**3.1 FT-IR spectral studies**

The assignments of the IR bands of the synthesized Co(II), Ni(II) and Cu(II) complexes had been made by comparing with the bands of ligand (LH) to determine the coordination sites involved in chelation. FT-IR spectra of LH (**2a**) showed a strong broad band at 3448–3071 cm<sup>−</sup><sup>1</sup> ; which was due to the hydrogen bonded phenolic group (▬OH) with H▬C(═N) group in the ligand (OH…N═C) [27, 28]. The broad band appeared at 3386–3429 cm<sup>−</sup><sup>1</sup> for the metal complexes (**3a**, **4a** and **5a**) suggested the presence of the solvated water molecules (probably for the presence of ▬NO2 group in the ligand and intrinsic property of the anion tetrafluoroborate) [29–31]. The band corresponding to the azomethine group (▬C═N) of the ligand was found at 1664 cm<sup>−</sup><sup>1</sup> . This band gets shifted in the range 1637– 1656 cm<sup>−</sup><sup>1</sup> because of coordination of N atom of azomethine linkage to the Co2+, Ni2+ and Cu2+ ions respectively [32]. The band for phenolic C▬O of free ligand was observed at 1293 cm<sup>−</sup><sup>1</sup> which moved to lower wave number 1172–1177 cm<sup>−</sup><sup>1</sup> for the complexes (**3a**, **4a** and **5a**) upon complexation. This fact established the bonding of ligand (**2a**) to the metal atoms through the N atom of azomethine and O atom of phenolic group [33]. The bands appeared in the region of 1102–1107 cm<sup>−</sup><sup>1</sup> for the metal complexes were assigned for B▬F stretching frequency. FT-IR spectra of the LH (**2a**) and its complexes showed strong bands at 1330–1343 cm<sup>−</sup><sup>1</sup> which were assigned for the NO2 group [34]. The spectra of the metal complexes exhibited bands at 633–651 and 471–526 cm<sup>−</sup><sup>1</sup> were attributed to M▬O and M▬N stretching vibrations, respectively [35]. IR spectra are given in **Figures 2–8**.

**Figure 2.** *SEM image of Co(II) complex (3a).*

**Figure 3.** *SEM image of Ni(II) complex (4a).*

**Figure 4.** *SEM image of Cu(II) complex (5a).*

#### **3.2 1 H NMR and 13C NMR spectral studies**

1 H NMR and 13C NMR spectra of Schiff base were recorded in DMSO-*d*6 (as shown in **Figures 9** and **10**). 1 H NMR spectra of the ligand showed singlet at 7.60 ppm which was assignable to proton of the azomethine linkage (▬CH═N▬) might be because of the effect of the *ortho*-hydroxyl group in the aromatic ring. A singlet at 8.88 ppm was assigned to hydroxyl proton (▬OH). The downfield shift of the phenolic (▬OH) proton was observed due to intramolecular (O▬H…N) hydrogen bonding in the ligand [36]. 13C NMR spectra of ligand exhibited peaks at *δ* 159.76 and 138.43 which were detected for the phenolic (C▬O) and imino

**87**

**Figure 7.**

**Figure 5.**

**Figure 6.**

*FT-IR spectra of Co(II) complex (3a).*

*FT-IR spectra of Ni(II) complex (4a).*

*FT-IR spectra of ligand (2a).*

*Imidazolium Ionic Liquid-Supported Schiff Base and Its Transition Metal Complexes: Synthesis…*

*DOI: http://dx.doi.org/10.5772/intechopen.86379*

*Imidazolium Ionic Liquid-Supported Schiff Base and Its Transition Metal Complexes: Synthesis… DOI: http://dx.doi.org/10.5772/intechopen.86379*

**Figure 5.** *FT-IR spectra of ligand (2a).*

*Solvents, Ionic Liquids and Solvent Effects*

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**3.2 <sup>1</sup>**

1

**Figure 4.**

**Figure 3.**

*SEM image of Ni(II) complex (4a).*

**H NMR and 13C NMR spectral studies**

shown in **Figures 9** and **10**). 1

*SEM image of Cu(II) complex (5a).*

H NMR and 13C NMR spectra of Schiff base were recorded in DMSO-*d*6 (as

7.60 ppm which was assignable to proton of the azomethine linkage (▬CH═N▬) might be because of the effect of the *ortho*-hydroxyl group in the aromatic ring. A singlet at 8.88 ppm was assigned to hydroxyl proton (▬OH). The downfield shift of the phenolic (▬OH) proton was observed due to intramolecular (O▬H…N) hydrogen bonding in the ligand [36]. 13C NMR spectra of ligand exhibited peaks at *δ* 159.76 and 138.43 which were detected for the phenolic (C▬O) and imino

H NMR spectra of the ligand showed singlet at

**Figure 6.** *FT-IR spectra of Co(II) complex (3a).*

**Figure 7.** *FT-IR spectra of Ni(II) complex (4a).*

**Figure 8.** *FT-IR spectra of Cu(II) complex (5a).*

**Figure 9.** *1 H NMR spectra of LH (2a).*

(▬CH═N) carbon atoms (due to keto-imine tautomerism). The aromatic carbons showed pecks at *δ* 134.08, 130.47, 130.31, 123.89, 119.80 and 118.65.

## **3.3 PXRD analysis**

The PXRD analysis of the synthesized compounds was carried out to find whether the particle nature of the samples was amorphous or crystalline. The PXRD spectrum of ligand (LH) exhibited sharp peaks because of their crystalline nature although the spectra of the two complexes did not show such peaks for their amorphous nature (as shown in **Figures 11–14**). The crystalline sizes were calculated using Debye Scherer's equation: D = 0.9 *λ*/*β*cos*θ*, where constant 0.9 is the shape factor, *λ* is the X-ray wavelength (1.5406 Å), *β* is the full width at half maximum (FWHM) and *θ* is the Bragg diffraction angle. The experimental average grain sizes of LH and its metal complexes were found to be 31.71 nm (**2a**), 7.76 nm (**3a**), 3.26 nm (**4a**) and 4.52 nm (**5a**).

**89**

**Figure 11.**

*PXRD spectra of LH (2a).*

**Figure 10.**

*13C NMR spectra of LH (2a).*

*Imidazolium Ionic Liquid-Supported Schiff Base and Its Transition Metal Complexes: Synthesis…*

*DOI: http://dx.doi.org/10.5772/intechopen.86379*

*Imidazolium Ionic Liquid-Supported Schiff Base and Its Transition Metal Complexes: Synthesis… DOI: http://dx.doi.org/10.5772/intechopen.86379*

**Figure 10.**

*Solvents, Ionic Liquids and Solvent Effects*

(▬CH═N) carbon atoms (due to keto-imine tautomerism). The aromatic carbons

The PXRD analysis of the synthesized compounds was carried out to find whether the particle nature of the samples was amorphous or crystalline. The PXRD spectrum of ligand (LH) exhibited sharp peaks because of their crystalline nature although the spectra of the two complexes did not show such peaks for their amorphous nature (as shown in **Figures 11–14**). The crystalline sizes were calculated using Debye Scherer's equation: D = 0.9 *λ*/*β*cos*θ*, where constant 0.9 is the shape factor, *λ* is the X-ray wavelength (1.5406 Å), *β* is the full width at half maximum (FWHM) and *θ* is the Bragg diffraction angle. The experimental average grain sizes of LH and its metal complexes

were found to be 31.71 nm (**2a**), 7.76 nm (**3a**), 3.26 nm (**4a**) and 4.52 nm (**5a**).

showed pecks at *δ* 134.08, 130.47, 130.31, 123.89, 119.80 and 118.65.

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**3.3 PXRD analysis**

*H NMR spectra of LH (2a).*

**Figure 9.** *1*

**Figure 8.**

*FT-IR spectra of Cu(II) complex (5a).*

*13C NMR spectra of LH (2a).*

**Figure 11.** *PXRD spectra of LH (2a).*

**Figure 12.** *PXRD spectra of Co(II) complex (3a).*

**Figure 13.** *PXRD spectra of Ni(II) complex (4a).*

#### **3.4 Mass spectral studies**

**90** To get information regarding the structure of the synthesized compounds at the molecular level, electrospray ionization (ESI) mass spectrometry was performed using methanol as solvent. Mass-spectra of the LH (**2a**) had a molecular ion peaks at m/z 289, that corresponds to [M-BF4] + , [M = C14H17N4O2] + . The metal complexes (**3a, 4a** and **5a**) exhibited molecular ion peaks (*m/z*) at 635 (M = [C28H32CoN8O6] + ), at 634 (M = [C28H32NiN8O6] + ) and at 639 (M = [C28H32CuN8O6] + ) which confirmed

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**Figure 15.**

**Figure 14.**

*PXRD spectra of Cu(II) complex (5a).*

*Imidazolium Ionic Liquid-Supported Schiff Base and Its Transition Metal Complexes: Synthesis…*

their stoichiometry as Co(L)2, Ni(L)2 and Cu(L)2 respectively. The mass spectra of the ligand and complexes were in good agreement with the respective structures as

The UV-visible spectra of the Schiff base and its metal complexes (as depicted

*UV-visible spectra in methanol (concentration of the solutions 1 × 10–4 M): (A) LH (2a); (B) Co(II) complex* 

*(3a); (C) Ni(II) complex (4a) and (D) Cu(II) complex (5a).*

in **Figure 15**) were recorded at room temperature using methanol as solvent.

*DOI: http://dx.doi.org/10.5772/intechopen.86379*

revealed by the elemental and other spectral analyses.

**3.5 Electronic spectra and magnetic moment**

*Imidazolium Ionic Liquid-Supported Schiff Base and Its Transition Metal Complexes: Synthesis… DOI: http://dx.doi.org/10.5772/intechopen.86379*

their stoichiometry as Co(L)2, Ni(L)2 and Cu(L)2 respectively. The mass spectra of the ligand and complexes were in good agreement with the respective structures as revealed by the elemental and other spectral analyses.
