Trisulfur

The molecule, known as trisulfur, sulfur trimer, thiozone, or triatomic sulfur, is a cherry-red allotrope of sulfur. It comprises about 10% of vaporised sulfur at and . It has been observed at cryogenic temperatures as a solid. Under ordinary conditions it converts to cyclooctasulfur.

:

Structure and bonding

In terms of structure and bonding and ozone () are similar. Both adopt bent structures and are diamagnetic. Although represented with S=S double bonds, the bonding situation is more complex.

The S–S distances are equivalent and are , and with an angle at the central atom of . However, cyclic , where the sulfur atoms are arranged in an equilateral triangle with three single bonds (similar to cyclic ozone and cyclopropane), is calculated to be lower in energy than the bent structure experimentally observed. A similar structure has been predicted for ozone, but has not been observed.

The name thiozone was invented by Hugo Erdmann in 1908 who hypothesized that comprises a large proportion of liquid sulfur. However its existence was unproven until the experiments of J. Berkowitz in 1964. Using mass spectrometry, he showed that sulfur vapour contains the molecule. Above is the second most common molecule after in gaseous sulfur. In liquid sulfur the molecule is not common until the temperature is high, such as . However, small molecules like this contribute to most of the reactivity of liquid sulfur. has an absorption peak of (violet) with a tail extending into blue light.

can also be generated by photolysis of embedded in a glass or matrix of solid noble gas.

Natural occurrence

occurs naturally on Io in volcanic emissions. is also likely to appear in the atmosphere of Venus at heights of 20 to 30 km, where it is in thermal equilibrium with and . The reddish colour of Venus' atmosphere at lower levels is likely to be due to .

Reactions

reacts with carbon monoxide to make carbonyl sulfide and .

Formation of compounds with a defined number of sulfur atoms is possible:

: (cyclic)

Radical anion

Although is elusive under ordinary conditions, the intensely blue radical anion is abundant. The anion is sometimes called thiozonide, by analogy with the ozonide anion, , to which it is valence isoelectronic. The preferred IUPAC name is trisulfanidylo. The gemstone lapis lazuli and the mineral lazurite (from which the pigment ultramarine is derived) contain . International Klein Blue, developed by Yves Klein, also contains the radical anion. The blue colour is due to the C²A₂ transition to the X²B₁ electronic state in the ion, causing a strong absorption band at 610– or (in the orange region of the visible spectrum). The Raman frequency is and another infrared absorption is at .

The ion has been shown to be stable in aqueous solution under a pressure of , and is expected to occur naturally at depth in the Earth's crust where subduction or high pressure metamorphism occurs. This ion is probably important in movement of copper and gold in hydrothermal fluids.

Lithium hexasulfide (which contains , another polysulfide radical anion) with tetramethylenediamine solvation dissociates acetone and related donor solvents to .

The radical anion was also made by reducing gaseous sulfur with in a matrix. The material is strongly blue-coloured when dry and changes colour to green and yellow in the presence of trace amounts of water. Another way to make it is with polysulfide dissolved in hexamethylphosphoramide where it gives a blue colour.

Other methods of production of include reacting sulfur with partially hydroxylated magnesium oxide at 400 °C.

Raman spectroscopy can be used to identify , and it can be used non-destructively in paintings. The bands are for symmetric stretch, for asymmetric stretch, and for bending. Natural materials can also contain which has an optical absorption at and Raman band at .

Trisulfide ion

The trisulfide ion, is part of the polysulfide series. The sulfur chain is bent at an angle of 107.88°. Strontium trisulfide () has a S–S bond length of . The bonds are single. It is isoelectronic to sulfur dichloride.

References

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{{Triatomic elements

Allotropes of sulfur
Homonuclear triatomic molecules
Gases with color