Tetramethylammonium pentafluoroxenate is a chemical compound with the chemical formula . This salt consists of tetramethylammonium cations and pentafluoroxenate(IV) anions . The ion was the first example of a pentagonal planar molecular geometry species.[1] It was prepared by the reaction of with xenon tetrafluoride, being chosen because it can be prepared in anhydrous form and is readily soluble in organic solvents.[1] 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°).[1] Other salts have been prepared with sodium, caesium and rubidium, and vibrational spectra show that these contain the same planar ion.[1] The isolated anion has the point group of D5h.[1]