Bismuth chloride (or butter of bismuth) is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistr ...

with the chemical formula BiCl₃. It is a covalent compound and is the common source of the Bi³⁺ ion. In the gas phase and in the crystal, the species adopts a pyramidal structure, in accord with

VSEPR theory Valence shell electron pair repulsion (VSEPR) theory ( , ), is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. It is also named the Gillespie-Nyholm th ...

Preparation

Bismuth chloride can be synthesized directly by passing

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is ...

over

bismuth Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs na ...

. :2 Bi + 3 Cl₂ → 2 BiCl₃ or by dissolving bismuth metal in aqua regia, evaporating the mixture to give BiCl₃·2H₂O, which can be distilled to form the anhydrous trichloride. Alternatively, it may be prepared by adding

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digestiv ...

bismuth oxide Bismuth(III) oxide is perhaps the most industrially important compound of bismuth. It is also a common starting point for bismuth chemistry. It is found naturally as the mineral bismite (monoclinic) and sphaerobismoite (tetragonal, much more rare) ...

and evaporating the solution. :Bi₂O₃ + 6 HCl → 2 BiCl₃ + 3 H₂O Also, the compound can be prepared by dissolving bismuth in concentrated

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitric ...

and then adding solid sodium chloride into this solution. :Bi + 6 HNO₃ → Bi(NO₃)₃ + 3 H₂O + 3 NO₂ :Bi(NO₃)₃ + 3 NaCl → BiCl₃ + 3 NaNO₃

Structure

In the gas phase BiCl₃ is pyramidal with a Cl–Bi–Cl angle of 97.5° and a bond length of 242 pm. In the solid state, each Bi atom has three near neighbors at 250 pm, two at 324 pm and three at a mean of 336 pm,Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition, pp. 879–884, Oxford Science Publications, the image above highlights the three closest neighbours. This structure is similar to that of AsCl₃, AsBr₃, SbCl₃ and SbBr₃.

Chemistry

Bismuth chloride is

hydrolyzed Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis i ...

readily to

bismuth oxychloride Bismuth oxychloride is an inorganic compound of bismuth with the formula Bi O Cl. It is a lustrous white solid used since antiquity, notably in ancient Egypt. Light wave interference from its plate-like structure gives a pearly iridescent light ...

, BiOCl: :(aq) + (aq) + (l) ⇌ BiOCl (s) + 2 (aq) This reaction can be reversed by adding an acid, such as

. Reaction of solid BiCl₃ with water vapour below 50 °C has been shown to produce the intermediate monohydrate, BiCl₃·H₂O. Bismuth chloride is an oxidizing agent, being readily reduced to metallic bismuth by reducing agents.

Chloro complexes

In contrast to the usual expectation by consistency with periodic trends, BiCl₃ is a

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

, forming a variety of chloro complexes such as iCl₆sup>3− that strongly violates the

octet rule The octet rule is a chemical rule of thumb that reflects the theory that main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The rul ...

. Furthermore, the octahedral structure of this

coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

does not follow the predictions of VSEPR theory, since the

lone pair In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lone ...

on bismuth is unexpectedly stereochemically inactive. The dianionic complex iCl₅sup>2− does however adopt the expected square pyramidal structure.

Organic catalysis

Bismuth chloride is used as a

catalyst Catalysis () is the process of increasing the reaction rate, rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the ...

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. In particular, it catalyzes the

Michael reaction In organic chemistry, the Michael reaction or Michael addition is a reaction between a Michael donor (an enolate or other nucleophile) and a Michael acceptor (usually an α,β-unsaturated carbonyl) to produce a Michael adduct by creating a carbon ...

and the

Mukaiyama aldol reaction The Mukaiyama aldol addition is an organic reaction and a type of aldol reaction between a silyl enol ether and an aldehyde or formate. The reaction was discovered by Teruaki Mukaiyama (1927–2018) in 1973. His choice of reactants allows for ...

. The addition of other metal

iodide An iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate. Worldwide, iodine defic ...

s increases its catalytic activity.

References

{{DEFAULTSORT:Bismuth Chloride Bismuth compounds Chlorides Metal halides