## Materials and Methods
### Preparation of Schiff Base Ligands
UV-Vis (DMSO): \(\lambda_{\rm max}\) (nm) = 320. _2.3. Preparation of Co (II) Complexes_  
All the complexes were prepared in a similar procedure. Solution of ligand in methanol (1 mmol) were mixed with CoCl\({}_{2}\)\(\cdot\)6H\({}_{2}\)O and refluxed for 3-5 h 45 \({}^{\circ}\)C. The precipitate was filtered, washed with methanol and ether and then dried in a vacuum desiccator. _Complex [Co\({}_{2}\)(1,4-phenylenebis(methanylylidene))bis(2-nitroaniline)Cl\({}_{4}\)]_ (**CoL\({}_{\bf 1}\)**): Pale Green solid. Yield: 84%. M.P. 248-250 \({}^{\circ}\)C. Molar conductivity (\(\Omega^{-1}\) mol\({}^{-1}\) cm\({}^{2}\)): 22. Selected IR data (v, cm\({}^{-1}\)): 3109, 2971, 1651, 1521, 1384, 598, 492. UV-Vis (DMSO): \(\lambda_{\rm max}\) (nm) = 300, 410, 600,690. Mass (see Supplementary Materials): \([m/z]^{+}=633\). _Complex [Co\({}_{2}\)(1,4-phenylenebis(methanolylidene))bis(2-methoxyaniline)Cl\({}_{4}\)]_ (**CoL\({}_{2}\)**): Dark Green solid. Yield: 68%. M.P. 313-315 \({}^{\circ}\)C. Molar conductivity (\(\Omega^{-1}\) mol\({}^{-1}\) cm\({}^{2}\)): 12. Selected IR data (v, cm\({}^{-1}\)): 3062, 3018, 1620, 1583, 1368, 511, 474. UV-Vis (DMSO): \(\lambda_{\rm max}\) (nm) = 290, 260, 610, 690, 750. Mass: \([m/z]^{+}=603\). _Complex [Co\({}_{2}\)(1,4-phenylenebis(methanolylidene))bis(azanylylidene))dipheno]Cl\({}_{4}\)]_ (**CoL\({}_{\bf 3}\)**): Dark Brown solid. Yield: 75%. M.P. 230-232 \({}^{\circ}\)C. Molar conductivity (\(\Omega^{-1}\) mol\({}^{-1}\) cm\({}^{2}\)): 14. Selected IR data (v, cm\({}^{-1}\)): 3100, 2841, 1650, 537, 485. UV-Vis (DMSO): \(\lambda_{\rm max}\) (nm) = 280, 370, 600, 680. Mass: \([m/z]^{+}=575\). _Complex [Co(4-((2-nitrophenyl)imino)methyl)benzaldehyde)Cl\({}_{2}\)]_ (**CoL\({}_{\bf 4}\)**): Green solid. Yield: 80%. M.P. 280-282 \({}^{\circ}\)C. Molar conductivity (\(\Omega^{-1}\) mol\({}^{-1}\) cm\({}^{2}\)): 8. Selected IR data (v, cm\({}^{-1}\)): 3181, 1599, 614. UV-Vis (DMSO): \(\lambda_{\rm max}\) (nm) = 320, 600,690. Mass: \([m/z]^{+}=503\). _Complex [Co(4-((2-methoxyphenyl)imino)methyl)benzaldehyde)Cl\({}_{2}\)]_ (**CoL\({}_{\bf 5}\)**): Orange-Red solid. Yield: 82%. M.P. 305-307 \({}^{\circ}\)C. Molar conductivity (\(\Omega^{-1}\) mol\({}^{-1}\) cm\({}^{2}\)): 16. Selected IR data (v, cm\({}^{-1}\)): 3100, 2900, 1619, 568, 509. UV-Vis (DMSO): \(\lambda_{\rm max}\) (nm) = 290, 370, 600, 670. Mass: \([m/z]^{+}=473\). _Complex [Co(4-((2-hydroxyethyl)imino)methyl)benzaldehyde)Cl\({}_{2}\)]_ (**CoL\({}_{\bf 6}\)**): Dark Pink solid. Yield: 87%. M.P. 236-238 \({}^{\circ}\)C. Molar conductivity (\(\Omega^{-1}\) mol\({}^{-1}\) cm\({}^{2}\)): 10. Selected IR data (v, cm\({}^{-1}\)): 2959, 1634, 649. UV-Vis (DMSO): \(\lambda_{\rm max}\) (nm) = 270, 350, 610, 670. Mass: \([m/z]^{+}=445\). _2.4. Antibacterial Study_  
All the synthesized compounds were evaluated to examine their in vitro antibacterial activities against _Escherichia coli_ (ATCC: 25922), _Serratia marcescens_ (ATCC: 13880) and _Pseudomonas aeruginosa_ (ATCC: 27853) as gram negative bacteria and _Bacillus subtilis_ (ATCC: 6633), and _Staphylococcus aureus_ (ATCC: 6838), as gram positive bacteria, by employing two methods: disk diffusion and broth dilution methods; which are recommended by the National Committee for Clinical Laboratory Standards (NCCLS) [24]. Accordingly, stock solution of each compound (2 mg/mL) was prepared by dissolving the compounds in DMSO. Prior to sensitivity testing, the bacteria strains were cultured onto Muller-Hinton agar plate and incubated for 18-24 h at 35 \({}^{\circ}\)C. The density of the bacteria culture required for the tests was adjusted to 0.5 McFarland (1.5 \(\times\) 10\({}^{8}\) CFU/mL) (CFU = Colony Forming Unit). These tests were repeated three times to ensure reliability.