Chloroauric acid

Chloroauric acid is an inorganic compound with the chemical formula . It forms hydrates . Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar anion. Often chloroauric acid is handled as a solution, such as those obtained by dissolution of gold in aqua regia. These solutions can be converted to other gold complexes or reduced to metallic gold or gold nanoparticles. The tetrahydrate crystallizes as and two water molecules. The oxidation state of gold in and anion is +3. The salts of (tetrachloroauric(III) acid) are tetrachloroaurates(III), containing anions (tetrachloroaurate(III) anions), which have square planar molecular geometry. The Au–Cl distances are around 2.28 Å. Other d8 complexes adopt similar structures, e.g. tetrachloroplatinate(II) . Solid chloroauric acid is a hydrophilic (ionic) protic solute. It is soluble in water and other oxygen-containing solvents, such as alcohols, esters, ethers, and ketones. For example, in dry dibutyl ether or diethylene glycol, the solubility exceeds 1 M. Saturated solutions in the organic solvents often are the liquid solvates of specific stoichiometry. Chloroauric acid is a strong monoprotic acid. When heated in air, solid melts in the water of crystallization, quickly darkens and becomes dark brown. Since is prone to hydrolyze, upon treatment with an alkali metal base, chloroauric acid converts to gold(III) hydroxide. The related thallium salt() is poorly soluble in all nonreacting solvents. Salts of quaternary ammonium cations are known. Other complex salts include and . Partial reduction of chloroauric acid gives oxonium dichloridoaurate(1−). Reduction may also yield other gold(I) complexes, especially with organic ligands. Often the ligand serves as reducing agent as illustrated with thiourea, : Chloroauric acid is the precursor to gold nanoparticles by precipitation onto mineral supports. Heating of in a stream of chlorine gives gold(III) chloride ().