Anomalous Property of Ag(BO2)2 Hyperhalogen: Does Spin–Orbit Coupling Matter?

Hyperhalogens were recently identified as a new class of highly electronagative species which are composed of metals and superhalogens. In this work, high‐level theoretical calculations and photoelectron spectroscopy experiments are systematically conducted to investigate a series of coinage‐metal‐containing hyperhalogen anions, Cu(BO₂)₂^?, Ag(BO₂)₂^?, and Au(BO₂)₂^?. The vertical electron detachment energy (VDE) of Ag(BO₂)₂^? is anomalously higher than those of Au(BO₂)₂^? and Cu(BO₂)₂^?. In quantitative agreement with the experiment, high‐level ab initio calculations reveal that spin–orbit coupling (SOC) lowers the VDE of Au(BO₂)₂^? significantly. The sizable magnitude of about 0.5 eV of SOC effect on the VDE of Au(BO₂)₂^? demonstrates that SOC plays an important role in the electronic structure of gold hyperhalogens. This study represents a new paradigm for relativistic electronic structure calculations for the one‐electron‐removal process of ionic Au^IL₂ complexes, which is characterized by a substantial SOC effect.