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 [NBun4][Fe4O2(O2CMe)7(pic)2] †

A variety of synthetic procedures have been employed that allow access to three new tetranuclear [M4(µ3-O)2]8+ (M = MnIII or FeIII) 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 57Fe Mössbauer studies on this compound showed that its structural asymmetry has little influence on these properties compared with the more symmetric types. The complex [NBun4][Fe4O2(O2CMe)7(pic)2] has been prepared by an unusual chelate substitution in [NBun4][Fe4O2(O2CMe)7(bpy)2] that does not disrupt the core or the bridging carboxylate groups.