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

Abstract

A new series of copper(II) mononuclear and copper(II)–metal(II) binuclear complexes [(H2L)Cu] ⋅ H2O, [CuLM] ⋅ nH2O, and [Cu(H2L)M(OAc)2] ⋅ nH2O, 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] ⋅ H2O and [Cu(H2L)M(OAc)2] ⋅ nH2O but tetrabasic hexadentate in [CuLM] ⋅ nH2O (n = 1–2). Thermal studies indicate that waters are of crystallization and the complexes are thermally stable to 347–402°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] ⋅ nH2O 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] ⋅ nH2O, [CuLM] ⋅ nH2O, 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] ⋅ H2O > [(H2L)Cu] ⋅ H2O > [CuLZn] ⋅ H2O > [CuLNi] ⋅ 2H2O ≈ [CuLCo] ⋅ H2O in order of biological activity. The data are discussed in terms of their compositions and structures.