Compounds

Although gold is a noble metal, it forms many and diverse compounds. The oxidation state of gold in its compound ranges from −1 to +5 but Au(I) and Au(III) dominate. Gold(I), referred to as the aurous ion, is the most common oxidation state with “soft” ligands such as thioethers, thiolates, and tertiary phosphines. Au(I) compounds are typically linear. A good example is Au(CN)₂⁻, which is the soluble form of gold encountered in mining. Curiously, aurous complexes of water are rare. The binary gold halides, such as AuCl, form zig-zag polymeric chains, again featuring linear coordination at Au. Most drugs based on gold are Au(I) derivatives.^[47]

Gold(III) (“auric”) is a common oxidation state and is illustrated by gold(III) chloride, AuCl₃. Its derivative is chloroauric acid, HAuCl₄, which forms when Au dissolves in aqua regia. Au(III) complexes, like other d⁸ compounds, are typically square planar.