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][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 µ 3-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. Solidstate, 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.