Mn₇ and Mn₁₂ Clusters From Use of 2-(Pyridine-2-yl)propan-2-ol: A New Half-Integer Single-Molecule Magnet

The syntheses, crystal structures, and magnetochemical characterization are reported for two new Mn clusters, [Mn₇O₃(OH)₃(O₂CBu^t)₇(dmhmp)₄] (<b>1</b>) and [Mn₁₂O₇(OH)(OMe)₂(O₂CPh)₁₂(dmhmp)₄(H₂O)] (<b>2</b>). They were obtained from the use of 2-(pyridine-2-yl)propan-2-ol (dmhmpH), a more bulky version of the 2-(hydroxymethyl)pyridine (hmpH) reagent commonly employed previously in Mn chemistry. The reaction of dmhmpH with MnCl₂·4H₂O and NaO₂CBu^t in MeCN/MeOH led to the heptanuclear complex <b>1</b>, whereas the analogous reaction with Mn(O₂CPh)₂ gave dodecanuclear complex <b>2</b>. Complexes <b>1</b> and <b>2</b> are both mixed-valent and are of unprecedented structural types. Complex <b>1</b> (Mn^II, 6Mn^III) can be described as the fusion of butterfly-like [Mn₄(μ₃-O)₂] and tetrahedral [Mn₄(μ₄-O)] units by the sharing of a common Mn atom. Complex <b>2</b> (3Mn^II, 9Mn^III) possesses a central [Mn₄O₆] face-sharing incomplete dicubane, on either side of which is a tetrahedral [Mn₄(μ₄-O)] unit attached to the oxide ions of the former. Solid-state dc and ac magnetic susceptibility measurements on <b>1</b> and <b>2</b> establish that they possess unusual <i>S</i> = 7/2 and 13/2 ground states, respectively. The ac susceptibility studies on <b>2</b> revealed nonzero frequency-dependent out-of-phase (χ_M′′) signals at temperatures below 3 K, indicating a single-molecule magnet (SMM). Magnetization versus applied dc field sweeps on single crystals of <b>2</b>·3CH₂Cl₂ down to 0.04 K exhibited hysteresis, thus confirming complex <b>2</b> to be a new half-integer SMM.