1. Introduction

1.1 Schiff bases and hydrazides

Schiff bases are usually prepared by the condensation of a carbonyl compound with a primary amine (Malakyan et al., 2016). Imine or azomethine groups are present in various natural, natural-derived and nonnatural compounds (Safoura, 2014). They are used in many fields such as biological activities, analytical chemistry, corrosion inhibitors, fungicidal, agrochemical, electrical conductivity, magnetism, ion exchange, nonlinear optics, catalysis (Emriye, 2016), crystal engineering (Al Zoubi, 2013), and medical substrates (Savalia et al., 2013). Hydrazides include C(=O)NHNH. group, and were produced as far back as 1895 by Kurzius (Majumdar et al., 2014). Hydrazides have been used widely in medicine, catalysis, and analytical chemistry (Salawu et al., 2018), and are highly useful starting materials and intermediates in the synthesis of heterocyclic intermediates in the synthesis of heterocyclic molecules. They have been investigated due to their antitumor and biocidal activity, also they have been used widely as antituberculosis compounds because of their ability to form metal chelates (Mathew et al., 2006). A large number of different Schiff base ligands have been used for excellent selectivity, sensitivity, and stability for specific metal ions such as Ag(II) Al(III), Co(II), Cu(II), Gd(III), Hg(II), Ni(II), Pb(II), Y(III), and Zn(II) (Ashraf et al., 2011).

The aim of the present work is to synthesize new compounds containing derivatives of ligands via Schiff base with hydrazide which is derived from 2-chlorobenzaldehyde, glycine and hydrazine hydrate which reacted with Co, Ni and Cu ions to form new complexes.

2. Experimental

2.1 Reagents and solutions

All chemicals used are commercially available from BDH.

2.2 Instrumentation

The melting points were determined in glass capillary tubes in degrees Celsius. Molar conductance in dimethyl sulfoxide (DMSO) (10^–3 mol L^–1 solution at 25 °C) and molar ratio were measured on Jenway conductivity meter model 4510. The ligand and its complexes were characterized by comparison of spectroscopic data, infrared (IR) spectra of the ligand and metal complexes were measured using FT/IR – 140, Jasco, Japan in KBr pellets. ¹H and ¹³C nuclear magnetic resonance (NMR) spectra were recorded in a Varian FT – 300 MHz spectrometer in d₆-DMSO solvent using tetramethylsilane as internal standard. Ultraviolet-visible (UV-Vis) spectra and antioxidant activity measurements (by ferric-bipyridine method) (Specord 200, Analytilk Jena, Germany) using DMSO and methanol as the reference and solvent, respectively. The magnetic susceptibilities of the complexes were measured at room temperature using Gouy’s method by a magnetic susceptibility balance from Johnson Metthey and Sherwood model. Carbon, hydrogen, and nitrogen were estimated by Vario ELFab. Nr. 11042023. The X-ray powder diffraction patterns of the ligand and the solid complexes were obtained using XD-2 (Shimadzu ED-720), X-ray powder diffractometer at a voltage of 35 KV and current of 20 mA using CuKα radiation generator in the range 5° < 2θ < 70° with a 1 min^–1 scanning rate and a wavelength of 0.154056 nm. Microbiological analysis was carried out using the filter paper disc method.

2.3 Synthesis of Schiff base hydrazide ((2-chlorobenzylidene)amino)acetohydrazide hydrate = L

The solid ligand was prepared in 1:1:1 molar ratio as shown in Fig. 1 by adding dropwise of an ethanolic solution of glycine (0.01 mol) to an ethanolic solution of the aldehyde (0.01 mol) with stirring. The mixture was refluxed for 3 h with constant stirring and heating (Gao, 2013) until light brown solution of the Schiff base is formed. Then, addition of hydrazine hydrate drop by drop with constant stirring to the hot solution of the first part of the Schiff base until light brown precipitate is formed. The resulting precipitate was filtered off and washed with ethanol until the solution become clear then was left to dry.

2.4 Synthesis of the complexes

Generally, all the solid complexes were prepared as shown in Fig. 2 by adding dropwise of an methanolic solution of the hydrated metal chlorides (0.008 mol) to an methanolic solution of the ligand (Schiff base hydrazide 0.008 mol) with stirring. The mixture of each was refluxed for 4 to 6 h with constant stirring until colored precipitates are formed. All the materials solutions were in 1:1 molar ratio. The resulting precipitates were filtered off and washed with methanol even become a clear solution, then left them to dry.

3. Results and discussion

All the compounds are colored solids and insoluble in common organic solvents except DMSO (Table 1). Molar conductance values of these compounds were in the range of 178–205 S cm. mol^–1, indicating their electrolytic nature (G. Mohamed et al., 2006) as recorded in Table 2.

3.1 Molar ratio by conductivity measurements

Through the conductivity measurements of the ligand with the divalent metals Co(II), Ni(II) and Cu(II) in order to calculate the molar ratio between the ligand and these metals, the following was found:

1. The resulting values were high, indicating that these complexes have a conductive nature (Tulu and Yimer, 2018). This was also confirmed using silver nitrate;

2. The ratio between these metals and chloride ion was 1:2 (G. Mohamed et al., 2006), where the resulting values were located between 186.7–115.9 S cm² mol^–1;

3. Through conductivity measurements for different concentrations of these complexes, conductivity readings were confirmed at a fixed molar value, which represents 1:1 between the ligand and these metals (Ghara et al., 2017) as show in Fig. 3.

3.2 IR spectra of the ligand and its complexes

Comparing the IR spectral data of the ligand and its complexes (Table 3 and Fig. 4) confirmed the complexation through the azomethine group υ_C=N. The band at 1663 cm^–1 assigned to υ_C=Nin the free ligand was shifted to lower wave number in the complexes, indicating the participation of the azomethine nitrogen in coordination (Jamil et al., 2022; E. Mohamed et al., 2014). The IR spectra of the Co(II) complex showed a band at 1654 cm^–1 which is characteristic of (C=O) group. This band is indicating coordination of this group through oxygen atom (Al-Salami et al., 2017). The band at 3106 cm^-1. can be assigned to vibration of the NH2 group in the ligand, which shifted to higher frequencies in the complexes, which identifies coordination of the amine nitrogen (Demirbaş et al., 2002).

The ligand and its complexes show additional broad bands in the range 3373–3436 cm^–1 due to the OH stretching of the water molecule, which is confirmed by the elemental analysis and gravimetric studies (Al-Salami et al., 2017; Jamil et al., 2022). Low intensity bands observed in far-IR region in the range 528–591 cm^-1. and 436–439 cm^-1. which may probably be due to the formation M-O and M-N bonds, respectively (Alomari, 2010; Hossain et al., 2019).

Other absorption bands of v(N-N) (Ali et al., 1997; Dzulkifli et al., 2012), v(NH) (Ali et al., 1997; Ejelonu et al., 2018), v(Ar-Cl) (Emriye, 2016; Kapadnis et al., 2016), v(CH2), v(C=C), (E. Mohamed et al., 2014), v(CH) (Al-Salami et al., 2017; E. Mohamed et al., 2014), v(NH2) (Demirbaş et al., 2002) are given in Table 3.

3.3 NMR spectroscopy of the ligand

3.3.1 ¹HNMR

The resonance of protons has been assigned on the basis of their integration and multiplicity pattern. The ¹HNMR spectra of the ligand (Table 4 and Fig. 5) in DMSO exhibits signal at 8.55 ppm attributed to CH=N- proton (Al-Salami et al., 2015). The signals within the 6.85 and 6.88 ppm are assigned to the NH and NH. respectively (Mathew et al., 2006). Spectra of aromatic range was observed at 7.67–7.70 ppm (Sakhare et al., 2015). The signals appeared at 2.50 and 3.20 ppm were indicated the protons of CH2 (Al-Garawi et al., 2012) and H2O, respectively.

3.3.2 ¹³C NMR

The ¹³CNMR spectra provide further support for the structural characterization of the ligand (Table 4 and Fig. 6) ¹³C NMR spectral data of the ligand has signal at 160.35 attributed to carbon of CH=N- (Neelofar et al., 2017). The aromatic carbon signals are present in the range 115.82–130.08 ppm (Oğuzhan et al., 2017). The ¹³CNMR spectral data of the carbon amide and CH. group are present at 160.58 (Shneine et al., 2017) and 40.00 ppm (Neelofar et al., 2017), respectively. The structural formula of the ligand (Fig. 7).

3.4 Magnetic and electronic of the ligand and its complexes

The absorption spectrum of the ligand (Fig 11a) shows two absorption bands appearing at 45,454 and 33,333 cm^–1. The band appearing at low energy side at 33,333 cm^–1 in the ligand is attributed to n-π. transitions of conjugation between the lone pair of electrons of p orbital of N-atom in C=N group and a conjugated π bond of aromatic rings (Hossain et al., 2019). The band appearing at higher energy 45,454 cm^–1 arise from π-π* transition within the phenyl and π-π* transitions of the C=N group (Sarwar et al., 2018).

The electronic spectrum of the Co(ΙΙ) complex as shown in Figs. 8 and 11b and Table 5, octahedral is suggested. This is based on the appearance of 13,513 cm^–1 in the spectra recorded in DMSO solution, which is attributed to the 4T_1g→4A_2g (ν2) transitions (Patel et al., 2012; Yousef et al., 2016), also Co(II) complex has magnetic moment of 4.8 Bohr's magneton, BM, which lie in the range reported for octahedral geometry around the Co(II) ion (Sharma et al., 1994; Tulu and Yimer, 2018). Moreover, the purple color of the complex is in good agreement with this reported for octahedral Co(II) complex (Tulu and Yimer, 2018).

The magnetic measurements indicates that Ni(II) complex is a diamagnetic (Tulu and Yimer, 2018) and the electronic spectra of this complex in DMSO solution (Fig,11c and Table 5) showed two bands in 21,276 and 18,867 cm^–1 attributed to 1A1g →1A2g and 1A1g →B1g transitions, respectively, for square planar Ni(II) complex (Fig. 9) and the green color of this complex is additional evidence for square planar structure (Al-Jiboury and Al-Nama, 2019).

The electronic spectrum (Fig. 11d) of Cu(II) complex show one band at 21,730 cm^–1, assigned to the transitions 2B1g-->2A1g, indicating square-planar geometry (Table 5 and Fig. 10) (Mahmood et al., 2013). This geometry is further supported as the values of the magnetic moment obtained 1.87 B.M, which is lying in the range reported for a square-planar structure (Mahmood et al., 2013; Mishra et al., 2012). The green color of this complex is additional evidence for square planar structure (Mahmood et al., 2013).

Also, the bands at 24,390, 22,222, and 24,691 cm^–1 should be attributed to the charge transfer of Co(II) (Mahmood et al., 2013), Ni(II) (G. Mohamed et al., 2006) and Cu(II) complexes (Hossain et al., 2019), respectively.

3.5 Powder X-ray diffraction of the ligand and its complexes

The powder X-ray powder diffraction patterns for the free ligand and its complexes were carried out in order to obtain an idea about the lattice dynamics of the resulted complexes. X-ray of these compounds are recorded and shown in Figs. 12 and 13.

The values of particle size, strain and relative intensity (%) of compounds are compiled in Table 6. The crystallite size could be estimated from X-ray diffraction (XRD) patterns by applying full width at half maximum (FWHM) of the characteristic peaks using Debye-Scherrer Eq. 1 (Al-Maydama et al., 2018; Refat et al., 2014a; b) and Williamson-Hall Eq. 2 (Abed et al., 2019).

where K is Scherrer constant and equals 0.94, λ is the Xray wavelength of Cu-Kα radiation (0.15405 nm), β is FWHM, and θ is Bragg diffraction angle in radian. The particle size of these compounds is located within the nano scale range (12.59–35.32 nm).

The strain calculated by applying Williamson-Hall Eq. 2 (Abed et al., 2019) which mean the slope as Eq. 3.

It was shown through crystal strain from William’s equation that the ligand, Co(II) and Cu(II) complexes have the property of crystal tensile, while the Ni(II) complex has the property of crystal compressive, which corresponds to the size of the crystals. It was found that the higher the compressive which negative values, the smaller the crystal size, while the higher the tensile with positive values, the higher the crystal size, and this is what was clarified in Table 6.

The percentage of crystallinity, Xc(%), was calculated on the basis of the integrated peak areas of the principal peaks (Al-Maydama et al., 2018). The crystallinity of the complex is calculated relative to the crystallinity of the ligand as a ratio (Eq. 4).

where A_complex and A_ligand are the areas under the principal peaks of the complex and the ligand sample, respectively. The results of these calculations were that the crystalline percentage of the Ni(II) complex is high compared to the ligand, while it was low for the Co(II) and Cu(II) complexes when compared to the ligand.

3.6 The ligand as antioxidant

The 2((2-chlorobenzylidene)amino)acetohydrazide hydrate=(L) has been synthesized, and the antioxidant properties were studied using ferric-bipyridine reducing capacity of total antioxidants method (Naji et al., 2020). As it was found that this ligand can be used as an antioxidant compared to ascorbic acid, which was used as a standard material in this analysis, but with less effectiveness than ascorbic acid, which gave 3.7453 mg compared with ascorbic acid, which was 1 mg, while the standard deviation of this ligand was ± 9.67 × 10^–8.

3.7 Antimicrobial of the ligand and its complexes

This analysis of the ligand and its mineral complexes clearly demonstrated that they have antibacterial and antifungal activity (Table 7, Figs. 14 and 15).

Comparison of the biological evaluation of the ligand and its complexes with standards of gentamicin (antibacterial agent), nystatin, miconazole, itraconazole and metronidazole (antifungal agents). The results of the highest-to-lowest-impact items can be summarized as follows:

a. Staphylococcus aureus

Ni > Co > Cu > ligand

b. Bacillus subtilis

Co > Cu > Ni > ligand

c. Pseudomonas aeruginosa

Co > Ni > ligand > Cu

d. Escherichia coli

Ni > ligand > Cu

e. Aspergillus flavus

Ni > Co > Cu > ligand

f. Candida albicans

ligand = Co > Ni > Cu

From these results, we can summarize that:

1. Generally, the active property of the free ligand and complexes against the used strains is enhanced;

2. The growth of S. aureus and A. flavus are inhibited by complex of Ni(II), Co(II), Cu(II), and the ligand, respectively;

3. Bacillus subtilis is inhibited by complex of Co(II) more than complexes of Cu(II), Ni(II) and the ligand. The growth of E. coli is just inhibited by complex of Ni(II), the ligand and complex of Cu(II) compared to the complex of Co(II) there is no inhibition;

4. The Inhibition zone of Co(II) complex toward P. aeruginosa was more than that of Ni(II), Cu(II) complexes and the ligand.

5. The ligand and complex of Co(II) have the same worthy effect against C. albicans, which are more than complexes of Ni(II) and Cu(II).

According to the concept of cell permeability, since the lipid membrane that surrounds the cell favors the passage of lipid-soluble substances since lipid solubility is an important factor, so the polarity of the metal ion is greatly reduced due to the overlap of the orbitals of the metal ion with the bound. It increases the delocalization of electrons on the chelated rings and enhances the lipophilicity of the complexes, which facilitates the penetration of the lipid membranes of microorganisms and facilitates the closure of the metal bonding sites with enzymes.

These compounds deactivate various cellular enzymes, which play a vital role in the various metabolic pathways of these organisms. It has also been suggested that the final action of the toxin is denaturation of one or more cell proteins, impairing normal cellular processes (Jamil et al., 2022; Omer and Al-Daher, 2019; Refat et al., 2015; Reiss et al., 2021).

4. Conclusions

The Schiff base hydrazide ligand derived from the condensation of 2-chlorobenzaldehyde, glycine and hydrazine hydrate have been successfully synthesized. These ligand were complexed with using Co(II), Ni(II) and Cu(II) ions. Coordination of amine nitrogen (-NH₂) and azomethine nitrogen (-C=N-) with Ni(II) and Cu(II) in additional to oxygen of carbonyl group with Co(II). These compounds have been indicated by various studies; hence, it has been liable for imparting the stability to the complexes. The structures of these compounds were characterized by elemental, ¹HNMR, ¹³CNMR, FTIR spectra, molar ratio, XRD diffraction, UV-Vis spectra, and magnetic studies. The coordination of the ligand with Co(II), Ni(II) and Cu(II) ions showed molar ratio of 1:1. The complexes of Co(II) and Cu(II) presented square planar geometries, while Ni(II) presented octahedral geometry. Antioxidant study for the ligand provided its activity. The ligand with Schiff base and hydrazide groups and its complexes showed better biological activity. The results showed that the metal complexes have much higher antibacterial and antifungal activity compare to the parent ligand. It was found that the Co(II) complex was more effective than other metal complexes used against all types of bacteria and it was more effective against P. aeruginosa with diameter inhibition zone of 23 mm, while Ni(II) complex was more effective than other complexes used against two types of fungi and it was more effective against A. flavus than C. albicans.

Authors’ contribution

Conceptualization: Al-Azab, F. M.; Jamil, Y. M.

Data curation: Al-Azab, F. M.; Jamil, Y. M.; Al-Gaadbi, A. A.

Formal Analysis: Al-Azab, F. M.; Jamil, Y. M.; Al-Gaadbi, A. A.

Funding acquisition: Not applicable.

Investigation: Al-Azab, F. M.; Jamil, Y. M.; Al-Gaadbi, A. A.

Methodology: Jamil, Y. M.; Al-Azab, F. M.

Project administration: Jamil, Y. M.; Al-Azab, F. M.

Resources: Al-Azab, F. M.; Jamil, Y. M.; Al-Gaadbi, A. A.

Software: Jamil Y. M.; Al-Gaadbi A. A.

Supervision: Al-Azab, F. M.; Jamil, Y. M.

Validation: Al-Azab, F. M.

Visualization: Al-Azab, F. M.; Jamil, Y. M.; Al-Gaadbi, A. A.

Writing – original draft: Al-Gaadbi, A. A.

Writing – review & editing: Jamil, Y. M.

Data availability statement

All data sets were generated or analyzed in the current study.

Funding

Not applicable.

Acknowledgments

Not applicable.

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