Synthesis and X-ray crystal structures of two trinuclear molybdenum clusters coordinated by p-nitrobenzoate: Mo3S4(dtp)3(p-NO2C6H 4COO)(L)

Article abstract of DOI:10.1016/S0277-5387(01)00862-2

Two new trinuclear molybdenum clusters Mo₃S₄(dtp)₃(p-NO₂C₆H ₄COO)(L) (dtp = diethyldithiophosphate, L = Py and DMF) have been synthesized by the ligand substitution reaction with p-nitrobenzoic acid using the precursors Mo₃S₄(dtp)₄(H₂O) and Mo₃S₄(dtp)₃(CCl₃COO)(Py), respectively. Their structures have been determined by X-ray diffraction analysis and confirmed by ³¹P NMR spectra. Both compounds contain [Mo₃S₄] cores in which three Mo atoms form an isosceles triangle and each Mo atom is octahedrally coordinated. High asymmetry of coordination on the different Mo atoms is observed. The ligand replacement of -dtp by the aromatic acid makes the whole molecule more stable in a dipolar solvent. The coordination difference between Py and DMF also affects the core structure, resulting in the corresponding Mo-Mo distances being different in these two similar cluster compounds.

Full text of DOI:10.1016/S0277-5387(01)00862-2

Polyhedron 20 (2001) 2911–2916
www.elsevier.com/locate/poly
Synthesis and X-ray crystal structures of two trinuclear
molybdenum clusters coordinated by p-nitrobenzoate:
Mo3S4(dtp)3(p-NO2C6H4COO)(L)
Yan-Hong Tang, Ye-Yan Qin, Ling Wu, Zhao-Ji Li, Yao Kang, Yuan-Gen Yao *
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou, Fujian 350002, China
Received 21 February 2001; accepted 9 May 2001
Abstract
Two new trinuclear molybdenum clusters Mo3S4(dtp)3(p-NO2C6H4COO)(L) (dtp=diethyldithiophosphate, L=Py and DMF)
have been synthesized by the ligand substitution reaction with p-nitrobenzoic acid using the precursors Mo3S4(dtp)4(H2O) and
Mo3S4(dtp)3(CCl3COO)(Py), respectively. Their structures have been determined by X-ray diffraction analysis and confirmed by
31P NMR spectra. Both compounds contain [Mo3S4] cores in which three Mo atoms form an isosceles triangle and each Mo atom
is octahedrally coordinated. High asymmetry of coordination on the different Mo atoms is observed. The ligand replacement of
–dtp by the aromatic acid makes the whole molecule more stable in a dipolar solvent. The coordination difference between Py
and DMF also affects the core structure, resulting in the corresponding Mo–Mo distances being different in these two similar
cluster compounds. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Trinuclear molybdenum cluster; Substitution reaction; X-ray crystal structures; 31P NMR spectra
2. Experimental
1. Introduction
All reactions were carried out in air. A. R. grade
p-nitrobenzoic acid and the solvents N,N-dimethylfor-
mamide (DMF), pyridine (Py), anhydrous ethanol and
dichloromethane were used without purification.
Mo3S4(dtp)3(m-dtp)(H2O), Mo3S4(dtp)3(m-CCl3COO)-
(Py) were prepared according to the literature methods
[6,7]. IR spectra were recorded on a Nicolet Magna 750
Fourier spectrophotometer in KBr. 31P NMR spectra
were measured on a Varian Unity-500 NMR spectrom-
eter in CHCl3 with reference to 85% H3PO4. Elemental
analyses were determined on an EA 1110 elemental
analyzer in Xiamen University.
The significance of molybdenum in biosystems, espe-
cially in nitrogenase [1,2], leads to our interest to study
molybdenum–sulfur compounds. Among the molybde-
numclusters obtained so far, the incomplete cuboidal
molybdenum sulfido cluster Mo3S4(dtp)3(m-dtp)(H2O),
where dtp=diethyldithiophosphate, has been exten-
sively studied due to the fascinating ligand properties of
m-dtp. Several derivatives containing aliphatate ligands
were synthesized and characterized structurally [3]. Re-
cently we have reported some aromatic acid-substituted
derivatives, which exhibit interesting structures and
properties [4,5]. Herein we report the synthesis and
structures of two new compounds Mo3S4(dtp)3(p-
NO2C6H4COO)(Py) (I) and Mo3S4(dtp)3(p-NO2C6H4-
COO) (DMF) (II), obtained by different synthesis de-
signs.
2.1. Synthesis
2.1.1. Preparation of
Mo3S4(dtp)3(p-NO2C6H4COO)(Py) (I)
A solution of Mo3S4(dtp)3(m-dtp)(H2O) (0.10 g, 0.085
mmol) and p-nitrobenzoic acid (0.02 g, 0.129 mmol) in
40.0 cm3 EtOH/CH2Cl2 (v/v=1:1) was refluxed while
* Corresponding author. Tel.: +86-591-379-2359; fax: +86-591-
371-4946.
E-mail address: yyg@ms.fjirsm.ac.cn (Y.-G. Yao).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00862-2

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Y.-H. Tang et al. / Polyhedron 20 (2001) 2911–2916
2.2. Crystal structure determination
stirring at 80 °C for 1 h. Then several drops of Py were
added and the mixture was stirred further for 10 min.
The resultant deep-brown mixture was then filtered.
Black crystals of Mo3S4(dtp)3(p-NO2C6H4COO)(Py)
were obtained when the filtrate was kept at room
temperature (r.t.) for a few days. Yield: 0.04 g (38.8%);
Anal. Calc. for C24H39Mo3N2O10P3S10: C, 23.69; H,
3.23; N, 2.30; S, 26.29. Found: C, 23.83; H, 3.45; N,
2.55; S, 26.20%. IR (KBr disc, cm−1): w 1603 (m), 1537
(s), 1392 (s), 1344 (s), 1009 (s), 964 (s), 648 (s), 536 (s).
Data collection of Mo3S4(dtp)3(p-NO2C6H4COO)-
(Py) (I) and Mo3S4(dtp)3(p-NO2C6H4COO)(DMF) (II)
were conducted on an Enraf–Nonius CAD4 and a
Siemens SMART CCD diffractometer, respectively, with
graphite-monochromatized Mo Ka radiation (u=
,
0.71073 A) at 293(2) K. The data reductions and struc-
tural analyses were performed on a workstation using
Enraf–Nonius MOLEN/VAX Software or SMART CCD
Software and the structures were refined on F2 through
the use of the SHELXL-PC programs [8–10]. Crystal
structure plots were drawn using ORTEP II [11]. The
positions of the molybdenum atoms were determined
by direct methods, and successive difference electron
density maps located the remaining non-hydrogen
atoms. All the non-hydrogen atoms were refined an-
isotropically by full-matrix least-squares technique. Hy-
drogen atoms were included but not refined. The
crystallographic data are listed in Table 1.
2.1.2. Preparation of
Mo3S4(dtp)3(p-NO2C6H4COO)(DMF) (II)
A solution of Mo3S4(dtp)3(m-CCl3COO)(Py) (0.10 g,
0.082 mmol) and p-NO2C6H4COOH (0.02 g, 0.129
mmol) in 3.0 cm3 DMF was stirred at 80 °C for 1 h.
After being filtrated, 20.0 cm3 EtOH was added to the
solution. When the solution was kept at room tempera-
ture for 3 days, black crystals of Mo3S4(dtp)3(p-
NO2C6H4COO)(DMF) were obtained. Yield: 0.065 g
(65.4%); Anal. Calc. for C22H41Mo3N2O11P3S10: C,
21.82; H, 3.41; N, 2.31; S, 26.43. Found: C, 22.37; H,
4.01; N, 2.46; S, 26.33%. IR (KBr disc, cm−1): w
1645 (s), 1537 (s), 1394 (m), 1344 (s), 1014 (s), 642
(m).
3. Results and discussion
3.1. Synthesis
The precursor in this work Mo3S4(dtp)3(m-dtp)(H2O)
Table 1
Crystallographic data for compounds I and II
I
II
Chemical formula
Formula weight
Crystal system
C
24H39Mo3N2O10P3S10
C22H41Mo3N2O11P3S10
1210.90
triclinic
1216.90
triclinic
(
(
Space group
Crystal dimension (mm)
Unit cell dimensions
P1
P1
0.75×0.25×0.08
0.40×0.35×0.30
,
a (A)
13.6576(1)
13.8672(1)
14.6284(1)
100.16(1)
114.69(1)
97.27(1)
2415.0(3)
2
10.556(3)
13.840(3)
16.994(5)
85.01(2)
77.22(2)
67.75(2)
2241.0(10)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
Dcalc (g cm−3
)
1.673
1.795
q Range for data collection (°)
Absorption correction
Reflections collected
1.53–25.97
empirical psi-scan
9481
1.23–25.03
empirical
11578
Reflections observed (\2|)
Data/restraints/parameters
R1, wR2 (I\2|(I)) a
Transmission min, max
Goodness-of-fit, S
5622
5528
9449/0/424
0.0827, 0.2041
0.8044, 0.9996
0.971
7786/1/460
0.0525, 0.1105
0.6511, 1.0000
1.006
Largest shift
Largest different peak (e A
0.001
2.04
0.050
0.82
−3
,
)
2 1/2
a R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ. wR=[Sw(ꢀFoꢀ−ꢀFcꢀ)2/SwꢀFoꢀ ]
.

Y.-H. Tang et al. / Polyhedron 20 (2001) 2911–2916
2913
has three different substitution sites [3,7]: bridging m-
dtp, terminal –dtp, and the loosely-coordinated ligand
H2O, as shown below:
cally stable and easier to deposit in the polar solvents
used. In DMF, Mo3S4(dtp)4(H2O) dissociates too much
but Mo3S4(dtp)3(RCOO)(Py) is relatively stable. This
enables the substitution to take place. More discussion
on the synthesis will be presented in the following 31P
NMR spectra section.
By choosing ligands of different chelating properties
for the precursor Mo3S4(dtp)3(m-L%)(L), (L%=dtp,
HCOO−, CH3COO−, CH2COO−, CCl3COO−; L=
H2O, CH3CN, Py, etc.), we can design many kinds of
derivatives with desired structures and functions. For
example, by the specific binding capability of the
groups on the benzene ring, oligomerized and polymer-
ized cluster compounds can be rationally synthesized
[13]. Other important applications of this reaction are
in the exploitation of new catalysts [14,15] and in the
synthesis of new optical limiting materials [16].
It has been confirmed that the loosely-coordinated
ligand H2O, the bridging –dtp, as well as the terminal
–dtp are dynamically labile in polar solvents such as
acetone and CHCl3. These ligands sites can be replaced
by other ligands to a different extent, forming a group
of new cluster derivatives, which are more stable than
the precursor in dipolar solvents.
The synthesis reactions of the title compounds can be
described as follows:
3.2. Crystal structure
Mo3S4(dtp)4(H2O)+p-NO2C6H4COOH
The crystal structures of compounds I and II are
shown in Fig. 1. Selected bond lengths and angles for
the two compounds are presented in Tables 2 and 3,
respectively. The structures of compounds I and II are
similar to the typical incomplete cuboidal structures
reported [17]. Each Mo atom is octahedrally coordi-
nated with high distortion as in the case of other
analogous clusters. The molecular core is [Mo3S4], in
which three Mo atoms construct an isosceles triangle.
Direct bonding is found between each pair of Mo
atoms. The ligand p-nitrobenzoate bridges Mo1 and
Mo3 via its –COO chelating group. The solvated Py or
DMF are coordinated to the remaining Mo atom with-
out –COO coordination.
EtOH/CH Cl
ꢀꢀꢀꢀꢀꢀꢀꢁ2Mo3S4(dtp)3(p-NO2C6H4COO)(Py)
(1)
2
Py
Mo3S4(dtp)3(CCl3COO)(Py)+p-NO2C6H4COOH
DMF
ꢀꢀꢁ Mo3S4(dtp)3(p-NO2C6H4COO)(DMF)
(2)
Compound I was obtained via the ligand substitution
of Py for H2O, and of the bridging ligand p-
NO2C6H4COO− for m-dtp. Similarly, the replacement
of CCl3COO− by p-NO2C6H4COO− and of Py by
DMF gives compound II.
It is noteworthy that, for the first time, we have
obtained the expected substitution products using
Mo3S4(dtp)3(RCOO)(Py) instead of Mo3S4(dtp)4(H2O)
as the starting material (see reaction (2)). Attempts to
prepare the same product from Mo3S4(dtp)4(H2O) in
DMF failed. Lu et al. [12] suggested that the coordina-
tion capability of substituents such as toluene-3,4-
In compound I, the bond length of Mo2–N1 (Py) is
,
2.347(7) A, far longer than that of normal Mo (+4)–N
,
(2.0–2.18 A), but similar to that of Mo–N (2.385–2.40
,
A) in Mo3S4(m-O2CR)(dtp)3(Py) (R=H, CH3,
dithiol
(TDT),
1-Pyrrolidinecarbodithioic
acid
CH2CH3) [18,19], showing that Py is also loosely coor-
dinated to Mo2 in this molecule.
(Hdtcpyr), diethyldithiocarbamic acid (Hdtc), RCOOH
and Hdtp, well conforms to their respective acidity. In
general, lower acidity corresponds to stronger coordina-
tion capability. The pKa of p-NO2C6H4COOH is 3.42,
while that of CCl3COOH is 0.64, so reaction (2) can
take place.
,
In compound II, Mo2–O41 is 2.219(6) A, compara-
,
ble to the Mo–O (DMF) distance (2.278 A) of
Mo3S4(dtc)4(DMF) [20], but shorter than that of Mo–
,
O (H2O) (2.361 A) in Mo3S4(dtp)4(H2O) [21], which
means DMF is coordinated stronger than H2O.
This can explain well reaction (1). Nevertheless, our
further experiments indicate that the same products can
also be crystallized out when Mo3S4(dtp)3(CH3COO)-
(Py) or Mo3S4(dtp)3(CH3CH2COO)(Py) is used as the
precursor in similar experiments. This is contradictory
to the acidity interpretation because the pKa value of
either CH3COOH (4.76) or CH3CH2COOH (4.87) is
higher than that of p-NO2C6H4COOH (3.42). We claim
that the stability of the clusters in the polar solvent will
determine whether the reaction will happen. The bulky
aromatic acid-substituted compounds are more dynami-
The only difference between compounds I and II is
the loosely-coordinated ligands, Py and DMF. How-
ever, their effects on the [Mo3S4] core and on the
alignment of the bridging ligand p-nitrobenzoate are
obvious. The average Mo–Mo distance of compound I
,
,
is 2.732 A, shorter than that of compound II (2.741 A).
The average Mo–m-S and Mo–m3-S distances of com-
,
pound I are 2.286 and 2.334 A, respectively, shorter
than those of compound II (Mo–m-S 2.294 A, Mo–m3-
S 2.335 A). Hence the [Mo3S4] core in I is more tightly
,
,
packed than that in II. We can conclude that DMF is

2914
Y.-H. Tang et al. / Polyhedron 20 (2001) 2911–2916
Fig. 1. ORTEP drawings of compounds I and II with thermal ellipsoids at the 20% probability level.
a stronger ligand than Py and it draws more electrons
of Mo into the Mo–O bond, weakening the central
Mo–Mo bond. This is consistent with the fact that
[Mo3S4(H2O)9]4+ has the shortest average Mo–Mo
distance [22], because H2O is very loosely coordinated
to Mo. p-Nitrobenzoates in these two molecules are
coordinated in different orientations. The dihedral an-
gles measured between the plane (Mo1, Mo2, Mo3) and
the benzene plane (C52, C53, C54, C55, C56, C57) is
146.6° for I and 52.4° for II.
precursor is selected, the choice of solvent used in the
synthesis is quite important to obtain the desired
derivatives bridged by organic acids. In low polar sol-
vents like ethanol, o-dichlorobenzene, the loosely-coor-
dinated ligand is kinetically labile, but other ligands are
quite stable [7]. However, in more polar solvents such
as Py, DMF, both the loosely-coordinated ligand and
the bridging ligand –dtp or RCO2 are kinetically labile.
Furthermore, for the derivatives substituted by aro-
matic acids, the influence of solvent is negligible. The
spectra in this experiment show that all the moieties of
compounds I and II are stable in highly polar solutions,
so are the other aromatic acid-substituted derivatives.
Whether we can get a desired product in the ligand
substitution reaction is determined by the relative sta-
bility of both the precursor and product in solution. In
practice, Mo3S4(dtp)4(H2O) is a good precursor in sol-
vents of low polarity like ethanol and o-dichloroben-
zene, but not in polar solvents such as Py and DMF
because it then becomes unstable. Mo3S4(dtp)3-
(RCO2)(L) of aliphatic-bridged acids are good precur-
sors in Py and DMF, but they cannot be the final
products because of their lability in strong polar sol-
vents.
3.3. 31P NMR spectra
The 31P NMR spectra of the two compounds were
measured in CHCl3, showing two peaks at 109.7 (T1)
and 108.8 ppm (T2) for compound I and 110.1 (T1) and
107.4 ppm (T2) for compound II (Fig. 2). The assign-
ment of the 31P resonances is consistent with the litera-
ture [7]. The relative positions and their line widths are
determined by the loosely-coordinated ligands [4,7]. We
have measured 31P NMR spectra to study the kinetic
behavior in organic solvents for all the substitution
derivatives from Mo3S4(dtp)4(H2O) and [Mo3S4-
(H2O)9]4+ using aliphatic and aromatic acids as the
substituent ligands. The result shows that, once the

Y.-H. Tang et al. / Polyhedron 20 (2001) 2911–2916
2915
Table 2
,
Selected bond lengths (A) and bond angles (°) for compound I
Bond lengths
Mo1–Mo2
Mo1–Mo3
Mo1–S
Mo1–S1
Mo1–S3
Mo1–O1
Mo2–Mo3
Mo2–S
2.744(1)
2.703(1)
2.337(2)
2.273(3)
2.292(3)
2.277(9)
2.7499(3)
2.327(3)
2.289(2)
Mo2–S2
Mo2–N1
Mo3–S
Mo3–S2
Mo3–S3
Mo3–O2
O1–C51
O2–C51
2.296(3)
2.347(7)
2.339(3)
2.278(3)
2.290(3)
2.309(9)
1.311(16)
1.348(16)
Mo2–S1
Bond angles
Mo1–Mo2–Mo3
Mo1–Mo3–Mo2
Mo3–Mo1–Mo2
S–Mo1–Mo2
S–Mo2–Mo1
S–Mo2–Mo3
S–Mo1–Mo3
S–Mo3–O2
S1–Mo2–Mo1
S1–Mo2–Mo3
S1–Mo1–O1
S1–Mo1–S
58.95(3)
60.42(3)
60.63(3)
53.78(7)
54.14(6)
54.10(7)
54.72(7)
83.5(2)
52.76(7)
97.36(8)
172.4(2)
105.57(10)
105.40(9)
96.69(10)
93.74(10)
168.3(2)
S2–Mo2–Mo1
S2–Mo2–Mo3
S2–Mo2–S
97.58(8)
52.74(7)
105.25(10)
105.43(10)
94.00(10)
170.9(3)
53.80(7)
97.28(8)
107.84(10)
84.7(2)
86.2(2)
34.33(19)
84.9(2)
113.5(13)
112.7(13)
S2–Mo3–S
S2–Mo3–S3
S2–Mo3–O2
S3–Mo1–Mo3
S3–Mo1–Mo2
S3–Mo3–S
S3–Mo3–O2
O1–Mo1–Mo3
O1–Mo1–Mo2
O1–Mo1–S3
O1–C51–C52
O2–C51–C52
S1–Mo2–S
S1–Mo2–S2
S1–Mo1–S3
S1–Mo2–N1
Fig. 2. 31P NMR spectra of compounds I and II.
Table 3
,
Selected bond lengths (A) and bond angles (°) for compound II
4. Supplementary data
Bond lengths
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Center, CCDC Nos. 152332 and 152333. Copies
of this information may be obtained free of charge
from The Director, CCDC, 12 Union Road, Cam-
bridge, CB2 1EZ, UK (fax: +44-1233-336-033; e-mail:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
Mo1–Mo2
Mo1–Mo3
Mo1–S
Mo1–S1
Mo1–S3
Mo1–O1
Mo2–Mo3
Mo2–S
2.760(1)
2.697(1)
2.340(2)
2.294(2)
2.297(2)
2.230(5)
2.766(1)
2.328(2)
2.279(2)
Mo2–S2
Mo2–O41
Mo3–S
Mo3–S2
Mo3–S3
Mo3–O2
O1–C51
O2–C51
2.303(2)
2.219(6)
2.338(2)
2.293(2)
2.297(2)
2.248(5)
1.272(8)
1.267(8)
Mo2–S1
Bond angles
Mo1–Mo2–Mo3
Mo1–Mo3–Mo2
Mo1–Mo3–O2
Mo1–Mo2–O3
Mo2–Mo3–O2
Mo3–Mo1–Mo2
S–Mo1–Mo3
S–Mo2–Mo1
S–Mo3–Mo1
S–Mo3–Mo2
S–Mo2–Mo3
S–Mo1–Mo2
S1–Mo2–S
58.42(3)
60.69(3)
84.04(13)
58.42(3)
132.41(13)
60.89(3)
54.75(5)
53.95(5)
54.83(5)
53.47(5)
53.80(5)
53.53(5)
105.34(7)
52.61(6)
104.46(7)
99.37(6)
98.22(8)
S1–Mo2–Mo1
S2–Mo2–Mo1
S2–Mo3–Mo1
S2–Mo2–S
S2–Mo3–Mo2
S3–Mo3–Mo2
S3–Mo1–Mo2
S3–Mo3–Mo1
S3–Mo1–Mo3
S3–Mo3–S
O1–Mo1–S1
O1–Mo1–Mo2
O1–Mo1–Mo3
O1–Mo1–S
O1–C51–C52
O2–C51–C52
53.10(6)
97.81(6)
99.86(6)
104.81(7)
53.15(6)
97.40(6)
97.53(6)
54.05(5)
54.04(5)
108.27(7)
173.42(14)
133.87(13)
84.77(13)
82.10(14)
116.4(6)
117.7(6)
Acknowledgements
The authors would like to thank the National Natu-
ral Science Foundation of China (no. 29733090) and 95
Key Program of the Chinese Academy of Sciences
(KJ952-J1-519) for financial support.
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