Stabilities and Electronic Structures of Transition Metal (Cu, Ag, Au, Ni, Pd, Pt) Cluster-Confined UiO-66

Transition-metal cluster-encapsulated UiO-66 composites have attracted great interest because of their excellent properties in catalysis, yet it is still a great challenge to explore the structures and electronic properties. In this study, ab initio molecular dynamics simulations combined with density functional theory-based methods were employed to explore the formation mechanism, stabilities, and electronic properties of the Mn@UiO-66 (M = Cu, Ag, Au, Ni, Pd, and Pt) composites. The computational results indicate that the thermodynamics of the different metal clusters are highly correlated with the deformation energy of the framework, while the values of charge transfer do not determine the stabilities. The stabilities of the confined metal clusters follow the order of Pt > Ni > Pd > Cu > Au > Ag, and intriguingly, all of the Cu, Ni, Pd, and Pt clusters were computed to be located in the tetrahedral cage of UiO-66, while the large Ag and Au clusters were preferably confined in the octahedral cage. This discrepancy is explained by their inherent electronic properties of the clusters as well as the different interaction energies between the host and the guest. The analyses show that the different electronic properties of the Mn@UiO-66 composites determine the aggregation behaviors of the confined metal clusters, well explaining the dramatically different sizes of the confined metal clusters reported in literature studies.