High–Field EPR Studies on Three Binuclear μ–oxo–Bridged Iron(III) Complexes: Na4[Fe(edta)]2O·3H2O, [Fe(phen)2(H2O)]2O(NO3)4·5H2O and [Fe(salen)]2O

Abstract A High–Field, High–Frequency Electron Paramagnetic Resonance (HFEPR) study was performed on the binuclear μ–oxo bridged complexes Na 4 [Fe(edta)] 2 O ⋅ 3H 2 O, [Fe(phen) 2 (H 2 O)] 2 O(NO 3 ) 4 ⋅ 5H 2 O and [Fe(salen)] 2 O, where edtaH 4 = ethylenediaminetetraacetic acid, phen=1,10–phenanthroline and salenH 2 is NN′–ethylenebis(salicylideneimine). The spin Hamiltonian parameters were determined for the thermally excited spin states with spin S=1, 2 and 3. The contributions to the zero–field splitting due to the local zero field splitting on individual iron ions and to the anisotropic metal–metal interactions were evaluated. Surprisingly large magnitudes of the anisotropic exchange interactions were found.