Draft:Bismuthyl (ion)

Bismuthyl — inorganic oxygen-containing radical, a singly charged ion with the chemical formula BiO$+$, is an oxycation of bismuth in the +3 oxidation state. Most often it is formed during the hydrolysis of trivalent bismuth salts, primarily nitrate, chloride and other halides. In chemical compounds, bismuthyl plays the role of a monovalent cation.

In inorganic chemistry bismuthyl has been used to describe compounds such as BiOCl which were assumed to contain the diatomic bismuthyl, BiO$+$, cation, that was also presumed to exist in aqueous solution.

This diatomic ion is not now believed to exist. Unlike other inorganic radicals such as hydroxyl, carbonyl, chromyl, uranyl or vanadyl, according to the current IUPAC rules, names such as bismuthyl and antimonyl (stibil) for BiO$+$ and SbO$+$ are not recommended, since individual molecules of these groups do not actually contain, and their presence in compounds preferably referred to as oxides. However, the latter position remains controversial. For example, to this day the Russian school of inorganic chemistry still operates with bismuthyl and stibil (antimonyl) cations as actually existing radicals.

In the history of chemistry
Until the last quarter of the 20th century, the real existence of the bismuthyl ion was not in doubt; it was fully present in all reference books and manuals on inorganic chemistry, including German and English ones. The most famous compound of this class was considered bismuthyl chloride, the chemical properties of which were studied in detail and were considered titular for all other bismuth compounds. In addition, the compound with the calculation formula BiOCl exists in nature in the form of bismoclitea, one of the secondary metamorphosed minerals from the class of halides.

In the fundamental three-volume book “Modern Inorganic Chemistry” by Nobel laureate Frank Cotton and Geoffrey Wilkinson, summarizing the latest achievements of science in the first half of the 20th century, the real existence of the bismuthyl cation is not only not questioned, but is not even discussed in any detail. This inorganic radical is mentioned without further explanation and is by default considered a legacy of the fundamental corpus of inorganic chemistry of the 19th century. First of all, the authors note that of the entire group of pnictogens, only bismuth has a truly extensive and detailed cation chemistry. According to the authors, aqueous solutions of bismuth salts contain well-defined hydrated cations. Moreover, bismuthyl in the newest version at that time also acquires quasi-polymeric properties, connecting into chains or hexagons. For example, in neutral perchlorate solutions the main ions are [Bi6O6]6+ or its hydrated form [Bi6(OH)12]6+, and at higher pH values [Bi6O6(OH)3]3+ are formed.

Chemical properties
The classic method for obtaining bismuthyl salts was the treatment of bismuth oxide with nitric acid. This reaction produces bismuthyl salts such as BiO(NO3 and Bi2O2(OH)(NO3) as end products. The same bismuthyl salts precipitate when strongly acidic solutions of various bismuth compounds are diluted.

The formation of bismuthyl was also considered to be a process that constantly occurs as a result of hydrolysis. Thus, bismuth nitrate, Bi(NO 3 ) 3 • 5H 2 0, crystallizes from a solution resulting from the reaction of bismuth with nitric acid. It dissolves in a small amount of water acidified with nitric acid. However, when the solution is diluted with larger quantities of water, hydrolysis occurs and basic salts precipitate, the composition of which depends on the conditions. A salt of the composition BiONO 3 is often formed.

Bismuthyl chloride (BiOCl) is readily soluble in hydrochloric acid. Moreover, this process, like nitrate, proceeds through a reversible reaction; a shift of the reaction to the left or right also occurs along the line of hydrolysis, depending on the relative amount of water and the (residual) hydrochloric acid present. Adding water to a slightly acidic solution of ВіСl$3$ immediately causes the appearance of a white precipitate of basic bismuth chloride, BiOCl. When hydrochloric acid is added, the precipitate dissolves again, but it immediately falls out when more water is added. All other bismuth compounds behave in aqueous solutions similarly to chloride.

At elevated temperatures, the vapors of the metal combine rapidly with oxygen, forming the yellow trioxide, Bismuth(III) oxide. When molten, at temperatures above 710 °C, this oxide corrodes any metal oxide and even platinum. On reaction with a base, it forms two series of oxyanions:, which is polymeric and forms linear chains, and. The anion in is a cubic octameric anion,, whereas the anion in  is tetrameric.

In addition to bismuthyl itself, thiocompounds corresponding to bismuthyl salts are also considered indicative for the chemistry of bismuth, for example, gray thiobismuthyl chloride with the formula BiSCl and others similar to it. These substances, unlike bismuthyl salts, are very stable with respect to water, and can be easily prepared by the action of hydrogen sulfide gas on the corresponding bismuth trihalide.