colour of tetrachloroaurate (AuCl4)

[Traveller11]

It seems pretty well established that the colour of auric chloride (AuCl3) in solution is a golden brown colour. Does anyone know the colour of tetrachloroaurate (AuCl4) in solution? Many of the ancient mining articles typically referred to it as a "clear pregnant liquor". I have not been able to deduce just what exactly was meant by the word "clear".

 

[jeneje]

http://en.wikipedia.org/wiki/Chloroauric_acid

 

[Traveller11]

http://en.wikipedia.org/wiki/Chloroauric_acid

It seems confusing. Both hydrogen tetrachloroaurate (HAuCl4) and sodium tetrachloroaurate (NaAuCl4) both seem to lead back to chloroauric acid, along with H3OAuCl4. Can they all be the same thing?

 

[butcher]

I think the acidity of solution, and concentration, or even evaporation of the salts are basically the difference.

 

[Traveller11]

Does tetrachloroaurate resemble the golden brown of auric chloride in solution or is it clear? Unfortunately, the Wikipedia article did not state this.

 

[jeneje]

Does tetrachloroaurate resemble the golden brown of auric chloride in solution or is it clear? Unfortunately, the Wikipedia article did not state this.

Traveller11, the only reference I found in the article was,

When heated in air of solid HAuCl4•n H2O, it melts in the water of crystallization, quickly darkens and becomes dark brown.

I don't know if this is what you were looking for.
Ken

 

[Lou]

It's a golden yellow ranging to deep red-orange.

When anhydrous AuCl3 is produced and crystallized from an ether (i.e. THF or dioxane) it makes ruby red crystals. You can get fairly large ones if you vapor distill over hexane into the ether-gold complex. Quite pretty, look like the philosopher's stone.

 

[Lino1406]

This means the color is red shifted by the absence of water crystallization molecules
meaning higher energy is absorbed vs. HAuCl4.4H2O
Compare: CuSO4 colorless (blue shift to) CuSO4.5H2O blue