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(O2CCH2But)16(ButOH)(H2O)3]·2ButOH (3·2ButOH) and [Mn12O12(O2CCH2But)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(O2CCH2But)16(solv)4] (solv = H2O, alcohols) family of SMMs. Only one bulky ButOH 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 3·2ButOH 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 (Ueff) 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.