Electronic and molecular structure studies of a (bio)inorganic complex - A multi-technique approach

The electronic structure of the dimeric iron complex [Fe-2(bbpo) Cl-4](n-) with the tetranionic ligand 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenyl) oxamide was studied in two different oxidation states. Combined Mossbauer and EPR investigations in conjunction with magnetic susceptibility measurements are used to demonstrate the complementarity of the techniques. The dianion [Fe-2(bbpo)Cl-4](2-)(2) is a high-spin iron(III) compound with magnetic properties resulting from competing exchange and zero-field interactions of the iron sites. Unusual integer-spin EPR spectra could be recorded from an excited spin septet, S-t = 3, of the coupled system. Electrochemical oxidation yields the monoanion [Fe-2(bbpo(ox1))Cl-4](-) (2(ox)) which also is an iron(III) compound; the ligand is redox non-innocent and forms a pi radical that is bound to one of the iron centers and the total spin S-t = 1/2 ground states of the molecule originates from exchange coupling of the three paramagnetic centers. A simplified spin coupling scheme assuming infinitively strong radical-iron( III) interaction yields a reasonable and rational interpretation of the magnetic and electronic properties of 2(ox).