The structure of noble gas compounds

The shapes of (a) Xep2 and (b) Xep4 molecules are correctly predicted by VSEPR theory. 

As in the case of the polyhalides, however, the situation with regard to ions in crystals is not quite so satisfactory. Consider first the case of the pentagonal ion, [XeFsJ (Structure 7.2), encountered in Section 7.5.1.1 (p. 93). 

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For the most part, the structures of noble-gas compounds follow readily from VSEPR theory. In the gas phase, xenon hexafluoride assumes a nonrigid, slightly distorted octahedral structure, even though it has seven electron pairs around the central xenon atom. In the solid, it is characterized by square pyramidal XeF cations bridged by fluoride ions. XeF is a square antiprism, and XeOF4 is nearly a perfect square pyramid. 

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