Two- and three-dimensional extended solids and metallization of compressed XeF2

The application of pressure, internal or external, transforms molecular solids into extended solids with more itinerant electrons to soften repulsive interatomic interactions in a tight space. Examples include insulator-to-metal transitions in O-2, Xe and I-2, as well as molecular-to-non-molecular transitions in CO2 and N-2. Here, we present new discoveries of novel two-and three-dimensional extended non-molecular phases of solid XeF2 and their metallization. At similar to 50 GPa, the transparent linear insulating XeF2 transforms into a reddish two-dimensional graphite-like hexagonal layered structure of semiconducting XeF4. Above 70 GPa, it further transforms into a black three-dimensional fluorite-like structure of the first observed metallic XeF8 polyhedron. These simultaneously occurring molecular-to-non-molecular and insulator-to-metal transitions of XeF2 arise from the pressure-induced delocalization of non-bonded lone-pair electrons to sp(3)d(2) hybridization in two-dimensional XeF4 and to p(3)d(5) in three-dimensional XeF8 through the chemical bonding of all eight valence electrons in Xe and, thereby, fulfilling the octet rule at high pressures.