Metal complexes of the flavonoid quercetin: antibacterial properties

Two types of complexes were obtained when quercetin (L) was reacted with metal ions in EtOH. The compounds M(L)Cl₂(H₂O)₂] (M = Mn^II or Co^II) and the semi-oxidized complexes M(L)₂CL₂] · 2H₂O (M = Cd^II or Hg^II) were characterized by elemental analysis., conductivity and magnetic susceptibility measurements, i.r., u.v.–vis. and e.p.r. spectroscopy. The (C=O) stretching mode located on the C ring of the ligand and the complexes remains in the same range, showing that this oxygen atom does not participate in coordination to the metal ions. Magnetic susceptibilities and e.p.r. spectra of powdered samples indicated that the monomeric form of the complexes in the solid state, and the paramagnetic nature of the Cd^II and Hg^II complexes is attributable to the semiquinone character of the ligand. The antibacterial activity of the metal complexes were tested against five bacterial strains and compared with penicillin activity.