Practically relevant host materials typically have irregular 3D morphologies and exhibit nonuniform surface structures and compositions, resulting in high polydispersity of coordination sites for SACs. Therefore, several energetically favorable configurations may coexist with minimal interchange barriers. As illustrated by molecular dynamics (MD) simulations in Figure , a wide range of surface and subsurface configurations of palladium atoms, dimers, and trimers were identified on the exfoliated carbon nitride (ECN) scaffold. In particular, the flexible lattice of ECN enables an almost continuously variable coordination pattern of palladium to the host during the catalytic cycle of Suzuki coupling. coupling. Likewise, reducible oxide supports such as TiO2, Fe2O3, and CeO2 are especially suitable for stabilizing single atoms due to the strong metal-substrate interaction. The unique Ce 3+ /Ce 4+ redox properties, associated with the reversible formation of oxygen vacancies, render CeO2 a widely used support. A theoretical analysis of platinum atoms on CeO2 identified the possible coexistence of several well-defined and dynamically interconnected charge and oxidation states, demonstrating the oversimplification of the current static picture of electronic structures. Such dynamic response in the local coordination environment has also been reported in the Rh1/TiO2 for reverse water-gas shift reaction, Pt1/TiO2 for CO oxidation, Cu-N-C and Ru-N-C SACs for hydrogen and oxygen evolution, respectively. 34, 35