Tetramethylammonium pentafluoroxenate is a chemical compound with the chemical formula [N(CH3)4]+[XeF5]−. This salt consists of tetramethylammonium cations [N(CH3)4]+ and pentafluoroxenate(IV) anions [XeF5]−. The [XeF5]- ion was the first example of a pentagonal planar molecular geometry AX5E2 species. It was prepared by the reaction of [N(CH3)4]F with xenon tetrafluoride, [N(CH3)4]F being chosen because it can be prepared in anhydrous form and is readily soluble in organic solvents. The anion is planar, with the fluorine atoms in a slightly distorted pentagonal coordination (Xe–F bond lengths 197.9–203.4 pm, and F–X–F bond angles 71.5°–72.3°). Other salts have been prepared with sodium, caesium and rubidium, and vibrational spectra show that these contain the same planar ion. The isolated anion has the point group of D5h.