High-Pressure Reactivity of Kr and F2—Stabilization of Krypton in the +4 Oxidation State

Abstract

Abstract:Since the synthesis of the first krypton compound, several other Kr-bearing connections have been obtained. However, in all of them krypton adopts the +2 oxidation state, in contrast to xenon which forms numerous compounds with an oxidation state as high as +8. Motivated by the possibility of thermodynamic stabilization of exotic compounds with the use of high pressure (exceeding 1 GPa = 10 kbar), we present here theoretical investigations into the chemistry of krypton and fluorine at such large compression. In particular we focus on krypton tetrafluoride, KrF 4 , a molecular crystal in which krypton forms short covalent bonds with neighboring fluorine atoms thus adopting the +4 oxidation state. We find that this hitherto unknown compound can be stabilized at pressures below 50 GPa. Our results indicate also that, at larger compressions, a multitude of other Kr m F n fluorides should be stable, among them KrF which exhibits covalent Kr-Kr bonds. Our results set the stage for future high-pressure synthesis of novel krypton compounds.

Fluorides of Silver Under Large Compression**

“…The reactivity of elemental fluorine at pressures exceeding 1GPa (= 10 kbar) has recentlya ttracted increased scientific attention because of the exotic nature of materials that are predicted to form in fluorine-richs ystems at large compression. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] These include compounds featuring elements in high oxidation states (e.g.,I F 8 ), [13] hypervalent second-rowe lements (NF 5 ), [8] as well as transients pecies that are not attainable at ambient conditions (AuF 2 , [3,4] AuF [6] ). In the case of transition metal fluorides, this novel chemistry might lead to species featuring exotic magnetic ions, such as Au 4 + (5d 7 electronic configuration) or Au 2 + (5d 9 ).…”

Electrostatic force driven helium insertion into ammonia and water crystals under pressure

“…Under high pressure, Xe can also gain electrons from Mg or Li 14,15 . The lighter NG elements such as Kr and Ar can also form compounds under high pressure via electron transfer [16][17][18] . As the radii of the NG elements become smaller, their ionization potential become higher and the electron affinity lower.…”