Synthesis, characterization and crystal structures of oxovanadium(V) complexes derived from similar aroylhydrazone ligands

Article abstract of DOI:10.4314/bcse.v29i3.10

Reaction of [VO(acac)₂] (acac = acetylacetonate) with N'-(5-chloro-2-hydroxybenzylidene)-3- methoxybenzohydrazide (H₂L¹) and N'-(2-hydroxy-4-methoxybenzylidene)-4-nitrobenzohydrazide (H₂L²) in methano

Full text of DOI:10.4314/bcse.v29i3.10

Bull. Chem. Soc. Ethiop. 2015, 29(3), 423-430.
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v29i3.10
ISSN 1011-3924
 2015 Chemical Society of Ethiopia
SYNTHESIS, CHARACTERIZATION AND CRYSTAL STRUCTURES OF
OXOVANADIUM(V) COMPLEXES DERIVED FROM SIMILAR
AROYLHYDRAZONE LIGANDS
Xiu-Zhen Zhang1, Li-Xue Li2, Hai-Hua Li2, Zhonglu You2* and Hai-Liang Zhu1*
1School of Life Sciences, Shandong University of Technology, ZiBo 255049, China
2Department of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian
116029, China
(Received February 1, 2015; revised August 6, 2015)
ABSTRACT. Reaction of [VO(acac)2] (acac = acetylacetonate) with N’-(5-chloro-2-hydroxybenzylidene)-3-
methoxybenzohydrazide (H2L1) and N’-(2-hydroxy-4-methoxybenzylidene)-4-nitrobenzohydrazide (H2L2) in
methanol affords methanol-coordinated mononuclear oxovanadium(V) complexes, [VOL1(OMe)(MeOH)] (1) and
[VOL2(OMe)(MeOH)] (2), respectively. The complexes were characterized by elemental analysis, FT-IR, 1H
NMR and 13C NMR spectra. Crystal and molecular structures of the complexes were determined by single crystal
X-ray diffraction method. Single crystal X-ray structural studies indicate that the hydrazone ligands coordinate to
the VO core through enolate oxygen, phenolate oxygen and azomethine nitrogen. The V atoms in the complexes
are in octahedral coordination. Thermal stabilities of the complexes have also been studied.
KEY WORDS: Oxovanadium complex, Aroylhydrazone ligand, Crystal structure, X-ray diffraction, Thermal
property
INTRODUCTION
Coordination chemistry of vanadium has attracted considerable attention in coordination and
bioinorganic chemistry [1–5] as well as for the efficient catalytic properties in several organic
synthesis procedures [6–9]. Schiff bases are a kind of interesting ligands in coordination
chemistry [10–15]. In recent years, a number of vanadium complexes with Schiff bases derived
from salicylaldehyde and primary amines have been reported [16–20]. 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. Vanadium complexes with hydrazone
ligands have been reported to possess interesting biological activities [21] and catalytic
properties [22]. However, oxovanadium(V) complexes derived from aroylhydrazone ligands
have been much less studied when compared to other types of organic ligands. In the present
work, we report the synthesis and structures of two new oxovanadium(V) complexes,
[VOL1(OMe)(MeOH)] (1) and [VOL2(OMe)(MeOH)] (2), where L1 and L2 are the dianionic
forms of N’-(5-chloro-2-hydroxybenzylidene)-3-methoxybenzohydrazide (H2L1) and N’-(2-
hydroxy-4-methoxybenzylidene)-4-nitrobenzohydrazide (H2L2), respectively.
H2L1 and H2L2
__________
*Corresponding author. E-mail: youzhonglu@126.com, hailiang_zhu@163.com

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Xiu-Zhen Zhang et al.
EXPERIMENTAL
Materials and measurements
Commercially available 5-chlorosalicylaldehyde, 4-methoxysalicylaldehyde, 3-methoxybenzo-
hydrazide and 4-nitrobenzohydrazide were purchased from Aldrich and used without further
purification. [VO(acac)2] was purchased from Shenyang Haizhongtian Chemical Company
(China). Other solvents and reagents were made in China and used as obtained. C, H and N
elemental analyses were performed with a Perkin-Elmer elemental analyser. Infrared spectra
were recorded on a Nicolet AVATAR 360 spectrometer as KBr pellets in the 4000–400 cm–1
region. Thermal stability analysis was performed on a Perkin-Elmer Pyris Diamond TG-DTA
1
thermal analyses system. H NMR and 13C NMR spectra were recorded on a Bruker DPX 300
model spectrometer at 25 °C with TMS and solvent signals allotted as internal standards.
Chemical shifts were reported in ppm (δ).
Synthesis of H2L1
5-Chlorosalicylaldehyde (1.0 mmol, 0.16 g) and 3-methoxybenzohydrazide (1.0 mmol, 0.17 g)
were dissolved in methanol (30 mL) with stirring. The mixture was stirred for about 30 min at
room temperature to give colorless solution. The solution was left still in air to slow evaporate
of most of the solvent, to give crystalline product of H2L2. The product was isolated by filtration
and washed with cold methanol. Yield, 83%; m.p. 181.0–182.5 °C. Analysis: found: C 59.23%,
H 4.26%, N 9.07%; calculated for C15H13ClN2O3: C 59.12%, H 4.30%, N 9.19%. IR data (cm-1,
KBr): 3447 (w), 3195 (w), 1653 (s), 1611 (m), 1589 (m), 1561 (m), 1494 (s), 1435 (s), 1357
(w), 1332 (w), 1301 (w), 1267 (m), 1153 (s), 1114 (m), 1080 (s), 1035 (m), 996 (m), 853 (s),
1
781 (w), 745 (w), 727 (w), 546 (w), 470 (w). H NMR (300 MHz, d6-DMSO): δ 12.41 (s, 1H),
11.72 (s, 1H), 8.61 (s, 1H), 7.85 (t, 1H), 7.60 (m, 2H), 7.38 (d, 1H), 7.19 (d, 1H), 6.91 (d, 1H),
6.85 (s, 1H), 3.79 (s, 3H). 13C NMR (75 MHz, d6-DMSO): δ 164.03, 161.54, 158.37, 145.71,
134.10, 132.82, 129.88, 128.75, 121.63, 120.70, 119.53, 117.37, 116.86, 112.45, 55.71.
Synthesis of H2L2
4-Methoxysalicylaldehyde (1.0 mmol, 0.15 g) and 4-nitrobenzohydrazide (1.0 mmol, 0.18 g)
were dissolved in methanol (30 mL) with stirring. The mixture was stirred for about 30 min at
room temperature to give yellow solution. The solution was left still in air to slow evaporate of
most of the solvent, to give crystalline product of H2L1. The product was isolated by filtration
and washed with cold methanol. Yield, 87%; m.p. 201.5–202.0 °C. Analysis: found: C 56.92%,
H 4.08%, N 13.47%; calculated for C15H13N3O5: C 57.14%, H 4.16%, N 13.33%. IR data (cm-1,
KBr): 3440 (w), 3227 (w), 1642 (s), 1606 (s), 1516 (s), 1455 (w), 1348 (s), 1281 (s), 1228 (m),
1164 (w), 1122 (w), 1024 (m), 963 (w), 909 (w), 853 (m), 803 (w), 711 (m), 636 (w), 607 (w),
518 (w), 470 (w). 1H NMR (300 MHz, d6-DMSO): δ 12.25 (s, 1H), 11.43 (s, 1H), 8.57 (s, 1H),
8.38 (d, 2H), 8.16 (d, 2H), 7.48 (d, 1H), 6.52 (d, 2H), 3.77 (s, 3H). 13C NMR (75 MHz, d6-
DMSO): δ 164.15, 162.37, 161.96, 152.13, 145.22, 139.10, 133.37, 129.75, 123.16, 112.11,
105.78, 102.19, 55.67.
Synthesis of [VOL1(OMe)(MeOH)] (1)
A methanolic solution (10 mL) of [VO(acac)2] (0.1 mmol, 27.0 mg) was added to a methanolic
solution (10 mL) of H2L1 (0.1 mmol, 30.5 mg) with stirring. The mixture was stirred for 30 min
to give a deep brown solution. The resulting solution was allowed to stand in air for a few days.
Brown 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 CaCl2. Yield, 53%. Analysis: found: C 47.0%, H 4.3%, N
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Synthesis, characterization and crystal structures of oxovanadium(V) complexes
425
6.4%; calculated for C17H18ClN2O6V: C 47.2%, H 4.2%, N 6.5%. IR data (cm-1, KBr): 3445 (w),
1603 (s), 1541 (m), 1450 (m), 1393 (s), 1287 (w), 1243 (w), 1186 (w), 1100 (m), 1047 (w), 998
(w), 960 (m), 877 (s), 823 (w), 781 (w), 723 (m), 670 (w), 616 (w), 558 (w).
Synthesis of [VOL2(OMe)(MeOH)] (2)
Complex (2) was prepared by the same method as described for complex (1), with H2L1
replaced by H2L2 (0.1 mmol, 31.5 mg). Yield, 61%. Analysis: found: C 46.2%, H 4.0%, N 9.3%;
calculated for C17H18N3O8V: C 46.1%, H 4.1%, N 9.5%. IR data (cm-1, KBr): 3445 (w), 1600
(s), 1520 (m), 1414 (w), 1340 (s), 1245 (w), 1228 (m), 1132 (w), 1036 (w), 999 (m), 961 (m),
850 (w), 797 (w), 755 (w), 708 (w), 643 (w), 590 (w), 468 (w).
Table 1. Crystallographic and experimental data for the complexes.
(1)
(2)
Formula
FW
C17H18ClN2O6V
432.7
C17H18N3O8V
443.3
Crystal shape/color
Crystal size/ mm
Crystal system
Space group
Black/brown
0.23 × 0.20 × 0.20
Triclinic
P-1
Black/brown
0.17 × 0.13 × 0.12
Monoclinic
P21/c
a/Å
b/Å
c/Å
α/°
7.346(2)
11.841(3)
11.879(3)
75.949(2)
72.381(2)
73.188(2)
929.0(4)
2
21.672(1)
8.5636(6)
11.0682(7)
90
103.329(2)
90
β/°
γ/°
V/Å3
1998.9(2)
4
Z
T/K
298(2)
0.715
1.547
298(2)
0.545
1.473
/mm-1(Mo-K)
Dc/g cm-3
Reflections/parameters
Independent reflections
Restraints
3404/250
2652
1
3701/268
3257
1
Index ranges/ h, k, l
F(000)
-8, 8; -14, 14; -14, 14
444
-26, 26; -10, 10 -12 13
912
Tmin
0.8529
0.9130
Tmax
0.8703
1.162
0.0733, 0.1932
0.0923, 0.2013
0.646, -0.406
0.9374
1.061
0.0351, 0.0954
0.0409, 0.1009
0.360, -0.296
Goodness of fit on F2
R1, wR2 [I  2(I)]a
R1, wR2 (all data)a
Largest diff. peak and hole/e Å-3
a R1 = Fo-Fc/Fo, wR2 = [w(Fo -Fc2)2/w(Fo )2]1/2
.
2
2
X-Ray diffraction
Diffraction intensities for the complexes were collected at 298(2) K using a Bruker D8 Venture
Photon diffractometer with MoK radiation ( = 0.71073 Å). The collected data were reduced
using SAINT [23], and multi-scan absorption corrections were performed using SADABS [24].
Structures of the complexes were solved by direct method and refined against F2 by full-matrix
least-squares methods using SHELXTL [25]. All the non-hydrogen atoms were refined
anisotropically. The methanol H atoms in both complexes were located from difference Fourier
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Xiu-Zhen Zhang et al.
maps and refined isotropically, with O–H distance restrained to 0.85(1) Å. The remaining 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.
Table 2. Selected bond lengths (Å) and angles (°) for the complexes.
(1)
V1–O2
V1–O5
V1–N1
(2)
V1–O2
V1–O7
V1–N1
V1–O1
V1–O4
V1–O6
1.857(4)
2.375(4)
1.567(5)
1.954(4)
1.759(4)
2.118(5)
V1–O1
V1–O6
V1–O8
1.8531(13)
1.5763(16)
1.7736(13)
1.9498(13)
2.3421(14)
2.1156(15)
O6–V1–O5 103.2(2)
O5–V1–O1 101.14(19)
O5–V1–O2 94.70(19)
O6–V1–N1 95.8(2)
O1–V1–N1 83.84(18)
O6–V1–O4 173.9(2)
O1–V1–O4 82.01(18)
N1–V1–O4 78.48(16)
O6–V1–O1 99.5(2)
O6–V1–O2 98.3(2)
O1–V1–O2 152.71(18)
O5–V1–N1 159.2(2)
O2–V1–N1 73.93(17)
O5–V1–O4 82.25(18)
O2–V1–O4 78.26(16)
O6–V1–O8 102.86(8)
O8–V1–O1 101.30(6)
O8–V1–O2 93.51(6)
O6–V1–N1 95.28(7)
O1–V1–N1 83.74(6)
O6–V1–O7 175.71(7)
O1–V1–O7 79.87(6)
N1–V1–O7 80.73(6)
O6–V1–O1 101.37(8)
O6–V1–O2 99.28(7)
O1–V1–O2 151.11(6)
O8–V1–N1 159.69(6)
O2–V1–N1 74.41(5)
O8–V1–O7 80.83(6)
O2–V1–O7 78.18(5)
RESULTS AND DISCUSSION
General
Replacement of two acetylacetonate ligands in [VO(acac)2] by aroylhydrazone, methanol and
methanolate ligands resulted in the mononuclear oxovanadium(V) complexes. The dinegative
ligands are coordinated to the VO cores via the phenolate-oxygen, imino-nitrogen and enolate-
oxygen. The complexes are soluble in methanol, ethanol and acetonitrile. Molar conductance of
the complexes at concentration of 10–4 M is about 30 Ω–1 cm2 mol–1, indicating they are non-
electrolyte [26].
IR spectra
The aroylhydrazone ligands showed stretching bands attributed to C=O, C=N, C–OH and NH at
about 1650, 1605, 1160 and 1230, and 3220 cm–1, respectively. The complexes exhibit two
bands at about 960 cm–1, assigned to stretching vibrations of the V=O groups [27]. The bands
due to νC=O are absent in the complexes, but new C–O stretch appeared at about 1245 cm–1. This
suggests occurrence of keto-imine tautomerization of the aroylhydrazone ligands during
complexation. The νC=N absorption observed at 1605 cm–1 in the free aroylhydrazone ligands
shifted to 1600 cm–1 upon coordination to the V atoms [28].
Thermal property
Differential thermal (DT) and thermal gravimetric analyses (TGA) were conducted to examine
the stability of the complexes (Figures 1 and 2). For the decomposition of complex (1), the first
step started from 90 °C and ended at 110 °C, corresponding to the loss of the ligand (CH3OH).
The observed weight loss of 7.2% is close to the calculated value of 7.4%. The second step,
from 150 °C to 210 °C, corresponds to the loss of the methanolate ligand (CH3O-). The observed
weight loss of 7.1% is close to the calculated value of 7.2%. The last step, from 250 °C to 510
°C, corresponds to the loss of the aroylhydrazone ligand (C15H11ClN2O32-), and the formation of
the final product (V2O5). The total weight loss of 79.3% is close to the calculated value of
79.0%. For the decomposition of complex (2), there are several stages of decomposition, and it
is very difficult to ascribe them. The complex decomposed from 100 °C and completed at 500
°C. The total weight loss of 79.5% is the same as the calculated value of 79.5%.
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Synthesis, characterization and crystal structures of oxovanadium(V) complexes
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100
100
80
60
80
40
20
60
0
-20
40
-40
-60
20
-80
200
400
600
800
1000
Temperature (oC)
Figure 1. DT-TGA curves of complex (1).
80
60
40
20
0
100
80
60
40
20
-20
-40
-60
200
400
600
800
1000
Temperature (oC)
Figure 2. DT-TGA curves of complex (2).
Structure description of the complexes
Molecular structures and atom numbering schemes of the complexes are shown in Figures 3-6.
Both structures are very similar except for the aroylhydrazone ligands. The V atoms in the
complexes are in octahedral coordination, with the phenolate O, azomethine N and enolate O
atoms of the aroylhydrazone ligands as well as the methanolate O atom defining the equatorial
plane, and with the methanol O atom and an oxo O atom locating at the axial positions. The V
atoms deviate from the least-squares planes defined by the equatorial atoms by 0.314(1) Å for
(1) and 0.332(1) Å for (2). The coordinate bond lengths in both complexes are similar to each
other, and also comparable to those observed in vanadium complexes with hydrazone ligands
[29, 30]. The distortion of the octahedral coordination can be observed from the coordinate bond
angles, ranging from 73.93(17) to 103.2(2)º for (1), and from 74.41(5) to 102.86(8)º for (2), for
the perpendicular angles, and from 152.71(18) to 173.9(2)º for (1), and from 151.11(6) to
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Xiu-Zhen Zhang et al.
175.71(7)º for (2), for the diagonal angles. The dihedral angles between the benzene rings of the
aroylhydrazone ligands are 9.7(3)° for (1) and 6.1(3)° for (2). In the crystal structure of complex
(1), adjacent two molecules are linked through intermolecular O–H···N hydrogen bonds [O4–
H4 = 0.85(1) Å, H4···N2i = 2.13(5) Å, O4···N2i = 2.853(6) Å, O4–H4···N2i = 142(7)°;
symmetry code for i: 1 – x, – y, 2 – z], to form a dimer (Figure 5). In the crystal structure of
complex (2), molecules are linked through intermolecular O–H···N hydrogen bonds [O7–H7 =
0.84(1) Å, H7···N2ii = 1.98(1) Å, O7···N2ii = 2.817(2) Å, O7–H7···N2ii = 173(3)°; symmetry
code for ii: x, 1/2 – y, 1/2 + z], to form 1D chains along the c axis (Figure 6).
Figure 3. Molecular structure of complex (1) at 30% probability displacement.
Figure 4. Molecular packing of complex (1). Hydrogen bonds are drawn as dashed lines.
Hydrogen atoms not related to hydrogen bonds are omitted for clarity.
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Synthesis, characterization and crystal structures of oxovanadium(V) complexes
429
Figure 5. Molecular structure of complex (2) at 30% probability displacement.
Figure 6.Molecular packing of complex (2). Hydrogen bonds are drawn as dashed lines.
Hydrogen atoms not related to hydrogen bonds are omitted for clarity.
CONCLUSION
In summary, two new methanol and methanolate-coordinated mononuclear oxovanadium(V)
complexes derived from similar aroylhydrazone ligands have been prepared and structurally
characterized by single crystal X-ray diffraction method, as well as elemental analysis and FT-
IR spectroscopic technique. The aroylhydrazone ligands coordinate to the VO core through the
enolate oxygen, phenolate oxygen and azomethine nitrogen. Thermal stability of the complexes
have also been studied.
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Supplementary data. The crystallographic data for the structures have been deposited with the
Cambridge Crystallographic Data Centre (CCDC 974790 for (1) and 974791 for (2)). Copies of
the data can be obtained free of charge on application to the Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (e-mail for deposition: deposit@ccdc.cam.ac.uk).
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