Disulfur dioxide, dimeric sulfur monoxide or SO dimer is an

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

with the formula S₂O₂. The solid is unstable with a lifetime of a few seconds at room temperature.

Structure

Disulfur dioxide adopts a ''cis'' planar structure with ''C''_2v

symmetry Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...

. The S−O bond length is 145.8 pm, shorter than in

sulfur monoxide Sulfur monoxide is an inorganic compound with formula . It is only found as a dilute gas phase. When concentrated or condensed, it converts to S2O2 (disulfur dioxide). It has been detected in space but is rarely encountered intact otherwise. Str ...

. 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. It is an asymmetric top molecule.

Formation

Sulfur monoxide Sulfur monoxide is an inorganic compound with formula . It is only found as a dilute gas phase. When concentrated or condensed, it converts to S2O2 (disulfur dioxide). It has been detected in space but is rarely encountered intact otherwise. Str ...

(SO) converts to disulfur dioxide (S₂O₂) spontaneously and reversibly. 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 Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...

. Another laboratory procedure is to react oxygen atoms with

carbonyl sulfide Carbonyl sulfide is the chemical compound with the linear formula OCS. It is a colorless flammable gas with an unpleasant odor. It is a linear molecule consisting of a carbonyl group double bonded to a sulfur atom. Carbonyl sulfide can be conside ...

carbon disulfide Carbon disulfide (also spelled as carbon disulphide) is a neurotoxic, colorless, volatile liquid with the formula and structure . The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non ...

vapour. 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: :S + SO₂ → S₂O₂ ⇌ 2 SO Disulfur dioxide is also produced upon a microwave discharge in sulfur dioxide diluted in

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

. At a pressure of , five percent of the result is S₂O₂. Disulfur dioxide is formed transiently when

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...

and oxygen undergo

flash photolysis Flash photolysis is a pump-probe laboratory technique, in which a sample is first excited by a strong pulse of light from a pulsed laser of nanosecond, picosecond, or femtosecond pulse width or by another short-pulse light source such as a fla ...

Properties

The

ionization energy Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...

of disulfur dioxide is . Disulfur dioxide absorbs at 320–400 nm, as observed of the

Venusian atmosphere The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of Supercritical carbon dioxide, supercritical carbon dioxide and is much denser and hotter than atmosphere of Earth, that of Earth. The temperature at the ...

, and is believed to have contributed to the

greenhouse effect The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...

on that planet.

Reactions

Although disulfur dioxide exists in equilibrium with

, it also reacts with sulfur monoxide to form

and

disulfur monoxide Disulfur monoxide or sulfur suboxide is an inorganic compound with formula S2O, one of the lower sulfur oxides. It is a colourless gas and condenses to give a roughly dark red coloured solid that is unstable at room temperature. occurs rarely in ...

Complexes

S₂O₂ can be a

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

with transition metals. It binds in the ''η''²-S–S position with both sulfur atoms linked to the metal atom. This was first shown in 2003. The bis(trimethylphosphine) thiirane ''S''-oxide complex of

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platinu ...

, when heated in

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) at ...

at 110 °C loses

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene i ...

, and forms a complex with S₂O₂: (Ph₃P)₂Pt(S₂O₂).

Iridium Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...

atoms can also form a complex: ''cis''- dppe)₂IrS₂l with

sodium periodate Sodium periodate is an inorganic salt, composed of a sodium cation and the periodate anion. It may also be regarded as the sodium salt of periodic acid. Like many periodates, it can exist in two different forms: sodium ''meta''periodate (formula‍ ...

oxidizes to dppe)₂IrS₂Oand then to dppe)₂IrS₂O₂ with dppe being 1,2-bis(diphenylphosphino)ethane. 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 Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists a ...

to form

triphenylphosphine oxide Triphenylphosphine oxide (often abbreviated TPPO) is the organophosphorus compound with the formula OP(C6H5)3, also written as Ph3PO or PPh3O (Ph = C6H5). This colourless crystalline compound is a common but potentially useful waste product in ...

and

triphenylphosphine sulfide Triphenylphosphine sulfide (IUPAC name: triphenyl-''λ''5-phosphanethione) is the organophosphorus compound with the formula , usually written (where Ph = phenyl). It is a colourless solid, which is soluble in a variety of organic solvents. Struc ...

Anion

The

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

has been observed in the gas phase. It may adopt a

trigonal In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crysta ...

shape akin to SO₃.

Spectrum

Microwave

In the Solar System

There is a some evidence that disulfur dioxide may be a small component in the

atmosphere of Venus The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of supercritical carbon dioxide and is much denser and hotter than that of Earth. The temperature at the surface is 740 K (467 °C, 872 ° ...

, and that it may substantially contribute of the planet's severe

. It is not found in any substantive quantity in Earth's atmosphere.

References

{{Oxides Sulfur oxides Sulfur(II) compounds