Synthesis and spectral investigations of mononuclear [N(6)], [N(8)] and dinuclear [N(10)] complexes of polyamide macrocycles: (57)Fe Mössbauer parameters of Fe(III) complexes.

New stable Fe(III) complexes of tetraamide [N(6)], [N(8)] and [N(10)] macrocyclic ligands are reported. One of them, [N(10)] 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, (1)H and (13)C NMR spectral studies. Magnetic moment studies indicate presence of anti-ferromagnetically coupled (Fe(3+)-Fe(3+)=S(5/2)-S(5/2)) spin-spin interactions in the dinuclear [N(10)] complex. (57)Fe 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.