Synthesis, crystal structures, magnetic properties and antimicrobial screening of octahedral nickel(II) complexes with substituted quinolin-8-olates and pyridine ligands

New nickel(II) compounds, viz. trans-[Ni(LHAQ)2(Py)2]·C6H6 (1), cis-[Ni(LHAQ)2(3-MePy)2] (2), cis-[Ni(L2−MeAQ)2(3-MePy)2] (3), trans-[Ni(L4−MeAQ)2(Py)2]·C6H6 (4), trans-[Ni(L4−OMeAQ)2(Py)2]·C6H6 (5), trans-[Ni(L4−OEtAQ)2(Py)2]·C6H6 (6), trans-[Ni(L4−BrAQ)2(Py)2]·C6H6 (7) and trans-[Ni(L4−ClAQ)2(3-MePy)2]·2(3-MePy) (8) (primary ligands: LXAQ = substituted 5-[(E)-2-(aryl)-1-diazenyl]quinolin-8-olate; secondary ligands: Py = pyridine or 3-MePy = 3-methylpyridine) have been synthesized and characterized by elemental analysis, IR, UV–vis spectroscopy. The magnetic susceptibilities of the compounds were also measured. Single-crystal X-ray diffraction analysis of the compounds revealed octahedral geometries with trans configurations for 1, 4–8 and cis configurations for 2 and 3. The occurrence of intramolecular Ni⋅⋅⋅Hpyridine interactions in 2 and in 3, may account for additional stabilization of their assemblies at least in the solid state. The effective magnetic moment (μeff) in the range 3.02–3.40 BM agree with the expected values for octahedral Ni(II) cations with two unpaired electrons. Ni(II) compounds were also screened for their antimicrobial activity.