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Bismuth forms mainly trivalent and a few pentavalent compounds. Many of its chemical properties are similar to those of arsenic and antimony, although much less toxic.[1]
Bismuth forms mainly trivalent and a few pentavalent compounds. Many of its chemical properties are similar to those of arsenic and antimony, although much less toxic.[1]
At elevated temperatures, vaporized bismuth metal and oxygen combine into the yellow trioxide, Bi
2O
3.[2][3] At temperatures above 710 °C, this (molten) oxide corrodes all known oxides and even platinum.[4] It forms two series of oxyanions in basic conditions: linear, chain-polymeric BiO−
2; and cubic BiO3−
3. In Li
3BiO
3, the anion forms the octamer Bi
8O24−
24; in Na
3BiO
3, the tetramer.[5]
The dark red bismuth(V) oxide, Bi
2O
5, is unstable, liberating O
2 gas upon heating.[6] The compound NaBiO3 is a strong oxidant.[7]
Bismuth sulfide, Bi
2S
3, occurs naturally in bismuth ores,[8] but can be synthesized from molten bismuth and sulfur.[9]
In oxidation state +3, bismuth forms salts with all the halogens: BiF
3, BiCl
3, BiBr
3, and BiI
3. All hydrolyze in water except BiF
3.[5] Bismuth(III) chloride reacts with hydrogen chloride in ether solution to produce the acid HBiCl
4.[10]
The oxidation state +5 is less frequently encountered. One such compound is the powerful oxidant and fluorinator, BiF
5. It is also a strong fluoride acceptor, forming the XeF+
3 cation from xenon tetrafluoride:[10]
The low-oxidation-state bismuth halides adopt unusual cluster structures. What was originally thought bismuth(I) chloride, BiCl, is in fact a lattice of Bi5+
9 cations and BiCl2−
5 and Bi
2Cl2−
8 anions.[5][11] The Bi5+
9 cation has a distorted tricapped trigonal prismatic molecular geometry and is also found in Bi
10Hf
3Cl
18, which is prepared by reducing a mixture of hafnium(IV) chloride and bismuth chloride with elemental bismuth, having the structure [Bi+
] [Bi5+
9] [HfCl2−
6]
3.[5]: 50 Other polyatomic bismuth cations are also known, such as Bi2+
8, found in Bi
8(AlCl
4)
2.[11]
There is a true monoiodide, BiI, which contains chains of Bi
4I
4 units. BiI decomposes upon heating to the triiodide, BiI
3, and elemental bismuth.[5]
Bismuth forms at least two "monobromides": one isostructural to "BiCl"[citation needed] and one isostructural to Bi
4I
4.[5]
In aqueous solution, the Bi3+
ion is solvated to form the aqua ion Bi(H
2O)3+
8 in strongly acidic conditions.[12] At pH > 0 polynuclear species exist, the most important of which is believed to be the octahedral complex [Bi
6O
4(OH)
4]6+
.[13]
Bismuth oxychloride (BiOCl) and bismuth oxynitrate (BiONO3) stoichiometrically appear simple anionic salts of the bismuthyl(III) cation (BiO+), which commonly occurs in aqueous bismuth compounds. However, in the case of BiOCl, the salt crystal forms alternating plates of Bi, O, and Cl atoms. Each oxygen coordinates with four bismuth atoms in the adjacent plane.[14]
Unlike the lighter pnictogens nitrogen, phosphorus, and arsenic, but similar to antimony, bismuth does not form a stable hydride. Bismuth hydride, bismuthine (BiH
3), is an endothermic compound that spontaneously decomposes at room temperature. It is stable only below −60 °C.[5] Bismuthides are intermetallic compounds between bismuth and other metals.[15]
In 2014 researchers discovered that sodium bismuthide admits bulk 3D Dirac fermions. As a topological Dirac semi-metal, it is a three-dimensional counterpart to graphene with similar electron mobility and velocity. While sodium bismuthide (Na
3Bi) is too unstable to be used in devices without packaging, it may offer distinct efficiency and fabrication advantages over planar graphene in semiconductor and spintronics applications.[16][17]
