A spectroscopic comparison between several high-symmetry S=10 Mn12 single-molecule magnets

Abstract

We report angle-dependent high-field electron-paramagnetic-resonance data collected for single-crystal samples of Mn 12 -Ac. The spectra reveal fine structures associated with various Mn 12 species corresponding to different disordered local environments. Each of the fine structures exhibits a distinct dependence on the field orientation, thereby highlighting the discrete nature of the disorder. We compare these data with the spectra obtained for two recently discovered analogs of Mn 12 -Ac, differing only in their ligand and solvent molecules. None of the fine structures seen for Mn 12 -Ac are found for the recently discovered Mn 12 complexes, thus confirming that the solvent significantly influences the magnetization dynamics in Mn 12 -Ac.

Crystal lattice desolvation effects on the magnetic quantum tunneling of single-molecule magnets

“…[20][21][22][23][24][25][26] Indeed, single-crystal high-frequency electron paramagnetic resonance ͑HFEPR͒ suggests that ϳ50% of the molecules expe-rience a significant rhombicity, characterized by a secondorder rhombic ZFS parameter E ϳ 0.01 cm 25,26,29 Effects attributed to the disordered acetic acid in 1 were found to be absent in 2 and 3, thus revealing the quantum dynamics of Mn 12 in a truly axially symmetric ͑S 4 ͒ environment for the first time. [25][26][27][28][29][30] Here, we report on a new Mn 12 complex that is still more closely related to the original acetate: ͓Mn 12 O 12 ͑O 2 CCH 3 ͒ 16 ͑CH 3 OH͒ 4 ͔ ·CH 3 OH ͓Mn 12 Ac/ CH 3 OH͑4͔͒. We also explore further the effects of disorder on the quantum dynamics of Mn 12 SMMs by deliberately removing solvent from crystals of the new high-symmetry complexes ͑2-4͒ by drying them under vacuum.…”

“…[20][21][22][23][24][25][26] While the average S 4 symmetry allows MQT interactions ͑transverse anisotropy͒ which are fourth order in the spin operators, intrinsic disorder associated with the noncentrosymmetric acetic acid solvent is found to lead to discrete local environments, resulting in a significant fraction of molecules possessing lower than fourfold symmetry. [20][21][22][23][24][25][26] Indeed, single-crystal high-frequency electron paramagnetic resonance ͑HFEPR͒ suggests that ϳ50% of the molecules expe-rience a significant rhombicity, characterized by a secondorder rhombic ZFS parameter E ϳ 0.01 cm 25,26,29 Effects attributed to the disordered acetic acid in 1 were found to be absent in 2 and 3, thus revealing the quantum dynamics of Mn 12 in a truly axially symmetric ͑S 4 ͒ environment for the first time. [25][26][27][28][29][30] Here, we report on a new Mn 12 complex that is still more closely related to the original acetate: ͓Mn 12 O 12 ͑O 2 CCH 3 ͒ 16 ͑CH 3 OH͒ 4 ͔ ·CH 3 OH ͓Mn 12 Ac/ CH 3 OH͑4͔͒.…”

Anisotropy barrier reduction in fast-relaxingMn12single-molecule magnets

“…Mn 12 BrAc, 26,44 Mn 12 tBuAc, 36,45,46 and Mn 12 Ac·MeOH, 34 i.e. the acetate crystallized from MeOH solvent instead of acetic acid and water.…”

“…Nevertheless, we note that comparable B 4 4 values are found for the SR Mn 12 complexes. 37,[40][41][42][43]45,46 In addition, given the low symmetry of SR Mn 12 and the presence of a very low-lying excited spin state, it is quite reasonable to expect a comparable rhombic 4 th order term. 70 Efforts to obtain improved simulations do not serve any useful purpose, because the applicability of the giant spin description is questionable for a molecule that clearly possesses such a low-lying excited spin multiplet (see Fig.…”

Ultra-low temperature structure determination of a Mn12 single-molecule magnet and the interplay between lattice solvent and structural disorder

“…However we have shown that full removal of the acetic acid of crystallisation resolves the disorder in the O atoms of the acetate ligands, producing species that have true, unbroken S 4 symmetry. We expect 2 and 3 to exhibit similar QTM dynamics [32][33][34][35] to other fully axial analogues in the Mn 12 family: Mn 12 -tBuAc and Mn 12 -BrAc. Hence, we are refining the single-crystal to single-crystal method used to produce species 2 and 3, in order that we can selectively produce pure samples of either material for further study.…”