The reaction of (NBu4n)[Mn8O6Cl6(O2CPh)(7)(H2O)(2)] (1) with 2-(hydroxymethyl)pyridine (hmpH) or 2-(hydroxyethyl)pyridine (hepH) gives the (Mn2Mn10III)-Mn-II 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 2.2Et(2)O.4CH(2)Cl(2), 3.7CH(2)Cl(2), and 4.2Et(2)O.1.4CH(2)-Cl-2 crystallize in the triclinic space group P (1) over bar, monoclinic space group C2/c, and tetragonal space group I4(1)/a, respectively. Complexes 2 and 3 represent a new structural type, possessing isomeric [(M10Mn2O16Cl2)-Mn-III-O-II] cores but with differing peripheral ligation. Complex 4 is essentially isostructural with 3. A magneto-chemical 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.