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 (AuL2)-L-I complexes, which is characterized by a substantial SOC effect.