**Table 1.**

*Antibacterial activity data of Schiff base (2a) and its metal complexes (3a, 4a and 5a) against E. coli, S. aureus and B. cereus with their minimum zone of inhibition and MIC (μg/mL) mm values.*


#### **Table 2.**

*Antibacterial activity data of Schiff base (2a) and its metal complexes (3a, 4a and 5a) against P. aeruginosa, P. vulgaris and E. aerogenes with their minimum zone of inhibition and MIC (μg/mL) mm values.*

**93**

**4. Conclusion**

**Figure 16.**

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

and also in **Figure 16**. Minimum inhibitory concentration (MIC) was measured by broth micro dilution susceptibility method. No inhibition zone was found for the solvent control (DMSO) for each bacterial suspension. A serial dilution of sample extracts was made in nutrient broth medium. Then 1 mL of standard (0.5 Mc Farland) bacterial suspension was inoculated into each of these tubes. A similar nutrient broth tube without sample extract was also inoculated and used as control. The samples under investigation have shown promising results against the tested bacterial strains. The LH (**2a**) was most effective against *S. aureus* only. The Co(II) complex (**3a**) showed most effectiveness against *S. aureus*, *E. aerogenes*. The Ni(II) complex (**4a**) showed higher activity against *E. aerogenes*. Although in other cases it showed moderate activity. It was found that Cu(II) complex (**5a**) was most effective against the tested bacteria. The observation suggested that the chelation could facilitate the capability of the complexes to penetrate bacterial cell membrane [44]. Such a chelation could enhance the lipophilic property of the corresponding metal ions that favors permeation towards the lipid layer of cell membrane. The activity of both the complexes and ligand enhanced as the concentration was increased

*Inhibition zones for the LH (2a), Co(II) complex (3a), Ni(II) complex (4a) and Cu(II) complex (5a).*

Herein this chapter, new Co(II), Ni(II) and Cu(II) complexes of an ionic liquidsupported Schiff base, 1-{2-(2-hydroxy-5-nitrobenzylideneamino)ethyl}-3-ethylimidazolium tetrafluoroborate were synthesized and characterized by different spectral and analytical techniques. The Schiff base ligand played as a potential bidentate ligand coordinating through the N-atom of azomethine and O-atom of phenolic group to the metal ions and thus formed 1:2 (M:L) complexes. Spectral and magnetic susceptibility data revealed that the ligand was arranged in square planner geometry around the central metal ions. The antibacterial study of the synthesized compounds was performed and metal complexes have exhibited promising activity against the tested bacteria.

which were due to the growth of degree of inhibition.

*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 16.**

*Solvents, Ionic Liquids and Solvent Effects*

A1g → <sup>1</sup>

assigned to the combination of <sup>2</sup>

**3.6 Molar conductance**

**3.7 Antimicrobial activity**

and <sup>1</sup>

B1g → <sup>2</sup>

400 nm due to <sup>1</sup>

The LH (**2a**) exhibited three absorption bands at 306, 234 and 206 nm due to n → π\*, π → π\* and transitions involved with the imidazolium moiety, respectively [37, 38]. For the complexes, the bands that appeared below 350 nm were ligand centered transitions (n → π\* and π → π\*). The Co(II) complex (**3a**) displayed

complex (**3a**) showed magnetic moment of 2.30 B.M. due to one unpaired electron. The Ni(II) complex (**4a**) was diamagnetic and the band appeared at around

environment [41]. UV-visible spectra of Cu(II) complex (**5a**) exhibited d → π\* metal-ligand charge transfer transition (MLCT) at the region 358 nm had been

square planar geometry. The experimental magnetic moment value for **5a** was 1.84 B.M. consistent with the presence of an unpaired electron [42, 43].

Eg and <sup>2</sup>

The molar conductance (*Λm*) of the metal complexes was determined by applying the relation *Λm* = 1000 × *κ*/*c*, where *κ* and *c* stands for the specific conductance and molar concentration of metal complexes respectively. The complexes (1 × 10<sup>−</sup><sup>3</sup>

were dissolved in DMF and their specific conductance was measured at (298.15 *±* 0.01)

Antibacterial study of LH (**2a**) and its complexes was carried out *in vitro* against the Gram-negative/positive bacterial strains, and the results are displayed in **Tables 1** and **2**

LH — 6 7 8 12 7 9 10 10 12 — — 6 8 12 Co(II) complex — — 6 7 8 6 7 7 9 10 — 6 6 8 10 Ni(II) complex 6 7 8 9 9 — — 7 8 10 — — 6 8 10 Cu(II) complex 8 9 14 15 18 6 8 10 17 17 — — — — 7

*Antibacterial activity data of Schiff base (2a) and its metal complexes (3a, 4a and 5a) against E. coli, S. aureus and B. cereus with their minimum zone of inhibition and MIC (μg/mL) mm values.*

LH — 6 9 15 16 — 6 9 10 14 — 6 8 10 13 Co(II) complex — 7 9 10 13 — — — 6 7 8 10 13 15 17 Ni(II) complex — — 6 7 9 — — 6 7 8 8 10 12 12 16 Cu(II) complex — 6 12 12 14 — 7 7 8 16 — — 6 7 10

*Antibacterial activity data of Schiff base (2a) and its metal complexes (3a, 4a and 5a) against P. aeruginosa,* 

*P. vulgaris and E. aerogenes with their minimum zone of inhibition and MIC (μg/mL) mm values.*

*E. coli S. aureus B. cereus* **10 20 30 40 50 10 20 30 40 50 10 20 30 40 50**

*P. aeruginosa P. vulgaris E. aerogenes* **10 20 30 40 50 10 20 30 40 50 10 20 30 40 50**

metal complexes **3a**, **4a** and **5a** respectively indicating their 1:2 electrolytic natures.

B1g → <sup>2</sup>

K. The molar conductance data was observed as 123, 128 and 131S cm<sup>−</sup><sup>1</sup>

**Specimen Concentration (μg/mL)**

**Specimen Concentration (μg/mL)**

Eg transitions and supporting square planar geometry [39, 40]. The

B1g transition is consistent with low spin square planar

B1g → <sup>2</sup>

B1g → <sup>1</sup>

B2g transitions in a distorted

A1g

M)

for the

mol<sup>−</sup><sup>1</sup>

a band at 354 nm which could be attributed to the combination of <sup>2</sup>

**92**

**Table 2.**

**Table 1.**

*Inhibition zones for the LH (2a), Co(II) complex (3a), Ni(II) complex (4a) and Cu(II) complex (5a).*

and also in **Figure 16**. Minimum inhibitory concentration (MIC) was measured by broth micro dilution susceptibility method. No inhibition zone was found for the solvent control (DMSO) for each bacterial suspension. A serial dilution of sample extracts was made in nutrient broth medium. Then 1 mL of standard (0.5 Mc Farland) bacterial suspension was inoculated into each of these tubes. A similar nutrient broth tube without sample extract was also inoculated and used as control. The samples under investigation have shown promising results against the tested bacterial strains. The LH (**2a**) was most effective against *S. aureus* only. The Co(II) complex (**3a**) showed most effectiveness against *S. aureus*, *E. aerogenes*. The Ni(II) complex (**4a**) showed higher activity against *E. aerogenes*. Although in other cases it showed moderate activity. It was found that Cu(II) complex (**5a**) was most effective against the tested bacteria. The observation suggested that the chelation could facilitate the capability of the complexes to penetrate bacterial cell membrane [44]. Such a chelation could enhance the lipophilic property of the corresponding metal ions that favors permeation towards the lipid layer of cell membrane. The activity of both the complexes and ligand enhanced as the concentration was increased which were due to the growth of degree of inhibition.
