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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 chemist ...
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.


Preparation

Bismuth chloride can be synthesized directly by passing chlorine over bismuth. :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 to bismuth oxide and evaporating the solution. :Bi2O3 + 6 HCl → 2 BiCl3 + 3 H2O Also, the compound can be prepared by dissolving bismuth in concentrated nitric acid and then adding solid
sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
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 ...
readily to bismuth oxychloride, BiOCl: :(aq) + (aq) + (l) ⇌ BiOCl (s) + 2 (aq) This reaction can be reversed by adding an acid, such as hydrochloric acid. 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. Furthermore, the octahedral structure of this coordination complex 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 in
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 and the Mukaiyama aldol reaction. The addition of other metal iodides increases its catalytic activity.


References

{{DEFAULTSORT:Bismuth Chloride Bismuth compounds Chlorides Metal halides