Two water-coordinated mononuclear molybdenum(VI) OXO complexes with similar tridentate hydrazone ligands: Synthesis and crystal structures

Article abstract of DOI:10.4067/S0717-97072013000100031

Reaction of [MoO₂(acac)₂] (where acac = acetylacetonate) with two similar hydrazone ligands in methanol yielded two water coordinated mononuclear molybdenum(VI) oxo complexes with general formula [MoO₂L(OH₂)], w

Full text of DOI:10.4067/S0717-97072013000100031

J. Chil. Chem. Soc., 58, Nº 1 (2013)
TWO WATER-COORDINATED MONONUCLEAR MOLYBDENUM(VI) OXO COMPLEXES WITH SIMILAR
TRIDENTATE HYDRAZONE LIGANDS: SYNTHESIS AND CRYSTAL STRUCTURES
1
2
2
2
1,
SHAO-SONG QIAN , MIAO-MIAO ZHEN , YUE ZHAO , NA ZHANG , ZHONG-LU YOU *,
1
,
AND HAI-LIANG ZHU *
1
School of Life Sciences, Shandong University of Technology, ZiBo 255049, P. R. China
2
Department of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029, P. R. China
(Received: August 29, 2012 - Accepted: November 26, 2012)
ABSTRACT
Reaction of [MoO (acac) ] (where acac = acetylacetonate) with two similar hydrazone ligands in methanol yielded two water coordinated mononuclear
2
2
1
1
molybdenum(VI) oxo complexes with general formula [MoO L(OH )], where L = L = N’-(2-hydroxy-3-methoxybenzylidene)-2-methoxybenzohydrazide (H L ),
and L = L = N’-(3-ethoxy-2-hydroxybenzylidene)-2-methoxybenzohydrazide (H L ). Crystal and molecular structures of the complexes were determined by
2
2
2
2
2
2
single crystal X-ray diffraction method. All of the investigated compounds were further characterized by elemental analysis and FT-IR spectra. Single crystal
X-ray structural studies indicate that the hydrazone ligands coordinate to the MoO cores through enolate oxygen, phenolate oxygen and azomethine nitrogen. The
2
Mo atoms in both complexes are in octahedral coordination.
Keywords: molybdenum complex; hydrazone ligand; crystal structure; X-ray diffraction.
INTRODUCTION
temperature to give a colorless solution. The solvent was evaporated to give
2
colorless crystalline product of H L . Yield, 92%. For C H N O : anal. calcd.,
2
17 18
2
4
The coordination chemistry of molybdenum(VI) has attracted considerable
%: C, 65.0; H, 5.8; N, 8.9. Found, %: C, 64.8; H, 5.7; N, 8.9.
1
–3
1
attention due to its recently discovered biochemical significance as well as
Synthesis of [MoO L (OH )] (1): A methanolic solution (10 mL) of
2 2
4
–7
for the efficient catalytic properties in several organic synthesis procedures.
In recent years, a great number of molybdenum(VI) complexes with Schiff
[MoO (acac) ] (0.1 mmol, 32.6 mg) was added to a methanolic solution (10
2 2
1
mL) of H L (0.1 mmol, 30.0 mg) with stirring. The mixture was stirred for
2
8
–10
bases derived from salicylaldehyde and primary amines have been reported.
20 min to give an orange solution. The resulting solution was allowed to stand
in air for a few days. Orange block-shaped crystals suitable for X-ray single
crystal analysis were formed at the bottom of the vessel. The isolated product
was washed three times with cold methanol, and dried in a vacuum over
anhydrous CaCl . Yield, 45%. For C H MoN O : anal. calcd., %: C, 43.3; H,
Hydrazones, bearing –C(O)–NH–N=CH– groups, are a kind of special
Schiff bases, which are of particular interest in coordination chemistry and
biological applications. However, molybdenum(VI) complexes derived
from hydrazone ligands have seldom been reported. In the present work, we
report the synthesis and structures of two dioxomolybdenum(VI) complexes
2
16 16
2
7
3.6; N, 6.3. Found, %: C, 43.2; H, 3.7; N, 6.4.
1
2
with the general formula [MoO L(OH )], where L = L = N’-(2-hydroxy-3-
Synthesis of [MoO L (OH )] (2): A methanolic solution (10 mL) of
2
2
2 2
1
2
methoxybenzylidene)-2-methoxybenzohydrazide (H L ), and L = L = N’-(3-
ethoxy-2-hydroxybenzylidene)-2-methoxybenzohydrazide (H L ).
[MoO (acac) ] (0.1 mmol, 32.6 mg) was added to a methanolic solution (10
2 2
1
2
2
mL) of H L (0.1 mmol, 31.4 mg) with stirring. The mixture was stirred for
2
2
2
0 min to give an orange solution. The resulting solution was allowed to stand
in air for a few days. Orange block-shaped crystals suitable for X-ray single
crystal analysis were formed at the bottom of the vessel. The isolated product
was washed three times with cold methanol, and dried in a vacuum over
anhydrous CaCl . Yield, 51%. For C H MoN O : anal. calcd., %: C, 44.6; H,
2
17 18
2
7
4
.0; N, 6.1. Found, %: C, 44.8; H, 3.9; N, 6.0.
Data collection, structural determination and refinement: Diffraction
intensities for the complexes were collected at 298(2) K using a Bruker D8
VENTURE PHOTON diffractometer with MoKa radiation (l = 0.71073 Å).
1
1
The collected data were reduced using the SAINT program, and multi-
1
2
scan absorption corrections were performed using the SADABS program.
2
The structures were solved by direct methods and refined against F by full-
matrix least-squares methods using the SHELXTL. All of the non-hydrogen
EXPERIMENTAL
13
atoms were refined anisotropically. The water H atoms in the complexes were
located in difference Fourier maps and refined isotropically, with O–H and
H···H distances restrained to 0.85(1) and 1.37(2) Å, respectively. All other H
atoms were placed in idealized positions and constrained to ride on their parent
atoms. The crystallographic data for the complexes are summarized in Table 1.
Selected bond lengths and angles are given in Table 2.
Materials
-methoxysalicylaldehyde,
-methoxybenzohydrazide were purchased from Aldrich and used without
further purification. Other solvents and reagents were made in China and used
as received. C, H and N elemental analyses were performed with a Perkin-
Elmer elemental analyser. The infrared spectra were recorded on a Nicolet
and
measurements:
Commercially
available
and
3
2
3-ethoxysalicylaldehyde,
–
1
AVATAR 360 spectrometer as KBr pellets in the 4000–400 cm region.
1
Synthesis of H L : 3-Methoxysalicylaldehyde (1.0 mmol, 0.152 g) and
2
2
-methoxybenzohydrazide (1.0 mmol, 0.166 g) were dissolved in methanol
(30 mL) with stirring. The mixture was stirred for about 30 min at room
temperature to give a colorless solution. The solvent was evaporated to give
1
colorless crystalline product of H L . Yield, 87%. For C H N O : anal. calcd.,
2
16 16
2
4
%
: C, 64.0; H, 5.4; N, 9.3. Found, %: C, 63.7; H, 5.4; N, 9.4.
2
Synthesis of H L : 3-Ethoxysalicylaldehyde (1.0 mmol, 0.166 g) and
2
2
-methoxybenzohydrazide (1.0 mmol, 0.166 g) were dissolved in methanol
(30 mL) with stirring. The mixture was stirred for about 30 min at room
email: youzhonglu@yahoo.com.cn
1647

J. Chil. Chem. Soc., 58, Nº 1 (2013)
Table 1. Crystallographic data and refinement parameters for the
complexes.
O6-Mo1-O1
O6-Mo1-O3
O5-Mo1-N1
O1-Mo1-N1
O5-Mo1-O7
O1-Mo1-O7
N1-Mo1-O7
103.15(10)
96.95(10)
95.82(10)
81.72(9)
O5-Mo1-O3
O1-Mo1-O3
O6-Mo1-N1
O3-Mo1-N1
O6-Mo1-O7
O3-Mo1-O7
95.72(11)
150.30(9)
156.13(10)
71.35(9)
82.87(9)
78.73(9)
1
2
Chemical formula
Mr
C H MoN O
C H MoN O
7
1
6
16
2
7
17 18
2
444.2
Orange, block
458.3
169.99(10)
82.28(10)
74.57(8)
Crystal color, habit
Orange, block
0
0
.20 × 0.20 ×
.18
0.20 × 0.20 ×
0.18
3
Crystal size (mm )
Crystal system
Space group
Unit cell parameters
a (Å)
Monoclinic
Monoclinic
RESULTS AND DISCUSSION
P2 /c
P2 /c
1
1
Replacement of two acetylacetonate ligands in [MoO (acac) ] by
hydrazone ligands resulted in the formation of water coordinated mononuclear
molybdenum(VI) oxo complexes. In both complexes, the dinegative ligands
2
2
8.5723(18)
11.724(2)
18.222(3)
100.318(2)
1801.7(6)
4
9.2195(19)
11.8999(11)
17.639(3)
102.926(1)
1886.1(5)
4
are coordinated to the cis-MoO cores via the phenolate-oxygen, imino-
b (Å)
2
nitrogen, and enolate-oxygen. The sixth coordination site is occupied by the
oxygen atom from a water solvent. The complexes are soluble in methanol,
ethanol, and acetonitrile. The molar conductance of the complexes 1 and
c (Å)
β (°)
-4
-1
2
-1
2
at the concentrations of 10 M are 17 and 14 Ω cm mol , respectively,
3
V (Å )
indicating they are non-electrolytes.
Structure Description of the Complexes: The molecular structures and
the atom numbering schemes of the complexes 1 and 2 are shown in Figures
1 and 2, respectively. The coordination geometry around each Mo atom is
highly distorted octahedral. In each complex, the hydrazone ligand behaves in
a tridentate manner in which the phenolate O, imino N, and enolate O atoms
occupy a meridonial plane. The coordination geometry around molybdenum
can be described as distorted octahedral in the complexes. The dianionic
hydrazone ligands act in planar tridentate manner, forming one five- and one
Z
-3
Dcalc (g cm )
1.638
1.614
Temperature (K)
298(2)
0.768
298(2)
0.737
-1
μ (mm )
F(000)
896
928
six-membered chelate rings involving the MoO core. The hydrazone ligand
Number of unique data
Number of observed data [I > 2σ(I)]
Number of parameters
Number of restraints
R , wR [I > 2σ(I)]
3917
4088
2
in each of the complexes is bonded to the MoO core in a planar fashion,
2
3166
3180
coordinating through the phenolate O, imino N, and enolate O, and an oxo
group lying trans to the nitrogen donor. In each of the complexes, a water
molecule completes the distorted octahedral coordination sphere which lies
trans to the other oxo group. The Mo–O(water) bonds are significantly longer
than the other Mo–O bonds, indicating that the water molecules are weakly
243
252
3
3
0.0297, 0.0768 0.0357, 0.0823
0.0412, 0.0837 0.0514, 0.0888
1
2
bonded to the MoO core and this position holds the possibility of functioning
2
as a substrate binding site.
R , wR (all data)
1
2
The atoms O(1), O(3), O(7), and N(1) in 1 and O(1), O(3), O(6), and N(1)
in 2 show high degree of planarity from the equatorial planes, the Mo atoms are
displaced by 0.332(1) Å (1) and 0.328(1) Å (2) toward the axial oxo groups. The
Mo=O bonds in the complexes are almost equal within the standard deviations,
2
Goodness of fit on F
Max and min electron density (e Å )
1.052
1.028
-3
0.374, -0.556
0.996, -0.347
1
4, 15
and are within previously reported ranges,
The angular distortion in the
Table 2. Selected bond distances (Å) and angles (°) for the complexes.
octahedral environment around Mo comes from the five- and six-membered
chelate rings taken by the hydrazone ligands. For the same reason, the trans
angles are significantly deviate from the ideal values of 180°. The hydrazone
ligands in the complexes are approximately planar, with the corresponding two
benzene rings make dihedral angles of for 2.6(3)° 1 and 2.7(3)° for 2.
In the crystal structures of both complexes (Figure 3 for 1 and Figure
1
Mo1-O1
1.903(2)
1.689(2)
1.7126(19)
106.16(10)
103.26(9)
96.91(9)
96.05(9)
81.41(8)
169.49(9)
81.95(9)
73.69(7)
Mo1-O3
1.9935(18)
2.3380(19)
2.238(2)
Mo1-O5
Mo1-O6
Mo1-O7
Mo1-N1
4
for 2), adjacent two molecules are linked by water molecules through
intermolecular O–H···N and O–H···O hydrogen bonds (Table 3), to form 1D
chains running along the axis.
O5-Mo1-O7
O7-Mo1-O1
O7-Mo1-O3
O5-Mo1-N1
O1-Mo1-N1
O5-Mo1-O6
O1-Mo1-O6
N1-Mo1-O6
2
O5-Mo1-O1
O5-Mo1-O3
O1-Mo1-O3
O7-Mo1-N1
O3-Mo1-N1
O7-Mo1-O6
O3-Mo1-O6
99.02(11)
96.37(10)
150.00(8)
156.09(9)
71.46(7)
Table 3. Geometrical Parameters for Hydrogen Bonds
o
Hydrogen bonds
D−H (Å)
H∙∙∙A (Å)
D∙∙∙A (Å)
D−H∙∙∙A ( )
1
#
1
2
2
O6−H6A∙∙∙O7
0.85(1)
0.85(1)
0.85(1)
1.88(2)
2.05(3)
2.43(7)
2.718(3)
2.850(3)
2.981(3)
169(8)
159(8)
124(7)
83.67(8)
#
O6−H6B∙∙∙N2
O6−H6B∙∙∙O4
2
78.43(8)
#
#
#
3
3
O7−H7B∙∙∙N2
O7−H7B∙∙∙O4
O7−H7A∙∙∙O6
0.85(1)
0.85(1)
0.85(1)
2.11(2)
2.39(3)
1.94(2)
2.899(3)
2.977(3)
2.764(3)
156(4)
127(3)
167(4)
Mo1-O1
1.907(2)
1.685(2)
2.225(3)
106.21(11)
Mo1-O3
1.989(2)
1.708(2)
2.340(2)
99.34(12)
Mo1-O5
Mo1-O6
#
4
Mo1-N1
Mo1-O7
#
1
#2
#3
#4
O5-Mo1-O6
O5-Mo1-O1
1 – x, – y, – z; – x, – y, – z; 1 – x, 1 – y, – z; 2 – x, 1 – y, – z.
1
648

J. Chil. Chem. Soc., 58, Nº 1 (2013)
Figure 1. ORTEP plot of the crystal structure of 1. Displacement ellipsoids
of non-hydrogen atoms are drawn at the 30% probability level.
Figure 4. Molecular packing arrangement of 2 displayed in the unit cell.
Hydrogen bonds are shown as dashed lines.
IR Spectra: The hydrazone ligands showed stretching bands attributed to
-1
C=O, C=N, C-OH and NH at 1656, 1627, 1148 and 1227, and 3246 cm for
1
-1
2
H L , and at 1656, 1626, 1148 and 1226, and 3237 cm for H L , respectively.
2
2
-1
1
2
In addition, strong bands observed at 1607 cm for H L and H L are attributed
2
2
to –C=N–N=C– groups. Both complexes exhibit two bands at ca. 891 and 940
-1
cm , assigned to symmetric and asymmetric vibrations respectively, of the cis-
MoO cores. The bands due to ν and νNH were absent in the complexes,
Figure 2. ORTEP plot of the crystal structure of 2. Displacement ellipsoids
of non-hydrogen atoms are drawn at the 30% probability level.
2
C=O
-1
-1
but new C–O stretches appeared at 1262 cm for 1 and 1263 cm for 2. This
suggests occurrence of keto-imine tautomerization of the ligands during
-1
complexation. The νC=N absorption observed at 1627 and 1626 cm in the free
-1
-1
hydrazone ligands shifted to 1606 cm for 1 and 1607 cm 2 upon coordination
to Mo atoms. The weak peaks in the low wave numbers in the region 450–800
-1
cm may be attributed to Mo-O and Mo-N bonds in the complexes.
CONCLUSION
Twowatercoordinatedmononuclearmolybdenum(VI)oxocomplexeswith
similar hydrazone ligands have been prepared and structurally characterized by
single crystal X-ray diffraction method, as well as elemental analysis and FT-
IR spectra. The hydrazone ligands coordinate to the MoO cores through the
2
enolate oxygen, the phenolate oxygen and the azomethine nitrogen.
Supplementary material
CCDC–897240 (1) and 897241 (2) contain the supplementary
crystallographic data for this paper. These data can be obtained free of charge
at http://www.ccdc.cam.ac.uk/const/retrieving.html or from the Cambridge
Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ,
UK; fax: +44(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk.
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