Synthesis, Structure, and Biological Activity of Some Transition Metal Complexes with the Mixed Ligand of Metformin and 1,4-Diacetylbenzene

Mononuclear complexes of Co(II), Ni(II), Cu(II), Zr(IV), Pd(II), and Cd(II) with metformin hydrochloride (MF) and 1,4-diacetylbenzene (DAB) have been synthesized, and their structures have been elucidated on the basis of FT-IR, H-1 NMR, and electronic spectra, molar conductance, magnetic susceptibility measurements, thermal, and elemental analysis. Molar conductance measurements indicate electrolytic nature of the complexes. According to FT-IR spectra, MF reacts with metal ions as a bidentate ligand through its two imino groups, and DAB reacts as a monodentate ligand through one of two equivalent keto groups. The complexes have octahedral structure, except Pd(II) complex which is square planar. TGA and DTG analyses support the suggested stereochemistry and subsequently the proposed mechanism of thermal decomposition. Coats-Redfern and Horowitz-Metzger equations have been used for calculating kinetic and thermodynamic parameters of the main decomposition step. Molecular modeling calculations confirm the structure of the complexes. The ligands and their complexes in vitro antimicrobial activity tests against some bacterial and fungal strains indicate higher activity of the complexes than that of MF and DAB.