Hexacoordinated nitrogen(V) stabilized by high pressure

Abstract

In all of its known connections nitrogen retains a valence shell electron count of eight therefore satisfying the golden rule of chemistry - the octet rule. Despite the diversity of nitrogen chemistry (with oxidation states ranging from + 5 to −3), and despite numerous efforts, compounds containing nitrogen with a higher electron count (hypervalent nitrogen) remain elusive and are yet to be synthesized. One possible route leading to nitrogen’s hypervalency is the formation of a chemical moiety containing pentavalent nitrogen atoms coordinated by more than four substituents. Here, we present theoretical evidence that a salt containing hexacoordinated nitrogen(V), in the form of an NF6− anion, could be synthesized at a modest pressure of 40 GPa (=400 kbar) via spontaneous oxidation of NF3 by F2. Our results indicate that the synthesis of a new class of compounds containing hypervalent nitrogen is within reach of current high-pressure experimental techniques.

Fluorides of Silver Under Large Compression**

“…where H(Ag m F n ) is the enthalpy of the most stable Ag m F n structure at ag iven pressure, while H(Ag) is the enthalpy of gold in the fcc (Fm " 3m)structure, [78] and H(F 2 ) is the enthalpy of the molecular crystal of the F 2 (a polymorph). [8,79] The projector-augmented-wave (PAW)m ethod, [80] as implemented in the VASP 5.4 code, [81,82] was used in the calculations. The cut-off energy of the plane-waves was set to 800 eV with as elf-consistentfield convergence criterion of 10 À6 eV.T he valence electrons (Ag: 4d 10 ,5 s 1 ;F :2 s 2 ,2 p 5 )w ere treated explicitly,w hile standard VASP pseudopotentials, accounting for scalar relativistic effects, were used for the description of core electrons.…”

“…where H( Ag m F n ) is the enthalpy of the most stable Ag m F n structure at a given pressure, while H( Ag ) is the enthalpy of gold in the fcc ( Fm m ) structure, [78] and H( F 2 ) is the enthalpy of the molecular crystal of the F 2 (α polymorph) [8, 79] …”

“…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 ).…”

“…The reactivity of elemental fluorine at pressures exceeding 1 GPa (=10 kbar) has recently attracted increased scientific attention because of the exotic nature of materials that are predicted to form in fluorine‐rich systems at large compression [1–14] . These include compounds featuring elements in high oxidation states (e.g., IF 8 ), [13] hypervalent second‐row elements (NF 5 ), [8] as well as transient species that are not attainable at ambient conditions (AuF 2 , [3, 4] AuF [6] ).…”

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

“…This might hint at the fact that the fluoride-donor properties of KrF 2 are suppressed at large compression. In general, it seems that in the case of the Kr/F system, ionic bonding is not a major driving force in stabilization of high-pressure phases, in contrast to what is found for the N/F system [57]. We hope that the insight into the high-pressure chemistry of krypton offered by this study will motivate future investigation, in particular, experimental attempts to obtain KrF 4 and KrF.…”