Metal complexes of Cu(II), Co(II), Ni(II), Cr(III), and Fe(III) chlorides with the Schiff base ligand (L) derived from the condensation reaction between leucine and 2-acetylpyridine were prepared. The isolated complexes were characterized by elemental analyses, spectral analyses (IR, UV), thermal analyses (TGA), magnetic measurements, and molar conductivities. The IR spectra show that the ligand can act as a neutral tridentate coordinating to Cu(II), Co(II), or Ni(II) through the pyridyl nitrogen, azomethine nitrogen, and carbonyl oxygen. Another mode of chelation has been suggested that the ligand can act as a mononegative tridentate coordinating to Fe(III) or Cr(III) through the pyridyl nitrogen, azomethine nitrogen, and carboxyl oxygen after displacement of hydrogen from the hydroxyl group. The results suggest tetrahedral geometry around Co(II) and Ni(II), octahedral geometry around Fe(III) and Cr(III), and square-planar geometry around Cu(II). Semi-empirical ZINDO/1 calculations have been used to study the harmonic vibrational spectra of Cu(II) and Fe(III) with the purpose to assist the experimental assignment of the complexes. The molar (Λ) and limiting molar (Λ) conductances of the prepared complexes were measured experimentally at 298 K. From the values of Λ and Λ, the ion-pair association constants (KA) and the free energy change of association (ΔGA) were calculated and discussed. Also, the densities (d) and the refractive indices (n) of the prepared complexes were determined in water and 50 % (V/V) dimethylformamide- water solvents at 298 K. Using the values of n and d, the excess refractive indices (n(E) and ń(E)), atomic polarizations (PA), polarizabilities (α), and molar refractions (Rm) were calculated and discussed. © 2008 American Chemical Society.
