Talk:Fluorine/Comparison between the highest oxidation states of oxides and fluorides

Comparison between the highest oxidation states of oxides and fluorides
For groups 1—6 and 13—16 the highest oxidation states of oxides and fluorides are always equal, and differences are only seen in groups 7—11, mercury, halogens, and the noble gases. The general trend is fluorination allows to achieve relatively low but hardly achievable oxidation states; for example, no binary oxide is known for krypton, but krypton difluoride is well-studied. However, very high oxidation states of several elements are known for oxygen only; for example, none has shown that existence of ruthenium octafluoride is possible yet, while ruthenium tetroxide is well-studied.

Later transition metals


With the exceptions of the +7 and +8 oxidation states, fluorine is the key in achieving many rare high oxidation states of the transition metals. For instance, direct reaction of the respective metals with fluorine gives rise to palladium(VI) and platinum(VI). The only occurrence of mercury(IV) is binary mercury(IV) fluoride, synthesized at temperatures close to absolute zero. Gold(V) is only known in the hexafluoroaurate(V) ion, which can be synthesized indirectly under extreme conditions, and the gold(V) fluoride, which is obtained during hexafluoroaurate(V) decomposition. The high oxidizing potential of fluorine has led to the claim of the gold(VII) existence in gold heptafluoride, but current calculations show that the claimed AuF7 molecule was AuF5·F2. The great oxidizing power of fluorine is also illustrated by the fluorine-containing complexes of copper(IV), silver(IV), nickel(IV), iridium(VI), and others. It is possible that the element 113, ununtrium, will be the first element in boron group to form a species in the +5 oxidation state, the fluorine-based hexafluoroununtrate(V), ; the possibility of a +5 oxygen-based species is not known to be calculated.

Fluorine is a generally stronger oxidizer than oxygen; however, this strength does not apply for every case. Dinitrogen pentoxide, with nitrogen in the oxidation state of +5, is known; but creating nitrogen pentafluoride would need to squeeze five fluorine atoms attached to the central atom. This is hard to perform, as a nitrogen atom is smaller than most other atoms. It is not known whether the molecule is possible to produce or not, and if possible, whether it is stable or not. Similarly, the highest oxidation states of several late transition metals may be achieved in oxides only: for example, even though only gold(V) is known now, and only in the form of a fluoride, calculations provided by Dementyev et al. in 1997 show that the element may be oxidized up to gold(IX), in the form of the tetroxoaurlyl(IX) ion, [AuO4]+, but not as a fluorine-based compound or ion. Similarly, this and another (Rother et al., 1969) calculations revealed that oxygen-based complexes that contain iridium(IX), platinum(X), and mercury(VIII) might be possible. However, these species were denied by the University of Würzburg in a 2006 paper; it expects platinum(VI), gold(V), and mercury(IV), known in binary fluorides, to be the highest for the elements. It has been shown osmium and iridium may form heptafluorides; for osmium, even an octafluoride may be possible.

Halogens and noble gases
Among halogens, chlorine and bromine form perchlorates and perbromates, both oxygen-based and with the representative halogen in +7 state; however, chlorine, unlike bromine, forms a binary heptoxide. Out of their stable fluorinated species, pentafluorides are the species in the highest oxidation state achieved; however, bromine hexafluoride, BrF6•, is known as well. Iodine shows the reverse picture: no heptoxide is known, unlike heptafluoride, a well-known stable compound; however, periodic acid, containing iodine(VII), is known as well.

Noble gases do not show a trend as well: as noted above, krypton has no known binary oxides, but has a well-studied difluoride. Xenon forms a tetroxide of oxygen-based species, but only a hexafluoride of fluorine-based ones. Neutral xenon octafluoride is not known nor expected to be stable, but octafluoroxenate(VI),, has been synthesized. Contradictory data is known about fluorides and especially oxides of radon; no binary fluoride or oxide of lighter noble gases are known.