Three fluorides are known: XeF2, XeF4, and XeF6. The fluorides are the starting point for the synthesis of almost all xenon compounds.
The solid, crystalline difluoride XeF2 is formed when a mixture of fluorine and xenon gases is exposed to ultraviolet light. Ordinary daylight is sufficient.[81] Long-term heating of XeF2 at high temperatures under an NiF2 catalyst yields XeF6.[82] Pyrolysis of XeF6 in the presence of NaF yields high-purity XeF4.
The xenon fluorides behave as both fluoride acceptors and fluoride donors, forming salts that contain such cations as XeF+ and Xe2F3+, and anions such as XeF5−, XeF7−, and XeF82−. The green, paramagnetic Xe2+ is formed by the reduction of XeF2 by xenon gas.
XeF2 is also able to form coordination complexes with transition metal ions. Over 30 such complexes have been synthesized and characterized.
Whereas the xenon fluorides are well-characterized, the other halides are not known, the only exception being the dichloride, XeCl2. Xenon dichloride is reported to be an endothermic, colorless, crystalline compound that decomposes into the elements at 80°C, formed by the high-frequency irradiation of a mixture of xenon, fluorine, and silicon or carbon tetrachloride.[84] However, doubt has been raised as to whether XeCl2 is a real compound and not merely a van der Waals molecule consisting of weakly bound Xe atoms and Cl2 molecules. Theoretical calculations indicate that the linear molecule XeCl2 is less stable than the van der Waals complex.