Preparation and properties of [NH2Et2][Mn10(OH)3(phth)9(bpy)6], a new decanuclear Mn(ii) compound with a variety of phthalate binding modes

Abstract

The synthesis and characterisation are reported of the new decanuclear manganese compound [NH₂Et₂][Mn₁₀(OH)₃(phth)₉(bpy)₆] (2; phthH₂ = phthalic acid, bpy = 2,2′-bipyridine), obtained from the reaction of phthH₂, bpy and NEt₃ with either [Mn₁₂O₁₂(O₂CMe)₁₆(H₂O)₄] (1) or manganese(II) acetate; the latter is by far the superior method. Complex 2 is the highest nuclearity Mn^II cluster yet prepared, and it crystallizes in the triclinic space group P. The structure of the anion consists of a pinwheel-like arrangement of ten Mn^II ions bridged by three μ₃-OH⁻ ions and nine bridging phth²⁻ groups. Six chelating bpy groups complete octahedral coordination at each Mn^II ion. There are three different bridging modes for the phth²⁻ groups, some of them unprecedented. Solid-state, variable-temperature dc and ac magnetic susceptibility measurements reveal weak, antiferromagnetic exchange interactions between the Mn^II ions resulting in a low-spin ground state of S ≈ 2 and low-lying excited states. The non-zero ground state is rationalized as due to the presence of competing exchange interactions (spin frustration) within the Mn₁₀ topology.