Trisulfur
Encyclopedia
The S3 molecule or trisulfur or sulfur trimer or thiozone or triatomic sulfur is an allotrope of sulfur. It occurs as a mixture in liquid and gaseous sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 and also at cryogenic temperatures as a solid. Under standard conditions it is unstable and self reacts to solid sulfur S8. The molecule shape is similar to ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

. S3 is found in sulfur vapour, comprising 10% of vapour species at 713 K (440 °C) and 1333 Pa (10 mmHg). It is cherry red in colour, with a bent structure, similar to ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

, O3.

The molecule has a distance between sulfur atoms of 191.7(1) pm (1.917(1) Å) and angle at the central atom of 117.36(6)°. However cyclic S3, where the sulfur atoms are arranged in an equilateral triangle with three bonds, should in theory be lower in energy than the bent structure actually observed.

The name Thiozone was invented by Hugo Erdmann
Hugo Erdmann
Hugo Wilhelm Traugott Erdmann was the German chemist who discovered, together with his doctoral advisor Jacob Volhard, the Volhard-Erdmann cyclization...

 in 1908 who hypothesized that S3 made up a large proportion of liquid sulfur. However its existence was unproven until the experiments of J. Berkowitz in 1964.
Using mass spectrometry
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...

, he showed that sulfur vapour contains the S3 molecule. Above 1200°C S3 is the second most common molecule after S2 in sulfur gas. In liquid sulfur the molecule is not common until the temperature is high, such as 500°. However small molecules like this contribute to most of the reactivity of liquid sulfur. S3 has an absorption peak of 425 nm with a tail extending into blue light.

S3 can also be made by photolosis of S3Cl2 embedded in a glass or matrix of solid noble gas.

Natural occurrence

It occurs naturally on Io
Io (moon)
Io ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....

 in volcanic emissions. Also S3 is likely to appear in the atmosphere of Venus at 20 to 30 km height, where it is in thermal equilibrium with S2 and S4. The reddish colour of Venus atmosphere at lower levels is likely to be due to S3.

Reactions

S3 reacts with carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 CO to make carbon oxysulfide and S2.

Tungsten and group 8 metal carbonyls, for example iron carbonyl, in theory can replace a carbonyl group with S3.

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

S3 + S2O → S5O (ring)

Radical anion

S3 can form a radical
Radical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...

 anion S3- with an intense blue colour. The ion is also called thiozonide. The gem stone Lapis Lazuli
Lapis lazuli
Lapis lazuli is a relatively rare semi-precious stone that has been prized since antiquity for its intense blue color....

 and the mineral lazurite
Lazurite
Lazurite is a tectosilicate mineral with sulfate, sulfur and chloride with formula: 8[2|]. It is a feldspathoid and a member of the sodalite group. Lazurite crystallizes in the isometric system although well formed crystals are rare. It is usually massive and forms the bulk of the gemstone lapis...

 contain S3- from which ultramarine
Ultramarine
Ultramarine is a blue pigment consisting primarily of a double silicate of aluminium and sodium with some sulfides or sulfates, and occurring in nature as a proximate component of lapis lazuli...

 the natural pigment is derived. International Klein Blue
International Klein Blue
International Klein Blue is a deep blue hue first mixed by the French artist Yves Klein. IKB's visual impact comes from its heavy reliance on Ultramarine, as well as Klein's often thick and textured application of paint to canvas.- History :...

 was developed by Yves Klein
Yves Klein
Yves Klein was a French artist considered an important figure in post-war European art. He is the leading member of the French artistic movement of Nouveau réalisme founded in 1960 by the art critic Pierre Restany...

 also making use of the S3- radical anion. This is isoelectric with the ozonide
Ozonide
Ozonide is an unstable, reactive polyatomic anion O3−, derived from ozone, or an organic compound similar to organic peroxide formed by a reaction of ozone with an unsaturated compound.-Inorganic ozonides:...

 ion. The spectrum of the colour shows a strong absorption band at 610–620 nm or 2.07 ev. The blue colour is due to the C2A2 transition to the X2B1 electronic state in the ion. The Raman frequency is 523 cm−1 and another infrared absorption is at 580 cm−1.

The S3- ion has been shown to be stable in aqueous solution under pressure of 0.5 GPa, 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 S6-) with tetramethylenediamine solvation reacts with acetone or donor solvents to form S3-.

The trisulfur S3- radical
Radical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...

 anion was also made by reducing sulfur gas with Zn+ in a matrix. The material is strongly blue coloured when dry and changes colour to green and yellow in the presence of water at the parts per million level. Another way to make it is with polysulfide dissolved in hexamethylphosphoramide where it gives a blue colour.

Other ways to make thiozonide are by reacting sulfur with slightly dampened magnesium oxide
Magnesium oxide
Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...

.

Raman spectroscopy
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...

 can be used to identify S3-, and it can be used non destructively in paintings. The bands are 549 cm−1 for symmetric stretch, 585 cm−1 for asymmetric stretch, and 259 cm−1 for bending. Natural materials can also contain S2- which has an optical absorption at 390 nm and Raman band at 590 cm−1.

Trisulfide ion

The trisulfide ion, S32- is part of the polysulfide
Polysulfide
Polysulfides are a class of chemical compounds containing chains of sulfur atoms. There are two main classes of polysulfides: anions and organic polysulfides. Anions have the general formula Sn2−. These anions are the conjugate bases of the hydrogen polysulfides H2nSn...

series. The sulfur chain is bent at an angle of 107° 53'. SrS3 has a bond length in the trisulfide ion of 0.205 nm.
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