Tetrachloroauric acid

Chloroauric acid

Names
Other names Hydrogen tetrachloroaurate, Chlorauric acid, Aurochloric acid, Aurate(1−), tetrachloro-, hydrogen, (SP-4-1)-, Hydrogen aurichloride
Identifiers
CAS Number	16903-35-8 Y 16961-25-4 (trihydrate) N
3D model (JSmol)	Interactive image
ChemSpider	26171 Y
ECHA InfoCard	100.037.211
PubChem CID	28133
InChI InChI=1S/Au.4ClH/h;4*1H/q+3;;;;/p-3 Y Key: VDLSFRRYNGEBEJ-UHFFFAOYSA-K Y InChI=1/Au.4ClH.Na/h;4*1H;/q+3;;;;;+1/p-4/rAuCl4.Na/c2-1(3,4)5;/q-1;+1 Key: IXPWAPCEBHEFOV-ACHCXQQJAP InChI=1/Au.4ClH/h;4*1H/q+3;;;;/p-3/rAuCl4/c2-1(3,4)5/q-1/p+1 Key: VDLSFRRYNGEBEJ-ZXMCYSOYAI
SMILES [H+].Cl[Au-](Cl)(Cl)Cl
Properties
Chemical formula	HAuCl4
Molar mass	339.785 g/mol (anhydrous) 393.833 g/mol (trihydrate) 411.85 g/mol (tetrahydrate)
Appearance	orange-yellow needle-like crystals hygroscopic
Density	3.9 g/cm3 (anhydrous) 2.89 g/cm3 (tetrahydrate)
Melting point	254 °C (489 °F; 527 K) (decomposes)
Solubility in water	350 g HAuCl4 / 100 g H2O
Solubility	soluble in alcohol, ester, ether, ketone
Structure
Crystal structure	monoclinic
Hazards
Safety data sheet	JT Baker
EU classification (DSD) (outdated)	not listed
NFPA 704	0 3 1
Related compounds
Other anions	Tetrabromoauric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Chloroauric acid is an inorganic compound with the chemical formula HAuCl
4. Both the trihydrate and tetrahydrate are known. It is an orange-yellow solid, a common precursor to other gold compounds and an intermediate in the purification of gold metal. Both the trihydrate and tetrahydrate are available commercially.

Chloroauric acid is a strong monoprotic acid.

The crystalline tetrahydrate is known to contain H
5O+
2·AuCl−
4 and two water molecules. The AuCl−
4 anion has square planar molecular geometry. The Au–Cl distances are around 2.28 Å. Other d⁸ complexes adopt similar structures, e.g. [PtCl₄]²⁻.

Solid chloroauric acid is a hydrophilic (ionic) protic solute. It is soluble not only in water, but also in many oxygen-containing solvents, such as alcohols, esters, ethers, and ketones. For example, in dry dibutyl ether of diethylene glycol, the solubility exceeds 1 mol/L. Saturated solutions in the organic solvents often are the liquid solvates of specific stoichiometry.

When heated in air, solid HAuCl₄·nH₂O melts in the water of crystallization, quickly darkens and becomes dark brown.

Upon treating chloroauric acid with a standard base, it converts to metal, tetrachloridoaurate and water. The related thallium salt is poorly soluble in all nonreacting solvents. Salts of quaternary ammonium cations are known. Other complex salts include [Au(bipy)Cl₂][AuCl₄] and [Co(NH₃)₆][AuCl₄]Cl₂.