Crystal structures of new isostructural oxovanadium(V) complexes with hydrazone ligands

Article abstract of DOI:10.1134/S0022476613030177

Two new isostructural methoxide-bridged dimeric oxovanadium(V) complexes [VO(L¹)(OMe)]₂ (1) and [VO(L²)(OMe)] ₂ (2), where L¹ and L² are the deprotonated forms of 3-bromo-N′-[1-(2-hydroxyphenyl)×ethylidene]benzohydrazide (H₂L¹) and 3-chloro-N′-[1-(2-hydroxyphenyl) ethylidene]benzohydrazide (H₂L²) respectively, are synthesized and characterized by elemental analyses, IR spectra, and single crystal X-ray determination. Both crystals crystallize in the triclinic space group P-1. For 1, a = 7.5237(15) A, b = 10.846(3) A, c = 11.195(3) A, α = 84.143(3), β = 72.244(3), γ = 77.869(3), V = 849.9(4) A³, Z = 1, R ₁ = 0.0634, wR ₂ = 0.1373. For 2, a = 7.493(2) A, b = 10.740(3) A, c = 11.109(3) A, α = 84.569(2), β = 71.783(2), γ = 79.822(2), V = 835.0(4) A³, Z = 1, R ₁ = 0.0511, wR ₂ = 0.1076. Each V atom in the complexes is octahedrally coordinated.

Full text of DOI:10.1134/S0022476613030177

Journal of Structural Chemistry. Vol. 54, No. 3, pp. 581-585, 2013
Original Russian Text Copyright © 2013 by J. Yu
CRYSTAL STRUCTURES OF NEW ISOSTRUCTURAL
OXOVANADIUM(V) COMPLEXES WITH HYDRAZONE LIGANDS
J. Yu
UDC 548.73:541.49:546.88
1
Two new isostructural methoxide-bridged dimeric oxovanadium(V) complexes [VO(L )(OMe)] (1) and
2
2
[VO(L )(OMe)] (2), where L and L are the deprotonated forms of 3-bromo-N′-[1-(2-hydroxyphenyl)×
1
2
2
1 2
ethylidene]benzohydrazide (H L ) and 3-chloro-N′-[1-(2-hydroxyphenyl)ethylidene]benzohydrazide (H L )
2
2
respectively, are synthesized and characterized by elemental analyses, IR spectra, and single crystal X-ray
determination. Both crystals crystallize in the triclinic space group P-1. For 1, a = 7.5237(15) Å,
3
b = 10.846(3) Å, c = 11.195(3) Å, α = 84.143(3)°, β = 72.244(3)°, γ = 77.869(3)°, V = 849.9(4) Å , Z = 1,
R = 0.0634, wR = 0.1373. For 2, a = 7.493(2) Å, b = 10.740(3) Å, c = 11.109(3) Å, α = 84.569(2)°, β =
1 2
3
71.783(2)°, γ = 79.822(2)°, V = 835.0(4) Å , Z = 1, R = 0.0511, wR = 0.1076. Each V atom in the
1
2
complexes is octahedrally coordinated.
DOI: 10.1134/S0022476613030177
Keywords: oxovanadium complex, synthesis, crystal structure, hydrazone.
INTRODUCTION
Oxovanadium complexes with multi-dentate ligands have been extensively investigated in recent years with respect
to their remarkable efficiency as insulin mimetic compounds [1–3]. Their usage as orally active medicaments would represent
an important advance in the treatment of human diabetes mellitus [4]. Hydrazones as well as their metal complexes are of
current interest for the pharmacological properties [5-7]. In recent years, a number of oxovanadium complexes with
hydrazones have been reported for their insulin mimetic properties [8, 9]. As an extension work on the construction of new
oxovanadium complexes with potential insulin mimetic properties, two isostructural oxovanadium(V) complexes derived
1
from the similar hydrazone ligands 3-bromo-N′-[1-(2-hydroxyphenyl)ethylidene]benzohydrazide (H L ; Scheme 1) and 3-
2
2
chloro-N′-[1-(2-hydroxyphenyl)ethylidene]benzohydrazide (H L ; Scheme 1) were synthesized and characterized.
2
Scheme 1. Hydrazone ligands.
1
X = Br for H L , X = Cl for
2
2
H L .
2
College of Biological and Chemical Sciences Engineering, Jiaxing University, Jiaxing P. R. China;
JXXYYuJ@yahoo.cn. The text was submitted by the authors in English. Zhurnal Strukturnoi Khimii, Vol. 54, No. 3, pp. 528-
532, May-June, 2013. Original article submitted February 1, 2012.
0022-4766/13/5403-0581 © 2013 Springer Science+Business Media, Inc.
581

EXPERIMENTAL
Materials and methods. 1-(2-Hydroxyphenyl)ethanone, 3-bromobenzohydrazide, and 3-chlorobenzohydrazide
were obtained from Lancaster. VO(acac) and other chemicals (analytical grade) were purchased and used as received. IR
2
spectra were recorded on a Nicolet 170SX spectrophotometer using KBr as support. Elemental analyses were performed on
an Italy 1106 apparatus.
1
Synthesis of H L . A mixture of 3-bromobenzaldehyde (0.215 g, 1 mmol) and 1-(2-hydroxyphenyl)ethanone (0.136 g,
2
1 mmol) in 50 ml of methanol was stirred at room temperature for 1 h. 80% of the solvent was evaporated by distillation, and the
mixture was cooled to room temperature, giving colorless microcrystals. The product was filtered out and washed with
methanol. Yield, 85%. Anal. Calcd. (%) for C H BrN O : C, 54.1; H, 3.9; N, 8.4. Found (%): C, 53.9; H, 4.0; N, 8.5.
15 13
2
2
2
Synthesis of H L . The preparation of colorless microcrystals of H L was analogous to that of H L , but with 3-
2
1
2
2
2
bromobenzohydrazide replaced by 3-chlorobenzohydrazide (0.186 g, 1 mmol). Yield, 93%. Anal. Calcd. (%) for
C H ClN O : C, 62.4; H, 4.5; N, 9.7. Found (%): C, 62.1; H, 4.5; N, 9.8.
15 13
2
2
1
Synthesis of [VO(L )(OCH )] (1). VO(acac) (52.6 mg, 0.2 mmol) dissolved in 10 ml of methanol was added
3
2
2
1
dropwise to a methanol solution of H L (66.6 mg, 0.2 mmol) with continuous stirring for 30 min to give a reddish-brown
2
solution. Evaporation of the solution at room temperature yielded deep brown block-shaped single crystals after a few days.
The crystals were isolated by filtration, and dried in air. Yield, 78%. Anal. Calcd. (%) for C H Br N O V : C, 44.8; H, 3.3;
32 28
2
4
8
2
N, 6.5. Found (%): C, 45.0; H, 3.4; N, 6.3.
2
Synthesis of [VO(L )(OCH )] (2). The preparation of deep brown block-shaped single crystals of 2 was analogous
3
2
1 2
to 1, but with H L replaced by H L (57.6 mg, 0.2 mmol). Yield, 82%. Anal. Calcd. (%) for C H Cl N O V : C, 50.0; H,
2
2
32 28
2
4
8
2
3.7; N, 7.3. Found (%): C, 49.7; H, 3.6; N, 7.1.
X-ray crystallography. The suitable single crystals of the complexes were carefully selected under a polarizing
microscope and glued at the top of thin glass fibers for data collection performed on a Bruker SMART APEX II CCD area
diffractometer (graphite-monochromatized MoK radiation (λ = 0.71073 Å)) using an ω-scan mode at 298(2) K. The
α
structures were solved by the direct method and refined with SHELXTL [10] by the full-matrix least-squares technique on
2
F . All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were included in the final refinement on the
calculated positions riding on their parent atoms. The crystallographic data of the complexes are summarized in Table 1, and
the selected bond lengths and bond angles are listed in Table 2. CIF files containing complete information on the studied
structures were deposited with CCDC, deposition numbers 800890 (1) and 800891 (2), and are freely available upon request
from the following web site: www.ccdc.cam.ac.uk/data_request/cif.
RESULTS AND DISCUSSION
Synthesis. The two oxovanadium(V) complexes were readily synthesized by the reaction of VO(acac) with
2
hydrazone ligands in methanol. The deep brown single crystals were obtained by recrystallization of the complexes in
methanol. The crystals are soluble in polar organic solvents such as DMF, DMSO, acetonitrile, methanol, and ethanol, but
insoluble in water. From the literature search it can be seen that most of the crystal structures of oxovanadium complexes
contain methanol molecules as coligands, instead of ethanol molecules [11-14]. It should be pointed out that vanadium in the
starting material is in the V(IV) oxidation state, while it appears to be V(V) in both complexes, indicating that it was oxidized
by air during the preparation and crystallization procedures.
Crystal structure description. The molecular structures including the atomic numbering scheme of the complexes
1 and 2 are shown in Figs. 1 and 2 respectively. The two structures are isostructural methoxide-bridged centrosymmetric
dimeric oxovanadium(V) complexes with the V⋯V distances of 3.400(1) Å for 1 and 3.369(1) Å for 2. The tridentate
hydrazone ligands coordinate to the V atoms through the phenolate O, imino N, and enolic O atoms. The two VOL groups are
linked by two methoxide bridges, forming a dimer. The V atom is in an octahedral coordination with three donor atoms of the
582

TABLE 1. Crystallographic and Experimental Data for the Complexes
1
2
Chemical formula
Fw
C H Br N O V
32 28 2 4 8
C H Cl N O V
32 28 2 4 8 2
2
858.3
769.4
Crystal shape/colour
Block/deep brown
Block/deep brown
3
Crystal size, mm
0.27×0.26×0.26
0.17×0.15×0.13
Crystal system
Space group
a, b, c, Å
Triclinic
Triclinic
P-1
P-1
7.5237(15), 10.846(3), 11.195(3)
7.493(2), 10.740(3), 11.109(3)
84.143(3), 72.244(3), 77.869(3)
84.569(2), 71.783(2), 79.822(2)
α, β, γ, deg
3
V, Å
849.9(4)
1
835.0(4)
1
Z
–1
2.956
0.776
μ(MoK ), cm
α
T
/T
min max
0.5024/0.5136
5624/3554
1771
0.8794/0.9058
6246/3522
2515
Measured/Unique refl.
Observed refl. [I ≥ 2σ(I )]
Parameters/restraints
219 / 0
219 / 0
2
GOOF on F
1.018
1.030
a
0.0634, 0.1373
0.1373, 0.1644
0.0511, 0.1076
0.0780, 0.1209
R , wR [I ≥ 2σ(I )]
1 2
a
R , wR (all data)
1 2
2
R = ∑||F | – |F ||/∑|F |, wR = [∑w(F –
0
2
2 1/2
) /∑w(F ) ] .
0
a
2
2
F
1
0
c
0
2
c
TABLE 2. Selected Bond Lengths (Å) and Bond Angles (deg) for the Complexes
1
V1–O1
V1–O3
V1–N1
V1–O2
V1–O4
V1–O3A
1.823(4)
1.826(3)
2.121(4)
1.927(4)
1.580(4)
2.428(4)
O4–V1–O1
O1–V1–O3
O1–V1–O2
O4–V1–N1
O3–V1–N1
O4–V1–O3A
O3–V1–O3A
N1–V1–O3A
101.35(19)
105.52(15)
151.14(17)
96.79(18)
155.19(17)
178.69(16)
74.75(15)
84.46(14)
O4–V1–O3
O4–V1–O2
O3–V1–O2
O1–V1–N1
O2–V1–N1
O1–V1–O3A
O2–V1–O3A
103.95(18)
99.76(19)
88.10(15)
83.20(17)
74.94(17)
79.14(15)
80.20(14)
2
V1–O1
V1–O3
V1–N1
V1–O2
V1–O4
V1–O3A
1.818(2)
1.8191(19)
2.111(3)
1.917(2)
1.583(2)
2.400(2)
O4–V1–O1
O1–V1–O3
O1–V1–O2
O4–V1–N1
O3–V1–N1
O4–V1–O3A
O3–V1–O3A
N1–V1–O3A
101.21(11)
106.20(9)
151.21(10)
96.70(11)
155.55(10)
178.13(10)
74.85(8)
O4–V1–O3
O4–V1–O2
O3–V1–O2
O1–V1–N1
O2–V1–N1
O1–V1–O3A
O2–V1–O3A
103.30(10)
99.70(11)
87.86(9)
83.17(10)
74.90(10)
79.23(9)
80.51(8)
85.14(8)
hydrazone ligand and one methoxide O atom defining the equatorial plane, and with one oxo O and one methoxide O atom
occupying two axial positions. The mean deviations of the four basal donor atoms from the least-squares planes are 0.0014 Å
for 1 and 0.0054 Å for 2. The displacement of the V atoms toward the oxo groups from the planes are 0.357(2) Å for 1 and
0.347(2) Å for 2. The coordinate bond lengths and angles in the complexes are comparable to each other and are also
583

Fig. 1. ORTEP drawing of 1 with 30% probability thermal ellipsoids.
Unlabeled atoms and those labeled with the suffix A are at the
symmetry position 1–x, 1–y, 2–z.
Fig. 2. ORTEP drawing of 2 with 30% probability thermal ellipsoids.
Unlabeled atoms and those labeled with the suffix A are at the
symmetry position –x, 1–y, –z.
comparable to those observed in other similar oxovanadium(V) complexes [11-18]. The V–O bonds are shorter in both
oxo
complexes than the other coordinate bonds, indicating that they are typical double bonds.
584

–1
IR spectra. The IR spectra of the hydrazone compounds exhibit two absorption bands in the regions 3200-3230 cm
–1
and 1650-1660 cm due to the ν(N–H) and ν(C=O) stretches. The absence of these bands in the spectra of the two
oxovanadium(V) complexes is consistent with the enolization of the amide functionality and subsequent proton replacement
–1
by the V atom. The strong bands at about 1610 cm in both complexes are assigned to the conjugated C=N–N=C moieties.
–1
The intense absorption bands in the spectra of both complexes corresponding to ν(V=O) are observed at about 983 cm and
–1
950 cm for both complexes [4].
CONCLUSIONS
In summary, the present paper reports the synthesis and characterization of two new isostructural centrosymmetric
dimeric oxovanadium(V) complexes with similar hydrazone compounds. Single crystal X-ray diffraction indicates that the
hydrazone ligands coordinate to the V atoms through the phenolate O, imino N, and enolic O atoms. Methanol, which readily
adopts the deprotonated bridging form, is the preferred solvent for the synthesis and crystallization of such complexes.
Further work can be carried out to investigate their insulin mimetic activities.
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