User:Kazyan1/List of Unsynthesized oxyanions

Oxygen can create polyatomic ions with many atoms in the center. A few of the possibilities are conspicuously absent from chemical records.

Fluorates
No oxyanions of fluorine have been discovered. This is a result of two complications: fluorine has a higher electronegativity than oxygen, and it has no d-subshell. A d-subshell is required to expand an atom's valence shell, so fluorine cannot form any oxyanio except FO-, hypofluorite. Technically, the oxidation numbers are reversed in this ion compared to XO - halides, and so it should not be considered hypofluorite.

Perastatate
The AtO3- ion is relatively stable, but even under highly oxidizing conditions, AtO4- does not form. This almost certainly has nothing to due with the nuclear instability of astatine. This is an unexplained phenomenon among halogens, aside from aforemetioned fluorates, and the reason there does not apply here.

Most noble gas anions
For obvious reasons. Hypohelite is unlikely, and because helium only has 2 valence electrons, helite through perheliate are strictly impossible. Neon has no d subshell, so neates are close to impossible. Argates and kryptates likely decompose, but the perxenate ion is stable and has been observed. Xenate and hypoxenite have been observed as well. Aside from these, all other noble gas oxyanions are elusive.

Hypouranite
Curiously, there are no reports of hypouranite. Uranium produces -ite, -ate and per-ate forms.