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Lower sulfur oxides

The lower sulfur oxides are a group of chemical compounds consisting of:

  • SO, sulfur monoxide and its dimer S2O2
  • S2O
  • cyclic sulfur monoxides, SnO where n is 5-10
  • S7O2
  • polymeric oxides, polysulfuroxides sometimes termed PSO's

In these the average oxidation state of sulfur is 2 or less. Interest in the lower sulfur oxides has increased because of the need to understand terrestrial atmospheric sulfur pollution and the finding that the extraterrestrial atmospheres of Io, one of Jupiters moons, and Venus contain significant amounts of sulfur oxides. Some compounds reported by early workers such as the blue "sesquioxide", S2O3, formed by dissolving sulfur in liquid SO3 appears to be a mixture of polysulfate salts of the S42+ and S82+ ions.

Sulfur monoxide, monomer (SO) and dimer (S2O2)
These are unstable molecules that have been trapped at low temperature (see sulfur monoxide article).
Disulfur monoxide, S2O
S2O has a non linear structure, like sulfur dioxide, SO2, ozone, O3 and S3. The S-S bond is 188.4pm, the S-O bond is 146.5pm and the SSO angle is 117.88. The two dipole moment components are μa = 0.875D and μb = 1.18D[1]
Trisulfur monoxide, S3O
This unstable neutral molecule has been found in the gas phase using neutralization-reionization mass spectrometry. Both ring and chain structures were found.[2]
A number of cyclic monoxides SnO are known where n= 5-10. They can be prepared by oxidising the related cyclo-Sn elemental sulfur rings (these are allotropes of sulfur) with trifluoroperoxoacetic acid, CF3C(O)OOH. The compounds are all dark coloured and decompose to give sulfur and sulfur dioxide.
S6O2, S7O2
S6O2 and S7O2 can be prepared by oxidising cyclo-S6 and cyclo-S7 respectively, with trifluoroperoxoacetic acid, although crystalline S6O2 has not been isolated.
Polymeric sulfuroxides
These have been studied to determine whether they are a factor in the observed colour of Io.[3]


Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. 

  1. ^ Meschi, D.J.; Myers R.J. (1959). "The microwave spectrum, structure, and dipole moment of disulfur monoxide". Journal of Molecular Spectroscopy 3 (1-6): 405-416. doi:10.1016/0022-2852(59)90036-0.
  2. ^ de Petris, G; Rosi M Troiani A (2006). "S3O and S3O+ in the gas phase: ring and open-chain structures". Chem. Commun: 4416 - 4418. doi:10.1039/b609646h.
  3. ^ Baklouti D., D; Schmitt, B.; Brissaud, O. (11 2004). "Infrared study of lower sulfur oxides on Io's surface". Bulletin of the American Astronomical Society Chem. Commun 36: 1099.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lower_sulfur_oxides". A list of authors is available in Wikipedia.
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