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]†

Abstract

A variety of synthetic procedures have been employed that allow access to three new tetranuclear [M₄(µ₃-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 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.