Flavonoids are widely occurring polyphenol compounds of plant origin with multiple biological and chemical activities. Due to the presence of carbonyl and hydroxyl groups they can coordinate metal ions and form complexes. Metal complexes of flavonoids have many interesting properties: they are colored, often fluorescent, anti- or pro-oxidant, antimicrobial, antiproliferative and biologically active in many other ways. There are many papers covering specific aspects of activity of flavonoid metal complexes, e.g. their antioxidant properties, enzyme-mimicking behavior, therapeutic potential or use in chemical analysis. However, for a researcher interested in this theme, it would be useful to find an extensive review on more than one selected area. Our aim was to cover a wide spectrum of possible activities and potential applications of flavonoids coordinated to metal ions in order to give our readers a broad view on the topic of this class of compounds, their activity and potential applications. While a significant amount of information on the chemical properties and biological activity of flavonoid metal complexes can be found in the literature, an in-depth understanding of structure–property relationships is still lacking. In an attempt to address this issue, a comprehensive discussion of the available data is presented.

The antimicrobial activity of silver( i ) complexes of the type [Ag(MTZ) ₂ X] (MTZ = metronidazole; X = NO ₃ ⁻ , ClO ₄ ⁻ , CF ₃ COO ⁻ , BF ₄ ⁻ and CH ₃ SO ₃ ⁻ ) was evaluated.

Selected aspects of the biological activity of a series of six nitrate silver(I) complexes with pyridine and (benz)imidazole derivatives were investigated. The present study evaluated the antibacterial activities of the complexes against three Gram-negative strains: Pseudomonas aeruginosa ATCC 15442, Escherichia coli ATCC 25922 and Proteus hauseri ATCC 13315. The results were compared with those of silver nitrate, a silver sulfadiazine drug and appropriate ligands. The most significant antibacterial properties were exerted by silver(I) complexes containing benzimidazole derivatives. The cytotoxic activity of the complexes was examined against B16 (murine melanoma) and 10T1/2 (murine fibroblasts) cells. All of the tested silver(I) compounds were not toxic to fibroblast cells in concentration inhibited cancer cell (B16) viability by 50%, which ranged between 2.44–28.65 µM. The molecular and crystal structure of silver(I) complex of 2,6-di(hydroxymethyl)pyridine was determined by single-crystal X-ray diffraction analysis. The most important features of the crystal packing and intermolecular non-covalent interactions in the Ag(I) complex were quantified via Hirshfeld surface analysis.