Synthesis, Structure, and Spectroscopic and Magnetic Characterization of [Mn12O12(O2CCH2But)16(MeOH)4]·MeOH, a Mn12 Single-Molecule Magnet with True Axial Symmetry

摘要

The synthesis and properties are reported of a rare example of a Mn12nsingle-molecule magnet (SMM) in truly axial symmetry (tetragonal, I4̅).n[Mn12O12(O2CCH2But)16(MeOH)4]·MeOH (3·MeOH) was synthesized by carboxylatensubstitution on [Mn12O12(O2CMe)16(H2O)4]·2MeCO2H·4H2O (1). The complex wasnfound to possess an S = 10 ground state, as is typical for the Mn12 family, and displayednboth frequency-dependent out-of-phase AC susceptibility signals and hysteresis loops innsingle-crystal magnetization vs DC field sweeps. The loops also exhibited quantumntunneling of magnetization steps at periodic field values. Single-crystal, high-frequencynelectron paramagnetic resonance spectra on 3·MeOH using frequencies up to 360 GHznrevealed perceptibly sharper signals than for 1. Moreover, careful studies as a function ofnthe magnetic field orientation did not reveal any satellite peaks, as observed for 1,nsuggesting that the crystals of 3 are homogeneous and do not contain multiple Mn12nenvironments. In the single-crystal 55Mn NMR spectrum in zero applied field, three wellresolvednpeaks were observed, which yielded hyperfine and quadrupole splitting at three distinct sites. However, observation of anslight asymmetry in the Mn4+ peak was detectable, suggesting a possible decrease in the local symmetry of the Mn4+ site. Spin−nlattice (T1) relaxation studies were performed on single crystals of 3·MeOH down to 400 mK in an effort to approach thenquantum tunneling regime, and fitting of the data using multiple functions was employed. The present work and other recentnstudies continue to emphasize that the new generation of truly high-symmetry Mn12 complexes are better models for thoroughninvestigation of the physical properties of SMMs than their predecessors such as 1.