Characterization and Crystal Structure of a Novel Mononuclear Cobalt(II) Complex with Hydrazone Derived from Protocatechuic Acid

Article abstract of DOI:10.1134/S0022476618010213

A novel complex [Co^II(L)₂·CH₃OH] with hydrazone derived from protocatechuic acid (HL=C₁₆H₁₄N₂O₄) is designed and synthesized. The complex is characterized by single crystal X-ray

Full text of DOI:10.1134/S0022476618010213

Journal of Structural Chemistry. Vol. 59, No. 1, pp. 140-144, 2018.
Original Russian Text © 2018 G.-H. Sheng, C.-F. Wang, S. Feng, X. Gao, H.-L. Zhu.
CHARACTERIZATION AND CRYSTAL STRUCTURE
OF A NOVEL MONONUCLEAR COBALT(II)
COMPLEX WITH HYDRAZONE DERIVED
FROM PROTOCATECHUIC ACID
G.-H. Sheng, C.-F. Wang, S. Feng, X. Gao,
and H.-L. Zhu*
II
A novel complex [Co (L) ⋅CH OH] with hydrazone derived from protocatechuic acid (HL=C H N O ) is
2
3
16 14
2
4
designed and synthesized. The complex is characterized by single crystal X-ray diffraction, elemental
analysis, IR, and thermal gravimetric analysis. The complex crystallizes in the monoclinic space group
C2/c, with unit cell dimensions a = 25.1715(11), b = 9.3518(4), c = 12.8700(6) Å, β = 103.6530(10)°,
3
V = 2943.98(75) Å , Z = 4, R = 0.0612, and wR = 0.1439.
1
2
DOI: 10.1134/S0022476618010213
Keywords: complex, hydrazine, protocatechuic acid, crystal structure, thermal stability.
INTRODUCTION
Metal complexes with hydrazones have received particular attention in biological and medicinal chemistry [1-4].
Transition metals exhibit biological activity in many biochemical processes [5]. Commonly used transition metals include
nickel, copper, cobalt, zinc, etc. They act as cofactors in some important enzymatic and organ functions, resulting in
increased activities of these enzymes [6]. Schiff bases are a kind of interesting ligands in coordination chemistry [7].
Hydrazones bearing –C(O)–NH–N=CH– groups are a kind of special Schiff bases being of particular interest in coordination
chemistry and biological applications. Metal complexes of hydrazones, including heterocyclic moieties containing nitrogen,
oxygen and sulfur as a heteroatoms, have been studied extensively in order to establish a probable relationship between the
chemical structure and biological activity [8-11]. In this paper, we report the synthesis of hydrazone derived from
protocatechuic acid and a new metallic complex with the hydrazone derivative as a ligand. The complex was characterized by
single crystal X-ray diffraction, elemental analysis, IR, and thermal gravimetric analysis (TGA).
EXPERIMENTAL
General methods and materials. All solvents were of reagent grade and purchased commercially except otherwise
stated. All chemicals were also commercially available and used without further purification. Elemental analyses for C, N,
and H were performed on a Perkin-Elmer 240°C elemental analyzer.
School of Life Sciences, Shandong University of Technology, P. R. China; *hailiang_zhu@163.com. The text was
submitted by the authors in English. Zhurnal Strukturnoi Khimii, Vol. 59, No. 1, pp. 144-148, January-February, 2018.
Original article submitted January 28, 2016; revised October 14, 2016.
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0022-4766/18/5901-0140 © 2018 by Pleiades Publishing, Ltd.

Scheme 1. Synthesis of HL. Reagents and conditions: (a) MeOH, H SO , reflux,
2 4
8 h; (b) Br(CH ) Br,K CO , acetone, reflux, 24 h; (c) hydrazine hydrate, ethanol,
2 2 2 3
reflux, 6 h; (d) salicylaldehyde, ethanol, stirring, 2 h.
Synthesis of the hydrazone ligand based on protocatechuic acid. The protocatechuic acid derivative ligand (HL)
was synthesized with protocatechuic acid, 1,2-dibromoethane, hydrazine hydrate, and salicylaldehyde (Scheme 1). The
synthesis steps include esterification, cyclization, hydrazinolysis, and condensation. The complex was synthesized by the
reaction of HL with Co(II) salts (Scheme 2) in organic solvents.
Synthesis of the ligand. Protocatechuic acid (0.0973 mol, 15 g) was dissolved in methanol (100 ml) with stirring,
catalyzed by concentrated sulfuric acid. The mixture was stirred for about 20 h at 63°C and evaporated. The concentrated
solution was poured into 200 ml of ethyl acetate and 100 ml of water and stilled. The ethyl acetate solvent was evaporated to
give white powdered compound 1.
Compound 1 (0.06 mol, 10.0824 g) and 1,2-dibromoethane (0.12 mol, 10.45 ml) were dissolved in acetone (100 ml)
with stirring, using K CO (0.24 mol, 33.16 g) as the acid binding agent. The mixture was stirred for about 24 h at 56°C. The
2
3
insoluble substance was removed by filtration; the solvent was evaporated to obtain yellow powdered compound 2.
A mixture of compound 2 (0.01 mol, 1.9406 g) and hydrazine hydrate (0.064 mol, 3.1 ml) in ethanol (200 ml) was
stirred at 80°C for 24 h. The solvent was evaporated to gain white powdered compound 3.
Compound 3 (0.01 mol, 1.9419 g) and salicylaldehyde (0.01 mol, 1.0438 ml) were dissolved in methanol (200 ml)
with stirring. The mixture was stirred for about 2 h at room temperature to give a yellow solution. The solvent was
evaporated to give a white powdered product of HL. Yield 80%. Analysis: Found (%): C 57.55, H 5.63, N 11.20. Calculated
for C H N O (%): C 57.59, H 5.64, N 11.19.
16 14
2
4
Scheme 2. Synthesis of the complex.
Synthesis of the complex. A methanol solution (0.5 ml) of CoCl (0.05 mmol, 0.0065 g) was added to 8ml of
2
a mixed solvent solution (methanol: acetone: acetonitrile = 1:1:1 v/v/v) of HL (0.1 mmol, 0.0298 g). The solutions were left
for 4 days at 80°C. Black block-shaped single crystals of the complex suitable for the structure determination were got at the
bottom of the vessel. Crystals of the complex were isolated by filtration and washed with ethanol and then dried in air. Yield
76%. Anal. Calc. for C H CoN O : C 57.82, H 4.41, N 8.17%. Found: C 57.71, H 4.33, N 8.08%.
33 30
4
9
X-ray crystallography. Single crystal X-ray diffraction data for the complex were collected using a Bruker
SMART APEX-II CCD area detector with graphite-monochromated MoK radiation (λ = 0.71073 Å) at 291 K. Absorption
α
correction was applied by the SADABS program [16]. Empirical absorption corrections were applied based on equivalent
2
reflections. The structure of the complex was solved by direct methods and refined by full-matrix least-squares on F using
Bruker’s SHELXS-97 crystallographic software package [17]. All atoms were refined anisotropically, except hydrogen
atoms.
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RESULTS AND DISCUSSION
Synthesis. HL was synthesized by four procedures (esterification, cyclization, hydrazinolysis, and condensation).
The complex was obtained by the coordination of HL with Co(II) salts. HL, white powder, yield 78%, m.p. 167.7-170.7°C.
1
H NMR (400 MHz, DMSO) δ: 4.30-4.33 (m, 4H), 6.90-7.02 (m, 3H), 7.28-7.32 (m, 1H), 7.48-7.54 (m, 3H), 8.62 (s, 1H),
13
11.18-11.37 (m, 1H), 12.00 (s, 1H). C NMR (400 MHz, DMSO) δ: 39.92, 64.48, 64.88, 116.98, 117.57, 119.14, 119.79,
121.71, 125.95, 130.03, 131.74, 143.55, 147.21, 148.34, 157.91, 162.33.
X-ray crystallography. Diffraction intensities for the complex were collected at 293 K using a Bruker D8
VENTURE PHOTON diffractometer with MoK radiation (0.71073 Å). The collected data were reduced using the SAINT
α
program and multi-scan absorption corrections were performed using the SADABS program. The structures were solved by
2
direct methods and refined against F by full-matrix least-squares methods using SHELXTL. All of the non-hydrogen atoms
were refined anisotropically. H atoms were placed in idealized positions and constrained to ride on their parent atoms.
Complex: C H CoN O , FW = 572.3, T = 293 K, crystal size 0.22×0.21×0.20 mm, monoclinic, C2/c, a = 25.1715(11) Å,
33 30 4 9
3 3
b = 9.3518(4) Å, c = 12.8700(6) Å, β = 103.6530(10)°, V = 2943.98(75) Å , Z = 4, d = 1.547 g/cm , a total of 13040, 2604
calc
unique (R = 0.0322), 213 parameters. GOOF = 1.081, R = 0.0489, wR = 0.1370 (I > 2σ ), R = 0.0612, wR = 0.1439 (all
1 2 I 1 2
int
3
data), max/min diff. peak 0.427/–0.281 e/Å .
Crystal structure description. Solid structures of the complex were determined by single crystal X-ray diffraction
and it showed that the complex is mononuclear. Crystal structures of the complex are shown in Fig. 1. Selected bond lengths
1
and angles are listed in Table 1. H NMR (400 MHz, DMSO) δ: 4.223-4.268 (m, 4H), 6.518-6.609 (m, 2H), 6.839-6.965 (m,
2H), 7.342-7.589 (m, 2H), 7.605-7.609 (m, 1H), 8.896 (s, 1H).
II
Description of the complex. As shown in Fig. 1, the [Co (L) ]⋅CH OH complex crystallizes in the triclinic space
2
3
group C2/c. Each molecule consists of one cobaltic ion, two HL anions, and a free methanol molecule. Each cobalt ion is six-
coordinated with four O atoms and two N atoms of two ligands. The coordination geometry around each Co atom is
octahedral. The free methanol molecules have no coordinate and hydrogen bonds.
IR and UV-Vis spectra. The IR spectra of the complex are compared with the spectra of HL in order to determine
the coordination sites that may be involved in the coordination of the complex. The important IR bands with their tentative
–1
assignments are depicted as follows. The IR spectrum of HL shows a medium intensity band at 3258 cm due to the O–H
Fig. 1. A perspective view of the complex with the atom labeling scheme.
H atoms are omitted for clarity.
142

TABLE 1. Selected distances (Å) and angles (deg) for the complex
Co(1)–N(2)#1
Co(1)–O(1)
1.871(2)
1.873(2)
N(2)#1–Co(1)–N(2)
N(2)–Co(1)–O(1)
171.65(14)
95.22(9)
90.67(9)
83.37(9)
89.06(9)
90.79(9)
178.47(8)
91.53(12)
N(2)#1–Co(1)–O(1)
N(2)#1–Co(1)–O(1)#1
O(1)–Co(1)–O(1)#1
N(2)–Co(1)–O(2)#1
O(1)#1–Co(1)–O(2)#1
N(2)–Co(1)–O(2)
90.67(9)
95.22(9)
90.38(13)
90.79(9)
178.47(8)
83.37(9)
89.06(9)
Co(1)–O(2)#1
Co(1)–N(2)
1.9079(19)
1.871(2)
N(2)–Co(1)–O(1)#1
N(2)#1–Co(1)–O(2)#1
O(1)–Co(1)–O(2)#1
N(2)#1–Co(1)–O(2)
O(1)–Co(1)–O(2)
Co(1)–O(1)#1
Co(1)–O(2)
1.873(2)
1.9079(19)
O(1)#1–Co(1)–O(2)
O(2)#1–Co(1)–O(2)
Complex (#1 –x, y, –z+1/2; #2 –x, y, –z–1/2).
Fig. 2. DT-TGA curve of the complex.
stretching vibration. The absence of this band in the spectra of the complex indicates the deprotonation and coordination of
–1
absorption band was observed at about 1610 cm in free HLs; in the complex, this band shifted to
the HL metal ion. The ν
C=N
–1
a lower frequency (3-4 cm ), indicating the participation of N in coordination.
–5
Electronic spectra of the complex were recorded with a concentration of 6.25×10 mol/L in DMSO. The complex
–5
showed the maximum absorption wavelengths at 280 nm. The molar extinction coefficient at 280 nm was 2.789×10 .
Thermal stability. Differential thermal analysis (DTA) and TGA were conducted to examine the stability of the
complex in the air atmosphere and with the standard corundum crucible sample holder. For the complex (Fig. 2), the first step
started at 160°C and was completed at 264°C, corresponding to the loss of the free methanol molecule. The observed weight
loss of 5.83% is close to the calculated value of 4.67%. The second step from 265°C to 607°C corresponds to the loss of HL
and the formation of the final product (Co O ). The observed weight loss of 83.19% at this step is close to the calculated
3
4
value of 83.69%.
CONCLUSIONS
Metal-based compounds have received great attention in medicinal chemistry for the diagnosis and treatment of
different human malignancies. In this paper, we report the synthesis of hydrazone with protocatechuic acid and the synthesis
of a new metallic complex with hydrazone as ligands. The complex was characterized by single crystal X-ray diffraction,
elemental analysis, IR spectroscopy. The heat stabilities were evaluated by TGA.
Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data
Center (CCDC-1449668). Copy of this information can be obtained free of charge from The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: (+44) 1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
143

We thank the financial support from the National Natural Science Foundation of China (Grant No. 31200090),
Scientific Research Foundation for Returned Scholars, Ministry of Education of China and National College Students′
Innovative and Entrepreneurial Training Plan of China (Grant No. 201410433033).
REFERENCES
1. M. F. Wang, Z. Y. Yang, Y. Li, et al., J. Coord. Chem., 64, No. 17, 2974-2983 (2011).
2. A. El-Dissouky, O. Al-Fulaij, M. K. Awad, et al., J. Coord. Chem., 63, No. 2, 330-345 (2010).
3. K. M. Ibrahim, I. M. Gabr, and R. R. Zaky, J. Coord. Chem., 62, No. 7, 1100-1111 (2009).
4. A. S. El-Tabl, F. A. El-Saied, and A. N. Al-Hakimi, J. Coord. Chem., 61, No. 15, 2380-2401 (2008).
5. U. Ermler, W. Grabarse, S. Shima, M. Goubeaud, and R. K. Thauer, Curr. Opin. Struct. Biol., 8, No. 6, 749-758 (1998).
6. S. Burt, Int. J. Food Microbiol., 94, 223 (2004).
7. a) R. Vafazadeh, A. Gorji, S. Ansari, and A. C. Willis, Acta Chim. Slov., 59, 897-903 (2012); b) R. Vafazadeh and
S. Bidaki, Acta Chim. Slov., 57, 310-317 (2010); c) I. Demir, M. Bayrakci, K. Mutlu, and A. I. Pekacar, Acta Chim.
Slov., 55, 120-124 (2008).
8. S. B. Padhy and G. B. Kauffman, Coord. Chem. Rev., 63, 127-160 (1985).
9. D. X. West, S. B. Padhy, P. B. Sonawane, and R. C. Chikte, Struct. Bonding, 76, 1-50 (1991).
10. R. Manikandan, P. Viswanathamurthi, and M. Muthukumar, Spectrochim. Acta A, 83, 297-303 (2011).
11. C. M. Sharaby, Spectrochim. Acta A, 66, 1271-1278 (2007).
144