Less common oxidation states

Less common oxidation states of gold include −1, +2, and +5.

The −1 oxidation state occurs in compounds containing the Au⁻ anion, called aurides. Caesium auride (CsAu), for example, crystallizes in the caesium chloride motif.^[48] Other aurides include those of Rb⁺, K⁺, and tetramethylammonium (CH₃)₄N⁺.^[49]

Gold(II) compounds are usually diamagnetic with Au–Au bonds such as [Au(CH₂)₂P(C₆H₅)₂]₂Cl₂. The evaporation of a solution of Au(OH)₃ in concentrated H₂SO₄ produces red crystals of gold(II) sulfate, AuSO₄. Originally thought to be a mixed-valence compound, it has been shown to contain Au4+2 cations.^[50][51] A noteworthy, legitimate gold(II) complex is the tetraxenonogold(II) cation, which contains xenon as a ligand, found in [AuXe₄](Sb₂F₁₁)₂.^[52]

Gold pentafluoride and its derivative anion, AuF−6, is the sole example of gold(V), the highest verified oxidation state.^[53]

Some gold compounds exhibit aurophilic bonding, which describes the tendency of gold ions to interact at distances that are too long to be a conventional Au–Au bond but shorter that van der Waals bonding. The interaction is estimated to be comparable in strength to that of a hydrogen bond.