Anti-Bacterial and Anti-Fungal Properties of a Set of Transition Metal Complexes Bearing a Pyridine Moiety and [B(C6F5)4]2 as a Counter Anion

Abstract

The synthesized complexes exhibited broad-spectrum antimicrobial activity, demonstrating variable efficacy compared to the reference antibiotic, oxytetracycline (positive control). Notably, complex <b>6</b> displayed exceptional antibacterial activity against <i>Streptococcus pyogenes</i>, with a minimum inhibitory concentration (MIC) of 4 µg/mL, outperforming the control (MIC = 8 µg/mL). Complexes <b>1</b>, <b>2</b>, and <b>4</b> showed promising activity against <i>Shigella flexneri</i>, <i>Klebsiella pneumoniae</i>, and <i>Streptococcus pyogenes</i>, each with MIC values of 8 µg/mL. Conversely, the lowest activity (MIC = 512 µg/mL) was observed for complexes <b>3</b>, <b>5</b>, and <b>6</b> against <i>Pseudomonas aeruginosa</i>, <i>Escherichia coli</i>, and <i>Klebsiella pneumoniae</i>, respectively. Regarding antifungal properties, complexes <b>5</b> and <b>6</b> demonstrated the highest activity against <i>Candida albicans</i>, with MIC values of 8 µg/mL, equivalent to that of the positive control, fluconazole. Density functional theory (DFT) calculations confirmed an overall octahedral coordination geometry for all complexes, with tetragonal distortions identified in complexes <b>3</b>, <b>4</b>, and <b>5</b>.