Synthesis, spectroscopic, thermal, voltammetric studies and biological activity of crystalline complexes of pyridine-2,6-dicarboxylic acid and 8-hydroxyquinoline

Two new compounds (8-H2Q)2[M(dipic)2]·6H2O (M = Co (1) and Ni (2), 8-HQ = 8-hydroxyquinoline, dipic = dipicolinate) have been prepared and characterized by elemental analysis, spectral (IR and UV–vis), thermal analyses, magnetic measurements and single-crystal X-ray diffraction techniques. Both 1 and 2 consist two 8-hydroxyquinolinium cations, one bis(dipicolinate)M(II) anion [M = Co(II), Ni(II)] and six uncoordinated water molecules. Both 1 and 2 crystallize in the monoclinic space group C2/c. In the compounds anion, each dipic ligand simultaneously exhibits tridentate coordination modes through N atom of pyridine ring and oxygen atoms of the carboxylate groups. The crystal packing of 1 and 2 is a composite of intermolecular hydrogen bonding and C–O⋯π interactions. The in vitro antibacterial and antifungal activities of 1 and 2 were evaluated by the agar well diffusion method by MIC tests. Both new compounds showed the same antimicrobial activity against Gram-positive bacteria and yeast and fungi expect Gram-negative bacteria.