Disulfur dioxide, dimeric sulfur monoxide or SO dimer is an oxide of sulfur with the formula S2O2.[2] The solid is unstable with a lifetime of a few seconds at room temperature.[3]
Names | |
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Other names
disulfur(II)oxide
SO dimer | |
Identifiers | |
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3D model (JSmol)
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PubChem CID
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Properties | |
S2O2 | |
Molar mass | 96.1299 g/mol |
Appearance | gas |
Structure | |
bent | |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards
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toxic |
Related compounds | |
Related compounds
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tetrasulfur SO, S3O S2O |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references
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Disulfur dioxide adopts a cis planar structure with C2v symmetry. The S−O bond length is 145.8 pm, shorter than in sulfur monoxide. The S−S bond length is 202.45 pm and the O−S−S angle is 112.7°. S2O2 has a dipole moment of 3.17 D.[4] It is an asymmetric top molecule.[1][5]
Sulfur monoxide (SO) converts to disulfur dioxide (S2O2) spontaneously and reversibly.[4] So the substance can be generated by methods that produce sulfur monoxide. Disulfur dioxide has also been formed by an electric discharge in sulfur dioxide.[5] Another laboratory procedure is to react oxygen atoms with carbonyl sulfide or carbon disulfide vapour.[6]
Although most forms of elemental sulfur (S8 and other rings and chains) do not combine with SO2, atomic sulfur does so to form sulfur monoxide, which dimerizes:[7]
Disulfur dioxide is also produced upon a microwave discharge in sulfur dioxide diluted in helium.[8] At a pressure of 0.1 mmHg (13 Pa), five percent of the result is S2O2.[9]
Disulfur dioxide is formed transiently when hydrogen sulfide and oxygen undergo flash photolysis.[10]
The ionization energy of disulfur dioxide is 9.93±0.02 eV.[6]
Disulfur dioxide absorbs at 320–400 nm, as observed of the Venusian atmosphere,[11] and is believed to have contributed to the greenhouse effect on that planet.[12]
Although disulfur dioxide exists in equilibrium with sulfur monoxide, it also reacts with sulfur monoxide to form sulfur dioxide and disulfur monoxide.[8][13]
Decomposition of S2O2 proceeds via the following disproportionation reaction:
S2O2 can be a ligand with transition metals. It binds in the η2-S–S position with both sulfur atoms linked to the metal atom.[14] This was first shown in 2003. The bis(trimethylphosphine) thiirane S-oxide complex of platinum, when heated in toluene at 110 °C loses ethylene, and forms a complex with S2O2: (Ph3P)2Pt(S2O2).[15] Iridium atoms can also form a complex: cis-[(dppe)2IrS2]Cl with sodium periodate oxidizes to [(dppe)2IrS2O] and then to [(dppe)2IrS2O2], with dppe being 1,2-bis(diphenylphosphino)ethane.[16][17] This substance has the S2O2 in a cis position. The same conditions can make a trans complex, but this contains two separate SO radicals instead. The iridium complex can be decomposed with triphenylphosphine to form triphenylphosphine oxide and triphenylphosphine sulfide.[16]
The S
2O−
2 radical anion has been observed in the gas phase. It may adopt a trigonal shape akin to SO3.[18]
Transition | Frequency (MHz)[5] |
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21,1−20,2 | 11013.840 |
41,3−40,4 | 14081.640 |
11,1−00,0 | 15717.946 |
40,4−31,3 | 16714.167 |
31,3−20,2 | 26342.817 |
42,2−41,3 | 26553.915 |
22,0−21,1 | 28493.046 |
60,6−51,5 | 30629.283 |
52,4−51,5 | 35295.199 |
51,5−40,4 | 35794.527 |
There is some evidence that disulfur dioxide may be a small component in the atmosphere of Venus, and that it may substantially contribute of the planet's severe greenhouse effect.[11] It is not found in any substantive quantity in Earth's atmosphere.