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 MnII 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 MnII ions bridged by three μ3-OH− ions and nine bridging phth2− groups. Six chelating bpy groups complete octahedral coordination at each MnII 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 MnII 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.