Synthesis, characterization and applications of copper(II) complexes with N– and O–donor ligands

Abstract

In the present study, four series of copper(II) carboxylates mixed with N-donor ligands have been synthesized by treating copper sulfate with a carboxylate moiety followed by reacting it with an N-donor compound in an aqueous medium. The carboxylate ligands used were substituted phenyl acetic acids [4–methyl (1, 1a, 1b, 1c), 4–H (2, 2a, 2b, 2c), 4–methoxy (3, 3a, 3b, 3c), 4–bromo (4, 4a, 4b, 4c), 4–chloro (5, 5a, 5b, 5c), 4–floro (6, 6a, 6b, 6c), 4–nitro (7, 7a, 7b, 7c) and 2–nitro (8, 8a, 8b, 8c)] while the N-donor ligands were pyridine (a), –bipyridine (b) and 1,10–phenanthroline (c). The coordination modes of ligands and the structure and geometry assignments of the complexes were determined using different analytical techniques such as FT-IR, UV-Visible spectroscopy, powder and single crystal XRD. Based on the results, the ligand was found to coordinate to the Cu(II) ion through the COO moiety in bridging bidentate (1-8, 1a-8a), monodentate (1b-6b and 8b) and chelating bidentate fashions (1c, 3c-8c and 7b). Complex 2c was found to be unique because it had OH bridges and the carboxylate ligand is lying uncoordinated in the crystal lattice while the 5th coordination site around each copper(II) ion of the dinuclear complex is occupied by a water molecule. The geometry and structure of the complexes, as confirmed through single crystal X-ray analyses was found to be square pyramidal and polynuclear (1-8, without N-donor ligand), square pyramidal and dinuclear (with pyridine, 1a-8a and –bipyridine, 1b-6b, 8b) and distorted octahedral and mono-nuclear (1c, 3c-8c, with 1,10-phenanthroline and 7b with –bipyridine). The bulk property such as the purity of the complexes was confirmed through powder XRD of the crystalline samples where the simulated and experimental spectra were in complete agreement with each other. The DNA binding ability of all the synthesized complexes was studied by cyclic voltammetry (CV) and UV-Visible spectroscopy. The diffusion coefficient of the free and DNA bound complexes were determined by the Randles-Sevcik equation. The positive peak potential shift in iii CV and the hypochromic effect in spectroscopy observed for complexes 4-8, 3a, 5a-8a, 1b, 5b, and 3c-7c evidenced the intercalative mode of interaction of these complexes with DNA while the negative potential shift observed for 3b, 4b, 8b, 1c, 2c, and 8c indicated electrostatic interactions. A mixed binding mode (electrostatic with intercalation) was observed for the rest of the complexes 1, 2, 3, 1a, 2a, 4a, 2b, 6b and 7b. The CV results revealed the highest binding strengths for 2, 3, 6, 5a, 6a, 1b, 3b-6b, 3c-6c and 7c (Kb range = 3.166 × 104 to 2.13 × 105). The UV-Vis spectroscopic data also indicated the same pattern of binding strength. Moreover, the λmax ε v w t UV-Vis spectroscopy. The peak ranges in spectroscopy show that the geometry around copper(II) in case of 1-8 and 1a-8a is square pyramidal while 1b-8b and 1c-8c exhibit an octahedral geometry in DMSO solution. Biological screening of the complexes against medically important bacterial and fungal strains has exhibited a significant antibacterial and antifungal activity for 1c, 2c, 6c and 7c and 1, 1b, 2, 2c, 3c, 5a, and 7c, respectively while 4a, 4b, 5, 5c, and 8c were found to have moderate antifungal activity. The potent DNA binding ability supported by biocidal activity indicated that these complexes can have a potential for the anti-cancer activity as well.