Hexafluorosilicate ions

The behavior of SiF4 as a Lewis acid enables it to add two additional fluoride ions to form the hexafluorosilicate ion ... 

All of the SiX4 tetrahalides except the fluoride hydrolyze rapidly to give hydrated sihca the fluoride also undergoes partial hydrolysis but also forms the hexafluorosilicate ion (equation 19). 

DECOMPOSITION OF HEXAFLUOROSILICATE ION In alkaline solution, decomposition of the hexafluorosilicate ion °... 

Silicon, germanium, tin and lead can make use of unfilled d orbitals to expand their covalency beyond four and each of these elements is able (but only with a few ligands) to increase its covalency to six. Hence silicon in oxidation state -f-4 forms the octahedral hexafluorosilicate complex ion [SiFg] (but not [SiCl] ). Tin and lead in oxidation state -1-4 form the hexahydroxo complex ions, hexahydroxostannate(IV). [Sn(OH) ] and hexahydroxoplum-bate(IV) respectively when excess alkali is added to an aqueous solution containing hydrated tin(IV) and lead(IV) ions. 

So far, there have been no studies to confirm or refute the suggestion that water supplies contain polymeric species, and there have been only very few studies on the relevant equilibria which are involved in liberating free fluoride ions from the hexafluorosilicate additives [123]. What data there are, though, suggest that equilibrium will have been reached by the time the water reaches the consumer, even though it may not have been achieved when the water left the waterworks. 

Evidence that something more than a proper Alf distribution is needed to create strong acidity first came from the experiments of Beyerlein et al. (7). Using the acid-catalyzed conversion of isobutane as a measure of strong acidity, they found that a dealuminated zeolite prepared by treatment with ammonium hexafluorosilicate (AHF) exhibited much less carbonium ion activity than might be expected, based on the number of Alf atoms. This treatment leaves very little extraframework Al in the zeolite. When the sample was mildly steamed, the activity became considerably greater. The authors concluded that the enhanced acidity was a result of a synergism between the framework Bronsted sites and the Lewis sites associated with extraframework aluminum. 

Barium hexafluorosilicate, preparation of, for decomposition to silicon tetrafluoride, 4 145 Barium paraperiodate (orthoperiodate), Ba3H4(I06)2, 1 171 Barium dezZro-tartrate, for resolution of tris(ethylenediamine)-cobalt(III) ion, 6 184 Barium thiocyanate, 3 24 Benzalazine, in recovery of hydrazine residues, 1 92 Benzoylacetone, beryllium derivative of, 2 19... 

In the early 19th century, Gay-Lussac discovered F Si 2 NHj. Three years later Davy obtained the same compound and Davy and Berzelius synthesized other compounds of six-coordinate silicon fluorosilicic acid, HjPiFg], and its salts, the hexafluorosilicates In the second half of the last century adducts of silicon tetrahalides with tertiary amines were synthesized . In 1903 Dilthey investigated silicon diketonates containing six-coordinate silicon In the first half of our century the possibility of the presence of Si(OH)g ions in silica was widely discussed Interest in five- and six-coordinate silicon compounds increased in the second half of the present century. As a result, new classes of silicon compounds with an expanded coordination sphere were discovered and were studied by various physical and chemical methods. Specific biological activity was observed for some of the compounds and promising ways of their practical application were planned... 

F3SiCH2CH2PMe2)2PdCl2 allowed the silicon atom to be penta-coordinated due to the Si<-Pd interaction . The F chemical shifts of anionic fluorosilicates correspond to the values for isolated ion only at inifinite dilution. The ion-pairs interaction between the hexafluorosilicates and various cations have been studied... 

Acid form of zeolite beta (Hp) was obtained from a commercial TEA-beta (Valfor CP806B-25) by calcination at 773 K for three hours to remove the template, followed by ion exchange with a 2M aqueous solution of NH4CI at 353 K for two hours, and a final calcination at 773 K for three hours. Then, the HP was dealuminated using three different procedures, i.e. steam calcination at 873 K during three hours (sample HPs,), acid treatment with HCl O.IM at reflux for two hours (sample HP, ), and ammonium hexafluorosilicate (HFS) treatment (sample HP ps2)- The latter two procedures produced almost EFAL-free beta samples. Moreover, the EFAL formed in HP during the calcination steps was also extracted with the required amount of ammonium hexafluorosilicate in order to avoid framework dealumination (sample HP fsi)- The HFS treatments were carried out in an ammonium acetate buffer at 348 K with slow addition of a 3M hexafluorosilicate solution (12 cm /h). Afterwards,... 

Mercury compounds can be classified into two basic groups - those involving mercury(i) , or more generally, those which contain mercury-mercury bonds, and the normal mercuty(n) compounds. In the first category, three relevant papers have appeared. Mercuiy(i) hexafluorosilicate dihydrate contains [H2bond lengths are 2.20 and 2.495 A, respectively. The system is not quite... 

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