Pentafluorosulfite or pentafluorosulfate(IV) is an anion with formula [SF5]−.
Most pentafluorosulfite salts are unstable, decaying info SF4 gas and a fluoride salt. So for example, tetramethyl ammonium pentafluorosulfite has a vapour pressure of 2-3 mm Hg of SF4.
Formation Some salts can be formed by reacting SF4 gas at low temperature with the fluoride salt.
Properties
Pentafluorosulfites are decomposed by water, but may be soluble in dimethylformamide.
The ion has a square pyramidal shape with C4v symmetry. The ion has a very similar spectrum and force constants to ClF5, and the spectrum is similar in form to other pentafluorides with a lone pair of electrons.
Force constants derived from the IR and Raman spectrum are: fR = 4.12 mdyn/Å, fr = 2.06 mdyn/Å, fα = 2.26 mdyn/Å radian, fβ = 0.86 mdyn/Å radian, frr' = 0.52, fββ' = 0.55 mdyn/Å radian, fαα' = 0.11 mdyn/Å radian, frr =0.23 mdyn/Å radian, fRβ =0.25mdyn/Å radian, frβ =0.15, frβ mdyn/Å radian, fββ = −0.20 mdyn/Å radian2.
+Spectrumpoint group assignmentdescriptionband idIR band cm−1Raman line cm−1A1vibration S-F axialv1793796A1vibration S-F4 equatorial v2520522A1deformation S-F4 umbrellav3466469B1stretch S-F4 out of phasev4 -435 overlapB1S-F4 out of planev5 -269B2deformation S-F4 in planev6 -342Evasv7590590Edeformation F'-S-F4v8430435 overlapEdeformation as SF4 in planev9 -241
Reactions Trichloroisocyanuric acid can react with pentafluorosulfite to form SF5Cl.
Related Selenium and tellurium also form similar anions and . The general term for these is pentafluorochalcogenate(IV) anions. In organic chemistry the -SF5 group is called pentafluoro-λ6-sulfane or pentafluorosulfane, or as a prefix: pentafluoro-λ6-sulfanyl or pentafluorosulfanyl.
List formulacrystal systemspace groupunit cellcell volumedensitycommentref[(CH3)4N+]SF5−tetragonalP4/na=13.503 c=19.471 Z=43550.21.48[(tmg)3PF]+SF5− tmg=tetramethylguanidyldissolve in THF or 1,2-difluorobenzene[(R1)3PF]+SF5− R1 = 1,3-di-tert-butylimidazolidin-2-ylidenaminoRb+SF5−orthorhombicPbnma = 7.76 b = 9.903 c = 6.141 Z = 4trans,trans-[Rh(Cl)2(CO)(IMes)2][SF5]deep red; decomposes at room temperaturetrans-[Rh(Cl)(F)(CO)(IMes)2][SF5]decomposes at room temperatureCs+SF5−tetrahedralPb2a = 10.32 c = 6.276 Z = 1(Cs+)6(SF5−)4 (HF2−)2[Cs+.(18-crown-6)2] [SF5−][Cs(tetraglyme)2][SF5]tetrahedralP21ca =13.1515 c=17.792
References