On the halide aggregation into the [Au4(PPh3)4]4+ cluster core. Insights from structural, optical and interaction energy analysis in [(Ph3PAu)4X2]2+ and [(Ph3PAu)4X]3+ species (X = Cl-, Br-, I-)

The aggregation of halide atoms into gold clusters offers an interesting scenario for the development of novel metal-based cavities for anion recognition and sensing applications. Thus, further understanding of the different contributing terms leading to efficient cluster-halide aggregation is relevant to guide their synthetic design. In this report, we evaluate the formation of [(Ph3PAu)4X2]2+ and [(Ph3PAu)4X]3+ species (X = Cl-, Br-, I-) in terms of different energy contributions underlying the stabilization of the cluster-halide interaction, and the expected UV-vis absorption profiles as a result of the variation in frontier orbital arrangements. Our results denote that a non-planar Au4 core shape enables enhanced halide aggregation, which is similar for Cl-, Br-, and I-, in comparison to the hypothetical planar Au4 counterparts. The electrostatic nature of the interaction involves a decreasing ion-dipole term along with the series, and for iodine species, higher-order electrostatic contributions become more relevant. Hence, the obtained results help in gaining further understanding of the different stabilizing and destabilizing contributions to suitable cluster-based cavities for the incorporation of different monoatomic anions.

Nature of hydride and halide encapsulation in Ag8 cages: insights from the structure and interaction energy of [Ag8(X){S2P(OiPr)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 [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.

The usefulness of energy decomposition schemes to rationalize host–guest interactions

The findings reported here reveal the robustness and practical application of EDA-NOCV in rationalizing molecular recognition situations in host–guest systems.

How the electron-deficient cavity of heterocalixarenes recognizes anions: insights from computation

The nature of bridging heteroatoms in a heterocalixarene structure has a crucial role in anion recognition.