Antimony pentafluoride, structure

The carbocations being reactive intermediates have short life and so they are unstable. But they have been rendered stable after being trapped in strongest super acids which are mixtures of fluorosulphuric and antimony pentafluoride dissolved in S02 or chlorofluorosulphuric acid S02CIF. Under these conditions their structure and stability have been correlated. 

It was indeed found necessary to have excess antimony pentafluoride present in order to obtain stable alkylcarbonium hexafluoroantimonate complexes. Antimony pentafluoride is a liquid Lewis acid fluoride (b.p. 148-150°) of low dielectric constant (e 3), which has been shown by fluorine N.M.R. studies in the pure liquid state and in solution to exist in both cyclic and acyclic polymeric forms involving fluorine bridges. The antimony is in approximately octahedral co-ordination with predominant bridging by coordinating fluorines (Gillespie and Rothenbury, 1963). As fluorine generally does not show bridging properties, the structure of antimony pentafluoride itself indicates the very... 

In the 40 years since Olah s original publications, an impressive body of work has appeared studying carbocations under what are frequently termed stable ion conditions. Problems such as local overheating and polymerization that were encountered in some of the initial studies were eliminated by improvements introduced by Ahlberg and Ek and Saunders et al. In addition to the solution-phase studies in superacids, Myhre and Yannoni have been able to obtain NMR spectra of carbocations at very low temperatures (down to 5 K) in solid-state matrices of antimony pentafluoride. Sunko et al. employed a similar matrix deposition technique to obtain low-temperature IR spectra. It is probably fair to say that nowadays most common carbocations that one could imagine have been studied. The structures shown below are a hmited set of examples. Included are aromatically stabilized cations, vinyl cations, acylium ions, halonium ions, and dications. There is even a recent report of the very unstable phenyl cation (CellJ)... 

More recently, development of the superacid solvent systems has permitted the preparation at low temperature of stable solutions of carbocations of many structural types. The solvents ordinarily used consist of the strong Lewis acid antimony pentafluoride with or without an added protonic acid, usually hydro-... 

Pure crystalline I2+Sb2F11 has been prepared by the reaction of iodine with antimony pentafluoride in liquid sulfur dioxide as solvent.789 After removal of insoluble SbF3, deep blue crystals of l2+Sb2Fn were obtained from the solution. An X-ray crystallographic structure determination showed the presence of the discrete... 

Electrolytic reduction of 4-cyclooctenone leads smoothly in 64 % yield to cis-bicyclo[3.3.0]octan-l-ol.106) The thermolysis of octachlorocyclooctatetraene produces perchlorinated bicyclo[3.3.0]octatrienes,107,108) several of which have been examined in detail by X-ray structural methods.109) The 1,3,5,7-tetramethyl-cyclooctatetraene dication (57), generated by oxidation of the neutral hydrocarbon with antimony pentafluoride in S02C1F at —78 °C and below, is subject to dis-rotatory cyclization above — 60°.1 °) The latter step does not follow orbital sym-... 

The blue solid prepared by Rulf et al. (9) in 1906 and thought to be (SbF5)aI was probably a mixture of an la fluoroantimonate salt, and some Sb(III)-containing material. Pure crystalline la SbaFu has recently been prepared by the reaction of iodine with antimony pentafluoride in liquid sulfur dioxide as solvent (11). After removal of insoluble SbFg, deep blue crystals of la SbaFi were obtained from the solution. An X-ray crystallographic structure determination showed the presence of the discrete ions la and SbaFu . Crystalline solids that can be formulated as la SbaFu and Ia TaaFii have also been prepared by Kemmitt et al. (4) by the reaction of iodine with antimony or tantalum pentafluorides in iodine pentafluoride solutions. 

Antimony pentafluoride forms 1 1 adducts with HCN and C2N2 and the structure of the latter reveals a linear NCCN-SbF5 linkage. Related adducts of SbCls including [SbCl5(L)] (L = ICN, BrCN, CICN, I/2C2N2, NH2CN, pyridine) have been prepared and the X-ray structures of... 

Both 1 1 and 1 2 complexes are formed between dimethyl ether and antimony pentafluoride 19F n.m.r. spectra and double-resonance experiments confirm the cis structure (101) for 2SbF5,Me20.736 A minor product... 

Antimony tri- and pentafluoride form very stable compounds, e.g., SbF6-2SbF3, which distills unchanged at 390°C (165). No exact study of their structures has so far been made. It is possible that they are saltlike in the solid state (e.g., [SbF2][SbF ]-SbF3) and go over to a molecular form on vaporization. Antimony pentafluoride dissolves in AsF3 and the conductiv-... 

The 1,2-dimethylbenzocyclobutadiene dication (316), a 6-7c-electron molecule, has been prepared by reaction of 1,2-dimethylbenzocyclobutene-l,2-diol with antimony pentafluoride in sulphuryl chlorofluoride at low temperature. The H n.m.r. spectrum of (316) showed equivalent methyl group signals at 84.42 and an aromatic proton signal at 8 9.10. The n.m.r. spectrum showed five signals at chemical shifts indicated below. The spectra are comparable with those of other cyclobutadiene dications, supporting the fully delocalized structure of (316). The ion was stable below 30 °C. Attempts to prepare the parent dication were not successful. 

Practice Problem A Draw the Lewis structure of phosphorus pentachloride (PCI5). Practice Problem B Draw the Lewis structure of antimony pentafluoride (SbF,). 

Burger H, KopUn R, Pawelke G (1983) Reaction of perfluototrimethylamine with antimony pentafluoride. Synthesis and X-ray structure of perfluorinated hexahydro-triazinedione derivative. J Fluor Chem 22 175-183... 

A substituted selenetan was obtained by treatment of pentaery thritol dth diethyl carbonate and KSeCN. A compound obtained in low yield by treatment of perfluoropropene with selenium and antimony pentafluoride was assigned tentatively a 1,3 diselenetan structure. ... 

Arsenic forms a gaseous pentafluoride and a solid pentachloride which decomposes at temperatures above -50°C. Antimony forms a pentachloride which may be vaporized without decomposition, and a pentafluoride which is tetrameric in the solid phase and trimeric in the gas phase. The structures of the trimer will be described in Chapter 16. The heaviest element in the group (Bi) forms a pentafluoride which is polymeric in the solid phase. The gas phase structure is unknown. 

---