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

Two new members of the Mn-12 family of single-molecule magnets (SMMs), [Mn12O12(O2CCH2But)(16)((BuOH)-O-t)-(H2O)(3)]center dot 2Bu(t)OH (3 center dot 2Bu(t)OH) and [Mn12O12(O2CCH2But)(16)(C5H11OH)(4)] (4) (C5H11OH is 1-pentanol), are reported. They were synthesized from [Mn12O12(O2CMe)(16)(H2O)(4)]center dot 2MeCO(2)H center dot 4H(2)O (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 (BuOH)-O-t 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 center dot 2Bu(t)OH 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 Mn-12 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 Mn-12 SMMS without major change to the ligation or oxidation state.