Ligand-core interaction in ligand-protected Ag 25 (XR) 18 (X = S, Se, Te) superatoms and evaluation of the anchor atom role via relativistic DFT calculations.

The isostructural and isoelectronic silver [Ag 25 (SR) 18 ] - (R = ligand) cluster, similar to [Au 25 (SR) 18 ] - gold clusters, allows for further understanding of the fundamental similarities between Au and Ag at the ultrasmall nanoscale (<2 nm), featuring an eight cluster electron (8-ce) M 13 core. Our results indicate a less favorable protecting-layer to core interaction, leading to a more symmetrical Ag 13 core owing to a less tight ligand shell. The stabilizing embrace of Ag 13 is of an electrostatic character, with bonding contributions occupying the formally unoccupied superatomic shells, given by 1D, 2S, and 2F, indicating their role as acceptor core orbitals to provide further core-ligand bonding upon the formation of the cluster. The optical properties exhibit a red-shift for the first 1P → 1D peak along the [Ag 25 (XMe) 18 ] - series, which is in contrast with the blue-shift observed for the gold counterpart, by replacing the S-anchor atom with Se and Te. Moreover, the S 1 → S 0 emission exhibits a red-shift. Thus, the role of the anchor atom is to modify the bonding and optical features of the [Ag 25 (XMe) 18 ] - species, affording fine-tuning of the molecular behavior.