Antimony trichloride

Preparation

Antimony trichloride is prepared by reaction of chlorine with antimony, antimony tribromide, antimony trioxide, or antimony trisulfide. It also may be made by treating antimony trioxide with concentrated hydrochloric acid.

Reactions

SbCl₃ is readily hydrolysed and samples of SbCl₃ must be protected from moisture. With a limited amount of water it forms antimony oxychloride releasing hydrogen chloride:

With more water it forms Sb₄O₅Cl₂ which on heating to 460° under argon converts to Sb₈O₁₁Cl_l2.

SbCl₃ readily forms complexes with halides, but the stoichiometries are not a good guide to the composition, for example the (C₅H₅NH)SbCl₄ contains a chain anion with distorted Sb^III octahedra. Similarly the salt (C₄H₉NH₃)₂SbCl₅ contains a polymeric anion of composition [SbCl₅²⁻]_n with distorted octahedral Sb^III.

With nitrogen donor ligands, L, complexes with a stereochemically active lone-pair are formed, for example Ψ-trigonal bipyramidal LSbCl₃ and Ψ-octahedral L₂SbCl₃.

SbCl₃ is only a feeble Lewis base, however some complexes are known for example the carbonyl complexes, Fe(CO)₃(SbCl₃)₂ and Ni(CO)₃SbCl₃.

Structure

In the gas phase SbCl₃ is pyramidal with an Cl-Sb-Cl angle of 97.2° and a bond length of 233 pm. In SbCl₃ each Sb has three Cl atoms at 234 pm showing the persistence of the molecular SbCl₃ unit, however there are a further five neighboring Cl atoms, two at 346 pm, one at 361 pm, and two at 374 pm. These eight atoms can be considered as forming a bicapped trigonal prism. These distances can be contrasted with BiCl₃ which has three near neighbors at 250 pm, with two at 324 pm, and three at a mean of 336 pm. The point to note here is that the all eight close neighbours of Bi are closer than the eight closest neighbours of Sb, demonstrating the tendency for Bi to adopt higher coordination numbers.

Uses

SbCl₃ is a reagent for detecting vitamin A and related carotenoids in the Carr-Price test. The antimony trichloride reacts with the carotenoid to form a blue complex that can be measured by colorimetry.

Antimony trichloride has also been used as an adulterant to enhance the louche effect in absinthe. It has been used in the past to dissolve and remove horn stubs from calves without having to cut them off.

It is also used as a catalyst for polymerization, hydrocracking, and chlorination reactions; as a mordant; and in the production of other antimony salts. Its solution is used as an analytical reagent for chloral, aromatics, and vitamin A.

Appearance in popular culture

In episode 12 of the third season of the popular British program All Creatures Great and Small, several calves died following an episode of nonspecific gastroenteritis, the cause of which was later determined to be ingestion of antimony trichloride present in a solution used to dissolve their horn stubs.