Spectroscopic Studies on Tetra (sulphonaphthyl) Porphine Iron (II) Solutions with Pyridine Substituents as a Ligands

Electronic absorption spectra at 15 ºC, Stability constants and ΔH, ΔG,ΔS of tetra (sulphonaphthyl) porphine iron (ІІ) solutions with pyridine substituents as a ligands are reported and discussed. Evidence for only one iron (ІІ)electronic environments , a low spin is found, and two as axial ligands can bind to four coordinate iron (ІІ)porphine in one step from spectrophotometric titrations of Fe (ІІ)TNPS with amines was abserved.The presence of the naphthyl substituents on the methane carbons stabilizes the low spin iron (ІІ) TNPS (L)2 species, the pyridine substituents also are shown to play an important role and lowering the values of keq and (ΔS) as increasing the order of δ- donor , addition to that, the π- electron accepter (low pka)are shown to have larger values for their keq and (ΔH) . Steric effects are also found lowering the values of keq for such ligand as 2- methyl pyridine.