Introduction

Pyrazole derivatives are found in a diverse from natural products. They are considered as materials with biological activity and have found applications in pharmaceutical industries [1].

The diverse in bioactivity of pyrazole-based compounds have encouraged researchers to attempt to synthesize new such compounds and to study their potential biological effects. In addition, the coordinated ability for these compounds has resulted in synthesis for more complexes with different applications [2-6].

Pyrazolones are an interesting group of such ligands and have been the subject of wide investigations.

They are used as chelating agents to stabilize metal ions in difference oxidation states and to synthesize coordinated compounds with interesting features [7-10]. Pyrazoline derivatives are the electron rich nitrogen heterocycles which play an important role in the diverse biological activities. These heterocyclic compounds widely occur in nature in the form of alkaloids, vitamins, pigments, and as constituents of plant and animal cell. Considerable attention has been focused on the pyrazolines and substituted pyrazolines due to their interesting biological activities.

Materials and Methods

The chemicals obtained from BDH, Merck. On a Shimadzu (FT-IR)-8400S spectrophotometer at range (4000-400 cm^-1), the U.V-Vis spectrophotometer kind double beam at range (200-1000) nm, Shimadzu UV160A nm were used for characterized of synthesized compounds.  The ¹H-NMR and ¹³C-NMR spectra of ligand were recorded on Brucker DRX kind system (500 MHz) in TMS as a standard in dimethyl sulfoxide-d₆ solution. Mass spectra for ligand were recorded by (EI) mass spectroscopic using MS Model: 5973 Network Mass Selective Detector. TGA analysis of some compounds was carried out using a STAPT-1000 Linseis company, Germany. Agar diffusion was applied to test antibacterial activity.

Synthesis of bidentate ligand (L³)

This organic compound was prepared following the procedure described by Weaam A.Mahmood [11]. Yellow precipitate formed which was washed with methanol and recrystallization with absolute ethanol to get a pure product and dried, melting point of ligand prepared (L³): 230-232 °C, molecular weight: 351 g/mol (C₂₃H₁₇N₃O), Yield: 91 %.

Synthesis of bidentate ligand (L³) complexes

A solution of (0.070 g, 1 mmole) of bidentate ligand (L³) in absolute ethanol was added to a solution of CoCl₂.6H₂O (0.238 g, 1 mmole) in absolute ethanol. The mixture was refluxed for (1 h) with stirring. Orange precipitate was formed, which washed several time with absolute ethanol to get a pure product and dried. The similar method of Co (II) complex was synthesized. The complexes MCl₂.nH₂O, M (II) = [Mn(n=4),Cu (n=2) ions, Ni (n=6) ion, Zn (n=0), Cd (n=2)      and Hg (n=0) ion [12]. The physical properties of ligand (L³) complexes are presented in Table 1.

Results and Discussion

FT-IR spectrum

The important characteristic bands for FT-IR spectra of bidentate ligand (L³) and its complexes were summarized in Table 2. The FT-IR spectrum of bidentate ligand (L³), which includes a new peak at (1627) cm^-1 refers to stretching frequency of azomethine group (υ C=N) [13]. The bands at (1678, 1597 and 3070) cm^-1 due to (C=O), (C=C) aromatic, and (C-H) aromatic stretching vibration, respectively. The FT-IR spectrum of bidentate ligand (L³) showed disappearance of two peaks of υ asy. NH₂, υ sy. NH₂ and band of (C=O) of anthrone and appearance of imine group indication on formation of ligand (L³) [14]. The specific peak at 1627 cm^-1 which was attributed to stretching vibration of imine group (υ C=N) in IR spectrum of free ligand (L³), it is peak shifted to lower or higher frequency at range 1620-1649 cm^-1 in spectra for synthesized complexes; this shift may be due to involved N atom for imine group in coordinated with metal ions [15].

Table 1: Physical properties of bidentate Schiff base (L³) complexes

The bands at range 1473-1495 cm^-1 and at range 2922-2924 cm^-1 are due to C=C and C-H aromatic stretching vibration, respectively. The peak at 1597 cm^-1 stretching vibration, which pointing to C=N of ring of free ligand, shifted at range 1580-1591 cm^-1 in the spectra for complexes, showing that coordination between N atom with metal ions had happened [16].

At the lower frequency region, the FT-IR spectra for prepared complexes revealed new peaks, not existing in spectrum for free Schiff base; these peaks appeared at 513-569 cm^-1, 468-520 cm^-1 due to M-N, M-O [17-18], respectively. The two bands at range 3410-3475 cm^-1 and at range 819-929 cm^-1 in spectra of complexes [Mn(L3)₂ (H₂O)₂] Cl₂, [Co(L³)₂ (H₂O)₂] Cl₂, [Ni(L³)₂(H₂O)₂] Cl₂, [Cu(L³)₂(H₂O)₂] Cl₂, [Zn(L³)₂(H₂O)₂] Cl₂ and [Hg(L³) (H₂O) Cl]Cl are attributed to the coordinated H₂O (aqua).

The band at 3412 cm^-1 in spectrum of complex [Cd(L³)(H₂O)(Cl)] Cl.H₂O refers to H₂O hydrate, while the coordinated H₂O (aqua) in these complexes was confirmed by new peak at 923 cm^-1 with first band at 3412 cm^-1.

(C=O) amide of (L³) 1658, ν(C=N) imin 1627, ν(C=N) ring 1597, (C=O) amide of  [Mn(L³)₂(H₂O)2]Cl₂ 1658 , ν(C=N) imin 1622, ν(C=N) ring 1585, M-N 565, M-O 511, (C=O) amide of  [Co(L³)₂(H₂O)₂]Cl₂ 1658, , ν(C=N) imin 1620, ν(C=N) ring 1590, M-N 513, M-O 468,  (C=O) amide of  [Ni(L³)₂(H₂O)₂]Cl₂ 1658, ν(C=N) imin 1622, ν(C=N) ring 1588, M-N 569, M-O 518, (C=O) amide of  [Cu(L₃)₂(H₂O)₂]Cl 1666, ν(C=N) imin 1620, ν(C=N) ring 1591, M-N 561, M-O 513,  (C=O) amide of  [Zn(L³)₂(H₂O)₂]Cl₂ 1680, ν(C=N) imin 1625, ν(C=N) ring 1585, M-N 569, M-O 520, (C=O) amide of  [Cd(L³)(H₂O)(Cl)] Cl.H₂O 1685, ν(C=N) imin 1633, ν(C=N) ring 1580, M-N 561, M-O 513, (C=O) amide of  Hg(L)(H₂O)(Cl)] Cl 1665, ν(C=N) imin 1649, ν(C=N) ring 1585, M-N 565, M-O 511 (Table 2).

Table 2: FT-IR data (cm^-1) of bidentate ligand (L³) complexes

Electronic spectrum

The all UV-Vis spectral data of bidentate ligand (L³) and its complexes were listed in Table 3. The electronic spectrum for (L³) displayed four absorption bands. The first and second appeared at (296) nm (37175) cm^-1, and also (330) nm and (30303) cm^-1 were attributed to (π → π*) electronic transitions. The third and the fourth band appeared at (356) nm (28090) cm^-1 and (383) nm, (26110) cm^-1 were related to (n→π*) electronic transitions [19]. The electronic spectra of all complexes exhibited four absorption peaks at range 3731-2597 cm^-1_, which can be attributed to the intra-ligand [20]. New absorption peak at range 2681-2386 cm^-1 is assigned to MLCT [21]. The new peaks in spectra of complexes Mn (II) at (419) nm (23866) cm^-1, (510) nm (19608) cm^-1; Co (II) at (681) nm (14684) cm^-1 and (756) nm (13228) cm^-1, (805) nm (12422) cm^-1; Ni (II) at (416) nm (24038) cm^-1, (748) nm (13369) cm^-1, (981) nm (10194) cm^-1 and Cu (II) at (625) nm (16000) cm^-1 and (895) nm (11173) cm^-1, were attributed to (d-d) electronic transitions, which indicated octahedral geometry around metal ion [22].

¹H-NMR and ¹³C-NMR spectra of bidentate ligand (L³)

¹H-NMR spectrum for (L³), in Figure 1 dislplays the resonances at chemical shift (δH = 6.84-8.59 ppm) are assigned to protons of aromatic ring (Ar–CH) [23]. The appearances of these protons as a multi are attributed to mutual coupling. The spectrum displayed chemical shifts at (δH = 2.49-2.50 ppm and 3.38 ppm) referred to DMSO, and the existence of water molecules HOD in the solvent respectively [24]. The spectrum displayed chemical shifts at (δH = 1.47 ppm and 2.01 ppm) are assigned to protons of (CH₂) group of anthrone and pyrozoline ring, respectively [23].

Figure 1: ¹H-NMR spectrum for bidentate ligand (L³) in DMSO-d₆

The ¹³CNMR spectrum for (L³), Figure 2, in DMSO-d₆ solvent showed chemical shift at range (δ= 116.74-135.02 ppm) assignable to aromatic carbon atoms. The chemical shifts at (δ=182.95 ppm) due to the carbonyl carbon atom (C₅), while the chemical shift at (δ= 156.64 ppm) due to the imine carbon atom (C₂₆). The chemical shift at (δ=38.45 ppm and δ=32.50 ppm) attributed to the methylene group (C₄, C₂₇). The chemical shift at (δ=135.36 ppm) due to the (C₇) [12].

Figure 2: ¹³C-NMR spectrum of bidentate ligand) L³) in DMSO-d₆

Mass spectra of bidentate ligand (L³)

The mass spectrum for (L³) is showed in Figure 3S. The molecular ion peak of the ligand is showed at m/z⁺ = 351 [M]⁺C₂₃H₁₇N₃O; requires = 351 ⁽¹⁹⁾.The other peaks detected at m/z = 239 to 51 correspond to [M₁]^●+ = C₂₂H₁₇N₃O to [M₁₅]⁺=C₄H₃. The suggested mass fragmentation of (L³) was showed in Scheme 1.

Figure 3: Mass Spectrum of bidentate ligand (L³)

Table 3: Electronic spectral data of bidentate ligand (L³) complexes

Molar conductance

The molar conductance measurement for complexes was used to detection the ionic formula of the complexes (electrolyte or non-electrolyte). The values of molar conductivity for compounds in Dimethyl Sulfoxide (10⁻³M) at 25 C are listed in Table 4. The molar conductance of compounds [Mn(L³)₂ (H₂O)₂] Cl₂, [Co(L³)₂ (H₂O)₂] Cl₂, [Ni(L₃)₂(H₂O)₂] Cl₂, [Cu(L³)₂(H₂O)₂] Cl₂ and [Zn(L³)₂(H₂O)₂] Cl₂ refer to 1:2 electrolytic natures. The molar conductance values of compounds [Cd (L³) (H₂O) Cl]Cl.H₂O and [Hg(L³) (H₂O) Cl]Cl refer to 1:1 electrolytic natures.

Magnetic properties

The magnetic moment μ_eff, X_M, and X_A values for Mn (II), Co (II), Ni (II), and Cu (II) complex were calculated according to gramic magnetic susceptibility (Xg).

The value of diamagnetic correction Factor (D) was obtained theoretically. The μ_eff values of Mn (II), Co (II), Ni (II), and Cu (II) refer to octahedral geometry around metal ion. The magnetic moment of complexes were listed in Table 4.

Scheme 1: The suggested mass fragmentation of bidentate ligand (L³)

Table 4: The molar conductance of bidentate Schiff base complexes

Thermal analysis

Thermal analysis of [Ni(L3)₂ (H₂O)₂]Cl₂

The thermo gram for [Ni(L3)₂               (H₂O)₂]Cl₂ is displayed in Figure 4. In TGA, peak recognized at 122.5 °C is specific to loss for (2H₂O) portions, (W.t = 0.39 mg, 4.14 %). The second step at 295.458 °C that pointing to loss for (Cl₂, C₆H₅, CH₂CO) fragment (W.t = 2. 10 mg, 21.89 %). The third step at 379. 041 °C that designated the loss of (C₂₃H₁₇N₃O) fragment (W.t = 3.89 mg, 40.45 %). The fourth step at 889.291 °C that designated the loss of (C₈H₄) fragment (W.t = 1.11 mg, 11.52 %). The final remainder of the compound that appeared above 890 °C is assigned to the (NiC₇H₆N₃), (W.t = 2.11, 21. 97 %) [25].

Figure 4: Thermal Analysis of [Ni(L3)₂ (H₂O)₂]Cl₂

Thermal analysis of [Cd(L3)(H₂O)(Cl)]Cl. H₂O

The thermo gram for [Cd(L³)                 (H₂O)(Cl)]Cl. H₂O is displayed in Figure 5. In TGA, peak recognized at 99.25 °C is specific to loss for (H₂O) portions, (W.t = 0.16 mg, 3.15 %). The second step at 305 °C that designated the loss of (H₂O, Cl₂, C₇H₈, and 2H₂) fragment (W.t = 1.70 mg, 32.45 %). The third step at 888.375 °C that designated the loss of (C₁₆H₂N₂O) fragment (W.t = 2.19 mg, 41. 75 %). The final remainder of the compound that appeared above 890 °C is assigned to (CdNH₃), (W.t = 1.19, 22.63 %) [26].

Figure 5: Thermal Analysis of [Cd (L3) (H₂O) ( Cl)]Cl. H₂O.Conclusion and suggested molecular structure for all compounds

According to the characterization data for new bidentate ligand (L³) and it's complexes by FT- IR, UV-Vis, (¹H-NMR, ¹³C-NMR), magnetic susceptibility, and molar conductivity along with melting point, we found the new ligand (L³) behaves as bidentate ligand via its a N atom in imine and N atom of pyrazol ring with the central metal ions Mn (II), Co (II), Ni (II), Cu (II), Zn (II), Cd (II), and Hg (II), as shown in Figure 6. The octahedral geometrical structure was also suggested for Mn (II), Co (II), Ni (II), Cu (II), and Zn (II) complexes. Furthermore, the tetrahedral geometrical structure was suggested for Cd (II) and Hg (II) two complexes.

Figure 6: Structure of bidentate ligand (L³) and it's complexes.

Biological activity of ligand (L³) and its complexes

The prepared of ligand (L³) and its metal complexes of this study were tested against types of bacteria gram negative (Bacillus and Escherichia coli) and gram positive (Pseudomonas auroginosa and Staphylococcus aurus), as showed in Figures 7-10. The job of dimethyl sulfoxide in bioeffect screened was clarified by separated study conducted with the solution for dmso only, which appearance not activate as antibacterial strains [27]. The result of measured area of inhibition is indicated in Table 5.            

Table 5: Bacterial activity of bidentate ligand (L³) and its complexes

Figure 7: Biological activity of ligand and its complexes against of Escherichia coli bacteria

Figure 8: Biological activity of ligand and its complexes against of Pseudomonas auroginosa bacteria

Figure 9: Biological activity of ligand and its complexes against of Staphylococcus aurus bacteria

Figure 10: Biological activity of ligand and its complexes against of Bacillus bacteria

Acknowledgments

The authors would like to express their sincere thanks with appreciation to the supervisor Prof. Dr. Sajid Mahmood Lateef. They would also like to thank the residents for the research for their efforts in correcting it.

Disclosure Statement

We have no conflicts of interest to disclose.

Funding

This study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors' contributions

All authors contributed toward data analysis, drafting, and revising the paper and agreed to responsible for all the aspects of this work.

Conflict of interest

The authors declare that they have no conflicts of interest in this article.

ORCID

Weaam A. M. Al-Shammari

https://www.orcid.org/0000-0002-1026-3475

HOW TO CITE THIS ARTICLE

Weaam A. M. Al-Shammari, Sajid M. Lateef, Structural, Spectroscopic, Thermal, and Biological Studies of New Schiff Base Ligand Derived from Anthrone and 3-Amino-1-Phenyl-2-Pyrazoline-5-One and Its Complexes with Metallic Ions. Chem. Methodol., 2023, 7(8) 637-649

DOI: https://doi.org/10.48309/chemm.2023.404436.1687  

URL: https://www.chemmethod.com/article_178404.html