Biological and spectral studies of transition metal complexes with a quinquedentate Schiff base, 2,6-diacetylpyridine bis(thiocarbohydrazone)

Manganese(II), cobalt(II), and copper(II) complexes with a quinquedentate Schiff base, 2,6-diacetylpyridine bis(thiocarbohydrazone), have been synthesized and characterized by elemental analysis, molar conductance, magnetic susceptibility, and IR, H-1 NMR, C-13 NMR, mass (for ligand), UV and Electron Paramagnetic Resonance spectroscopies. The complexes are [M(L)X]X, where M = Mn(II), Co(II), and Cu(II), L = 2,6-diacetylpyridine bis(thiocarbohydrazone), and X = NO3- and Oac(-). The ligand with five coordination sites forms six-coordinate complexes with octahedral geometry for manganese(II), whereas the cobalt(II) and copper(II) complexes were of tetragonal geometry. The A(iso) values, nephelauxetic parameter (beta), and orbital reduction factor (k) indicate the covalent nature of the metal-ligand bond. The compounds have been screened for their antipathogenic activities against Alternaria brassicae, Aspergillus niger, Fusarium oxysporum, Xanthomonas compestris, and Pseudomonas aeruginosa.