Mixed ligand complexes of bis(phenylimine) Schiff base ligands incorporating pyridinium moiety

The synthesis and structural characterization of mixed ligand complexes derived from 2,6-pyridinedicarboxaldehydebis(o-hydroxyphenylimine), 2,6-pyridinedicarboxaldehydebis(p-hydroxyphenylimine) (1ry ligands) and 2-aminopyridne (2ry ligand) are reported. The ligands and their transition metal complexes were characterized on the bases of their elemental analyses, IR, solid reflectance, magnetic moment, molar conductance and thermal analysis (TGA). The mixed ligand complexes are formed in the 1:1:1 (M:L1 or L2:L′) ratio as found from the elemental analyses and found to have the formulae [MX2(L1 or L2)(L′)]·nH2O where M = Co(II), Ni(II), Cu(II) and Zn(II), L1 = 2,6-pyridinedicarboxaldehydebis(p-hydroxyphenylimine), L2 = 2,6-pyridine dicarboxaldehydebis(o-hydroxyphenylimine), L′ = 2-aminopyridine, X = Cl− in case of Cu(II) complex and Br− in case of Co(II), Ni(II) and Zn(II) complexes and y = 0-3. The molar conductance data reveal that the chelates are non-electrolytes. IR spectra show that the Schiff bases are coordinated to the metal ions in a terdentate manner with NNN donor sites of the pyridine-N and two azomethine-N. While 2-aminopyridine coordinated to the metal ions via its pyridine-N. Magnetic and solid reflectance spectra are used to infer the coordinating capacity of the ligand and the geometrical structure of these complexes are found to be octahedral. The thermal behaviour of these chelates shows that the hydrated water molecules and the anions are removed in a successive two steps followed immediately by decomposition of the ligands (L1, L2 and L′) in the subsequent steps. The activation thermodynamic parameters, such as, E*, ΔH*, ΔS* and ΔG* are calculated from the TG curves and discussed. The ligands and their metal chelates have been screened for their antimicrobial activities and the findings have been reported, explained and compared with some known antibiotics.