Synthesis, characterization, and crystal structures of dioxomolybdenum(VI) complexes [MoO2L1(CH3OH)] and [MoO 2L2(CH3OH)] Derived from 4-Halo-2-[(2- hydroxypropylimino)methyl]phenol

Article abstract of DOI:10.1080/15533174.2012.751414

Two new mononuclear dioxomolybdenum(VI) complexes, [MoO₂L ¹(CH₃OH)] (1) and [MoO₂L²(CH ₃OH)] (2), have been prepared by the reaction of MoO ₂(acac)₂ with the tridentate Schiff base ligands 4-chloro-2-[(2-hydroxypropylimino)methyl]phenol (H₂L¹) and 4-bromo-2-[(2-hydroxypropylimino)methyl]phenol (H₂L²), respectively, in methanol. The complexes were characterized by elemental analyses, infrared spectra, and single-crystal X-ray diffraction. Complex 1 crystallizes in triclinic space group with unit cell dimensions a = 6.970(2), b = 10.350(2), c = 10.570(2) A, α = 68.680(3), β = 78.813(3), γ = 77.321(3)°, V = 687.5(3) A³, Z = 2, R₁ = 0.0381, and wR₂ = 0.0860. Complex 2 crystallizes in triclinic space group with unit cell dimensions a = 7.075(2), b = 10.473(2), c = 10.691(2) A, α = 68.744(3), β = 77.959(3), γ = 76.320(3)°, V = 710.8(3) A³, Z = 2, R₁ = 0.0477, and wR₂ = 0.1171. Both complexes consist of cis-MoO₂ core coordinated by a Schiff base ligand through two deprotonated hydroxyl groups and one imino nitrogen atom. The octahedral coordination around the molybdenum atom is completed by the neutral methanol ligand. Supplemental materials are available for this article. Go to the publisher's online edition of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry to view the supplemental file.

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Synthesis, Characterization, and Crystal Structures of
Dioxomolybdenum(VI) Complexes [MoO2L1(CH3OH)]
and [MoO2L2(CH3OH)] Derived from 4-Halo-2-[(2-
hydroxypropylimino)methyl]phenol
Hong-Ge Zhang a
a Department of Chemistry and Chemical Engineering , Baoji University of Arts and
Sciences , Baoji , P. R. China
Accepted author version posted online: 18 Mar 2013.Published online: 02 May 2013.
To cite this article: Hong-Ge Zhang (2013) Synthesis, Characterization, and Crystal Structures of Dioxomolybdenum(VI)
Complexes [MoO2L1(CH3OH)] and [MoO2L2(CH3OH)] Derived from 4-Halo-2-[(2-hydroxypropylimino)methyl]phenol, Synthesis
and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:8, 933-936, DOI: 10.1080/15533174.2012.751414
To link to this article: http://dx.doi.org/10.1080/15533174.2012.751414
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:933–936, 2013
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.751414
Synthesis, Characterization, and Crystal Structures
of Dioxomolybdenum(VI) Complexes [MoO2L1(CH3OH)]
and [MoO2L2(CH3OH)] Derived from
4-Halo-2-[(2-hydroxypropylimino)methyl]phenol
Hong-Ge Zhang
Department of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences,
Baoji, P. R. China
num enzymes that are often referred to as oxomolybdenum
enzymes.[2] Therefore, the mononuclear dioxomolybdenum
complexes might be interesting model systems. In recent years,
a number of dioxomolybdenum complexes have been synthe-
sized and characterized to mimic the biological systems.[3–5]
Schiff bases are a kind of important ligands in coordination
chemistry, however, the number of dioxomolybdenum com-
Two new mononuclear dioxomolybdenum(VI) complexes,
[MoO2L1(CH3OH)] (1) and [MoO2L2(CH3OH)] (2), have been pre-
pared by the reaction of MoO2(acac)2 with the tridentate Schiff
base ligands 4-chloro-2-[(2-hydroxypropylimino)methyl]phenol
(H2L1) and 4-bromo-2-[(2-hydroxypropylimino)methyl]phenol
(H2L2), respectively, in methanol. The complexes were character-
ized by elemental analyses, infrared spectra, and single-crystal X-
ray diffraction. Complex 1 crystallizes in triclinic space group P1 plexes with Schiff bases is small. I report here the synthesis
with unit cell dimensions a = 6.970(2), b = 10.350(2), c = 10.570(2)
and characterization of two new dioxomolybdenum(VI)
Å, α = 68.680(3), β = 78.813(3), γ = 77.321(3)◦, V = 687.5(3) Å3,
Z = 2, R1 = 0.0381, and wR2 = 0.0860. Complex 2 crystallizes in
triclinic space group P1 with unit cell dimensions a = 7.075(2),
b = 10.473(2), c = 10.691(2) Å, α = 68.744(3), β = 77.959(3),
γ = 76.320(3)◦, V = 710.8(3) Å3, Z = 2, R1 = 0.0477, and wR2 =
0.1171. Both complexes consist of cis-MoO2 core coordinated by a
Schiff base ligand through two deprotonated hydroxyl groups and
one imino nitrogen atom. The octahedral coordination around the
molybdenum atom is completed by the neutral methanol ligand.
complexes, [MoO2L1(CH3OH)] (1) and [MoO2L2(CH3OH)]
(2), derived from the tridentate Schiff base ligands 4-
chloro-2-[(2-hydroxypropylimino)methyl]phenol (H2L1) and
4-bromo-2-[(2-hydroxypropylimino)methyl]phenol (H2L2).
EXPERIMENTAL
Materials and Physical Measurements
The chemicals 5-chlorosalicylaldehyde, 5-bromosalicyl
aldehyde, 1-aminopropan-2-ol (Fluka), and solvents (AR grade)
were used without further purification. [MoO2(acac)2] was pre-
pared as described in literature.[6] Elemental analyses of the
Schiff bases and the complexes were carried out using a Vario EL
III CHNS analyzer. Infrared spectra were recorded on a JASCO
FT/IR-4100 type A spectrometer in the range 4000–400 cm–1
using KBr pellets.
Supplemental materials are available for this article. Go to the
publisher’s online edition of Synthesis and Reactivity in Inorganic,
Metal-Organic, and Nano-Metal Chemistry to view the supplemen-
tal file.
Keywords crystal structure, hydrogen bonding, molybdenum, Schiff
bases, X-ray diffraction
INTRODUCTION
Synthesis of the Schiff Bases
Molybdenum has been found to be a very important element
in biological systems. Apart from the nitrogenases in where
a molybdenum atom can be a component of the multinuclear
active sites,[1] there are a number of mononuclear molybde-
H2L1: To a stirred methanolic solution (50 mL) of 5-
chlorosalicylaldehyde (10 mmol, 1.56 g) was added dropwise a
methanolic solution (30 mL) of 1-aminopropan-2-ol (10 mmol,
0.75 g). The mixture was then stirred for 1 h at reflux. Af-
terwards the mixture was cooled to room temperature, and the
yellow products formed were collected by filtration. Yield, 82%.
Anal. Calcd. for C10H12ClNO2: C, 56.2; H, 5.7; N, 6.6. Found,
C, 56.1; H, 5.6; N, 6.7%.
Received 22 June 2012; accepted 16 November 2012.
This research was supported by the Scientific Research Projects of
the Education Department of Shaanxi Province (Grant No. 12JK0630).
Address correspondence to Hong-Ge Zhang, Department of Chem-
istry and Chemical Engineering, Baoji University of Arts and Sciences,
Baoji 721007, P. R. China. E-mail: zhang hongge@126.com
H2L1: This compound was prepared by the similar method
as described for H2L1, but with 5-chlorosalicylaldehyde re-
placed by 5-bromosalicylaldehyde (10 mmol, 2.01 g). Yield,
933

934
H.-G. ZHANG
87%. Anal. Calcd. for C10H12BrNO2: C, 46.5; H, 4.7; N, 5.4. were re-crystallized from methanol solvent. Anal. Calcd. for
Found: C, 46.7; H, 4.7; N, 5.5%.
C11H14ClMoNO5: C, 35.6; H, 3.8; N, 3.8. Found: C, 35.5; H,
3.8; N, 3.7%.
Synthesis of 1
To a methanolic solution (10 mL) of H2L1 (1.0 mmol, 0.21 g)
was added a methanolic solution (10 mL) of MoO2(acac)2
(1.0 mmol, 0.33 g) at room temperature. The mixture was
stirred for 1 h and the solvent was removed under reduced
pressure to give a quantitative yield of the product. Analytically
pure samples and crystals for X-ray structural determination
Synthesis of 2
This complex was prepared by the similar method as de-
scribed for 1, but with H2L1 replaced by H2L2. Anal. Calcd. for
C11H14BrMoNO5: C, 35.6; H, 3.5; N, 3.8. Found: C, 35.8; H,
3.6; N, 3.7%.
X-Ray Structure Determination
Intensity data for complexes 1 and 2 were collected on a
Bruker APEX II CCD area diffractometer (College of Chem-
istry and Chemical Engineering, Lanzhou University, China)
equipped with graphite-monochromatized Mo-Kα radiation
(λ = 0.71073 Å) and ω scan technique. Crystal data, exper-
imental conditions, details of structure determination, and fi-
nal refinement parameters are summarized in Table 1. Selected
bond distances and angles are listed in Table 2. The struc-
tures were solved by direct method and Fourier synthesis using
SHELXS97[7] and refined by full-matrix least-squares method
assuming anisotropic temperature factors for all non-hydrogen
atoms using SHELXL97.[8] The final Fourier maps revealed po-
sitions of all H atoms, but some with poor geometry. Therefore
all hydrogen atoms attached to carbon atoms were generated on
geometrical grounds. The hydrogen atoms bound to the oxygen
TABLE 1
Crystallographic and experimental data for the complexes 1
and 2
Complex
1
2
Empirical formula C11H14ClMoNO5 C11H14BrMoNO5
Formula weight
371.6
416.1
Crystal color, shape Yellow, block
Yellow, block
Crystal size (mm)
Crystal system
Space group
a (Å)
0.32 × 0.30 × 0.27 0.27 × 0.23 × 0.23
Triclinic
P1
Triclinic
P1
6.970(2)
10.350(2)
10.570(2)
68.680(3)
78.813(3)
77.321(3)
687.5(3)
2
7.075(2)
10.473(3)
10.691(3)
68.744(3)
77.959(3)
76.320(3)
710.8(3)
2
b (Å)
c (Å)
α (◦)
β (◦)
TABLE 2
γ (◦)
Selected bond lengths (Å) and angles (◦) for complexes 1 and 2
V (Å3)
1
Z
ρcalc (g cm–3)
F(000)
1.795
1.944
408
3.747
2.1–24.3
4169
Mo1-O1
Mo1-O3
Mo1-O5
1.944(3)
2.324(3)
1.696(2)
106.6(1)
96.5(1)
102.1(1)
93.6(1)
74.8(1)
170.6(1)
82.3(1)
77.2(1)
Mo1-O2
Mo1-O4
Mo1-N1
O4-Mo1-O2
O4-Mo1-O1
O2-Mo1-O1
O5-Mo1-N1
O1-Mo1-N1
O5-Mo1-O3
O1-Mo1-O3
1.939(2)
1.683(3)
2.243(3)
97.1(1)
97.1(1)
152.2(1)
159.0(1)
80.6(1)
82.8(1)
79.8(1)
372
μ(MoKα) (mm−1
θ range (◦)
)
1.162
2.4–27.3
5544
O4-Mo1-O5
O5-Mo1-O2
O5-Mo1-O1
O4-Mo1-N1
O2-Mo1-N1
O4-Mo1-O3
O2-Mo1-O3
N1-Mo1-O3
No. of reflections
measured
Unique reflections 2911
Observed reflections 2487
[I > 2σ(I)]
2999
2287
Parameters
Restraints
Rint
177
1
177
1
0.0246
1.060
0.0229
2
Goodness-of-fit on 1.081
Mo1-O1
Mo1-O3
Mo1-O5
1.964(4)
2.334(4)
1.714(4)
106.5(2)
96.8(2)
102.0(2)
93.6(2)
74.6(2)
170.8(2)
82.0(2)
77.3(2)
Mo1-O2
Mo1-O4
Mo1-N1
O4-Mo1-O2
O4-Mo1-O1
O2-Mo1-O1
O5-Mo1-N1
O1-Mo1-N1
O5-Mo1-O3
O1-Mo1-O3
1.960(4)
1.692(4)
2.267(4)
97.1(2)
97.0(2)
152.2(2)
159.1(2)
80.7(2)
82.7(2)
80.3(2)
F2
Max. and min.
Transmission
Final R indices
[I > 2σ(I)]
0.7074, 0.7443
0.4311, 0.4794
O4-Mo1-O5
O5-Mo1-O2
O5-Mo1-O1
O4-Mo1-N1
O2-Mo1-N1
O4-Mo1-O3
O2-Mo1-O3
N1-Mo1-O3
R1 = 0.0358,
wR2 = 0.0737
R1 = 0.0459,
wR2 = 0.0775
0.510, −0.494
R1 = 0.0477,
wR2 = 0.1171
R1 = 0.0676,
wR2 = 0.1297
0.886, –1.058
R indices
Largest difference
in peak and hole
(e Å–3)

DIOXOMOLYBDENUM(VI) COMPLEXES
935
FIG. 1. ORTEP plot of 1 showing the labeling system of non-hydrogen atoms. Displacement ellipsoids are plotted at 30% probability level.
thine groups, ν(C=N).[9] The weak and broad bands centered at
3421 cm–1 for 1 and 3433 cm–1 for 2 are assigned to the O–H
vibrations of the methanol ligands. Each spectrum of the com-
plexes exhibits two strong bands in the region 900–930 cm–1
characteristic of the cis-[MoO2].[9,10] The middle stretching fre-
quencies at about 1130 cm–1 for both complexes were attributed
to the coordinated C–O groups.
atoms of coordinated methanol molecules were located from
difference Fourier maps and refined isotropically, with O−H
distances restrained to 0.85(1) Å.
RESULTS AND DISCUSSION
Schiff base ligands H2L1 and H2L2 were synthesized in-situ
from 5-chlorosalicylaldehyde and 5-bromosalicylaldehyde, re-
spectively, with 1-aminopropan-2-ol in methanol. The Schiff
bases reacted with bis(acetylacetonato)dioxomolybdenum(VI)
in methanol to form the methanol-coordinated dioxomolybde-
num(VI) complexes. The complexes are yellow solids and could
be crystallized from methanol. The complexes are soluble in
chloroform, DMSO, methanol, and acetonitrile.
Structure Description of the Complexes
The crystal structures of complexes 1 and 2 are built up of
mononuclear complex molecules with cis-MoO2 core (Figures 1
and 2). In both complexes, the Schiff base ligands act in a di-
anionic tridentate manner. The coordination geometry around
the Mo center in these molybdenum complexes can be best de-
scribed as a distorted octahedron in which the ONO tridentate
Infrared Spectra
In the infrared spectra of the complexes the intense bands at ligand occupies meridional position with two anionic oxygens
1651 cm–1 for 1 and 1650 cm–1 for 2 are assigned to the azome- mutually trans and are cis to the oxygens of cis-dioxo group.
FIG. 2. ORTEP plot of 2 showing the labelling system of non-hydrogen atoms. Displacement ellipsoids are plotted at 30% probability level.

936
H.-G. ZHANG
SUPPLEMENTARY MATERIALs
Crystallographic data for the structures reported in this paper
have been deposited at the Cambridge Crystallographic Data
Centre, CCDC Nos. 885123 (1) and 885124 (2). Copies of this
information may be obtained free of charge from The Direc-
tor, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
+44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk; www:
http://www.ccdc.cam.ac.uk).
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FIG. 3. Molecular packing diagram of the complexes, viewed along the a-axis.
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The octahedral geometry of molybdenum center is additionally
completed by coordinated methanol solvent molecule. In 1 and
2, the Mo atoms deviate from the corresponding least-squares
planes defined by the equatorial donor atoms by 0.306(1) and
0.309(1) Å, respectively, toward the O4 axial donor atoms. Both
Mo=O distances, ranging from 1.683(2) to 1.714(2) Å, and
the O=Mo=O angles, from 106.5(2) to 106.6(1)◦, are in the
usual range for cis-MoO2 complexes.[11–13] In the structures of
both complexes, the tridentate Schiff base ligands form one six-
and one five-membered chelate rings, with Mo-O bond lenghts
varying from 1.939(2) to 1.964(2) Å, and Mo-N distances vary-
ing from 2.243(2) to 2.267(2) Å. The longest Mo-O bonds are
Mo-Omethanol, ranging from 2.324(2) to 2.334(2) Å, as already
observed in the similar structures with coordinated methanol
molecules.[11–13]
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J.S.; Rissanen, K. Recognition of oxovanadium(V) species and its sepa-
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acyclic ligands. Polyhedron 1999, 18, 289–297.
In the crystal structures of the complexes 1 and 2, adja-
cent two molecules are linked through intermolecular O−H···O
hydrogen bonds [for 1, O−H = 0.85(1) Å, H···O = 1.82(2)
Å, O···O = 2.645(4) Å, O−H···O = 167(6)◦; for 2, O−H =
0.85(1) Å, H···O = 1.84(3) Å, O···O = 2.657(5) Å, O−H···O =
161(7)◦], to form centrosymmetric dimeric structures, as shown
in Figure 3.