Bismuthine

Bismuthine is the chemical compound with the formula BiH₃. As the heaviest analogue of ammonia, BiH₃ is unstable, decomposing to bismuth metal well below 0 °C. In fact, the compound has only been characterized (by infra-red spectroscopy and microwave spectroscopy) as a component of a mixture. This compound is also predicted to have a pyramidal structure with H-Bi-H angles of 90°. Bismuthines also describes a family of organobismuth(III) species; for example Bi(CH₃)₃ is trimethylbismuthine.

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Preparation and properties

BiH₃ is prepared by the redistribution of methylbismuthine BiH₂Me:^[1]

3 BiH₂Me → 2 BiH₃ + BiMe₃

The required BiH₂Me, which is also thermally unstable, is generated by reduction of methylbismuth dichloride, BiCl₂Me with LiAlH₄.^[2]

As suggested by the behavior of SbH₃, BiH₃ is unstable with respect to its elements. The gas decomposes according to the following equation:

2 BiH₃ → 3 H₂ + 2 Bi

ΔH_f'^o_gas = −278 kJ/mol

The methodology used for detection of arsenic ("Marsh Test") can also be used to detect BiH₃. This test relies on the thermal decomposition of these trihydrides to the metallic mirrors of metallic As, Sb, and Bi. These deposits can be further distinguished by their distinctive solubility characteristics: As dissolves in NaOCl, Sb dissolves in ammonium polysulfide, and Bi resists both reagents.^[1]

Uses and safety considerations

The low stability of BiH₃ preclude significant hazards and technical applications.

References

1. ^ ^{a b} Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001.ISBN 0-12-352651-5.
2. ^ Jerzembeck, W.; Bürger, H.; Constantin, L.; Margulès, L.; Demaison, J.; Breidung, J.; Thiel, W. "Bismuthine BiH₃: Fact or Fiction? High-Resolution Infrared, Millimeter-Wave, and Ab Initio Studies" Angewandte Chemie International Edition 2002, Volume 41, pages 2550-2552. doi:10.1002/1521-3773