Binding of Higher Alcohols onto Mn₁₂ Single-Molecule Magnets (SMMs): Access to the Highest Barrier Mn₁₂ SMM

Two new members of the Mn₁₂ family of single-molecule magnets (SMMs), [Mn₁₂O₁₂(O₂CCH₂Bu^t)₁₆(Bu^tOH)(H₂O)₃]·2Bu^tOH (3·2Bu^tOH) and [Mn₁₂O₁₂(O₂CCH₂Bu^t)₁₆(C₅H₁₁OH)₄] (4) (C₅H₁₁OH is 1-pentanol), are reported. They were synthesized from [Mn₁₂O₁₂(O₂CMe)₁₆(H₂O)₄]·2MeCO₂H·4H₂O (1) by carboxylate substitution and crystallization from the appropriate alcohol-containing solvent. Complexes 3 and 4 are new members of the recently established [Mn₁₂O₁₂(O₂CCH₂Bu^t)₁₆(solv)₄] (solv = H₂O, alcohols) family of SMMs. Only one bulky Bu^tOH can be accommodated into 3, and even this causes significant distortion of the [Mn₁₂O₁₂] core. Variable-temperature, solid-state alternating current (AC) magnetization studies were carried out on complexes 3 and 4, and they established that both possess an S = 10 ground state spin and are SMMs. However, the magnetic behavior of the two compounds was found to be significantly different, with 4 showing out-of-phase AC peaks at higher temperatures than 3. High-frequency electron paramagnetic resonance (HFEPR) studies were carried out on single crystals of 3·2Bu^tOH and 4, and these revealed that the axial zero-field splitting constant, D, is very different for the two compounds. Furthermore, it was established that 4 is the Mn₁₂ SMM with the highest kinetic barrier (U_eff) to date. The results reveal alcohol substitution as an additional and convenient means to affect the magnetization relaxation barrier of the Mn₁₂ SMMs without major change to the ligation or oxidation state.