A new example of a tetranuclear iron(III) cluster containing the [Fe4O2]8+ core: preparation, X-ray crystal structure, magnetochemistry and Mössbauer study of [Fe4O2(O2CMe)6(N3)2(phen)2]

Two synthetic procedures have been employed that allow access to the new tetranuclear cluster [Fe4O2(O2CMe)6(N3)2(phen)2] (1), where phen is 1,10-phenanthroline. Complex 1 · 3MeCN displays an unusual structural asymmetry (observed for the second time) in its [Fe4O2]8+ core that can be considered as a hybrid of the bent (butterfly) and planar dispositions of four metal ions seen previously in such compounds with transition metals. Complex 1 has been characterized by variable-temperature magnetic susceptibility studies, and by IR and variable-temperature 57Fe Mössbauer spectroscopies. Magnetochemical data reveal a diamagnetic ground state (S=0) with antiferromagnetic body–body and body–wingtip interactions between the iron(III) ions of the butterfly core (Jbb=−11 cm−1, Jwb=−70 cm−1). Magnetochemical and Mössbauer studies on 1 show that its structural asymmetry has practically no influence on these properties compared with the more symmetric types.