Synthesis, Physicochemical Studies and Biological Properties of Mixed-Ligand Nickel(II) Complexes Containing β-Diketones With N-donor Ligands

Some mixed ligand nickel(II) complexes of thenoyltrifluoroacetone (tta-H) with 2,2ꞌ-bipyridine (bipy), 1,10-phenanthroline (phen) and tetramethylethylenediamine (tmen) [Ni(tta)(N-N)(NO3)]; N-N= bipy, phen, or tmen] have been synthesized and characterized by molar conductance measurements, elemental analysis, mass spectrometry, spectral measurements and antimicrobial activities. Attempt to prepare the mixed ligand nickel(II) complexes containing acetylacetone (acacH), benzoylacetone (bzacH), dibenzoylmethane (dbm-H) and thenoyltrifluoroacetone (tta-H) with ethylenediamine associated with NO3 counter ion led to the formation of [Ni(β-diketone)2en]. The β-diketones enolized acting as bidentate ligand, coordinating to the metal with carbonyl and enolic oxygen, ethylenediamine (en) coordinates to the metal using N, N chromophores. The nickel complexes of the type [Ni(tta)(N-N)NO3)] are five-coordinate square pyramidal in geometry while those of the type [Ni(β-diketone)2en] are six-coordinate octahedral geometry. The conductivity measurement in nitromethane revealed that the [Ni(tta)(N-N)NO3)] complexes are non-electrolyte. The complexes were screened for their in-vitro antimicrobial activity against six microorganisms. A comparison of the complexes with gentamicin showed that most of the complexes are resistant to tested organisms except [Ni(tta)2(en)].H2O, [Ni(bzac)2(en)] and [Ni(bta)2(en)] which compared favourably well in Staphylococcus aureus.