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

The synthesis and characterisation are reported of the new decanuclear manganese compound [NH2Et2][Mn-10(OH)(3)(phth)(9)(bpy)(6)] (2; phthH(2) = phthalic acid, bpy = 2,2'-bipyridine), obtained from the reaction of phthH(2), 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 (1) over bar. The structure of the anion consists of a pinwheel-like arrangement of ten Mn-II ions bridged by three mu(3)-OH- ions and nine bridging phth(2-) groups. Six chelating bpy groups complete octahedral coordination at each Mn-II ion. There are three different bridging modes for the phth(2-) 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 approximate to 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 Mn-10 topology.