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.