Syntheses and X-ray Crystal Structures of α- and β-[XeO2F][SbF6], [XeO2F][AsF6], [FO2XeFXeO2F][AsF6], and [XeF5][SbF6]·XeOF4 and Computational Studies of the XeO2F+ and FO2XeFXeO2F+ Cations and Related Species

Crystal Structures of Xenon(VI) Salts: XeF5Ni(AsF6)3, XeF5AF6 (A = Nb, Ta, Ru, Rh, Ir, Pt, Au), and XeF5A2F11 (A = Nb, Ta)

Experiments on the preparation of the new mixed cations XeF₅M(AF₆)₃ (M = Cu, Ni; A = Cr, Nb, Ta, Ru, Rh, Re, Os, Ir, Pt, Au, As), XeF₅M(SbF₆)₃ (M = Sn, Pb), and XeF₅M(BF₄)_x(SbF₆)_3-x (x = 1, 2, 3; M = Co, Mn, Ni, Zn) salts were successful only in the preparation of XeF₅Ni(AsF₆)₃. In other cases, mixtures of different products, mostly XeF₅AF₆ and XeF₅A₂F₁₁ salts, were obtained. The crystal structures of XeF₅Ni(AsF₆)₃, XeF₅TaF₆, XeF₅RhF₆, XeF₅IrF₆, XeF₅Nb₂F₁₁, XeF₅Ta₂F₁₁, and [Ni(XeF₂)₂](IrF₆)₂ were determined for the first time on single crystals at 150 K by X-ray diffraction. The crystal structures of XeF₅NbF₆, XeF₅PtF₆, XeF₅RuF₆, XeF₅AuF₆, and (Xe₂F₁₁)₂(NiF₆) were redetermined by the same method at 150 K. The crystal structure of XeF₅RhF₆ represents a new structural type in the family of XeF₅AF₆ salts, which crystallize in four different structural types. The XeF₅A₂F₁₁ salts (M = Nb, Ta) are not isotypic and both represent a new structure type. They consist of [XeF₅]⁺ cations and dimeric [A₂F₁₁]^- anions. The crystal structure of [Ni(XeF₂)₂](IrF₆)₂ is a first example of a coordination compound in which XeF₂ is coordinated to the Ni²⁺ cation.

Mixed Noble-Gas Compounds of Krypton(II) and Xenon(VI); [F5 Xe(FKrF)AsF6 ] and [F5 Xe(FKrF)2 AsF6 ]

The coordination chemistry of KrF₂ has been limited in contrast with that of XeF₂ , which exhibits a far richer coordination chemistry with main-group and transition-metal cations. In the present work, reactions of [XeF₅ ][AsF₆ ] with KrF₂ in anhydrous HF solvent afforded [F₅ Xe(FKrF)AsF₆ ] and [F₅ Xe(FKrF)₂ AsF₆ ], the first mixed krypton/xenon compounds. X-ray crystal structures and Raman spectra show the KrF₂ ligands and [AsF₆ ]^- anions are F-coordinated to the xenon atoms of the [XeF₅ ]⁺ cations. Quantum-chemical calculations are consistent with essentially noncovalent ligand-xenon bonds that may be described in terms of σ-hole bonding. These complexes significantly extend the XeF₂ -KrF₂ analogy and the limited chemistry of krypton by introducing a new class of coordination compound in which KrF₂ functions as a ligand that coordinates to xenon(VI). The HF solvates, [F₅ Xe(FH)AsF₆ ] and [F₅ Xe(FH)SbF₆ ], are also characterized in this study and they provide rare examples of HF coordinated to xenon(VI).

Chromium Oxide Tetrafluoride and Its Reactions with Xenon Hexafluoride; the [XeF5 ]+ and [Xe2 F11 ]+ Salts of the [CrVI OF5 ]- , [CrV OF5 ]2- , [CrV 2 O2 F8 ]2- , and [CrIV F6 ]2- Anions

Molten mixtures of XeF₆ and Cr^VI OF₄ react by means of F₂ elimination to form [XeF₅ ][Xe₂ F₁₁ ][Cr^V OF₅ ]⋅2 Cr^VI OF₄ , [XeF₅ ]₂ [Cr^IV F₆ ]⋅2 Cr^VI OF₄ , [Xe₂ F₁₁ ]₂ [Cr^IV F₆ ], and [XeF₅ ]₂ [Cr^V ₂ O₂ F₈ ], whereas their reactions in anhydrous hydrogen fluoride (aHF) and CFCl₃ /aHF yield [XeF₅ ]₂ [Cr^V ₂ O₂ F₈ ]⋅2 HF and [XeF₅ ]₂ [Cr^V ₂ O₂ F₈ ]⋅2 XeOF₄ . Other than [Xe₂ F₁₁ ][M^VI OF₅ ] and [XeF₅ ][M^VI ₂ O₂ F₉ ] (M=Mo or W), these salts are the only Group 6 oxyfluoro-anions known to stabilize noble-gas cations. Their reaction pathways involve redox transformations that give [XeF₅ ]⁺ and/or [Xe₂ F₁₁ ]⁺ salts of the known [Cr^V OF₅ ]^2- and [Cr^IV F₆ ]^2- anions, and the novel [Cr^V ₂ O₂ F₈ ]^2- anion. A low-temperature Raman spectroscopic study of an equimolar mixture of solid XeF₆ and CrOF₄ revealed that [Xe₂ F₁₁ ][Cr^VI OF₅ ] is formed as a reaction intermediate. The salts were structurally characterized by LT single-crystal X-ray diffraction and LT Raman spectroscopy, and provide the first structural characterizations of the [Cr^V OF₅ ]^2- and [Cr^V ₂ O₂ F₈ ]^2- anions, where [Cr^V ₂ O₂ F₈ ]^2- represents a new structural motif among the known oxyfluoro-anions of Group 6. The X-ray structures show that [XeF₅ ]⁺ and [Xe₂ F₁₁ ]⁺ form ion pairs with their respective anions by means of Xe- - -F-Cr bridges. Quantum-chemical calculations were carried out to obtain the energy-minimized, gas-phase geometries and the vibrational frequencies of the anions and their ion pairs and to aid in the assignments of their Raman spectra.

Resonance bonding in XNgY (X = F, Cl, Br, I; Ng = Kr or Xe; Y = CN or NC) molecules: an NBO/NRT investigation

Several noble-gas-containing molecules XNgY were observed experimentally. However, the bonding in such systems is still not understood. Using natural bond orbital and natural resonance theory (NBO/NRT) methods, the present work investigated bonding of the title molecules. The results show that each of the studied XNgY molecules should be better described as a resonance hybrid of ω-bonding and [Formula: see text]-type long-bonding structures: X:^- Ng⁺ - Y, X - Ng⁺: Y^-, and X^{^}Y. The ω-bonding and long-bonding make competing contributions to the composite resonance hybrid due to the accurately preserved bond order conservation principle. We find that the resonance bonding is highly tunable for these noble-gas-containing molecules due to its dependence on the nature of the halogen X or the central noble-gas atoms Ng. When the molecule XNgY consists of a relatively lighter Ng atom, a relatively low-electronegative X atom, and the CN fragment rather than NC, the long-bonding structure X^{^}Y tends to be highlighted. In contrast, the heavy Ng atom and high-electronegative X atom will enhance the ω-bonding structure. Overall, the present work provides electronic principles and chemical insights that help understand the bonding in these XNgY species.

Reactive p-block cations stabilized by weakly coordinating anions

The chemistry of the p-block elements is a huge playground for fundamental and applied work. With their bonding from electron deficient to hypercoordinate and formally hypervalent, the p-block elements represent an area to find terra incognita. Often, the formation of cations that contain p-block elements as central ingredient is desired, for example to make a compound more Lewis acidic for an application or simply to prove an idea. This review has collected the reactive p-block cations (rPBC) with a comprehensive focus on those that have been published since the year 2000, but including the milestones and key citations of earlier work. We include an overview on the weakly coordinating anions (WCAs) used to stabilize the rPBC and give an overview to WCA selection, ionization strategies for rPBC-formation and finally list the rPBC ordered in their respective group from 13 to 18. However, typical, often more organic ion classes that constitute for example ionic liquids (imidazolium, ammonium, etc.) were omitted, as were those that do not fulfill the - naturally subjective -"reactive"-criterion of the rPBC. As a rule, we only included rPBC with crystal structure and only rarely refer to important cations published without crystal structure. This collection is intended for those who are simply interested what has been done or what is possible, as well as those who seek advice on preparative issues, up to people having a certain application in mind, where the knowledge on the existence of a rPBC that might play a role as an intermediate or active center may be useful.

3c/4e -type long-bonding competes with ω-bonding in noble-gas hydrides HNgY (Ng = He, Ne, Ar, Kr, Xe, Rn; Y = F, Cl, Br, I): a NBO/NRT perspective

Novel resonance bonding for the HNgY molecule is demonstrated based on natural resonance theory analyses. Ng/Y affects the ω-bonding vs. long-bonding propensity in each of the HNgY molecules.

Predicted organic compounds derived from rare gas atoms and formic acid

Organic insertion compounds of rare gas atoms into formic acid were investigated at the MP2(full)/aug-cc-pVTZ level. There are two configuration isomers for each molecule based on the location of H atoms: trans- and cis-HCOORgH (Rg = Ar, Kr, Xe). Their structures, harmonic frequencies, and decomposition energies have been calculated using the above ab initio method. Using trans-HCOOXeH as an example, natural bond orbital (NBO) and atom-in-molecules (AIM) analyses were also carried out to explore the binding nature of the rare gas atoms. The formation mechanism of molecular orbitals is also presented in this paper. The presented results indicate that HCOOXeH and HCOOKrH are potential candidates for experimental observation.

Ab initio study of the organic xenon insertion compound into ethylene and ethane

This paper studies Xe-insertion ethylene and ethane compounds, i.e., HXeC2H3 and HXeC2H5. The structures, harmonic frequencies, and energetics for both molecules have been calculated at the MP2(full)/6-311++G(2d,2p) level. Our theoretical results predict the existence of HXeC2H3 and the instability of HXeC2H5. Natural bond orbital (NBO) analysis shows a strong ionic bond between the xenon atom and hydrocarbon radical. In addition, the interaction between the donor (Xe lone pair) and acceptor (the C-C antibonding orbital, i.e., π*(C-C)) increases the stability of HXeC2H3.

XeOF2, F2OXeN identical with CCH3, and XeOF2.nHF: rare examples of Xe(IV) oxide fluorides

The syntheses of XeOF2, F2OXeNCCH3, and XeOF2.nHF and their structural characterizations are described in this study. All three compounds are explosive at temperatures approaching 0 degrees C. Although XeOF2 had been previously reported, it had not been isolated as a pure compound. Xenon oxide difluoride has now been characterized in CH3CN solution by 19F, 17O, and 129Xe NMR spectroscopy. The solid-state Raman spectra of XeOF2, F2OXeNCCH3, and XeOF2.nHF have been assigned with the aid of 16O/18O and 1H/2H enrichment studies and electronic structure calculations. In the solid state, the structure of XeOF2 is a weakly associated, planar monomer, ruling out previous speculation that it may possess a polymeric chain structure. The geometry of XeOF2 is consistent with a trigonal bipyramidal, AX2YE2, VSEPR arrangement that gives rise to a T-shaped geometry in which the two free valence electron lone pairs and Xe-O bond domain occupy the trigonal plane and the Xe-F bond domains are trans to one another and perpendicular to the trigonal plane. Quantum mechanical calculations and the Raman spectra of XeOF2.nHF indicate that the structure likely contains a single HF molecule that is H-bonded to oxygen and also weakly F-coordinated to xenon. The low-temperature (-173 degrees C) X-ray crystal structure of F2OXeNCCH3 reveals a long Xe-N bond trans to the Xe-O bond and a geometrical arrangement about xenon in which the atoms directly bonded to xenon are coplanar and CH3CN acts as a fourth ligand in the equatorial plane. The two fluorine atoms are displaced away from the oxygen atom toward the Xe-N bond. The structure contains two sets of crystallographically distinct F2OXeNCCH3 molecules in which the bent Xe-N-C moiety lies either in or out of the XeOF2 plane. The geometry about xenon is consistent with an AX2YZE2 VSEPR arrangement of bond pairs and electron lone pairs and represents a rare example of a Xe(IV)-N bond.

Atypical compounds of gases, which have been called ‘noble’

In this critical review I describe fascinating experimental and theoretical advances in 'noble gas' chemistry during the last twenty years, and have taken a somewhat unexpected course since 2000. I also highlight perspectives for further development in this field, including the prospective synthesis of compounds containing as yet unknown Xe-element and element-Xe-element bridging bonds, peroxide species containing Xe, adducts of XeF(2) with various metal fluorides, Xe-element alloys, and novel pressure-stabilized covalently bound and host-guest compounds of Xe. A substantial part of the essay is devoted to the-as yet experimentally unexplored-behaviour of the compounds of Xe under high pressure. The blend of science, history, and theoretical predictions, will be valued by inorganic and organic chemists, materials scientists, and the community of theoretical and experimental high-pressure physicists and chemists (151 references).