New tetranuclear metal carboxylate clusters with the [M4(μ3-O)2]8+ (M = MnIII or FeIII) cores:: crystal structures and properties of [Mn4O2Cl2(O2CC6H3F2-3,5)6(py)4], [Fe4O2Cl2(O2CMe)6(bpy)2] and [NBu4n][Fe4O2(O2CMe)7(pic)2]

A variety of synthetic procedures have been employed that allow access to three new tetranuclear [M-4(mu(3)-O)(2)](8+) (M = Mn-III or Fe-III) complexes. The complex [Fe4O2Cl2(O2CMe)(6)(bpy)(2)] displays an unusual structural asymmetry in its core that can be described as a hybrid of the bent (butterfly) and planar dispositions of four M atoms seen previously in such compounds. Magnetochemical and Fe-57 Mossbauer studies on this compound showed that its structural asymmetry has little influence on these properties compared with the more symmetric types. The complex [NBu4n][Fe4O2(O2CMe)(7)(pic)(2)] has been prepared by an unusual chelate substitution in [NBu4n][Fe4O2(O2CMe)(7)(bpy)(2)] that does not disrupt the core or the bridging carboxylate groups.