A new example of a tetranuclear iron(III) cluster containing the [Fe4O2]8+ core:: preparation, X-ray crystal structure, magnetochemistry and Mossbauer 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)(N-3)(2)(phen)(2)] (1), where phen is 1, 10-phenanthroline. Complex 1(.)3 MeCN displays an unusual structural asymmetry (observed for the second time) in its [Fe4O2](8divided by) 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 Fe-57 Mossbauer spectroscopies. Magnetochemical data reveal a diamagnetic ground state (S = 0) with antiferromagnetic body-body and body-wingtip interactions between the iron(Ill) ions of the butterfly core (J(bb) = - 11cm(-1), J(wb) = -70 cm(-1)). Magnetochemical and Mossbauer studies on 1 show that its structural asymmetry has practically no influence on these properties compared with the more symmetric types. (C) 2003 Elsevier B.V. All rights reserved.