Crystal structures of aroylhydrazones derived from 5-methoxysalicylaldehyde

Article abstract of DOI:10.1134/S002247661306022X

Two new aroylhydrazones 3-bromo-N′-(2-hydroxy-5-methoxybenzylidene) benzohydrazide (1) and 4-hydroxy-3-methoxy-N′-(2-hydroxy-5- methoxybenzylidene)benzohydrazide (2), derived from 5- methoxysalicylaldehyde, are prepared and determined by means of infrared and ¹H NMR spectroscopy and single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic space group P2₁/n with a = 5.9406(7) A, b = 31.833(3) A, c = 7.6460(8) A, β = 94.522(4)°, V = 1441.4(3) A3, Z = 4. Compound 2 crystallizes in the monoclinic space group P21/c with a = 14.3471(9) A, b = 11.3893(7) A, c = 9.6853(6) A, β = 94.063(2)°, V = 1578.6(2) A3, Z = 4. Both molecules have very similar bond lengths and angles. The crystal structures of both compounds are stabilized by N-H...O and O-H...O hydrogen bonds as well as φ...φ interactions.

Full text of DOI:10.1134/S002247661306022X

Journal of Structural Chemistry. Vol. 54, No. 6, pp. 1151-1156, 2013
Original Russian Text © 2013 Q.-S. Zong, J.-Y. Wu
CRYSTAL STRUCTURES OF AROYLHYDRAZONES
DERIVED FROM 5-METHOXYSALICYLALDEHYDE
1,2
Q.-S. Zong and J.-Y. Wu
1
UDC 548.737:541.12:543.422
Two new aroylhydrazones 3-bromo-N'-(2-hydroxy-5-methoxybenzylidene)benzohydrazide (1) and 4-
hydroxy-3-methoxy-N'-(2-hydroxy-5-methoxybenzylidene)benzohydrazide (2), derived from 5-
1
methoxysalicylaldehyde, are prepared and determined by means of infrared and H NMR spectroscopy and
single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic space group P21/n with
3
a = 5.9406(7) Å, b = 31.833(3) Å, c = 7.6460(8) Å, β = 94.522(4)°, V = 1441.4(3) Å , Z = 4. Compound 2
crystallizes in the monoclinic space group P21/c with a = 14.3471(9) Å, b = 11.3893(7) Å, c = 9.6853(6) Å,
3
β = 94.063(2)°, V = 1578.6(2) Å , Z = 4. Both molecules have very similar bond lengths and angles. The
crystal structures of both compounds are stabilized by N–H⋯O and O–H⋯O hydrogen bonds as well as
π⋯π interactions.
DOI: 10.1134/S002247661306022X
Keywords: aroylhydrazone, Schiff base, synthesis, X-ray structure, hydrogen bonding.
Aroylhydrazones derived from salicylaldehyde and various benzohydrazides have attracted much attention for their
structures [1-3], coordination ability [4-6], biological activities [7-9] as well as promising properties for analytical
applications [10, 11]. Aroylhydrazones containing the typical –C(O)–NH–N=CH– functional groups are also regarded as
Schiff base compounds. The detailed investigation of the structures of such compounds may supply important information
about their properties. Although there is a number of crystal structures of aroylhydrazones, to the best of our knowledge, the
compounds described here are the first examples derived from 5-methoxysalicylaldehyde. In this paper, we report the
synthesis and structures of two new aroylhydrazones derived from 5-methoxysalicylaldehyde with 3-bromobenzohydrazide
and 4-hydroxy-3-methoxybenzohydrazide (Scheme 1).
Experimental. Materials and methods. 5-Methoxysalicylaldehyde, 3-bromobenzohydrazide, and 4-hydroxy-3-
methoxybenzohydrazide were obtained from Fluka. IR spectra of KBr discs were recorded with a Perkin Elmer 783
Scheme 1. Aroylhydrazones
1
College of Biology and Chemical Engineering, Jiaxing University, Jiaxing Zhejiang, P. R. China;
2
zongqianshou@163.com. School of Pharmaceutical Sciences, Zhejiang University, Hangzhou Zhejiang, P. R. China. The
text was submitted by the authors in English. Zhurnal Strukturnoi Khimii, Vol. 54, No. 6, pp. 1121-1126, November-
December, 2013. Original article submitted May 19, 2012.
0022-4766/13/5406-1151 © 2013 by Pleiades Publishing, Ltd.
1151

spectrometer. NMR spectra were recorded on a Varian XL gemini 300 spectrometer using tetramethylsilane as the internal
standard. The electronic spectrum was recorded in a Cary 5000 spectrophotometer in the region 250-800 nm using DMF as a
–4
solvent (10 M).
Preparation of 3-bromo-N′-(2-hydroxy-5-methoxybenzylidene)benzohydrazide (1). 5-Methoxysalicylaldehyde
(1.0 mmol, 0.15 g) and 3-bromobenzohydrazide (1.0 mmol, 0.22 g) were mixed and stirred in absolute ethanol (30 ml). The
reaction mixture was refluxed for 1 h on a water bath, then cooled to room temperature. Colorless block-like single crystals of
the compound were obtained by slow evaporation of the solution in air. Yield, 83%. Elemental analysis for C15H13BrN2O3,
1 6
calculated: C 51.6%, H 3.8%, N 8.0%; found: C 51.4%, H 3.7%, N 8.1%. H NMR (DMSO-d ): δ (ppm) 3.85 (s, 3H), 6.90
(m, 2H), 7.30–8.01 (m, 4H), 8.27 (s, 1H), 8.81 (s, 1H), 11.23 (s, 1H), 12.17 (s, 1H).
Preparation of N′-(2-hydroxy-5-methoxybenzylidene)-4-hydroxy-3-methoxybenzohydrazide (2). The same
procedure as described for 1 was used for the preparation of 2, with 3-bromobenzohydrazide replaced by 4-hydroxy-3-
methoxybenzohydrazide (1.0 mmol, 0.18 g). Yield, 72%. Elemental analysis for C16H16N2O5, calculated: C 60.8%, H 5.1%,
1 6
N 8.9%; found: C 60.6%, H 5.1%, N 8.8%. H NMR (DMSO-d ): δ (ppm) 3.85 (d, 6H), 6.90 (m, 2H), 7.20-7.59 (m, 4H),
8.81 (s, 1H), 11.15 (s, 1H), 12.22 (s, 1H), 12.53 (s, 1H).
TABLE 1. Crystal Data and Structure Refinement for the Compounds
1
C15H13BrN2O3
349.2
2
Empirical formula
Formula weight
Temperature, K
Wavelength, Å
C16H16N2O5
316.3
298(2)
298(2)
0.71073
Monoclinic
P21/n
0.71073
Monoclinic
P21/c
Crystal system
Space group
Unit cell dimensions a, b, c, Å;
β, deg
5.9406(7), 31.833(3), 7.6460(8);
94.522(4)
14.3471(9), 11.3893(7), 9.6853(6);
94.063(2)
3
Volume, Å
1441.4(3)
4
1578.6(2)
4
Z
3
Calculated density, mg/m
1.609
1.331
–1
Absorption coefficient, mm
2.863
0.100
F(000)
704
664
Crystal size, mm
0.17×0.15×0.15
2.5-28.3
0.6418 and 0.6733
0.21×0.18×0.18
2.8-28.5
0.9793 and 0.9822
θ range for data collection, deg
Tmin and Tmax
Index ranges
–7 ≤ h ≤ 7; –38 ≤ k ≤ 36;
–17 ≤ h ≤ 17; –13 ≤ k ≤ 13;
–8 ≤ l ≤ 9
10442
2498
–11 ≤ l ≤ 11
16471
Reflections collected
Unique reflections
Observed reflections [I > 2σ(I )]
Parameters
2920
2062
2312
195
215
Restraints
1
1
Rint
0.0588
0.0252
2
GOOF on F
1.118
1.048
R1 = 0.0671, wR2 = 0.1845
R1 = 0.0818, wR2 = 0.2075
0.939, –0.762
R1 = 0.0391, wR2 = 0.0996
R1 = 0.0536, wR2 = 0.1082
0.171, –0.131
Final R indices [I > 2σ(I )]
R indices (all data)
–3
Largest difference peak and hole, e/Å )
1152

Fig. 1. Anisotropic ellipsoid representation of compound 1 together with
the atom labeling scheme. The ellipsoids are drawn at the 30%
probability level; hydrogen atoms are shown as spheres of arbitrary radii.
Fig. 2. Anisotropic ellipsoid representation of compound 2 together with
the atom labeling scheme. The ellipsoids are drawn at the 30%
probability level; hydrogen atoms are shown as spheres of arbitrary radii.
X-ray diffraction. Single crystal X-ray diffraction experiments were performed on a Bruker SMART APEX CCD
diffractometer using graphite monochromated MoK radiation (λ = 0.71073 Å) at 298(2) K. Crystals with the dimensions of
α
0.17×0.15×0.15 mm for 1 and 0.21×0.18×0.18 mm for 2 were used. The structures were solved by direct methods with the
2
program SHELXS-97 and refined by full matrix least squares on F with SHELXL-97 [12]. All non-hydrogen atoms were
refined anisotropically. The amino hydrogen atoms were located from difference Fourier maps. The remaining hydrogen atoms
were placed geometrically in idealized positions (C–H distances of 0.93-0.96 Å, O–H distances of 0.82 Å) and refined as rigid
groups with their Uiso’s as 1.2 or 1.5 times Ueq of the appropriate carrier atoms. The crystallographic data are listed in Table 1.
Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre, supplementary
publication Nos. CCDC — 879963 (1) and 879964 (2). Copies of the data may be obtained free of charge on application to
CSD, 12 Union Road, Cambridge CB2 1EZ, UK (fax: 1441223/336033, e-mail: deposit@ccdc.cam.ac.uk).
Results and discussion. Crystal structures of the compounds. The molecular structures showing 30%
displacement ellipsoids with atomic numbering schemes of compounds 1 and 2 are shown in Figs. 1 and 2 respectively.
Selected bond lengths and angles are listed in Table 2. The structures of the compounds reveal quasi-coplanarity of the whole
molecular skeleton with double bonds located in the central –C=N–NH–C(O)– group. They have E-configuration with
respect to the double bonds of hydrazone bridges. The dihedral angles between the two benzene rings are 6.7(3)° for 1 and
22.0(3)° for 2. In each molecule of the compounds, the C1–C6 benzene ring is nearly coplanar with the plane defined by the
C7–N1–N2 moiety, with the dihedral angles being 8.1(3)° for 1 and 1.5(3)° for 2. This planarity is assisted by the formation
of an intramolecular O–H⋯N hydrogen bond (Table 3), which makes an S(6) ring motif [13]. The C7–N1 and C8–O2 bonds
in the compounds have a double bond character, whereas the C8–N2 bonds are typical of single bonds. All the bond lengths
in the compounds are in agreement with the values found in analogous compounds [1-3].
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TABLE 2. Selected Bond Lengths (Å) and Bond Angles (deg) for the Compounds
1
Br1–C11
N2–C8
1.894(6)
1.342(7)
1.371(8)
116.5(5)
118.7(5)
123.7(5)
119.3(5)
115.7(5)
116.5(5)
N1–C7
O1–C2
1.280(7)
1.343(8)
1.421(10)
118.3(5)
121.8(5)
125.5(7)
122.4(5)
119.7(5)
120.4(5)
N1–N2
O2–C8
1.383(6)
1.226(7)
1.492(8)
118.3(5)
118.2(6)
115.0(6)
121.8(5)
123.7(5)
118.1(5)
O3–C5
O3–C15
C8–C9
C7–N1–N2
C6–C1–C7
O1–C2–C1
N1–C7–C1
N2–C8–C9
C10–C9–C8
C8–N2–N1
C2–C1–C7
C6–C5–O3
O2–C8–N2
C14–C9–C10
C12–C11–Br1
C5–O3–C15
O1–C2–C3
O3–C5–C4
O2–C8–C9
C14–C9–C8
C10–C11–Br1
2
N1–C7
O1–C2
1.282(2)
1.355(2)
1.412(2)
1.416(2)
116.9(1)
118.2(1)
118.2(2)
115.8(1)
122.6(1)
118.2(1)
118.9(1)
N1–N2
O2–C8
1.379(2)
1.232(2)
1.359(2)
1.450(2)
118.6(1)
122.1(1)
122.8(1)
120.3(1)
115.8(1)
126.0(1)
121.5(1)
N2–C8
O3–C5
1.351(2)
1.377(2)
1.364(2)
1.485(2)
118.2(1)
118.6(1)
124.3(2)
121.6(1)
122.5(1)
114.0(1)
O3–C15
O4–C12
O5–C11
O5–C16
C1–C7
C8–C9
C7–N1–N2
C11–O5–C16
O1–C2–C3
O3–C5–C4
O2–C8–C9
C10–C9–C8
O4–C12–C13
C8–N2–N1
C2–C1–C7
O1–C2–C1
N1–C7–C1
N2–C8–C9
O5–C11–C10
O4–C12–C11
C5–O3–C15
C6–C1–C7
C6–C5–O3
O2–C8–N2
C14–C9–C8
O5–C11–C12
TABLE 3. Hydrogen Bonding Information
D–H⋯A
D–H, Å
H⋯A, Å
D⋯A, Å
D–H⋯A, Å
1
i
N2–H2⋯O2
0.900(10)
0.82
2.03(4)
1.91
2.877(6)
2.619(6)
157(8)
144
O1–H1⋯N1
2
1.90
O1–H1⋯N1
0.82
0.82
2.6143(17)
2.7984(16)
2.6678(16)
2.7952(15)
145
142
ii
O4–H4⋯O3
2.11
O4–H4⋯O5
0.82
2.23
114
iii
N2–H2⋯O2
0.902(9)
1.897(10)
174(2)
i
Symmetry codes: –1/2+x, 1/2–y, –1/2+z; –1+x, 1/2–y, –1/2+z; x, 1/2–y, 1/2+z.
ii
iii
In the crystal packing of compound 1, the molecules are linked through intermolecular N–H⋯O hydrogen bonds to
form chains running along the c axis (Fig. 3). In the crystal packing of compound 2, the molecules are linked through
intermolecular O–H⋯O hydrogen bonds to form chains running along the a axis. The adjacent two chains are further
connected through N–H⋯O hydrogen bonds to form a twin chain (Fig. 4). In both compounds, the infinite chains are
subjected to π⋯π interactions (Table 4) acting between the aromatic rings.
–1
IR spectra. In the IR spectra of the compounds, the OH stretching vibrations are centered at 3387 cm for 1 and
–1
–1
–1
3365 cm for 2. The peaks at 3172 cm for 1 and 3156 cm for 2 could be attributed to N–H symmetric stretching. The
–1
aromatic C–H stretching vibrations are located at 3030-3060 cm . The aliphatic C–H stretching vibrations are observed at
–1 –1
2860-2980 cm . Both compounds exhibit stretching vibration frequencies of imino bonds at about 1610 cm . Intense bands
1154

Fig. 4. Molecular packing diagram of 2 as seen along
the c direction. Hydrogen bonds are shown as dashed
lines.
Fig. 3. Molecular packing diagram of 1 as
seen along the a direction. Hydrogen
bonds are shown as dashed lines.
TABLE 4. π⋯π Interactions (Å)
1
2
iv
vi
Cg1⋯Cg2
4.320(2)
4.024(2)
Cg3⋯Cg3
4.206(2)
v
Cg1⋯Cg2
Cg1 and Cg2 are the centroids of the C1–C6 (benzene) and
C9–C14 (benzene) rings, respectively.
Cg3 is the centroid of the C1–C6 (benzene) ring.
iv
Symmetry codes: 1/2+x, 1/2–y, –1/2+z; 1/2+x, 1/2–y, 1/2+z; –x, 1–y, –z.
v
vi
–1 –1
originating from the stretching vibrations of C=O groups are located at 1649 cm for 1 and 1647 cm for 2. The C–O
stretching vibration frequencies of hydroxy and methoxy groups substituted on benzene rings are in the region 1220-
–1 –1
1230 cm . The peaks at about 780 cm are due to N–H out-of-plane bending.
Electronic spectra. In the electronic spectra of the compounds, two strong bands in the region 250-280 nm were
observed with εmax values of 7500-8200 respectively. These two bands may be due to π → π* absorption of the substituted
benzene rings and the azomethine bonds. Weak and broad bands in the region 270-280 nm with εmax values of 23 (1) and 25
(2) were also observed. This absorption is assigned to the n → π* transition of the carbonyl groups [14].
We thank the Natural Science Foundation of China (No. 21302063), the Excellent Yong Teachers Program
(No. 00511024) and China Postdoctoral Science Foundation (No. 2011M500989) for the financial support.
1155

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