SYNTHESIS AND CHARACTERIZATION OF A MONONUCLEAR IRON(III) COMPLEX WITH A TRIPODAL TRIAMIDE LIGAND

A new potentially heptadentate tripodal ligand has been synthesized by the condensation reaction between tris(2-aminoethyl)amine and acetylsalicyclic acid in a 1 : 3 molar ratio. The o-acetyl linkage is cleaved by treating with KOH to form the desired ligand with the donors that include three amide nitrogens, three phenolate oxygens and one bridge-head nitrogen. Fe(acac)3 readily forms a dark red 1 : 1 complex with the ligand. The complex behaves as a non-electrolyte in acetonitrile. The electronic absorption spectrum in the visible region is dominated by a strong absorption with lambda(max) at 425 nm, assignable to an LMCT transition from phenolate oxygen to iron(III) in an octahedral coordination geometry. The magnetic moment value at room temperature (5.5 mu(eff)/mu(B)) and the EPR spectra in the solid state and in solution (g = 4.06) are consistent with high-spin rhombically distorted octahedral iron(III). Room-temperature Mossbauer data provide the following values: isomer shift 0.37 mm s-1 and quadrupole splitting 0.82 mm s-1. These data are consistent with a discrete, high-spin octahedral iron(III) complex.