The Role of Radical Bridges in Polynuclear Single‐Molecule Magnets

Employing radical bridges between anisotropic metal ions has been a viable route to achieve high‐performance single‐molecule magnets (SMMs). While the bridges have been mainly considered for their ability to promote exchange interactions, the crystal‐field effect arising from them has not been taken into account explicitly. This lack of consideration may distort the understanding and limit the development of the entire family. To shed light on this aspect, herein we report a theoretical investigation of a series of N23- ‐radical‐bridged diterbium complexes. It is found that while promoting strong exchange coupling between the terbium ions, the N23- ‐radical induces a crystal field that interferes destructively with that of the outer ligands, and thus reduces the overall SMM behavior. Based on the theoretical results, we conclude that the SMM behavior in this series could be further maximized if the crystal field of the outer ligands is designed to be collinear with that of the radical bridge. This conclusion can be generalized to all exchange‐coupled SMMs. In N23−‐radical‐bridged diterbium complexes, the radical bridge induces crystal‐field and magnetic anisotropy that interferes destructively with that of the outer ligands. The performance of polynuclear exchange‐coupled SMMs may be significantly enhanced if the crystal‐field and magnetic anisotropy induced by the local ligands and the bridging ligands are engineered collinear to each other.