New asymmetric Schiff base ligand derived from allylamine and 2,3-dihydroxybenzaldehyde and its molybdenum(VI) complex: Synthesis, characterization, crystal structures, computational studies and antibacterial activity together with synergistic effect against Pseudomonas aeroginosa PTTC 1570

Abstract

A new unsymmetrical Schiff base ligand (H2L) was derived from the 1:1M condensation of 2,3-dihydroxybenzaldehyde with allylamine. Molybdenum(VI) complex, MoO2L2, was synthesized from the reaction of MoO2(acac)2 with the Schiff base ligand in a 1:2 ratio in methanol at ambient temperature. The Schiff base ligand and its Mo(VI) complex were characterized by elemental analyses, FT-IR, 1H NMR, 13C NMR and UV–Vis spectroscopies and single crystal X-ray analysis. The molecular structure of schiff base ligand and Mo(VI) complex showed pseudo-scorpionate structure in solid state. The MoO2L2 complex adopts an octahedral environment around the Mo center with a cis-oxo configuration. The other coordination sites are occupied by the hydroxyl oxygen atoms of the two Schiff base ligands. The pseudo-scorpionate interaction in ligand was investigated by theoretical calculation. The Schiff base ligand and its Mo(VI) complex were also tested for their in vitro antimicrobial activity against Staphylococcus aureus (ATCC 29737) and Pseudomonas aeroginosa (PTTC 1570) as examples of Gram-positive and Gram-negative bacterial strains, respectively, by disc diffusion method. The results indicated that the Schiff base ligand had a better antibacterial activity than its Mo(VI) complex and surprisingly, they were synergistic when used against P. aeroginosa PTTC 1570.