Synthesis, spectral, magnetic, DFT calculations, antimicrobial studies and phenoxazinone synthase biomimetic catalytic activity of new binary and ternary Cu(II), Ni(II) and Co(II) complexes of a tridentate ONO hydrazone ligand

New mononuclear copper(II), nickel(II) and cobalt(II) hydrazone complexes of 2-cyano-N′-((4-oxo-4H-chromen-3-yl)methylene)acetohydrazide have been synthesized. Structure identification of the prepared complexes was carried out by physicochemical and spectroscopic techniques including elemental analyses, infrared, electronic, mass and electron spin resonance spectra, thermal analysis, conductivity and magnetic susceptibility measurements, powder x-ray diffraction and transmission electron microscope. The isolated binary complexes are neutral mononuclear complexes (with 1:1 and 1:2; M:L stoichiometries) and ternary complexes (with 1:1:1; M:L:L′ stoichiometry). The analytical and spectroscopic techniques illustrated the monoanionic tridentate behavior of the hydrazone ligand with γ-pyrone oxygen, enolic oxygen and azomethine nitrogen coordinating sites. The metal complexes displayed square planar, tetrahedral and octahedral geometries. Density Functional Theory calculations were carried out for the chelating agent and its copper(II) chelates. The phenoxazinone synthase activity of the binary copper(II) complexes was studied and discussed. The antimicrobial activity of the hydrazone ligand and its complexes was evaluated toward some sorts of Gram–positive bacteria, Gram–negative bacteria, yeast and fungus.