Synthesis, characterization, crystal structures and electrochemical properties of heteroleptic Cu(II), Mn(II) and Zn(II) complexes of metronidazole with benzoic acid derivatives

Abstract Cu(II), Mn(II) and Zn(II) complexes of metronidazole with benzoic acid derivatives formulated as [Cu2(met)4(4-nba)4] (1), [Mn(met)2(2bba)2(H2O)2] (2) and [Zn(met)2(3,5-dnba)2] (3) [met = metronidazole, 4-nba = 4-nitrobenzoic acid, 2-bba = 2-bromobenzoic acid and 3,5-dnba = 3,5-dinitrobenzoic acid] were synthesized and characterized by elemental analysis and spectroscopic techniques and two of them by single crystal X-ray crystallography. Single crystal X-ray crystallography revealed a five-coordinate, trigonal bipyramidal arrangement in compound 1, while compound 2 is six coordinate octahedral geometry. The molar conductance indicates the complexes are non-electrolytes in solution. The EPR spectra of 1 and 2 showed broad signals centered on g = 2.125, 2.116 and 1.970, 2.005. A hyperfine quartet was observed in the solid state for 1 typical of Cu(II) ion, I = 3/2; while a hyperfine sextet characteristic of 55Mn nucleus, I = 5/2 was observed for 2. Cyclic voltammetry revealed a one-step redox couple for 1 at a potential range of −0.4 to +0.1 V assigned to the reduction peak of Cu(II)/Cu(I). The linearity of Randles-Sevcik plot (R2 = 0.999) suggests a diffusion-controlled redox couple.