Gold oxide (III) is an inorganic compound with the chemical formula Au 2 O 3 . Theoretically one might expect its nature to be of covalent type. However, the presence of a certain ionic character in its solid cannot be completely ruled out; Or what is similar, assume the absence of Au cation 3+ anion next to O2- .
It may seem contradictory that gold, a noble metal, can rust. Under normal conditions, gold fragments (like the stars in the image below) cannot be oxidized by exposure to oxygen in the atmosphere; However, when irradiated with ultraviolet radiation in the presence of ozone, or 3 , the picture is different.
If gold stars were subjected to these conditions, they would turn a reddish brown, characteristic of Au 2 O 3 .
Other methods of obtaining this oxide would include chemical treatment of said wires; For example, converting the mass of gold into its corresponding chloride, AuCl 3 .
After, AuCl is added to 3 , and the remaining possible gold salts are formed, a strong basic medium is added; And with that, you get the hydrated oxide or hydroxide, Au(OH) 3 . Finally, it is thermally dehydrated to obtain the final compound Au 2 O 3 .
Structure of gold oxide (III)
The crystal structure of gold(III) oxide is shown in the upper image. The arrangement of gold and oxygen atoms in solids is shown as neutral atoms (covalent solids), or ions (ionic solids). Individually, this is sufficient to terminate or keep the Au-O link in any case.
According to the image, it is assumed that the covalent character prevails (which would be logical). For that reason, atoms and bonds are represented with spheres and bars, respectively. The gold spheres correspond to the gold atoms (Au III -O), and the red ones to the oxygen atoms.
If you look carefully, you will see that there are aq units 4 , which are joined by oxygen atoms. Another way to imagine this would be to consider each Au 3+ surrounded by four O2- ; Of course, from an ionic standpoint.
This structure is crystalline because the atoms are ordered to follow the same long-range pattern. Thus, its unitary cell corresponds to the rhombohedral crystalline system (similar to the upper image). Therefore, all Au 2 O 3 could be created if all those regions of the unit cell were distributed in space.
electronic aspect
Gold is a transition metal, and it should be expected that its 5d orbitals interact directly with the 2p orbitals of the oxygen atom. This overlap of their orbitals should theoretically generate a conduction band, which would convert Au 2 O 3 into a solid semiconductor.
Therefore, the exact structure of Au 2 O 3 is even more complicated to take into account.
hydrates
Gold oxide can retain water molecules within its rhombohedral crystals, giving rise to a hydrate. When such hydrates are formed, the structure becomes amorphous, that is, disordered.
The chemical formula for such hydrates can be any of the following, which are not really clear in depth: Au 2 O 3 zH 2 O (z = 1, 2, 3, etc.), Au (OH) 3 , or au x o and (OH) z .
The formula Au(OH) 3 represents an oversimplification of the actual structure of the said hydrates. This is because within the gold hydroxide (III), researchers have also detected the presence of Au 2 O 3 ; And therefore, it makes sense to treat it in isolation as a “simple” transition metal hydroxide.
On the other hand, a solid with the formula Au X O and (OH) z an amorphous structure can be expected; Since, it depends on the coefficients x , and and z , whose variations give rise to all kinds of structures that could hardly exhibit a crystalline pattern.
Property
physical appearance
It is a reddish brown solid.
molecular mass
441.93 g/mol.
density
11.34 g / ml.
Melting point
It melts and decomposes at 160ºC. Therefore it lacks boiling point, so this oxide never reaches boiling point.
Stability
The Au 2 O 3 It is thermodynamically unstable because, as mentioned at the beginning, gold does not oxidize under normal temperature conditions. So it is easily reduced to become noble gold again.
The higher the temperature, the faster the reaction, which is known as thermal decomposition. So, A.U. 2 O 3 at 160 °C it is proposed to produce metallic gold and release molecular oxygen:
2 O 2 O 3 => 4 Au + 3 O 2
A very similar reaction can occur with other compounds that side said reduction. Why the shortage? Because gold returns to gain the electrons that oxygen took away from it; Which is similar to saying that it loses the link with oxygen.
solubility
It is insoluble soluble in water. However, it is soluble in hydrochloric acid and nitric acid, causing the formation of gold chlorides and nitrates.
Glossary
Gold oxide (III) is the name governed by stock nomenclature. There are other ways to mention it:
-Traditional nomenclature: aceric oxide, because the valence 3+ is highest for gold.
-Systematic nomenclature: diro trioxide.
Applications
color of glasses
Its most prominent use is to impart a red color to some materials such as glasses, in addition to imparting some of the properties inherent in gold atoms.
Synthesis of Aurates and Replenishment of Gold
If Au 2 O 3 is added to a medium where it is soluble, and in the presence of metals, after the addition of a strong base, aricetates may precipitate; Which, are formed by AuO ions in the company of 4 – metallic cations.
In addition, A.U. 2 O 3 reacts with ammonia to form a gold-plating compound, Au. 2 O 3 (NH 3 ) 4 . Its name derives from the fact that it is highly explosive.
Handling of Self-Assembled Monolayers
On gold and its oxides, some compounds, such as dialkyl disulfides, RSSRs, are not classified in the same way. When this adsorption occurs, an Au–S bond is spontaneously formed, where the sulfur atom exhibits and defines the chemical characteristics of the said surface depending on the functional group.
RSSR cannot adsorb on Au 2 O 3 , but on the metal gold. Therefore, if the gold surface and its degree of oxidation are modified, as well as the size of the particles or the layers of Au 2 O 3 , a more heterogeneous surface can be designed. This surface au 2 O 3 -AusR interacts with the metallic oxides of some electronic devices, thus developing future slick surfaces.
