Difluorodisulfanedifluoride
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IUPAC name
1,1,1,2-tetrafluoro-1λ4-disulfane
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| Other names
1,2-difluorodisulfane 1,1-difluoride;
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| Identifiers | |
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3D model (JSmol)
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| ChemSpider | |
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| Properties | |
| FSSF3 | |
| Molar mass | 140.124 g/mol |
| Appearance | liquid |
| Density | 1.81 |
| Melting point | -98°C |
| Boiling point | 39°C |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
1,1,1,2-tetrafluorodisulfane, also known as 1,2-difluorodisulfane 1,1-difluoride or just difluorodisulfanedifluoride (FSSF3) is an unstable molecular compound of fluorine and sulfur. The molecule has a pair of sulfur atoms, with one fluorine atom on one sulfur, and three fluorine atoms on the other. It has the uncommon property that all the bond lengths are different. The bond strength is not correlated with bond length but is inversely correlated with the force constant (Badger's rule). The molecule can be considered as sulfur tetrafluoride in which a sulfur atom is inserted into a S-F bond.
Atoms are labelled with the sulfur atom connected to three fluorine atoms as Shyp (for hypervalent) and Stop. The fluorine atoms are labelled Ftop attached to Stop, and on the hypervalent S atom: Fcis, the closest F atom to Ftop, Ftrans the furthest away F atom from Ftop, and Feq
Carlowitz first determined the structure in 1983.
Feq is 90° from Ftrans, and 84° from Fcis, and the torsion compared to Ftop is about 95°.
The dimerization reaction 2SF2 ⇌ FSSF3 is reversible. It also disproportionates: SF2 + FSSF3 → FSSF + SF4. A side reaction also produces the intermediate F3SSSF3.hydrogen fluoride catalyses disproportionation to sulfur and sulfur tetrafluoride by forming a reactive intermediate HSF molecule. When FSSF3 dissociates, the Fcis atom forms a new bond to the Stop atom, and the S-S bond breaks. As a gas, at ambient and totally clean conditions, FSSF3 decomposes with a half life of about 10 hours. Disproportionation to SSF2 and SF4 catalysed by metal fluorides can take place in under one second. However it is indefinitely stable at -196 °C.
A symmetrical molecule F2SSF2 is calculated to be 15.1 kcal/mol higher in energy than FSSF3.
FSSF3 is easily hydrolysed with water.
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