New complexes of manganese (II), nickel (II) and copper (II) with derived benzoxazole ligands: Synthesis, characterization, DFT, antimicrobial activity, acute and subacute toxicity

•New complexes with derived benzoxazole ligands were synthesized and characterized.•DFT confirms the proposed distorted octahedral geometry of all complexes.•The Mn (II) complexes inhibit dramatically the growth of yeasts and mould tested.•The Cu (II) complexes show excellent antibacterial activity.•The subacute toxicity indicates the absence of cumulative toxicity with Mn (II) complexes.

A series of new manganese (II), nickel (II) and copper (II) complexes with two ligands derived from benzoxazole have been prepared and characterized by elemental analysis, emission atomic spectroscopy, TGA measurements, ESR, magnetic measurements, FTIR, UV–Vis spectra and conductivity. The experimental results and the calculated molecular parameters (DFT) revealed a distorted octahedral geometry for the synthesized complexes ([M(L)2(Cl)2]·nH2O).The antimicrobial activity of ligands and their complexes was evaluated in vitro against different human bacteria and fungi using agar-diffusion method. A significant activity was observed with copper complexes against Gram negative bacteria. The manganese complexes showed a remarkable inhibition against yeasts and mould tested. The acute and subacute toxicity studies revealed that the manganese complexes are not toxic at 2000 mg/kg, and the results showed that the oral administration did not cause adverse effects on body weight, hematology and serum biochemistry. Thus, it can be concluded that manganese complexes have beneficial health effects.

Graphical abstractSynthesis, spectral characterization, DFT calculations and antimicrobial activity evaluated in vitro against different human bacteria and fungi of Mn (II), Ni (II) and Cu (II) complexes formed with 2-(4-trifluoropyridin-2-yl)-benzoxazole (L1), 2-(4-methylpyridin-2-yl)-benzoxazole) (L2) were reported. Also, in order to obtain data on the safety-in-use of these complexes, the acute and subacute toxicity were evaluated in an animal model according to OECD guideline.Figure optionsDownload full-size imageDownload as PowerPoint slide