The new Schiff base 4-[(4-Hydroxy-3-fluoro-5-methoxy-benzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-one: Experimental, DFT calculational studies and in vitro antimicrobial activity

• The compound was characterized by spectroscopic methods such as FT-IR, NMR and UV.
• Quantum chemical computations of the compound were performed with B3LYP/6-311++G(d,p) level.
• The antimicrobial activity of the compound was determined against the selected 11 bacteria and 8 fungi.

The synthesized Schiff base, 4-[(4-Hydroxy-3-fluoro-5-methoxy-benzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-one (I), has been characterized by 13C NMR, 1H NMR, 2D NMR (1H–1H COSY and 13C APT), FT-IR, UV–vis and X-ray single-crystal techniques. Molecular geometry of the compound I in the ground state, vibrational frequencies and chemical shift values have been calculated by using the density functional method (DFT) with 6-311++G(d,p) basis set. The obtained results indicate that optimized geometry can well reflect the crystal structural parameters. The differences between experimental and calculated results of FT-IR and NMR have supported the existence of intermolecular (O–H⋯O type) and intramolecular (C–H⋯O type) hydrogen bonds in the crystal structure. Molecular electrostatic potential (MEP), frontier molecular orbital analysis (HOMO–LUMO) and electronic absorption spectra were carried out at B3LYP/6-311G++(d,p). HOMO–LUMO electronic transition of 3.92 eV is due to contribution of the bands the n → π∗. The antimicrobial activity of the compound I was determined against the selected 11 bacteria and 8 fungi by microdilution broth assay with Alamar Blue. In vitro studies showed that the compound I has no antifungal effect for selected fungal isolates. However, the compound I shows remarkable antibacterial effect for the bacteria; Streptococcus pneumoniae, Haemophilus influenzae and Enterococcus faecalis.

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