The gold (III) oxide is an inorganic compound whose chemical formula is AutwoOR3. Theoretically, its nature could be expected to be of the covalent type. However, the presence of a certain ionic character in its solid cannot be completely ruled out; or what is the same, assume the absence of the Au cation3+ next to the anion Otwo-.
It may seem contradictory that gold, being a noble metal, can rust. Under normal conditions, pieces of gold (such as the stars in the image below) cannot be oxidized by contact with oxygen in the atmosphere; however, when irradiated with ultraviolet radiation in the presence of ozone, OR3, the panorama is different.
If gold stars were subjected to these conditions, they would turn a reddish-brown color, characteristic of AutwoOR3.
Other methods to obtain this oxide would imply the chemical treatment of said stars; for example, by converting the mass of gold to its respective chloride, AuCl3.
Then to AuCl3, and the rest of the possible gold salts formed, a strong basic medium is added; and with this, the hydrated oxide or hydroxide is obtained, Au (OH)3. Finally, this last compound is thermally dehydrated to obtain AutwoOR3.
Article index
The upper image shows the crystal structure of gold (III) oxide. The arrangement of the gold and oxygen atoms in the solid is shown, either considering them neutral atoms (covalent solid), or ions (ionic solid). Indifferently, it is enough to remove or place the Au-O links in any case.
According to the image, it is assumed that the covalent character predominates (which would be logical). For that reason, atoms and bonds are shown, represented by spheres and bars, respectively. The golden spheres correspond to the gold atoms (AuIII-O), and the reddish ones to oxygen atoms.
If you look closely you will see that there are AuO units4, which are joined by oxygen atoms. Another way to visualize it would be to consider that each Au3+ is surrounded by four O'stwo-; of course, from an ionic perspective.
This structure is crystalline because the atoms are arranged obeying the same long-range pattern. Thus, its unit cell corresponds to the rhombohedral crystalline system (the same one in the upper image). Therefore, all AutwoOR3 could be constructed if all those spheres of the unit cell were distributed in space.
Gold is a transition metal, and its 5d orbitals are expected to interact directly with the 2p orbitals of the oxygen atom. This overlapping of their orbitals should theoretically generate conduction bands, which would convert AutwoOR3 in a solid semiconductor.
Therefore, the true structure of AutwoOR3 it is even more complex with this in mind.
Gold oxide can retain water molecules within its rhombohedral crystals, giving rise to hydrates. When such hydrates are formed, the structure becomes amorphous, that is, disorderly.
The chemical formula for such hydrates can be any of the following, which in fact are not fully clarified: AutwoOR3∙ zHtwoO (z = 1, 2, 3, etc.), Au (OH)3, or AuxORY(OH)z.
The formula Au (OH)3 represents an oversimplification of the true composition of said hydrates. This is because within the gold (III) hydroxide, researchers have also found the presence of AutwoOR3; and therefore it makes no sense to treat it in isolation as a “simple” transition metal hydroxide.
On the other hand, of a solid with formula AuxORY(OH)z an amorphous structure could be expected; since, it depends on the coefficients x, Y Y z, whose variations would give rise to all kinds of structure that could hardly exhibit a crystalline pattern.
It is a reddish brown solid.
441.93 g / mol.
11.34 g / mL.
Melts and decomposes at 160ºC. Therefore, it lacks a boiling point, so this oxide never reaches a boil..
AUtwoOR3 it is thermodynamically unstable because, as mentioned at the beginning, gold does not tend to oxidize under normal temperature conditions. So it is easily reduced to become the noble gold again.
The higher the temperature, the faster the reaction, which is known as thermal decomposition. Thus, the AutwoOR3 at 160ºC it decomposes to produce metallic gold and release molecular oxygen:
2 AutwoOR3 => 4 Au + 3 Otwo
A very similar reaction can occur with other compounds that promote said reduction. Why reduction? Because gold regains the electrons that oxygen took from it; which is the same as saying that it loses bonds with oxygen.
It is a solid insoluble in water. However, it is soluble in hydrochloric acid and nitric acid, due to the formation of gold chlorides and nitrates..
Gold (III) oxide is the name governed by the stock nomenclature. Other ways to mention it are:
-Traditional nomenclature: auric oxide, because the 3+ valence is the highest for gold.
-Systematic nomenclature: dioro trioxide.
One of its most eminent uses is to add a reddish color to certain materials, such as glass, in addition to conferring certain properties inherent to gold atoms..
If Au is addedtwoOR3 to a medium where it is soluble, and in the presence of metals, aurates can precipitate after the addition of a strong base; which are formed by AuO anions4- in the company of metal cations.
Also, the AutwoOR3 reacts with ammonia to form the fulminant gold compound, AutwoOR3(NH3)4. Its name derives from the fact that it is highly explosive.
Certain compounds, such as dialkyl disulfides, RSSR, are not adsorbed in the same way on gold and its oxide. When this adsorption occurs, an Au-S bond forms spontaneously, where the sulfur atom exhibits and defines the chemical characteristics of said surface depending on the functional group to which it is attached..
RSSRs cannot be adsorbed on AutwoOR3, but yes on metallic gold. Therefore, if the surface of the gold is modified and its degree of oxidation, as well as the size of the particles or layers of AutwoOR3, a more heterogeneous surface can be designed.
This surface AutwoOR3-AuSR interacts with the metal oxides of certain electronic devices, thus developing future smarter surfaces.
Yet No Comments