Synthesis, X-ray Structure Analysis and Spectroscopic Characterization of trans-Aquabis(μ-benzoato-κ2 O:O′) bis[μ-N,N′-bis(4-methoxyphenyl) formamidinato-κ2 N:N′] dimolybdenum(II)

Article abstract of DOI:10.1007/s10870-017-0698-7

Abstract: The title compound, trans-Mo₂(DAniF)₂(OOCC₆H₅)₂(H₂O) (I) has a quadruply bonded Mo₂ ⁴⁺ unit equatorially coordinated by two N,N′-bis(4-methoxyphenyl)formamidinate (referred as DAniF) ligands and two benzoate (OOCC₆H₅) groups in transverse, and axially coordinated by one aqua oxygen atom. The compound crystallizes in the space group C2/c with one molecule in the asymmetric unit and features a Mo–Mo bond length of 2.0983(4) ?, which is typical for dimolybdenum quadruple bonds. In the crystal, the offsetstacking between pairs of phenyl rings creating a one-dimensional linear chain perpendicular to the Mo–Mo directions, with a distance between phenyl rings of 3.44?? and the center-to-center distance of 3.83??. The coordinated water oxygen atoms act as donors and uncoordinated methoxyl group oxygen atoms act as acceptors in intermolecular O–H?O hydrogen bonds.stacking between phenyl rings assemble the molecules into a three-dimensional framework. Graphical Abstract: The offsetstacking between phenyl rings of quadruply bonded Mo₂ ⁴⁺ paddle-wheel molecules create a one-dimensional linear chain. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10870-017-0698-7

J Chem Crystallogr
DOI 10.1007/s10870-017-0698-7
ORIGINAL PAPER
Synthesis, X-ray Structure Analysis and Spectroscopic
Characterization of trans-Aquabis(µ-benzoato-κ2O:O′)
bis[µ-N,N′-bis(4-methoxyphenyl) formamidinato-κ2N:N′]
dimolybdenum(II)
Ya-Jie Kong1 · Li-Juan Han1
Received: 4 September 2014 / Accepted: 8 August 2017
© Springer Science+Business Media, LLC 2017
Abstract The title compound, trans-Mo2(DAniF)2
(OOCC6H5)2(H2O) (I) has a quadruply bonded Mo24+ unit
equatorially coordinated by two N,N′-bis(4-methoxyphenyl)
formamidinate (referred as DAniF) ligands and two benzoate
(OOCC6H5) groups in transverse, and axially coordinated
by one aqua oxygen atom. The compound crystallizes in
the space group C2/c with one molecule in the asymmetric
unit and features a Mo–Mo bond length of 2.0983(4) Å,
which is typical for dimolybdenum quadruple bonds. In the
crystal, the offset π–π stacking between pairs of phenyl rings
creating a one-dimensional linear chain perpendicular to the
Mo–Mo directions, with a distance between phenyl rings
of 3.44 Å and the center-to-center distance of 3.83 Å. The
coordinated water oxygen atoms act as donors and unco-
ordinated methoxyl group oxygen atoms act as acceptors
in intermolecular O–H⋯O hydrogen bonds. π–π stacking
between phenyl rings assemble the molecules into a three-
dimensional framework.
Graphical Abstract The offset π–π stacking between phe-
4+
nyl rings of quadruply bonded Mo2 paddle-wheel mol-
ecules create a one-dimensional linear chain.
Keywords Crystal structure · Dimolybdenum ·
Quadruple bonds · Intermolecular interactions
* Ya-Jie Kong
kongyaj@jnxy.edu.cn
Introduction
1
Key Laboratory of Inorganic Chemistry in Universities
of Shandong Province, Department of Chemistry
and Chemical Engineering, Jining University, Qufu 273155,
Shandong, China
Intermolecular weak interactions generally include hydro-
gen bonds, π–π stacking, cation-π interactions, and others,
Vol.:(0123456789)
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J Chem Crystallogr
with hydrogen bonds playing a prominent role in supermo-
lecular and template chemistry [1–3]. The intermolecular
interaction of benzene has been studied extensively, espe-
cially in the last three decades, both by experimental and
theoretical methods as a prototype for the π–π stacking [4–7]
as phenyl–phenyl π–π stacking plays an important role in
determining the conformation of organic molecules [8], the
structure and stability of proteins and polynucleotides, [9]
and in directing the stereoselectivity of organic transforma-
tions [10].
solution (0.5 M in methanol). After stirring for about 2 h,
a colorless microcrystalline material was removed by fil-
tration. An excess of benzoic acid (0.16 g, 1.3 mmol) was
added to the filtrate. After stirring at room temperature for
an additional 1 h, the solvent was removed under vacuum,
and the residue was washed with ethanol (2×15 mL), then
dried under vacuum. The yellow solid was dissolved in THF
(15 mL) and the solution was layered with hexanes. Yel-
low block-shaped crystals formed after several days. Yield:
0.26 g (55%). Anal. Calcd for C44H42Mo2N4O9: C, 54.89; H,
4.40; N, 5.82; found: C, 54.94; H, 4.38; N, 5.87 (Scheme 1).
We became interested in making dimetal compounds
having phenyl rings suitable for forming novel supramo-
lecular arrays using phenyl–phenyl π–π stacking. The key
to success in creating dimetal units is a design that selec-
tively blocks some coordination sites, for example by
using one to three nonlabile three-atom bridging ligands.
For this purpose, a new quadruply bonded dimolybde-
num compound with two transoid C6H5 pendants was
prepared. Compound I is a mixed–ligand complex, trans-
Mo2(DAniF)2(OOCC6H5)2·(H2O), on which auxiliary
ligands DAniF [11] [N,N′-bis(4-methoxyphenyl) forma-
midinate] are used to block the unnecessary coordination
sites. Given the transoid geometry of the building block,
intermolecular phenyl–phenyl π–π stacking was expected
to generate infinite extension of the supramolecular motifs.
X-ray Crystal Structure Determinations
Determination of unit cell and data collection of the
compound I were performed on a Bruker CCD diffrac-
tometer using graphite monochromated MoKα radiation
(λ=0.71073 Å) at 293 K. The data integration and reduc-
tion were carried out with SAINT-plus software [15]. An
empirical absorption correction was applied to the collected
reflections with SADABS [16], and the space group was
determined using XPREP [17]. The structure was solved
by the direct methods with SHELXS-2014 and refined
by full matrix least-squares with SHELXL-2014 [18] on
F2. All nonhydrogen atoms were refined with anisotropic
thermal parameters. The water H atoms were located from
the difference Fourier map and included as riding atoms,
with O–H = 0.85 Å (lattice water). The C-bound H atoms
were positioned geometrically and refined as riding atoms,
with C–H = 0.93 Å (aromatic) or 0.96 Å (methyl) and
Uiso(H)=kUeq(C), where k=1.5 for the methyl group and
1.2 for all H atoms bonded to the aromatic C atoms. All
structures were examined using the Addsym subroutine of
PLATON [19] to ensure that no additional symmetry could
be applied to the models. The molecular graphics were done
using XP in SHELXTL [20] and DIAMOND [21]. Crystal
data and structural refinement parameters are summarized
in Table 1 and selected bond lengths and bond angles are
listed in Table 2.
Experimental
Materials and Methods
All manipulation and procedures were performed in a
nitrogen atmosphere, using either a nitrogen drybox or
standard Schlenk line techniques. Solvents were freshly
distilled in a nitrogen atmosphere by employing stand-
ard procedures or dried and degassed using a Glass
Contour solvent purification system. The starting mate-
rials DAniF [11], Mo2(OOCCH3)4 [12, 13] and trans-
Mo2(DAniF)2(OOCCH3)2 [14] were prepared according to
published methods. Elemental analyses for C, H and N were
performed with a Vario EL III elemental analyzer. 1H NMR
spectra were recorded with a Mercury-300 NMR spectrom-
eter with chemical shifts (δ in ppm) referenced to CDCl3.
Electronic spectra in CH2Cl2 were measured in a range of
300 to 800 nm on a Agilent 8453 UV–Vis spectrophotom-
eter. Raman spectra were collected on a Nicolet Almega XR
laser Raman spectrometer.
Results and Discussion
Crystal Structure
Crystals trans-Mo2(DAniF)2(OOCC6H5)2·(H2O) (I) were
obtained by crystallization from THF/C6H14 solution.
The single crystal structure of (I) is shown in Fig. 1. The
title compound crystallized in the space group C2/c with
one molecule in the asymmetric unit. The molecule has a
quadruply bonded Mo24+ unit, equatorially coordinated by
two DAniF ligands and two benzoate (OOCC6H5) groups
in transverse forming a paddle-wheel-type structure,
Synthesis of the trans-Mo2(DAniF)2(OOCC6H5)2(H2O)
(I)
To the solution of trans-Mo2(DAniF)2(OOCCH3)2 (0.41 g,
0.50 mmol) in 15 mL of THF, was added 2.0 mL NaOCH3
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J Chem Crystallogr
OCH3
Scheme 1 Reaction scheme
for the synthesis of the title
compound
OCH3
H3CO
H
O
O
O
H
+
2
CH3CH2OH
+
3
N
H
N
N
H
H
DAniF
H3C
O
O
O
O
O
Cl
Cl
Mo
O
O
hexanes
reflux
Mo(CO)6
+
+
H3C
+
CH3
OH
Mo
O
O
O
O
O
CH3
N
H3C
O
OCH3
H3CO
2
O
N
O
Mo
NaOCH3
Mo
O
O
O
H
H3C
H3C
+
CH3
CH3
Mo
O
O
Mo
O
O
N
N
O
N
H
O
N
CH3
OCH3
H3CO
H
=
N
N
_
N
N
and axially coordinated by one aqua oxygen atom with a
Mo2–O1w distance of 2.475(2) Å. The Mo1–Mo2 bond
length of 2.0983(4) Å is typical for dimolybdenum quadru-
ple bonds [22]. The Mo–O lengths in the equatorial positions
range from 2.1002 (16) Å for Mo1–O4 to 2.1329 (16) Å for
Mo2–O3, and the Mo–N lengths are 2.132 (2) Å for Mo1–N2
and 2.149 (2) Å for Mo2–N1, respectively (Table 2). The
dihedral angle between the phenyl ring and the adjacent five-
membered ring (Mo2O2C) is 18.706(8)°. In comparison, in
compound trans-Mo2(DAniF)2(OOCC6F5)2·(THF)2 (II)
[23], the dihedral angle between the pentafluoro-phenyl ring
and adjacent five-membered ring (Mo2O2C) is 26.902(9)°,
and the larger dihedral angle can be attributed to the strong
O⋯F repulsion. The presence of Mo–Mo quadruple bonds,
which act as an electron withdrawing group, increase the
electron density on the oxygen atoms, and thus enhance
O⋯F repulsion.
illustrated in Fig. 2. The perpendicular distance between
phenyl rings is 3.44 Å and the center-to-center distance
is 3.83 Å.
In compound II, perfluorophenyl–perfluorophenyl inter-
action occurs in an offset face to face stacking fashion with
an interplanar distance of 3.30 Å and a center to center
distance of 3.53 Å. The above results suggest that the π–π
stacking interactions between perfluorophenyl rings are
stronger than those between phenyl rings. While, in com-
pound Mo2(DAniF)3(OOCC6H5) (III) having only one
phenyl ring in the equatorial position of the paddle–wheel
structure [24], the π–π stacking between pairs of phenyl
rings was not observed owing to the steric effect of DAniF
ligand in transverse of the phenyl ring. The phenyl ring
and the (Mo2O2C) fragment are nearly co-planar, making
a dihedral angle of 3.24 (13)°. So we infer that the dihedral
angle of 18.706(8) ° is induced by π–π stacking between
phenyl rings in compound I (Fig. 3).
In compound I, the offset π–π stacking between pairs
of phenyl rings creates a one-dimensional ladder chain as
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J Chem Crystallogr
Table 1 Crystal data and structure refinement for Compound I
Empirical formula
C44H42Mo2N4O9
Formula weight
Crystal color
Crystal size (mm)
Crystal system
space group
a (Å)
b (Å)
c (Å)
α (deg)
962.70
Yellow
0.23×0.20×0.20
Monoclinic
C2/c
16.2976 (13)
22.6595 (17)
11.6105 (9)
90.00
β (deg)
101.2570 (10)
90.00
4205.2 (6)
4
1.521
0.657
γ (deg)
Volume (Å3)
Z
dcalcd (g/cm3)
μ (mm−1
F (000)
λ (Å)
)
1960
0.71073
293(2) K
2.18 to 25.00
−19≤h≤19
−26≤k≤21
−13≤l≤13
Temperature
θrange (deg)
h,k,l range
Fig. 1 Molecular structure of the title compound drawn with dis-
placement ellipsoids at the 30% probability level
Reflections collected/unique
10,803/3709
are assembled by O–H⋯O hydrogen bonds and π–π stacking
between phenyl rings into a three-dimensional framework,
as shown in Fig. 5.
[R(int)=0.0226]
Completeness to θ
99.9% (θ=25.00)
0.877 and 0.860
3701/0/270
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
1.030
1H NMR Spectra
Final R indices [I>2σ(I)]a
R1 =0.0257
wR2 =0.0641
The 1H NMR of compound I is depicted in Fig. 6. 1H NMR
(CDCl3): 8.35 (s, 2H, –NCHN–), 8.31 (d, 2H, aromatic),
7.48 (s, 1H, aromatic), 7.46 (d, 2H, aromatic), 6.84 (d, 8H,
aromatic), 6.79 (d, 8H, aromatic), 3.75 (s, 12H, –OCH3).
There are two doublets and one singlet in the range from
8.31 to 7.46 ppm, which correspond to the aromatic protons
from the phenyl ligands. Two sets of doublets at 6.84 to
6.76 ppm stem from hydrogen atoms of the anisyl groups.
The signals for the methoxy groups of the anisyl groups
R indices (all data)
R1 =0.0348
wR2 =0.0693
Largest diff. Peak and hole(e·Å−3
)
0.455 and −0.327
aR1 =Σ||Fo|–|Fc||/Σ|Fo|; wR2 = [Σw(Fo2–Fc2)2/ΣwFo4]1/2
Table 2 Selected bond lengths
Mo1–Mo2
2.0983 (4)
2.1002 (16)
2.132 (2)
2.1329 (16)
2.149 (2)
(Å) for I
Mo1–O4
Mo1–N2
Mo2–O3
Mo2–N1
Mo2–O1W
1
appear as singlets at 3.74 ppm. The H NMR spectra are
consistent with the above described crystal structure.
2.475 (2)
Absorption and Raman Spectra
Figure 7a shows the absorption spectra in visible region of
compound I. The intense absorption at lower energy, λmax
541 nm (ε, 2.2 × 104 L mol−1 cm−1), can be assigned as a
MLCT (metal ligand charge transfer) δ–π* transition. More-
over, Fig. 7b shows the Raman spectrum of compound I, In
which the band at 402 cm−1 is attributed to ν (Mo–Mo), and
Intermolecular O–H⋯O hydrogen bonds link the Mo
dimers into two-dimensional sheet (Fig. 4), where coordi-
nated water oxygen atoms serve as H-bond donors and unco-
ordinated methoxyl group oxygen atoms serve as H-bond
acceptors [O1w⋯O1i=2.797(3) Å]. In summary, the dimers
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J Chem Crystallogr
Fig. 2 Part of a one-dimen-
sional linear chain formed by
the π–π stacking in compound I
Fig. 3 Part of a one-dimen-
sional linear chain formed by
π–π stacking in compound II
[23]
Fig. 5 Crystal packing of compound I
Conclusion
In summary, a novel dimolybdenum paddle–wheel struc-
ture has been synthesized and characterized in which
O–H⋯O hydrogen bonds and π–π stacking between
phenyl rings assemble the compound I into a three-
dimensional framework. Moreover, the dihedral angle of
18.706(8)° in I is induced by the π–π stacking between
phenyl rings, but the π–π stacking interactions between
phenyl rings are weaker than those between perfluoro-
phenyl rings.
Fig. 4 A view of O–H⋯O hydrogen bonds in compound I
the vibrations observed at 1395, 1490 and 1594 cm−1 cor-
respond to ν (C–C) and ν (CO2–C) [25]. The Raman spec-
trum is in agreement with the structure determined by X-ray
diffraction.
1 3

J Chem Crystallogr
Fig. 6 1H NMR spectrum of
the title compound
Fig. 7 a Electronic spectrum of the title compound; b Raman spectrum of the title compound with laser excitation at 514.5 nm
(CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax:
Supplementary Materials
+44(0)1223-336033; email: deposit@ccdc.cam.ac.uk.
CCDC-1021162 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge at http://www.ccdc.cam.ac.uk/conts/retrieving.
html or from the Cambridge Crystallographic Data Centre
Acknowledgements This work was supported by the Natural Science
Foundation of Shandong Province (No. ZR2013BL004) and the Youths
Science Foundation of Jining University (No. 2012QNKL01).
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J Chem Crystallogr
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