Synthesis, characterization, and crystal structures of 4-hydroxy-N’-(2-hydroxy-5-methylbenzylidene)benzohydrazide and its copper(II) complexes with antibacterial activity

A hydrazone compound 4-hydroxy-N’-(2-hydroxy-5-methylbenzylidene)benzohydrazide (HL) was prepared from the condensation reaction of 5-methylsalicylaldehyde with 4-hydroxybenzohydrazide. The compound was characterized by IR, UV-Vis, 1H NMR, and 13C NMR spectra. Reaction of HL with copper nitrate and copper chloride, respectively, afforded two new copper(II) complexes, [Cu2L2(CH3OH)2]·2NO3 (1) and [CuL(DMF)]·Cl (2). The complexes were characterized by IR and UV-Vis spectra. Structures of HL and the complexes were confirmed by single-crystal X-ray determination. The powder X-ray diffraction was performed to verify the purity of the bulk samples of the complexes. The hydrazone compound coordinates to the Cu atoms through phenolate oxygen, imino nitrogen, and carbonyl oxygen. The Cu atoms in complex 1 are in square pyramidal coordination, while that in complex 2 is in square planar coordination. The antibacterial study using the free hydrazone compound and the two copper complexes against both Gram-positive and Gram-negative bacteria are performed, the two complexes showed antibacterial activity against both Gram-positive and Gram-negative bacteria, whereas the free ligand shows no activity.