3-Hydroxy-2-(5-hydroxypentyl)-4H-chromen-4-one:  A Bidentate or Tridentate Iron(III) Ligand?

The pK(a) value and iron affinity constants for 3-hydroxy-2-(5-hydroxypentyl)-4H-chromen-4-one 1 have been determined by spectrophotometry using aqueous methanol solutions. The extrapolated affinity constants, beta(1), beta(2), and beta(3) for iron(III) in aqueous solution were 9.95, 18.69, and 26.02, respectively, with a corresponding pFe(3+) value of 14.64. Job plot and MS spectra data demonstrated that the 3:1 species is favored at pH 7.0. These results indicate that 1 acts as a bidentate ligand when coordinated to iron(III).