273(10)
3.402(10)
3.350(9)
149.8
126.5
125.8
C(5)–H(5A)ꢀ ꢀ ꢀO(4)#2
C(6)–H(6A)ꢀ ꢀ ꢀO(4)#2
#1
#2
Symmetry code:
ꢁx + 1, ꢁy + 2, ꢁz + 2;
ꢁx + 3/2, y + 1/2, ꢁz + 3/2
b (Å)
c (Å)
Compound 2
C(5)–H(5A)ꢀ ꢀ ꢀO(4)#1
C(6)–H(6A)ꢀ ꢀ ꢀO(4)#1
C(7)–H(7A)ꢀ ꢀ ꢀO(13)#2
0.93
0.93
0.96
0.96
2.59
3.251(6)
3.330(5)
3.320(6)
3.624(8)
128.6
b (°)
2.77
2.58
2.69
119.9
133.8
165.6
V (Å3)
Z
C(7)–H(7A)ꢀ ꢀ ꢀO(10)#2
Dcalc.(g/cm3)
1.748
1.394
1.739
1.387
#1
#2
Symmetry code:
ꢁx + 3/2, y + 1/2, ꢁz + 3/2;
ꢁx + 1, ꢁy + 1, ꢁz + 2
l
(mm-1
)
F(000)
2984
2984
h for data collection
Reflections collection
Reflections unique
Rint
3.00–26.00
37108
10 145
0.0368
10145
1.079
0.0529
0.1661
3.08–26.00
46031
10979
0.0389
10972
1.058
0.0367
0.1044
(1.668(5)–1.692(5) Å), because the electronegativity of nitrogen
atom is less than that of oxygen atom. The Mo–Ob bond length of
imido-bearing molybdenum atom (Mo(1)–O(1) (2.227(4) Å)) is
obviously shorter than that of other Mo–Oc bonds (2.315(2)–
2.364(2) Å) owing to the so-called ‘‘trans influence’’; the average
separation of Mo(1)ꢀ ꢀ ꢀMo (3.239 Å) is slightly shorter than that of
other Moꢀ ꢀ ꢀMo (3.291 Å). The –SCH3 group stands on the para posi-
tion of hexamolybdates, the bond length of S(1)–C(4) and S(1)–C(4)
are 1.758(7) and 1.775(10) Å, respectively, which are slightly
shorter than that of the ligand of NH2C6H4SCH3-p (1.765 Å and
1.788 Å) [28].
Independent reflections
GOF on F2
Final R
Final Rw
[w(Fo ꢁ Fc2)2]/
2
R =
R
||Fo| ꢁ |Fc||/
R
|Fo| and Rw = [
R
R
w(Fo2)2]1/2 with w = 1/[
r
2(Fo2) +
(aP)2 + bP], where P = (Fo2 + 2Fc2)/3. 1: a = 0.0841, b = 5.7830; 2: a = 0.0477,
b = 4.6789.
Compound 2 crystallizes in monoclinic system, P2(1)/n space
group. There are two cations of [Bu4N]+ and one anion of
[Mo6O18(NC6H4SCH3-m)]2ꢁ in the asymmetric unit. The anion clus-
ter structure of compound 2 is close to that of compound 1 except
that the –SCH3 group stands on the meta position of the bound
hexamolybdates.
Weak interactions, such as hydrogen bonds,
p
ꢀ ꢀ ꢀ
p interactions,
and anionꢀ ꢀ ꢀ interactions play a key role in supramolecular
p
assembly [29]. The intermolecular hydrogen-bond interactions
are found in compound 1. As seen in Fig. 2, two adjacent anion
clusters form a dimer with graph set symbol [30] of R2 2(24) via
two C–Hꢀ ꢀ ꢀO hydrogen bonds (C(7)–H(7A)ꢀ ꢀ ꢀO(11)#2 3.273(10) Å,
symmetry code#2: ꢁx + 1, ꢁy + 1, ꢁz + 2). Those dimers are further
connected into a 2D network through C–Hꢀ ꢀ ꢀO hydrogen bonds
(C(5)–H(5A)ꢀ ꢀ ꢀO(4)#1 3.402(10) Å, C(6)–H(6A)ꢀ ꢀ ꢀO(4)#1 3.350(9) Å,
symmetry code#1: ꢁx + 3/2, y ꢁ 1/2, ꢁz + 3/2). One five-membered
hydrogen-bond ring with graph set symbol of R1 2(5) is formed via
C(5)–H(5A)ꢀ ꢀ ꢀO(4)#1 and C(6)–H(6A)ꢀ ꢀ ꢀO(4)#1. In compound 2,
adjacent anion clusters form a dimer containing a large hydrogen-
bond ring with graph set symbol of R2 2(20) via four C–Hꢀ ꢀ ꢀO
hydrogen bonds (C(7)–H(7A)ꢀ ꢀ ꢀO(13)#2 3.320(6) Å, C(7)–H(7A)ꢀ ꢀ ꢀ
O(10)#2 3.624(8) Å, symmetry code#2: ꢁx + 1, ꢁy + 1, ꢁz + 2), and
those dimers are further connected into a 2D network via four
C–Hꢀ ꢀ ꢀO hydrogen bonds (C(5)–H(5A)ꢀ ꢀ ꢀO(4)#1 3.251(6) Å,
C(6)–H(6A)ꢀ ꢀ ꢀO(4)#1 3.330(5) Å, symmetry code#1: ꢁx + 3/2, y + 1/
2, ꢁz + 3/2) (Fig. 3).
Fig. 1. ORTEP drawing of anion cluster of compounds 1 and 2 with 40% probability
thermal ellipsoids.
3.3. UV–Vis absorption spectra
UV–Vis absorption spectra of compounds 1, 2 and hexamolyb-
dates were studied in the solvent of CH3CN (Fig. 4). The lowest
energy electronic transition for compound 1 and 2 are found at
around 376 and 336 nm, respectively, while that of
(TBA)2[Mo6O19] appear at about 325 nm. The large bathchromic
shift (51 nm) of the lowest energy electronic transition between
compound 1 and hexamolybdate indicates the presence of a strong
Table 2
Selected bond lengths and angles of compounds 1–2.
1
2
C–N (Å)
1.429(9)
1.723(5)
1.667(4)–1.692(5)
1.861(5)–1.987(5)
2.227(4)–2.359(4)
160.2(6)
1.388(5)
1.732(3)
1.676(3)–1.688(3)
1.871(3)–1.976(3)
2.218(2)–2.360(2)
169.5(3)
Mo–N (Å)
Mo–Ot (Å)
Mo–Ob (Å)
Mo–Oc (Å)
Mo–N–C (°)
d–p conjugation interaction in compound 1 [10]. That is because
the methylthio group in compound 1 lies on the para position of
–[N@(Mo6O18)]2ꢁ. There is an electron-denoting conjugated inter-
action (+C) besides the electron-drawing inductive effects of –SMe

4
H. Guo et al. / Polyhedron 92 (2015) 1–6
#1
#2
Fig. 2. Ball-and-stick viewing of two dimensional hydrogen bond network of compound 1 (Symmetry code:
ꢁx + 1, ꢁy + 2, ꢁz + 2,
ꢁx + 3/2, y + 1/2, ꢁz + 3/2).
#1
#2
Fig. 3. Ball-and-stick viewing of two dimensional hydrogen bond network of compound 2 (Symmetry code:
ꢁx + 3/2, y + 1/2, ꢁz + 3/2,
ꢁx + 1, ꢁy + 1, ꢁz + 2).
(–I) in compound 1, but the electron-denoting ability of –SMe is
stronger than its electron-drawing ability. Therefore, the
methylthio group in compound 1 acted as electron-denoting func-
group, which went against the electron transfer from the aryl ring
to the hexamolybdates and resulted in a small bathchromic shift.
The big difference of bathchromic shift between compound 1 and
2 indicates that the position of substituents plays an important role
in the electron interaction and electronic spectra of organic deriva-
tized POMs.
tional group and favor the formation of the D–p–A system in the
anion of [Mo6O18(NC6H4SCH3-p)]2ꢁ, which renders the lowest
energy electronic transition of compound 1 to shift to 376 nm. As
for compound 2, there is a small bathchromic shift (11 nm) of
the lowest energy electronic transition compared to that of
hexamolybdates, this is due to the methylthio group sites on the
3.4. FT-IR spectra
meta position of –N=(Mo6O18
action (–I) is the only electronic interaction of the methylthio
)
2ꢁ. Electron-drawing inductive inter-
FT-IR spectra of compounds 1 and 2 demonstrate some similar
features of monofunctionalized organoimido derivatives of

H. Guo et al. / Polyhedron 92 (2015) 1–6
5
Table 4
Cyclic voltammetry data of hexamolybdates and compounds 1–2.
Compound Epc (V) Epa (V)
Epa ꢁ Epc (V) E1/2 (V) Cathodic shift (V)
2ꢁ
[Mo6O19
]
ꢁ0.268 ꢁ0.163 0.105
ꢁ0.435 ꢁ0.346 0.089
ꢁ0.439 ꢁ0.334 0.105
ꢁ0.216
0
1
2
ꢁ0.390 0.174
ꢁ0.386 0.170
is less than oxygen atom and the nitrogen atom is conjugated with
aryl ring in aryl imido derivatives, therefore the aryl imido ligands
are superior electron-denoting ligands in relative to oxygen atoms
[10,14], which render compound 1 and 2 to bear higher electronic
density than hexamolybdates.
4. Conclusion
In summary, two organoimido derivatives of hexamolybdates
containing methylthio groups, (Bu4N)2[Mo6O18(NC6H4-SCH3-p)]
(1) and (Bu4N)2[Mo6O18(NC6H4-SCH3-m)] (2), were successfully
prepared using DCC assisting dehydration protocol. Single crystal
X-ray diffraction structural study reveals that the anion clusters
of both compounds demonstrate typical monosubstituted struc-
tural features of hexamolybdates with different substituted posi-
tion of methylthio groups. The lowest energy electronic
transition of compound 1 shows a large bathchromic shift owing
Fig. 4. UV–Vis spectra of compound
hexamolybdates (black, straight).
1 (red, dashed), 2 (blue, dotted) and
hexamolybdate. In the IR spectrum of hexamolybdate, two strong
peaks of Mo–Ot and Mo–Ob–Mo are found to appear at 957 and
798 cmꢁ1, respectively. In the IR spectra of compounds 1 and 2,
the peaks of Mo„Ot are split into two peaks with approximate
20 cmꢁ1 intervals. The shoulder peak around 975 cmꢁ1 (975 cmꢁ1
for 1 and 2) is tentatively ascribed as Mo„N stretching vibration,
and the strong peak around 955 cmꢁ1 (955 cmꢁ1 for 1 and 2) is
attributed to Mo„Ot stretching vibration [14]. The Mo–Ob–Mo
stretching vibration is found at 793 cmꢁ1 in 1, 795 cmꢁ1 in 2,
respectively, demonstrating a slight red-shift compared to that in
[Mo6O19] owing to the attachment of organoimido ligand.
to the formation of D–p–A system, while that of compound 2
shows a slight bathchromic shift. 1H NMR of aryl hydrogen atoms
in compounds 1 and 2 show obvious downfield shifts compared to
that of free amine owing to the electron-withdrawing effect of
POMs. CV study indicates that both compounds are more difficult
to be reduced than (TBA)2[Mo6O19].
3.5. 1H NMR spectra
Acknowledgements
1H NMR spectra of compounds 1 and 2 in d6-DMSO solution dis-
play clearly resolved signals, all of which can be unambiguously
assigned. The integration matches well with their structures. 1H
NMR signals of aryl hydrogen atoms in compound 1 appear at
7.29 and 7.15 ppm, while that of aryl hydrogen atoms in
corresponding free amines locate at 7.07 and 6.56 ppm. The down-
field shift of aryl hydrogen in compound 1 indicates that they are
influenced by deshielding effect, in other words, POMs are an elec-
tron-drawing functional group. 1H NMR signals of aryl hydrogen
atoms in compound 2 appeared at 7.37, 7.09 and 6.98 ppm, while
that of aryl hydrogen atoms in corresponding free amines appeared
at 6.96, 6.47 and 6.36 ppm. There is an obvious downfield chemical
We thank Dr. PanChao Yin, Ms. Cyndi Rowton, Dr. JunJun Tan,
and Dr. ChunYan Wang for their help in the improvement of
English. The authors thank the financial support of the National
Natural Science Foundation of China (Nos. 21101062, 21271068,
21203059), Educational Commission of Hubei Province of China
(No. Q21021402), Chutian Scholar Fundation of Hubei Province
(No. 4032401). National Training Programs of Innovation and
Entrepreneurship for Undergraduates (No. 201210500012).
Wuhan Applied Basic Research Program (No. 2014010101010020).
Appendix A. Supplementary data
shift of aryl hydrogen atoms between compound
(methylthio)aniline owing to the electron-drawing effect of
attached POMs cluster.
2 and 3-
CCDC 1031869 and 1031870 contains the supplementary crys-
tallographic data for compounds 1 and 2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/re-
trieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
336 033; or e-mail: deposit@ccdc.cam.ac.uk.
3.6. Cyclic voltammetry
Electrochemical data of compounds 1, 2 and hexamolybdates
were recorded in ca. 1 mmol/L DMF solutions with [n-Bu4N]PF6
(0.1 mol/L) as the supporting electrolyte. In the range of ꢁ1.6 to
+1.6 V (versus SCE), both compounds 1 and 2 show a reversible
redox possess (Table 4), which is found at ꢁ0.390 V for 1, and
ꢁ0.386 V for 2, respectively. Under the same conditions, the parent
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