Synthesis and spectral investigations of mononuclear [N6], [N8] and dinuclear [N10] complexes of polyamide macrocycles: 57Fe Mössbauer parameters of Fe(III) complexes

New stable Fe(III) complexes of tetraamide [N6], [N8] and [N10] macrocyclic ligands are reported. One of them, [N10] is dinucleating, with two Fe(III) nuclei in the macrocyclic cavities. The structural features have been discussed on the basis of analytical, ESI mass, FT-IR, electronic, 1H and 13C NMR spectral studies. Magnetic moment studies indicate presence of anti-ferromagnetically coupled (Fe3+–Fe3+ = S5/2–S5/2) spin–spin interactions in the dinuclear [N10] complex. 57Fe Mössbauer measurements confirm Fe(±3/2 → ±1/2) nuclear transitions supporting high–spin configuration of Fe(III) nuclei with the presence of Kramer's double degeneracy.