Insight into the Ligand-to-Ligand Charge-Transfer Process in Rare-Earth Metal Diradical Complexes
Haihan Yan, Botao Wu, Junnian Wei, and Wen-Xiong Zhang*
Inorg. Chem. 2023, 62, 8052–8057. https://doi.org/10.1021/acs.inorgchem.3c00900
While ligand-to-ligand charge-transfer (LLCT) process is an important way to understand the interactions between metal-bridged radicals for late transition metal complexes, there is little clear and evident observation of LLCT process for rare-earth metal complexes. In this work, rare-earth metal diradical complexes supported by diazabutadiene (DAD) ligands [(DAD)2RE(BH4)] (RE = Yb (1), Sm (2)) were synthesized and studied. Coordination geometry of 1 and 2 are different due to the different ionic radii. Reduction of 1 or 2 generated monoradical complexes, with one of their DAD radical anions being reduced. In all of the complexes, Sm and Yb remain +3 valence state. On UV-Vis spectra, the LLCT transition of 1 could be clearly observed, but complex 2 did not show the same transition. These results could be related to the geometric structures of the complexes as well as exchange coupling between diradicals, thus clearly expanding the model for late transition metal bridged diradicals to rare-earth systems experimentally.