# Stibine

Stibine (IUPAC name: stibane) is a chemical compound with the formula SbH$_3$. A pnictogen hydride, this colourless, highly toxic 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 170.7 pm (1.707 Å). The smell of this compound from usual sources (like from reduction of antimony compounds) is reminiscent of arsine, i.e. garlic-like.

## Preparation

SbH$_3$ is generally prepared by the reaction of Sb$^{3+}$ sources with H− equivalents:
    2 Sb$_2$O$_3$ + 3 LiAlH$_4$ → 4 SbH$_3$ + 1.5 Li$_2$O + 1.5 Al$_2$O$_3$
    4 SbCl$_3$ + 3 NaBH$_4$ → 4 SbH$_3$ + 3 NaCl + 3 BCl$_3$
Alternatively, sources of Sb$^{3−}$ react with protonic reagents (even water) to also produce this unstable gas:
    Na$_3$Sb + 3 H$_2$O → SbH$_3$ + 3 NaOH

## Properties

The chemical properties of SbH$_3$ resemble those for AsH$_3$. Typical for a heavy hydride (e.g. AsH$_3$, H$_2$Te, SnH$_4$), SbH$_3$ is unstable with respect to its elements. The gas decomposes slowly at room temperature but rapidly at 200 °C:
       2 SbH$_3$ → 3 H$_2$ + 2 Sb
The decomposition is autocatalytic and can be explosive.
SbH$_3$ is readily oxidized by O$_2$ or even air:
       2 SbH$_3$ + 3 O$_2$ → Sb$_2$O$_3$ + 3 H$_2$O
SbH$_3$ exhibits no basicity, but it can be deprotonated:
       SbH$_3$ + NaNH$_2$ → NaSbH$_2$ + NH$_3$
The salt NaSbH$_2$ is called sodium stibinide, and contains the stibinide anion SbH−2.

## Uses

Stibine is used in the semiconductor industry to dope silicon with small quantities of antimony via the process of chemical vapour deposition (CVD). It has also been used as a silicon dopant in epitaxial layers. Reports claim the use of SbH$_3$ as a fumigant but its instability and awkward preparation contrast with the more conventional fumigant phosphine.

## History

As stibine (SbH$_3$) is similar to arsine (AsH$_3$); it is also detected by the Marsh test. This sensitive test detects arsine generated in the presence of arsenic. This procedure, developed circa 1836 by James Marsh, treats 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 gas could be determined, partly because a suitable synthesis was not available. In 1876 Francis Jones tested several synthesis methods, but it was not before 1901 when Alfred Stock determined most of the properties of stibine.

## Safety

SbH$_3$ is an unstable flammable gas. It is highly toxic, with an LC50 of 100 ppm in mice.

## Toxicology

The toxicity of stibine is distinct from that of other antimony compounds, but similar to that of arsine. 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 symptoms of hemolytic anemia (high levels of unconjugated bilirubin), hemoglobinuria, and nephropathy.