3D model (JSmol)
|Molar mass||96.198 g/mol|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
3 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 and also at cryogenic temperatures as a solid. Under standard conditions it is unstable and self reacts to solid sulfur cyclooctasulfur. The molecule shape is similar to that of ozone. S
3 is found in sulfur vapour, comprising 10% of vapour species at 713 K (440 °C; 824 °F) and 1,333 Pa (10.00 mmHg; 0.1933 psi). It is cherry red in colour, with a bent structure, similar to ozone, O
3. The bonds between the atoms are not full double bonds (as this would require two fewer electrons, similar to carbon disulfide), and the molecule can be thought of as a resonance between two states, in each of which one of the end atoms has a negative formal charge while the central atom has a positive formal charge, making it valence isoelectronic to ozone.
The molecule has a distance between sulfur atoms of 191.70 ± .01 pm (1.9170 ± 0.0001 Å) and angle at the central atom of ±0.006°. 117.36° However, cyclic S
3, where the sulfur atoms are arranged in an equilateral triangle with three bonds (similar to cyclic ozone), should in theory be lower in energy than the bent structure actually observed.
The name thiozone was invented by Hugo Erdmann in 1908 who hypothesized that S
3 made up 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 S
3 molecule. Above 1,200 °C (2,190 °F) S
3 is the second most common molecule after S
2 in sulfur gas. In liquid sulfur the molecule is not common until the temperature is high, such as 500 °C (932 °F). However, small molecules like this contribute to most of the reactivity of liquid sulfur. S
3 has an absorption peak of with a tail extending into blue light. 425 nm
3 can also be made by photolysis of S
2 embedded in a glass or matrix of solid noble gas.
It occurs naturally on Io in volcanic emissions. Also S
3 is likely to appear in the atmosphere of Venus at heights of 20 to 30 km (12 to 19 mi), where it is in thermal equilibrium with S
2 and S
4. The reddish colour of Venus atmosphere at lower levels is likely to be due to S
Formation of compounds with a defined number of sulfur atoms is possible:
3 + S−
2 → S−
3 can form the radical anion S−
3, which has an intense blue colour. The ion is also called thiozonide, by analogy with the ozonide anion, O−
3. The gemstone lapis lazuli and the mineral lazurite (from which the pigment ultramarine is derived) contain S−
3. International Klein Blue, developed by Yves Klein, also contains the S−
3 radical anion. This is valence isoelectronic with the ozonide ion. The spectrum of the colour shows a strong absorption band at 610–nm or 620 eV. 2.07  The blue colour is due to the C2A2 transition to the X2B1 electronic state in the ion. The Raman frequency is cm−1 and another infrared absorption is at 523 . 580 cm−1
3 ion has been shown to be stable in aqueous solution under pressure of 0.5 GPa (73,000 psi), 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.
3 radical anion was also made by reducing sulfur gas with Zn2+
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.
Raman spectroscopy can be used to identify S−
3, and it can be used non-destructively in paintings. The bands are for symmetric stretch, 549 cm−1 for asymmetric stretch, and 585 cm−1 for bending. 259 cm−1 Natural materials can also contain S−
2 which has an optical absorption at and Raman band at 390 nm. 590 cm−1
The trisulfide ion, S2−
3 is part of the polysulfide series. The sulfur chain is bent at an angle of 107° 53'. SrS
3 has a bond length in the trisulfide ion of . 0.205 nm The bonds are single. It is isoelectronic to sulfur dichloride.
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