Investigating the spin state and electronic structure of the Fe3O cluster from MOF MIL-100(Fe)

In this paper, we investigate the spin state of the Fe3O cluster from MIL-100(Fe), each Fe site of which possesses either one unpaired electron, three unpaired electrons, or five unpaired electrons. Total energies with respect to different spin states were optimized with the PBE, B3LYP, HF, and MP2 methods in combination with various basis sets (6-31G, 6-31G*, 6-311G(d,p)) for non-metal ions and pseudopotentials for Fe (SDD and LanL2DZ). The results of B3LYP, MP2, and HF methods predicted that each Fe site had five unpaired electrons in the most stable spin state. However, the results of PBE show two opposite cases. In one case, PBE predicted each Fe had one unpaired electron, while in the remaining PBE cases, each Fe site was predicted to exhibit five unpaired electrons. We finally conclude the Fe3O cluster with 15 unpaired electrons is the most stable structure.