The lower sulfur oxides are a group of chemical compounds consisting of :
- SO, sulfur monoxide and its dimer S2O2
- S2O
- sulfur monoxides, SnO, based on cyclic Sn rings where n is 5-10
- S7O2
- polymeric sulfur oxides, sometimes termed PSO's
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 Jupiter's 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 stable 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 trisulfur, 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
- 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.
- SnO
- A number of monoxides SnO are known where n= 5-10, where the oxygen is bonded to one member of the Sn sulfur ring. 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 sulfur oxides
- These have been studied to determine whether they are a factor in the observed colour of Io.