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• A new Schiff base ligand N1, N5-bis[2-hydroxyphenyl]−2-methyl-1,5-diaminopentane is synthesized and characterized. • In-Silico studies of compounds to support the in-vitro results. • The increase in the spacer group in Schiff base compounds increases the biological activities. A novel ONNO donor tetradentate Schiff base ligand N,N' -bis[2- hydroxyphenyl]-2-methyl-1,5-diaminopentane (1) is synthesized and characterized by using 1H, 13C NMR spectroscopy and mass spectrometry. Biological studies on newly synthesized ligand are carried out and results are compared with the biological activities of known Schiff base ligands: N,N' -bis[{2- hydroxyphenyl }]-1,4-diaminobutane (2) and N,N' -bis[{2- hydroxyphenyl }]-1,3-diaminopropane (3). This comparative study highlights the effect of increasing methylene linkage on the biological activity of these ligands. The anti-microbial activities of all three ligands have been screened against two distinct gram-positive and gram-negative bacteria. In-vitro results of this comparative analysis are also supported by comprehensive molecular docking studies with DNA gyrase subunit B protein of gram-positive bacterium S. aureus and FabH–CoA complex of gram-negative bacterium E. coli. Experimental studies reveal that the spacer group plays a vital role in controlling the biological activities of the ligand. These findings are in good agreement with the theoretical findings. The study demonstrates that the biological activity of ligands is enhanced with increments in the number of spacers. Thus, the newly synthesized ligand (1) with the most extended spacer among the three showed the highest biological activity compared to other two ligands, similar to the popular drug Ciprofloxacin. [Display omitted] [ABSTRACT FROM AUTHOR]