Synthesis, spectral characterization and antimicrobial activity of copper [II] complexes with 2,3-dihydroxyquinoxaline and their adducts with some heterocyclic Nitrogen donors

ABSTRACT

The reaction of 2,3-dihydroxyquinoxaline, H2dhq with Cu [Ac]2-H2O or CuX2-H2o [X = Cl or Br] gave complexes of stoichiometry [[Hdhq [2]Cu] and [[H2dhq]2CuX2], respectively. Mixed-ligand complexes [[Hdhq[2]CuL[2]] [L = pyridine, 3-picoIine, 4-pincoline, imidazole, 1-methylimidazole or 1,2-dimethylimidazole were also prepared. The complexes were characterized by elemental analyses as well as by infrared, electronic and ESR spectral studies. The IR data showed that H[2]dhq acted as a monobasic or neutral bidentate ligand bonded to copper[II] via enolate and ketoamide-O atoms in [[H[2]dhq[2]Cu] and via ketoamide-O atoms in [[H2dhq]2CuX2]. The electronic spectra indicated that both [[H2dhq]2CuX2] and [[Hdhq]2CuL2] complexes possessed distorted octahedral structures containing CuO[4]X2 and CuO4N2 chromophores, respectively. On the other hand, [[Hdhq[2]Cu] was associated with a square planar structure having a CuO[4] chromophore. ESR studies revealed that metal-ligand covalency increased upon bonding of nitrogen donors to copper [II]. Study of the antimicrobial activity showed that introduction of axial N-donors significantly increased the efficiency of inhibition