The chemistry of gold as an anion

Abstract

Due to relativistic and classical shell structure effects, the 6s orbital of gold is significantly contracted and energetically stabilized. This is reflected by a strikingly high electron affinity, and a distinct tendency to adopt negatively polarized valence states. This tutorial review focuses on the chemistry of gold as an anion, displaying the integral ionic charge number of 1−. Two synthetic approaches to compounds containing monoatomic gold anions have become available: (1) reacting elemental gold with molten caesium and an oxide, e.g.Cs₂O; (2) metathesis reactions involving Au⁻ dissolved in liquid ammonia. Both procedures have proven to be rather versatile. Aurides synthesized along these routes are surveyed, in particular with respect to their structures and bonding properties.