Fluorides fluoro complexes

The IV state. This is the most important oxidation state of Ti where the main chemistry is that of Ti02 and TiCl4 and its derivatives. This is also an important state for vanadium which forms the vanadyl ion V02+ and many derivatives, cationic, anionic, and neutral containing the VO group. For the remaining elements, Cr-Ni, the IV state is found mainly in fluorides, fluoro complex anions, and cation complexes however, an important class of compounds are the salts of the oxo ions and other oxo species. 

In forming the fluoro complex [Aup4] mentioned above, and indeed in forming the simple fluoride AuFb, Au differs from the isoelectronic Pt since the corresponding [PtF4] and Ptp2 are unknown. 

Tantalum is severely attacked at ambient temperatures and up to about 100°C in aqueous atmospheric environments in the presence of fluorine and hydrofluoric acids. Flourine, hydrofluoric acid and fluoride salt solutions represent typical aggressive environments in which tantalum corrodes at ambient temperatures. Under exposure to these environments the protective TajOj oxide film is attacked and the metal is transformed from a passive to an active state. The corrosion mechanism of tantalum in these environments is mainly based on dissolution reactions to give fluoro complexes. The composition depends markedly on the conditions. The existence of oxidizing agents such as sulphur trioxide or peroxides in aqueous fluoride environments enhance the corrosion rate of tantalum owing to rapid formation of oxofluoro complexes. 

The stepwise formation of fluoro complexes in aqueous solution has been extensively studied in recent years by standard techniques (192). The introduction of the LaF3 electrode has enabled fluoride activities to be measured directly, even with the "insoluble fluorides such as CaF2 or PbF2 (34, 81). Values obtained depend on the salts added to maintain constant ionic strength, and care must be taken in making comparisons since not all results are extrapolated to zero strength (15). Key references to work in this field can be gleaned from standard compilations of stability constants. 

HF is weakly ionized (pH <3.2), and soluble alumino-fluoro complexes are formed resulting in the presence of aluminum ions in the treated water and lowering of the active sites. At near neutral pHs, the uptake of fluoride is maximum. Assuming that the pHpzc of AA is about 8-9 as reported in several literatures, then at near neutral pHs the active sites consist of = AI-OH (protonated) and = AI-OH (non-protonated) aluminol sites. The interaction between fluoride and the protonated aluminol sites leads to the formation of inner-sphere complexes and elimination of water. The reaction can be represented by... 

In this example, the anionic species is a neutral water molecule. If the rate of dissolution is equated to the rate of appearance of CL species in aqueous solution (as in the case C = Al, L = F, where more than one fluoro-complex of A1 is possible in aqueous solution, depending on pH and fluoride concentration38), then a rate law analogous to Eq. 3.64 can be postulated ... 

The chemistry of osmium fluorides and fluoro complexes differs sufficiently from that of the chloro, bromo and iodo species to warrant separate treatment here. The early review of Canterford and Colton is still useful for the general halide chemistry of the element.736... 

All four halides, HgX2, are known their structures are summarized in Table 15-6 and some properties are given in Table 15-7. Mercury(II) fluoride has the fluorite structure and is not volatile. It is decomposed by water, as might be expected since HgO and HF are both weakly dissociated. No fluoro complex of Hg2+ is known. 

The metal is not attacked by mineral acids at room temperature or even by hot aqueous alkali. It dissolves in hot HC1, giving Ti111 species, whereas hot HN03 converts it into a hydrous oxide that is rather insoluble in acid or base. The best solvents are HF or acids to which fluoride ions have been added. Such media dissolve Ti and hold it in solution as fluoro complexes. 

In general, Group 5 fluorides tend to adopt a preference for higher oxidation states, and as a consequence, over the past few years, there have been virtually no reported examples of low valent fluoro complexes of vanadium, niobium or tantalum. 

Bicyclic aziridines 17 with a l-azabicyclo[n.l, 0]alkane framework can also be subjected to ring opening with either hydrogen fluoride or the hydrogen fluoride-pyridine complex to give 3-fluoro-l-azacycloalkanes 18. ° ° ... 

Copper-fluoro complexes are more frequently encountered for the Cu ion than for the Cu ion, although not to the extent one might predict. Fluoride bound in a monodentate fashion is extremely rare, while bridging fluoride ligands and coordinated F-containing anions, such as BF4 and PFe", are more coimnon. 8imilar to that found for Cu, chloride is found extensively in Cu chemistry, followed distantly by bromide. Iodide coordination to Cu is, as one might expect, limited seen only in complexes such as [Cu(bipy)I]I. The section on binary and simple compounds above also discusses a number of Cu halide compounds. 

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