Nature of hydride and halide encapsulation in Ag8cages: insights from the structure and interaction energy of [Ag8(X){S2P(OiPr)2}6]+(X = H−, F−, Cl−, Br−, I−) from relativistic DFT calculations

Abstract

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 [Ag8(X){S2P(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 Ag8-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 [Ag8{S2P(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.