Stibine

Stibine is the chemical compound with the formula SbH₃. This colourless gas is the principal covalent hydride of antimony and a heavy analogue of ammonia. The molecule is pyramidal with H–Sb–H angles of 91.7° and Sb–H distances of 1.707 Å (170.7 pm).

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Preparation and properties

SbH₃ is generally prepared by the reaction of Sb³⁺ sources with H⁻ equivalents:^[1]

2 Sb₂O₃ + 3 LiAlH₄ → 4 SbH₃ + 1.5 Li₂O + 1.5 Al₂O₃

SbCl₃ + 3/4 NaBH₄ → SbH₃ + 0.75 NaCl + 0.75 BCl₃

Alternatively, sources of Sb³⁻ react with protonic reagents (even water) to also produce this unstable gas:

Na₃Sb + 3 H₂O → SbH₃ + 3 NaOH

The chemical properties of SbH₃ resemble those for AsH₃.^[2] Typical for a heavy hydride (e.g. AsH₃, H₂Te, SnH₄), SbH₃ is unstable with respect to its elements. The gas decomposes slowly at room temperature but rapidly at 200 °C:

2 SbH₃ → 3 H₂ + 2 Sb

The decomposition is autocatalytic and can be explosive.

SbH₃ is readily oxidized by O₂ or even air:

2 SbH₃ + 3 O₂ → Sb₂O₃ + 3 H₂O

SbH₃ exhibits no basicity, but it can be deprotonated:

SbH₃ + NaNH₂ → NaSbH₂ + NH₃

Uses

Stibine is used in the semiconductor industry to dope small quantities of antimony via the process of chemical vapour deposition (CVD). Reports claim the use of SbH₃ as a fumigant but its instability and awkward preparation contrast with the more conventional fumigant PH₃.

History

As stibine (SbH₃) is very similar to arsine (AsH₃), it is also detected by the Marsh test. This sensitive test detects arsine generated in the presence of arsenic.^[2] This procedure, developed around 1836 by James Marsh, is based upon treating a sample with arsenic-free zinc and dilute sulfuric acid: if the sample contains arsenic, gaseous arsine will form. The gas is swept into a glass tube and decomposed by means of heating around 250–300 °C. The presence of arsenic is indicated by formation of a deposit in the heated part of the equipment. The formation of a black mirror deposit in the cool part of the equipment indicates the presence of antimony.

In 1837 Lewis Thomson and Pfaff independently discovered stibine. It took some time before the properties of the toxic case could be determined, partly because a suitable synthesis was not available. In 1876 Francis Jones tested several synthesis methods,^[3] but it was not before 1901 when Alfred Stock determined most of the properties of stibine.^[4][5]

Safety

SbH₃ is an unstable flammable gas. It is highly toxic, with an LC50 of 100 ppm in mice. Fortunately, SbH₃ is so unstable that it is rarely encountered outside of laboratories.

Toxicology

For the toxicology of other antimony compounds, see Antimony trioxide.

The toxicity of stibine is distinct from that of other antimony compounds, but similar to that of arsine.^[6] Stibine binds to the haemoglobin of red blood cells, causing them to be destroyed by the body. Most cases of stibine poisoning have been accompanied by arsine poisoning, although animal studies indicate that their toxicities are equivalent. The first signs of exposure, which can take several hours to become apparent, are headaches, vertigo and nausea, followed by the syptoms of hemolytic anemia (high levels of unconjugated bilirubin), hemoglobinuria and nephropathy.

References

1. ^ Bellama, J. M.; MacDiarmid, A. G. (1968). "Synthesis of the Hydrides of Germanium, Phosphorus, Arsenic, and Antimony by the Solid-Phase Reaction of the Corresponding Oxide with Lithium Aluminum Hydride". Inorg. Chem. 7: 2070–2. doi:10.1021/ic50068a024.
2. ^ ^{a b} Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001
3. ^ Francis Jones (1876). "On stibine". Journal of the Chemical Society 29 (2): 641. doi:10.1039/JS8762900641.
4. ^ Alfred Stock, Walther Doht (1901). "Die Reindarstellung des Antimonwasserstoffes". Berichte der deutschen chemischen Gesellschaft 34 (2): 2339-2344. doi:10.1002/cber.190103402166.
5. ^ Alfred Stock, Oskar Guttmann (1904). "Ueber den Antimonwasserstoff und das gelbe Antimon". Berichte der deutschen chemischen Gesellschaft 37 (1): 885-900. doi:10.1002/cber.190403701148.
6. ^ Institut national de recherche et de sécurité (INRS), Fiche toxicologique n° 202 : Trihydrure d'antimoine, 1992.