Green synthesis of niflumic acid complexes with some transition metal ions (Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II)). Spectroscopic, thermoanalytical and antibacterial studies

New complexes of Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) ions with niflumic acid (Hnif) were obtained in solid state using a green synthesis method and their physico-chemical properties, thermoanalytical behaviour in air and nitrogen as well as antibacterial activity were studied. Employing the results of elemental analysis (EA), complexometric titration with EDTA and TG/DTG-DSC analysis it was established that a minimal formula for the obtained compounds is M(nif)(2)center dot nH(2)O (where M means metal ion, nif is niflumate ion and n = 1-2.25). The exception is the complex with Fe(III) ions of formula Fe(nif)(3)center dot H2O. It was concluded that niflumate ligands bind to metal ions in two different manners. TG/DTG-DSC analysis showed that thermal decomposition of the obtained compounds is a multi-stage process depending on the metal ion and atmosphere in which was conducted. Based on the detailed DSC analysis it was shown that the dehydration of these compounds proceeds in two steps. By the use of the coupled TG-FTIR-MS techniques the decomposition pathways of the synthesized compounds were examined and the gaseous products released during thermal oxidation and pyrolysis of the complexes were identified. The antibacterial study showed an increase in the activity of some of the obtained complexes in comparison to the ligand. The complex with Zn(II) ions has the most effective antibacterial activity against both E. coli and P. aeruginosa. The MIC values for this compound against E. coli was 31-fold lower than for niflumic acid. Furthermore, this compound was 5- and 1.25-fold more potent than chloramphenicol (MIC = 0.50 mg mL(-1)) and kanamycin (MIC = 0.12 mg mL(-1)) that are the reference drugs against P. aeruginosa. The complexes with Mn(II), Fe(III) and Co(II) ions showed antibacterial activity against Gram positive bacteria (S. aureus) and the MIC values for these compounds were respectively 10-, 3.4-, 2.5-fold lower than for niflumic acid.