Single-Molecule Magnets:  A New Family of Mn<sub>12</sub> Clusters of Formula [Mn<sub>12</sub>O<sub>8</sub>X<sub>4</sub>(O<sub>2</sub>CPh)<sub>8</sub>L<sub>6</sub>]

The reaction of (NBu<i><sup>n</sup></i><sup></sup><sub>4</sub>)[Mn<sub>8</sub>O<sub>6</sub>Cl<sub>6</sub>(O<sub>2</sub>CPh)<sub>7</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>1</b>) with 2-(hydroxymethyl)pyridine (hmpH) or 2-(hydroxyethyl)pyridine (hepH) gives the Mn<sup>II</sup><sub>2</sub>Mn<sup>III</sup><sub>10</sub> title compounds [Mn<sub>12</sub>O<sub>8</sub>Cl<sub>4</sub>(O<sub>2</sub>CPh)<sub>8</sub>(hmp)<sub>6</sub>] (<b>2</b>) and [Mn<sub>12</sub>O<sub>8</sub>Cl<sub>4</sub>(O<sub>2</sub>CPh)<sub>8</sub>(hep)<sub>6</sub>] (<b>3</b>), respectively, with X = Cl. Subsequent reaction of <b>3</b> with HBr affords the Br<sup>-</sup> analogue [Mn<sub>12</sub>O<sub>8</sub>Br<sub>4</sub>(O<sub>2</sub>CPh)<sub>8</sub>(hep)<sub>6</sub>] (<b>4</b>). Complexes <b>2</b>·2Et<sub>2</sub>O·4CH<sub>2</sub>Cl<sub>2</sub>, <b>3</b>·7CH<sub>2</sub>Cl<sub>2</sub>, and <b>4</b>·2Et<sub>2</sub>O·1.4CH<sub>2</sub>Cl<sub>2</sub> crystallize in the triclinic space group <i>P</i>1̄, monoclinic space group <i>C</i>2/<i>c</i>, and tetragonal space group <i>I</i>4<sub>1</sub>/<i>a</i>, respectively. Complexes <b>2</b> and <b>3</b> represent a new structural type, possessing isomeric [Mn<sup>III</sup><sub>10</sub>Mn<sup>II</sup><sub>2</sub>O<sub>16</sub>Cl<sub>2</sub>] cores but with differing peripheral ligation. Complex <b>4</b> is essentially isostructural with <b>3</b>. A magnetochemical investigation of complex <b>2</b> reveals an <i>S</i> = 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 [Mn<sub>12</sub>O<sub>12</sub>(O<sub>2</sub>CR)<sub>16</sub>(H<sub>2</sub>O)<i><sub>x</sub></i>]. A detailed investigation of forms of complex <b>2</b> with different solvation levels reveals that the magnetic properties of <b>2</b> 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 <b>3</b> and <b>4</b> are low-spin molecules with an <i>S</i> = 0 ground state.