Gold compounds

Au(I), referred to as the aurous ion, is the most common oxidation state with soft ligands such as thioethers, thiolates, and organophosphines.

The binary gold halides, such as AuCl, form zigzag polymeric chains, again featuring linear coordination at Au.

The gold atom centers in Au(III) complexes, like other d8 compounds, are typically square planar, with chemical bonds that have both covalent and ionic character.

These alloys can be produced to modify the hardness and other metallurgical properties, to control melting point or to create exotic colors.

It does however, react with sodium or potassium cyanide under alkaline conditions when oxygen is present to form soluble complexes.

The added metal is oxidized and dissolves, allowing the gold to be displaced from solution and be recovered as a solid precipitate.

[13] Gold has the highest electron affinity of any metal, at 222.8 kJ/mol, making Au− a stable species,[14] analogous to the halides.

Gold also has a –1 oxidation state in covalent complexes with the group 4 transition metals, such as in titanium tetraauride and the analogous zirconium and hafnium compounds.

The evaporation of a solution of Au(OH)3 in concentrated H2SO4 produces red crystals of gold(II) sulfate, Au2(SO4)2.