Synthesis, characterization, and biological activity studies of copper(II)-metal(II) binuclear complexes of dipyridylglyoxal bis(2-hydroxybenzoyl hydrazone)

A new series of copper(II) mononuclear and copper(II)-metal(II) binuclear complexes [(H2L)Cu]center dot H2O, [CuLM]center dot nH(2)O, and [Cu(H2L)M(OAc)(2)]center dot nH(2)O, n = 1-2, M = Co(II), Ni(II), Cu(II), or Zn(II), and L is the anion of dipyridylglyoxal bis(2-hydroxybenzoyl hydrazone), H4L, were synthesized and characterized. Elemental analyses, molar conductivities, and FT-IR spectra support the formulation of these complexes. IR data suggest that H4L is dibasic tetradentate in [(H2L)Cu]center dot H2O and [Cu(H2L)M(OAc)(2)]center dot nH(2)O but tetrabasic hexadentate in [CuLM]center dot nH(2)O (n = 1-2). Thermal studies indicate that waters are of crystallization and the complexes are thermally stable to 347-402 degrees C depending upon the nature of the complex. Magnetic moment values indicate magnetic exchange interaction between Cu(II) and M(II) centers in binuclear complexes. The electronic spectral data show that d-d transitions of CuN2O2 in the mononuclear complex are blue shifted in binuclear complexes in the sequences: Cu-Cu > Cu-Ni > Cu-Co > Cu-Zn, suggesting that the binuclear complexes [CuLM]center dot nH(2)O are more planar than the mononuclear complex. The structures of complexes were optimized through molecular mechanics applying MM+ force field coupled with molecular dynamics simulation. [(H2L)Cu]center dot nH(2)O, [CuLM]center dot nH(2)O, and the free ligand were screened for antimicrobial activities on some Gram-positive and Gram-negative bacterial species. The free ligand is inactive against all studied bacteria. The screening data showed that [CuLCu]center dot H2O4[(H2L)Cu]center dot H2O > [CuLZn]center dot H2O > [CuLNi]center dot 2H(2)O approximate to [CuLCo]center dot H2O in order of biological activity. The data are discussed in terms of their compositions and structures.