Relieving Frustration: the Case of Antiferromagnetic Triangular Mn$_{3}$ Complexes

Recently, various trianglular [Mn$^{III}$]$_{3}$ complexes have been extensively studied due to the fact that one can modulate the magnitude and the sign of the inter-ion exchange, thereby giving rise to very simple molecular clusters that constitute some of the cleanest and best examples of so-called single-molecule magnets (SMMs) [Inorg. Chem. \textbf{48}, 3480; Phys. Rev. Lett. \textbf{103}, 017202; Dalton Trans. \textbf{2009}, 9157]. However, magnetic and electron paramagnetic resonance (EPR) characterizations of low-spin antiferromagnetic [Mn$^{III}$]$_{3}$ complexes have been problematic due to the significant spin frustration that exists for this topology. We show that this frustration is relieved in the highly distorted [NEt$_{4}$]$_{3}$[Mn$_{3}$Zn$_{2}$(salox)$_{3}$O(N$_{3})_{8}$]$\cdot$MeOH molecule: susceptibility data suggest a well isolated $S$ = 2 ground state; EPR measurements support this conclusion and further indicate the presence of a very significant zero-field-splitting (ZFS) separating the lowest-lying $m_{S}$~=~$\pm$2 states from excited levels. Remarkably, this ZFS is sufficient to give rise to magnetic bistability, as evidenced through the observation of low-temperature hysteresis.