Metal-metal bond in lanthanide single-molecule magnets

Lanthanide (Ln) compounds represent a unique chemical platform for developing high-temperature single-molecule magnets (SMMs). The shift in research focus from increasing the magnetic anisotropy barrier (U_eff) to raising the blocking temperature (T_B) has upgraded the design criteria from considering only the static crystal field (CF) to paying attention to the effects of molecular vibrations beyond the first coordination environment on the relaxation of magnetization. Although the realization of high working temperatures for Ln SMMs remains a formidable challenge, recent remarkable advances in dimetallofullerenes (di-EMFs) with Ln ions and mixed-valence dilanthanide complexes both feature single-electron Ln-Ln bonds to afford room-temperature molecular magnets. In this review, we provide critical discussion on the achievements of metal-metal (MM) bonded lanthanide SMMs, focusing on the effects of MM bonds on the magnetization dynamics, and shedding light on the future developments of high-temperature Ln SMMs.