Gold(III) oxide (also known as gold trioxide, gold sesquioxide, or auric oxide) is an inorganic compound of gold and oxygen with the chemical formula Au₂O₃. It is the most stable oxide of gold.
Properties
Gold(III) oxide is a red-brown to brownish-black solid at room temperature. According to X-ray crystallography, Au₂O₃ features square planar gold centers with both 2- and 3-coordinated oxides. The four Au–O bond distances range from 193 to 207 picometers. The compound has a molecular weight of 441.93 g/mol and a density of approximately 11.34 g/cm³. It is insoluble in water but soluble in hydrochloric acid, concentrated nitric acid, and aqueous solutions of sodium or potassium cyanide.
Thermal Decomposition
Gold(III) oxide is thermally unstable. It begins to release oxygen at approximately 110 °C and decomposes fully to metallic gold and oxygen at temperatures around 250–298 °C. The decomposition temperature is reported variably in the literature, with some sources citing 150 °C and others 298 °C, depending on the crystallinity and hydration state of the sample. The decomposition proceeds directly to metallic gold with no evidence of intermediate oxide phases such as Au₂O.
Preparation
Crystalline gold(III) oxide can be prepared by heating amorphous hydrated gold(III) oxide with perchloric acid and an alkali metal perchlorate in a sealed quartz tube at approximately 250 °C and 30 MPa pressure. More commonly, it is produced by the thermal dehydration of gold(III) hydroxide, Au(OH)₃, at 130–140 °C.
Structure
The crystal structure of Au₂O₃ has been determined to be orthorhombic, space group Fdd2, with lattice parameters a = 1.2827 nm, b = 1.052 nm, and c = 0.3838 nm.
Applications
Gold(III) oxide is used in porcelain enameling, glass dyeing, ceramic coloring, and in aerospace and electrochemical applications such as fuel cells. It also serves as a precursor in the halogen-free synthesis of gold nanoparticles, where it can be reduced by aliphatic amines such as oleylamine to produce sub-10 nm gold particles.
Safety
Gold(III) oxide is classified as a skin and eye irritant (H315, H319). Standard precautionary measures include wearing protective gloves, eye protection, and washing thoroughly after handling. It should be stored in a cool, dark, dry place away from strong oxidizing agents and light.
Identifiers
- CAS Number: 1303-58-8
- EC Number: 215-122-1
- IUPAC Name: Gold(III) oxide
- PubChem CID: 164805
- UNII: LW5Y686RUP
