Nature of hydride and halide encapsulation in Ag 8 cages: insights from the structure and interaction energy of [Ag 8 (X){S 2 P(O i Pr) 2 } 6 ] + (X = H - , F - , Cl - , Br - , I - ) from relativistic DFT calculations.

Unraveling the different contributing terms to an efficient anion encapsulation is a relevant issue for further understanding of the underlying factors governing the formation of endohedral species. Herein, we explore the favorable encapsulation of hydride and halide anions in the [Ag 8 (X){S 2 P(OPr) 2 } 6 ] + (X - = H, 1, F, 2, Cl, 3, Br, 4, and, I, 5) series on the basis of relativistic DFT-D level of theory. The resulting Ag 8 -X interaction is sizable, which decreases along the series: -232.2 (1) > -192.1 (2) > -165.5 (3) > -158.0 (4) > -144.2 kcal mol -1 (5), denoting a more favorable inclusion of hydride and fluoride anions within the silver cage. Such interaction is mainly stabilized by the high contribution from electrostatic type interactions (80.9 av%), with a lesser contribution from charge-transfer (17.4 av%) and London type interactions (1.7 av%). Moreover, the ionic character of the electrostatic contributions decreases from 90.7% for hydride to 68.6% for the iodide counterpart, in line with the decrease in hardness according to the Pearson's acid-base concept (HSAB) owing to the major role of higher electrostatic interaction terms related to the softer (Lewis) bases. Lastly, the [Ag 8 {S 2 P(OPr) 2 } 6 ] 2+ cluster is able to adapt its geometry in order to maximize the interaction towards respective monoatomic anion, exhibiting structural flexibility. Such insights shed light on the physical reasoning necessary for a better understanding of the different stabilizing and destabilizing contributions related to metal-based cavities towards favorable incorporation of different monoatomic anions.