Binding of Higher Alcohols onto Mn<sub>12</sub> Single-Molecule Magnets (SMMs): Access to the Highest Barrier Mn<sub>12</sub> SMM

Two new members of the Mn<sub>12</sub> family of single-molecule magnets (SMMs), [Mn<sub>12</sub>O<sub>12</sub>(O<sub>2</sub>CCH<sub>2</sub>Bu<sup>t</sup>)<sub>16</sub>(Bu<sup>t</sup>OH)(H<sub>2</sub>O)<sub>3</sub>]·2Bu<sup>t</sup>OH (<b>3</b>·2Bu<sup>t</sup>OH) and [Mn<sub>12</sub>O<sub>12</sub>(O<sub>2</sub>CCH<sub>2</sub>Bu<sup>t</sup>)<sub>16</sub>(C<sub>5</sub>H<sub>11</sub>OH)<sub>4</sub>] (<b>4</b>) (C<sub>5</sub>H<sub>11</sub>OH is 1-pentanol), are reported. They were synthesized from [Mn<sub>12</sub>O<sub>12</sub>(O<sub>2</sub>CMe)<sub>16</sub>(H<sub>2</sub>O)<sub>4</sub>]·2MeCO<sub>2</sub>H·4H<sub>2</sub>O (<b>1</b>) by carboxylate substitution and crystallization from the appropriate alcohol-containing solvent. Complexes <b>3</b> and <b>4</b> are new members of the recently established [Mn<sub>12</sub>O<sub>12</sub>(O<sub>2</sub>CCH<sub>2</sub>Bu<sup>t</sup>)<sub>16</sub>(solv)<sub>4</sub>] (solv = H<sub>2</sub>O, alcohols) family of SMMs. Only one bulky Bu<sup>t</sup>OH can be accommodated into <b>3</b>, and even this causes significant distortion of the [Mn<sub>12</sub>O<sub>12</sub>] core. Variable-temperature, solid-state alternating current (AC) magnetization studies were carried out on complexes <b>3</b> and <b>4</b>, and they established that both possess an <i>S</i> = 10 ground state spin and are SMMs. However, the magnetic behavior of the two compounds was found to be significantly different, with <b>4</b> showing out-of-phase AC peaks at higher temperatures than <b>3</b>. High-frequency electron paramagnetic resonance (HFEPR) studies were carried out on single crystals of <b>3</b>·2Bu<sup>t</sup>OH and <b>4</b>, and these revealed that the axial zero-field splitting constant, <i>D</i>, is very different for the two compounds. Furthermore, it was established that <b>4</b> is the Mn<sub>12</sub> SMM with the highest kinetic barrier (<i>U</i><sub>eff</sub>) to date. The results reveal alcohol substitution as an additional and convenient means to affect the magnetization relaxation barrier of the Mn<sub>12</sub> SMMs without major change to the ligation or oxidation state.