Some have third anions, including nitrate (NO−3), molybdate (MoO2−4), oxalate (C2O2−4), selenate (SeO2−4), silicate (SiO2−4) and tellurate (TeO2−4).
A selenite fluoride compound may also be called a fluoride oxoselenate(IV) using IUPAC naming for inorganic compounds.
Rare earth selenite fluorides can be produced by dissolving the rare earth selenate into molten lithium fluoride at over 800°C, whereupon the selenate loses oxygen to become selenite, and crystals of the selenite fluoride can form.
[1] Another similar method involves heating the rare earth oxide, with a rare earth fluoride and selenium dioxide with a caesium bromide flux.
If glass or silica containers are used, they are eaten away by the molten flux and silicates are formed some of which may be fluoride selenite silicate compounds.