PUB - Publikationen an der Universität Bielefeld

We have synthesized the triplesalen-based single-molecule magnet (SMM) [Mn-III Mn-6(III)](3+) as a variation of our SMM [Mn-III Cr-6(III)](BPh4)(3). The use of the rod-shaped anion lactate (lac) was intended to enforce a rod packing and resulted in the crystallization of [ MnIII 6MnIII](lac) 3 in the highly symmetric space group R3. This entails a crystallographic S-6 symmetry of the [Mn-III Mn-6(III)](3+) molecules, which in addition are all aligned with the crystallographic c axis. Moreover, the molecular environment of each [Mn-III Mn-6(III)](3+) molecule is highly symmetric. Single-crystals of [Mn-III Mn-6(III)](lac) (3) exhibit a double hysteresis at 0.3 K with a hysteretic opening not only for the spin ground state up to 1.8 T, but also for an excited state becoming the ground state at approximate to 3.4 T with a hysteretic opening up to 10 T. Ab initio calculations including spin-orbit coupling establish a nonmagnetic behavior of the central MnIII low-spin (l.s.) ion at low temperatures, demonstrating that predictions from ligand-field theory are corroborated in the case of MnIII l.s. by ab intio calculations. Simulations of the field-and temperature-dependent magnetization data indicate that [Mn-III Mn-6(III)](3+) is in the limit of weak exchange (J << D) with antiferromagnetic interactions in the trinuclear Mn-3(III) triplesalen subunits resulting in intermediate S* = 2 spins. Slight ferromagnetic interactions between the two trinuclear Mn-3(III) subunits lead to a ground state in zero-field that is approximately described by a total spin quantum number S = 4. This ground state exhibits only a very small anisotropy barrier due to the misalignment of the local zero-field splitting tensors. At higher magnetic fields of approximate to 3.4 T, the spin configuration changes to an all-up orientation of the local MnIII spins, with the main part of the Zeeman energy needed for the spin-flip being required to overcome the local MnIII anisotropy barriers, while only minor contributions of the Zeeman energy are needed to overcome the antiferromagnetic interactions. These combined theoretical analyses provide a clear picture of the double-hysteretic behavior of the [Mn-III Mn-6(III)](3+) single-molecule magnet with hysteretic openings up to 10 T.