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.