Copper(II) and cobalt(II) complexes of 5-methyl pyrazole-3-carboxylic acid: synthesis, X-ray crystallography, thermal analysis and in vitro antimicrobial activity

Abstract

The coordination behavior of 5-methylpyrazole-3-carboxylic acid (Hmpca) has been demonstrated by the solid state isolation and characterization of [Cu(mpca)2(H2O)] 3H2O (1) [Cu(mpca)2] H2O (2) and Co(mpca)2(H2O)2] (3). The new compounds are characterized by X-ray crystallography, thermogravimetric analysis and DFT study. The redox properties of the complexes are examined by cyclic voltammetric analysis. The antibacterial and antifungal activities of the compounds against eight bacteria (Escherichia coli, Enterococcus faecalis, Bacillus subtilis, Klebsiella pneumoniae, Proteus vulgaris, Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella typhi) and two fungi (Aspergillus flavus and Candida albicans) are screened using modified agar well diffusion method. The metal complexes demonstrate better inhibition on all bacteria and fungi than the ligand. The high lipophilicity of the complexes accounts for good inhibitory action toward microbes. Among the reported complexes, 3 emerges as an excellent antifungal agent and a better antibiotic than standard fluconazole. The structure and activity relationship indicate that complexes having sufficient Jahn–Teller distortion with high logP values, cross the cell membrane of the microbes creating intercellular damage.