Rationalization of Room-Temperature Single-Molecule Toroics via Exchange Coupling

Single-molecule toroics (SMTs) are a type of multi-metal coordination complexes where onsite magnetic moments are well defined in a vortex arrangement, exhibiting a toroidal magnetic ground state with well-separated excited states. Due to their ability to generate at least two degenerate ground doublets and insensitivity to the external field, SMTs are a promising material for ultrahigh-dense data storage as well as for magnetoelectric couplings. Typically, SMTs can be divided into two groups according to the constitutional metal ions, namely, dysprosium(III)-based and heterometallic-based SMTs. The former is the pioneer, mainly taking advantage of strong magnetic anisotropy of the Dy(III) ion to produce a vortex-arranged magnetic moment where intramolecular dipole-dipole interactions serve as the magnetic links. However, those links are too weak to support the rationalization of SMT behavior at room temperature. In this chapter, we mainly focus on reviewing the latter type, which shows much stronger magnetic exchange couplings. Thus, the energy gap between the ground and the first excited states can be significantly enhanced by 10–100 times compared to the former type. Such advances are inspiring to achieve toroidal moments at much higher temperatures. Other than the 3d-4f SMTs, the pure 3d transition metal and 3d transition metal-radical system are also promising to develop. Moreover, an enhanced toroidal moment approach to connect SMTs to further strengthen the toroidal magnetic moments and enlarge the energy gaps is discussed.