Single-Molecule Magnets:  A New Family of Mn12 Clusters of Formula [Mn12O8X4(O2CPh)8L6]

The reaction of (NBun4)[Mn8O6Cl6(O2CPh)7(H2O)2] (1) with 2-(hydroxymethyl)pyridine (hmpH) or 2-(hydroxyethyl)pyridine (hepH) gives the MnII2MnIII10 title compounds [Mn12O8Cl4(O2CPh)8(hmp)6] (2) and [Mn12O8Cl4(O2CPh)8(hep)6] (3), respectively, with X = Cl. Subsequent reaction of 3 with HBr affords the Br- analogue [Mn12O8Br4(O2CPh)8(hep)6] (4). Complexes 2·2Et2O·4CH2Cl2, 3·7CH2Cl2, and 4·2Et2O·1.4CH2Cl2 crystallize in the triclinic space group P1̄, monoclinic space group C2/c, and tetragonal space group I41/a, respectively. Complexes 2 and 3 represent a new structural type, possessing isomeric [MnIII10MnII2O16Cl2] cores but with differing peripheral ligation. Complex 4 is essentially isostructural with 3. A magnetochemical investigation of complex 2 reveals an S = 6 or 7 ground state and frequency-dependent out-of-phase signals in ac susceptibility studies that establish it as a new class of single-molecule magnet. These signals occur at temperatures higher than those observed for all previously reported single-molecule magnets that are not derived from [Mn12O12(O2CR)16(H2O)x]. A detailed investigation of forms of complex 2 with different solvation levels reveals that the magnetic properties of 2 are extremely sensitive to the latter, emphasizing the importance to the single-molecule magnet properties of interstitial solvent molecules in the samples. In contrast, complexes 3 and 4 are low-spin molecules with an S = 0 ground state.