Noble gas anions: a theoretical investigation of FNgBN- (Ng = He-Xe)

Noble Gas Anions: An Overview of Strategies and Bonding Motifs

This review article aims to provide an overview of the strategies employed to prepare noble gas anions under different environments and experimental conditions, and of the bonding motifs typically occurring in these species. Observed systems include anions fixed into synthesized salts, detected in the gas phase or in high-pressure devices. The major role of the theoretical calculations is also highlighted, not only in support of the experiments, but also as effective in predicting still unreported species. The chemistry of noble gas anions overall appears as a varied and rich paint, offering fascinating opportunities for both experimentalists and theoreticians.

Noble gas hydrides: theoretical prediction of the first group of anionic species

The first group of anionic noble-gas hydrides with the general formula HNgBeO- (Ng = Ar, Kr, Xe, Rn) is predicted through MP2, Coupled-Cluster, and Density Functional Theory computations employing correlation-consistent atomic basis sets. We derive that these species are stable with respect to the loss of H, H-, BeO, and BeO-, but unstable with respect to Ng + HBeO-. The energy barriers of the latter process are, however, high enough to suggest the conceivable existence of the heaviest HNgBeO- species as metastable in nature. Their stability arises from the interaction of the H- moiety with the positively-charged Ng atoms, particularly with the σ-hole ensuing from their ligation to BeO. This actually promotes relatively tight Ng-H bonds featuring a partially-covalent character, whose degree progressively increases when going from HArBeO- to HRnBeO-. The HNgBeO- compounds are also briefly compared with other noble-gas anions observed in the gas phase or isolated in crystal lattices.

Theoretical prediction of donor-acceptor type novel complexes with strong noble gas-boron covalent bond

The experimental identification of NgBeO molecules, followed by the recent theoretical exploration of super-strong NgBO+ (Ng = He-Rn) ions motivated us to investigate the stability of iso-electronic NgBNH+ (Ng = He-Rn) ions using various ab initio-based quantum chemical methods. The hydrogen-like chemical behavior of gold in small clusters and molecules also inspired us to study the nature of the bonding interactions in NgBNAu+ ions compared to that in NgBNH+ ions. The calculated Ng-B bond lengths in the predicted ions have been found to be much lower than the corresponding covalent limits, indicating a covalent Ng-B interaction in both the NgBNH+ and NgBNAu+ ions. In addition, the Ng-B bond dissociation energies are found to be in the range of 136.7-422.8 kJ mol-1 for NgBNH+ and 77.4-319.1 kJ mol-1 for NgBNAu+, implying the stable nature of the predicted ions. Interestingly, the Ng-B bond length (except for Ne) is the lowest reported to date together with the highest He-B and Ne-B binding energies considering all the neutral and cationic complexes containing Ng-B bonding motifs. Moreover, the natural bonding orbital (NBO) and electron density-based atoms-in-molecule (AIM) analysis reveal the covalent nature of the Ng-B bond in the predicted ions. Furthermore, the energy decomposition analysis together with the natural bond orbital in the chemical valence (EDA-NOCV) studies indicate that the orbital interaction energy is the main contributor to the total attraction energy in the Ng-B bonds. All the calculated results indicate the hydrogen-like chemical behavior of gold in the predicted NgBNM+ ions, showing further evidence of the concept of "gold-hydrogen analogy". Also, for comparison, the corresponding Cu and Ag analogs are investigated. All the computed results together with the experimental identification of the NgMX (Ng = Ar-Xe; M = Cu, Ag, Au; X = F, Cl), ArOH+, and NgBeO (Ng = Ar-Xe) systems clearly indicate that it may be possible to prepare and characterize the predicted NgBNM+ ions experimentally using suitable technique(s).

Superstrong Chemical Bonding of Noble Gases with Oxidoboron (BO+) and Sulfidoboron (BS+)

Inspired by the overwhelming exploration of noble gas-boron (Ng-B) bond containing chemical compounds, the stability of the Ng bound BY⁺ and AlY⁺ (Y = O and S) has been investigated by using various ab initio based quantum chemical methods. Ng atoms are found to form exceptionally strong bonds with BO⁺ species in the predicted NgBO⁺ (Ng = He-Rn) complexes with remarkably high Ng-B dissociation energies ranging from 138.0 to 462.2 kJ mol^-1 for the He-Rn series. It is the highest ever Ng-B binding energy in conjunction with the smallest Ng-B bond length for any of the cationic species involving a Ng-B bond as reported until today. More importantly, the calculated Ng-B bond lengths have been found to be much lower than the respective covalent limits in both NgBO⁺ and NgBS⁺ ions. The electronegativity difference between O and S atoms has been reflected nicely in the Ng-B and Ng-Al binding energies, which are found to be 91.9-346.5, 9.6-169.2, and 6.8-142.1 kJ mol^-1 in NgBS⁺, NgAlO⁺, and NgAlS⁺, respectively. The strong covalent bonding between Ng and B/Al atoms in the predicted chemical systems has also been supported by the natural bonding orbital (NBO) and electron density based atoms-in-molecule (AIM) analysis. In addition, the energy decomposition analysis (EDA) in combination with the natural bond orbital for chemical valence (NOCV) indicates that the orbital interaction term is the prime contributor to the total attraction energy in the Ng-B and Ng-Al bonds. Furthermore, Ng-B and Ng-Al bonding can be assessed using the donor-acceptor model where the σ-electron donation that takes place from Ng (HOMO) → XY⁺ (LUMO) (X = B and Al; Y = O and S) is the major contributor to the orbital interaction energy. All the computational results along with the very recent experimental observation of ArOH⁺ and NgMX (Ng = Ar-Xe; M = Cu, Ag, Au; X = F, Cl) clearly indicate that it might be possible to synthesize and characterize these superstrong complexes, NgXY⁺ (Ng = He-Rn; X = B and Al; Y = O and S), under suitable experimental technique(s).

Existence of Noble Gas Inserted Phosphorus Fluorides: FNgPF2 and FNgPF4 with Ng-P Covalent Bond (Ng = Ar, Kr, Xe and Rn)

Very limited literature on noble gas (Ng)-phosphorous chemical bonding and our recent theoretical prediction of FNgP molecule motivates us to explore a unique novel class of neutral noble gas inserted...

Noble Gas in a Ring

We have designed a new type of molecule with a noble gas (Ng = Kr and Xe) atom in a six-membered ring. Their structures and stability have been studied by density functional theory and by correlated electronic structure calculations. The results showed that the six-membered ring is planar with very short Ng–O and Ng–N polar covalent bonds. The calculated energy barriers for all the unimolecular dissociation pathways are higher than 20 and 35 kcal/mol for Ng = Kr and Xe, respectively. The current study suggests that these molecules and their derivatives might be synthesized and observable at cryogenic conditions.

Theoretical Prediction on the New Types of Noble Gas Containing Anions OBONgO- and OCNNgO- (Ng = He, Ar, Kr and Xe)

The fluorine-less noble gas containing anions OBONgO⁻ and OCNNgO⁻ have been studied by correlated electronic structure calculation and density functional theory. The obtained energetics indicates that for Ng=Kr and Xe, these anions should be kinetically stable at low temperature. The molecular structures and electron density distribution suggests that these anions are stabilized by ion-induced dipole interactions with charges concentrated on the electronegative OBO and OCN groups. The current study shows that in addition to the fluoride ion, polyatomic groups with strong electronic affinities can also form stable noble gas containing anions of the type Y⁻…NgO.

Anomaly in the stability of the hydroxides of icosagens (B and Al) and their noble gas (Xe and Rn) derivatives: a comparative study

Motivated by the discovery of neutral noble gas hydrides, herein, we have explored the possibility of the existence of a novel class of neutral noble gas compounds, HNgBO, HNgOB, HNgAlO and HNgOAl (Ng = Xe and Rn), through the insertion of a Ng atom into the hydroxides of icosagens and their isomers, namely, HBO, HOB, HAlO and HOAl. Second-order Møller-Plesset perturbation theory (MP2), density functional theory (DFT), and coupled-cluster theory (CCSD(T))-based methods have been employed to investigate the structures, stabilities, energetics, harmonic vibrational frequencies, and charge distribution of the predicted molecules. The HXeBO, HXeOAl, HRnBO, HRnAlO and HRnOAl molecules are found to be thermodynamically stable with respect to all plausible 2-body and 3-body dissociation channels except the 2-body dissociation pathway, leading to the formation of global minimum products (Ng + HBO), (Ng + HOAl) and (Ng + HAlO). However, the very large activation energy barrier heights provide enough kinetic stability to the predicted metastable molecules, which in turn can prevent them from dissociating into the global minimum products. Between the HNgBO-HNgOB isomers, HNgBO is found to be more stable, where both HNgBO and the precursor molecule HBO are linear. On the other hand, HNgOAl is more stable between the HNgAlO-HNgOAl isomers, where the precursor molecule HOAl is bent and HNgOAl is linear in contradiction and in agreement with Walsh's rule, respectively. Moreover, in contrast to the more stable HNgBO case, where the Ng atom is bonded with the icosagen atom, in the more stable HNgOAl, the Ng atom is connected to the chalcogen atom. All the detailed aforementioned analyses concerning the predicted molecules clearly indicate that a strong covalent bond exists between the H and Ng atoms, while an ionic interaction is found between the Ng and B atoms in HNgBO and Ng and O atoms in the HNgOAl molecules. In addition, the charge distribution and atoms-in-molecules (AIM) analyses are in agreement with the above-mentioned conclusion and also suggest that the predicted metastable HNgBO and HNgOAl molecules should essentially exist in the form of [HNg]⁺[BO]^- and [HNg]⁺[OAl]^-, respectively. All the calculated results reported in this work indicate that it might be possible to prepare and characterize the predicted molecules via suitable experimental technique(s) under cryogenic conditions.

Unprecedented stability enhancement of multiply charged anions through decoration with negative electron affinity noble gases

The present communication reports unprecedented stabilization of multiply charged anion, B12F122-, through insertion of noble gas (Ng) atoms possessing negative electron affinity into B-F bonds, resulting in the formation of stable icosahedral B12Ng12F122-, where the HOMO is stabilized significantly and the binding energy of the second excess electron is increased remarkably. Unprecedented stability enhancement with Ng is attributed to a strong covalent B-Ng bond, increased charge delocalization and increased electrostatic interaction between the oppositely charged centers.

Classifying the chemical bonds involving the noble-gas atoms

The Ng–X bonds are classified into covalent (Cov), and different types of non-covalent (nCov), or partially-covalent (pCov) interactions.

Quantum chemical prediction of a superelectrophilic dianion and its binding with noble gas atoms

A counterintuitive superelectrophilic dianion with a positive charge as well as lowest occupied molecular orbital (LUMO) localized on free-Be1 in Dianion1 embedded in the negatively charged framework, forms stable [NgBeB₁₁(CN)₁₁]²⁻ compounds.

Compounds with Rare Gas-Selenium/Tellurium Bonds: A Theoretical Investigation on FRgLF n and FRgLF n-1+ (Rg = Kr-Rn, L = Se and Te, n = 1, 3, and 5)

A new type of interesting insertion compounds FRgLF _n (Rg = Kr-Rn, L = Se and Te, n = 1, 3 and 5) and ionic FRgLF _n-1⁺ obtained through the insertion of a rare gas atom into the selenium fluorides and tellurium fluorides have been explored theoretically using MP2, CCSD(T), and PBE0 calculations. These predicted species were examined to present the optimized geometries, vibrational modes, molecular properties, thermodynamic and kinetic stabilities and bond nature. The optimized structures are without imaginary frequencies and metastable. In neutral FRgLF _n, F-Rg bonds should be of ionic character with large dissociation energy ranging from 150-200 kcal mol^-1 that could be best described by F^-(RgLF _n)⁺. Rg-L bonds have some covalent character with lower interaction energies within the range 25-40 kcal mol^-1. In FRgL⁺ and FRgLF₂⁺, the bonding nature of the F-Rg and Rg-L bonds are somewhat similar to that of the neutral compounds. In FRgLF₄⁺, the F-Rg bond could be of partial covalent type but the Rg-L bond could be considered as an ionic bond.

Noble gas supported boron-pentagonal clusters B5Ngn3+: exploring the structures and bonding

A novel type of trivalent BNg five-membered cational species B₅Ng_n³⁺(Ng = He~Rn, n = 1~5) has been found and investigated theoretically using the B3LYP and MP2 methods with the def2-QZVPPD and def2-TZVPPD basis sets. The geometry, harmonic vibrational frequencies, bond energies, charge distribution, bond nature, aromaticity, and energy decomposition analysis of these structures were reported. The calculated B-Ng bond energy is quite large (the averaged bond energy is in the range of 209.2~585.76 kJ mol^-1) for heavy rare gases and increases with the Ng atomic number. The analyses of the molecular wavefunction show that in the BNg compounds of heavy Ng atoms Ar~Rn, the B-Ng bonds are of typical covalent character. Nuclear independent chemical shifts display that both B₅³⁺ and B₅Ng_n³⁺(n=1~5) have obvious aromaticity. Energy decomposition analysis shows that these BNg compounds are mainly stabilized by the σ-donation from the Ng valence p orbital to the B₅³⁺ LUMO. These findings offer valuable clues toward the design and synthesis of new stable Ng-containing compounds.

Preparation and characterization of chemically bonded argon-boroxol ring cation complexes

Infrared spectroscopy combined with quantum chemical calculations indicates that the [ArB₃O₅]⁺, [ArB₄O₆]⁺ and [ArB₅O₇]⁺ cation complexes each involve an aromatic boroxol ring and an argon–boron covalent σ bond.

The cation complexes [ArB₃O₄]⁺, [ArB₃O₅]⁺, [ArB₄O₆]⁺ and [ArB₅O₇]⁺ were prepared via a laser vaporization supersonic ion source in the gas phase. Their vibrational spectra were measured via mass-selected infrared photodissociation spectroscopy. Spectroscopy combined with quantum chemical calculations revealed that the [ArB₃O₅]⁺, [ArB₄O₆]⁺ and [ArB₅O₇]⁺ cation complexes have planar structures each involving an aromatic boroxol ring and an argon–boron covalent bond. In contrast, the [ArB₃O₄]⁺ cation is characterized to be a weakly bound complex with a B₃O₄⁺ chain structure.

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12 Cl11 ]<sup/>

It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B₁₂ Cl₁₁ ]^- spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of "superelectrophilic" dications. [B₁₂ Cl₁₁ Ng]^- adducts, with Ng binding energies of 80 to 100 kJ mol^-1 , contain B-Ng bonds with a substantial degree of covalent interaction. The electrophilic nature of the [B₁₂ Cl₁₁ ]^- anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B₁₂ Cl₁₁ CO]^- and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B₁₂ Cl₁₁ ]^- results in an energy barrier for the approach of polar molecules and facilitates the formation of Ng adducts that are not detected with reactive cations such as [C₆ H₅ ]⁺ . This introduces the new chemical concept of "dipole-discriminating electrophilic anions."

BNg3F3: the first three noble gas atoms inserted into mono-centric neutral compounds - a theoretical study

Following the study of HXeOXeH and HXeCCXeH, in which two Xe atoms were inserted into H2O and C2H2 theoretically and experimentally, the structures and stability of BNg3F3 (Ng = Ar, Kr and Xe), in which three Ng atoms are inserted into BF3, have been explored theoretically using DFT and ab initio calculations. It is shown that BNg3F3 (Ng = Ar, Kr and Xe) with D3h symmetry are local minima with short B-Ng bond lengths of 1.966, 2.027 and 2.214 Å at the CCSD(T)/aug-cc-pVTZ/LJ18 level, which are close to their covalent limits. Note that although BNg3F3 (Ng = Kr and Xe) are energetically higher than the dissociation products 3Ng + BF3, they are still kinetically stable as metastable species with protecting barriers of 13.38 and 17.99 kcal mol(-1) for BKr3F3 and BXe3F3. Moreover, BKr3F3, the tri-Kr-inserted compound, even has comparable kinetic stability to HXeOXeH and HXeOXeF. In addition, upon the formation of BNg3F3, there is a large amount of charge transferred from B to Ng of at least 0.619 e. The calculated Wiberg Bond Indices (WBI) suggest that B-Ng bonds are naturally singly bonded; the large vibrational frequencies of B-Ng and Ng-F stretching modes and the negative Laplacian electron density of B-Ng bonds confirm further that BNg3F3 are stiff molecules with covalent B-Ng bonds. It should be noted that three Ng atoms inserted into mono-centric neutral molecules have not been reported previously. We hope that the present theoretical study may provide important evidence for the experimental synthesis of BNg3F3.

Theoretical Study on the Noble Gas Exchange Reactions of Ng + HNBNg'(+) → Ng' + HNBNg(+) (Ng, Ng' = He, Ne, Ar, Kr, and Xe)

High-level correlated electronic structure calculation and dual-level variational transition state theory with multidimensional tunneling calculation for rate constants have been performed on four noble gas exchange reactions [(1) He + HNBHe'(+) → He' + HNBHe(+), (2) He + HNBNe(+) → Ne + HNBHe(+), (3) Ne + HNBNe'(+) → Ne' + HNBNe(+), and (4) Ar + HNBAr'(+) → Ar' + HNBAr(+)] and on three (3)He isotopic analogues (He + HNB(3)He(+), (3)He + HNBHe(+), and (3)He + HNB(3)He(+)) of the first reaction. The classical barrier heights were predicted to be 8.9, 6.8, 5.7, and 5.5 kcal/mol for the four reactions, respectively. The tunneling effects were found to be important below 250 K for the He reactions and below 150 K for the Ne and Ar reactions. Kinetic helium isotope effects as large as 7.8 at 100 K were predicted for the (3)He + HNB(3)He(+) reaction. Additionally, the structures and energies of the Kr + HNBKr'(+) and Xe + HNBXe'(+) systems have also been studied.

Noble gas supported B3+ cluster: formation of strong covalent noble gas–boron bonds

Ar to Rn atoms formed exceptionally strong bonds with B₃⁺, where the Ng (HOMO) → B₃Ng₂⁺ (LUMO) σ-donation is the key term to stabilize the complexes.

Stable Lithium Argon compounds under high pressure

High pressure can fundamentally alter the bonding patterns of chemical elements. Its effects include stimulating elements thought to be “inactive” to form unexpectedly stable compounds with unusual chemical and physical properties. Here, using an unbiased structure search method based on CALYPSO methodology and density functional total energy calculations, the phase stabilities and crystal structures of Li−Ar compounds are systematically investigated at high pressure up to 300 GPa. Two unexpected Li_mAr_n compounds (LiAr and Li₃Ar) are predicted to be stable above 112 GPa and 119 GPa, respectively. A detailed analysis of the electronic structure of LiAr and Li₃Ar shows that Ar in these compounds attracts electrons and thus behaves as an oxidizing agent. This is markedly different from the hitherto established chemical reactivity of Ar. Moreover, we predict that the P4/mmm phase of Li₃Ar has a superconducting transition temperature of 17.6 K at 120 GPa.

Theoretical investigation of HNgNH3(+) ions (Ng = He, Ne, Ar, Kr, and Xe)

The equilibrium geometries, harmonic frequencies, and dissociation energies of HNgNH3(+) ions (Ng = He, Ne, Ar, Kr, and Xe) were investigated using the following method: Becke-3-parameter-Lee-Yang-Parr (B3LYP), Boese-Matrin for Kinetics (BMK), second-order Møller-Plesset perturbation theory (MP2), and coupled-cluster with single and double excitations as well as perturbative inclusion of triples (CCSD(T)). The results indicate that HHeNH3(+), HArNH3(+), HKrNH3(+), and HXeNH3(+) ions are metastable species that are protected from decomposition by high energy barriers, whereas the HNeNH3(+) ion is unstable because of its relatively small energy barrier for decomposition. The bonding nature of noble-gas atoms in HNgNH3(+) was also analyzed using the atoms in molecules approach, natural energy decomposition analysis, and natural bond orbital analysis.

Noble-Gas-Inserted Fluoro(sulphido)boron (FNgBS, Ng = Ar, Kr, and Xe): A Theoretical Prediction

The possibility of the existence of a new series of neutral noble gas compound, FNgBS (where Ng = Ar, Kr, Xe), is explored theoretically through the insertion of a Ng atom into the fluoroborosulfide molecule (FBS). Second-order Møller-Plesset perturbation theory, density functional theory, and coupled cluster theory based methods have been employed to predict the structure, stability, harmonic vibrational frequencies, and charge distribution of FNgBS molecules. Through energetics study, it has been found that the molecules could dissociate into global minima products (Ng + FBS) on the respective singlet potential energy surface via a unimolecular dissociation channel; however, the sufficiently large activation energy barriers provide enough kinetic stability to the predicted molecules, which, in turn, prevent them from dissociating into the global minima products. Moreover, the FNgBS species are thermodynamically stable, owing to very high positive energies with respect to other two two-body dissociation channels, leading to FNg + BS and F(-) + NgBS(+), and two three-body dissociation channels, corresponding to the dissociation into F + Ng + BS and F(-) + Ng + BS(+). Furthermore, the Mulliken and NBO charge analysis together with the AIM results reveal that the Ng-B bond is more of covalent in nature, whereas the F-Ng bond is predominantly ionic in character. Thus, these compounds can be better represented as F(-)[NgBS](+). This fact is also supported by the detail analysis of bond length, bond dissociation energy, and stretching force constant values. All of the calculated results reported in this work clearly indicate that it might be possible to prepare and characterize the FNgBS molecules in cryogenic environment through matrix isolation technique by using a mixture of OCS/BF3 in the presence of large quantity of noble gas under suitable experimental conditions.

A theoretical study of stabilities, reactivities and bonding properties of XKrOH (X = F, Cl, Br and I) as potential new krypton compounds using coupled cluster, MP2 and DFT calculations

DFT andAb initiocalculations were employed to disclose the conceivable existence of new noble gas molecules, XKrOH.

Theoretical prediction of XRgCO(+) ions (X = F, Cl, and Rg = Ar, Kr, Xe)

In this work we have predicted novel rare gas containing cationic molecules, XRgCO(+) (X = F, Cl and Rg = Ar, Kr, Xe) using ab initio quantum chemical methods. Detail structural, stability, vibrational frequency, and charge distribution values are reported using density functional theory, second-order Møller-Plesset perturbation theory, and coupled-cluster theory based methods. These ions are found to be metastable in nature and exhibit a linear geometry with C∞v symmetry in their minima energy structures, and the nonlinear transition state geometries are associated with Cs symmetry. Except for the two-body dissociation channel (Rg + XCO(+)), these ions are stable with respect to all other dissociation channels. However, the connecting transition states between the above-mentioned two-body dissociation channel products and the predicted ions are associated with sufficient energy barriers, which restricts the metastable species to transform into the global minimum products. Thus, it may be possible to detect and characterize these metastable ions using an electron bombardment technique under cryogenic conditions.

Theoretical prediction of rare gas containing hydride cations: HRgBF+ (Rg = He, Ar, Kr, and Xe)

The existence of rare-gas-containing hydride ions of boron (HRgBF(+)) has been predicted by using ab initio quantum chemical methods. The HRgBF(+) ions are obtained by inserting a rare gas (Rg) atom in between the H and B atoms of a HBF(+) ion, and the geometries are optimized for minima as well as transition states using second-order Møller-Plesset perturbation theory (MP2), density functional theory (DFT), and coupled-cluster theory (CCSD(T)) based techniques. The predicted HRgBF(+) ions are found to be metastable, and they exhibit a linear structure at the minima and a nonlinear planar structure at the transition state, corresponding to C∞v and Cs symmetries, respectively. All of the predicted HRgBF(+) ions show negative binding energies with respect to the two-body dissociation channel, leading to global minima (HBF(+) + Rg) on the singlet potential energy surface. In contrast, the dissociation energies corresponding to another two-body dissociation channel leading to HRg(+) + BF and two three-body dissociation channels corresponding to the dissociation into H + Rg + BF(+) and H(+) + Rg + BF show very high positive energies. Apart from positive dissociation energies, the predicted ions show finite barrier heights corresponding to the transition states involving a H-Rg-B bending mode, leading to the global minima products (HBF(+) + Rg). The finite barrier heights in turn would prevent the metastable HRgBF(+) species from transforming to global minima products. Structure, harmonic vibrational frequencies, stability, and Mulliken and natural bonding orbital (NBO) charge distribution values for all of the species are reported using the MP2 and DFT methods. Furthermore, the intrinsic reaction coordinate analysis confirms that the metastable minimum-energy structure and the global minimum products are connected through the corresponding transition state for each of the species on the respective singlet potential energy surface. Atoms-in-molecules (AIM) analysis indicates that the HRgBF(+) ions are best described as HRg(+)BF and are analogous to the isoelectronic HRgCO(+) and HRgN2(+) ions. The energetic along with charge redistribution and spectroscopic data strongly support the possible existence of HRgBF(+) ions. Hence, it might be possible to generate HRgBF(+) ions in the DC discharge plasma of a BF3/H2/Rg mixture at low temperature, and the predicted ions may be characterized using the magnetic field modulated infrared laser spectroscopic technique, which has been used earlier to characterize HBF(+) ions.

Theoretical prediction of new noble-gas molecules FNgBNR (Ng = Ar, Kr, and Xe; R = H, CH3, CCH, CHCH2, F, and OH)

We have computationally predicted a new class of stable noble-gas molecules FNgBNR (Ng = Ar, Kr, Xe; R = H, CH3, CCH, CHCH2, F, and OH). The FNgBNR were found to have compact structures with F-Ng bond lengths of 1.9-2.2 Å and Ng-B bond lengths of ~1.8 Å. The endoergic three-body dissociation energies of FNgBNH to F + Ng + BNH were calculated to be 12.8, 31.7, and 63.9 kcal mol(-1), for Ng = Ar, Kr, and Xe, respectively at the CCSD(T)/CBS level. The energy barriers of the exoergic two-body dissociation to Ng + FBNH were calculated to be 16.1, 24.0, and 33.2 kcal mol(-1) for Ng = Ar, Kr, and Xe, respectively. Our results showed that the dissociation energetics is relatively insensitive to the identities of the terminal R groups. The current study suggested that a wide variety of noble-gas containing molecules with different types of R groups can be thermally stable at low temperature, and the number of potentially stable noble-gas containing molecules would thus increase very significantly. It is expected some of the FNgBNR molecules could be identified in future experiments under cryogenic conditions in noble-gas matrices or in the gas phase.

Theoretical prediction on the structures and stability of the noble-gas containing anions FNgCC- (Ng=He, Ar, Kr, and Xe)

We have made high-level theoretical study on a new type of noble-gas (Ng) containing anions FNgCC(-). The calculated short Ng-CC bond lengths of 1.13, 1.77, 1.89, and 2.04 Å for Ng=He, Ar, Kr, and Xe, respectively, and the electron density distributions indicated strong covalent interactions between the Ng and CC induced by the polarizing fluoride ion. Except for FHeCC(-), the structures of all other FNgCC(-) were predicted to be linear. The intrinsic stability of the FNgCC(-) was studied by calculating the energies of the three-body dissociation reaction: FNgCC(-) → F(-) + Ng + CC and by calculating the energy barriers of the two-body dissociation reaction: FNgCC(-) → Ng + FCC(-). The results showed that FNgCC(-) (Ng=Ar, Kr, Xe) could be kinetically stable in the gas phase with the three-body dissociation energies of 17, 37, and 64 kcal/mol and two body-dissociation barriers of 22, 31, and 42 kcal/mol, respectively, at the coupled-cluster single double (triple)/aug-cc-pVQZ level of theory. The structures and the stability were also confirmed using the multi-reference CASPT2 calculation. Future experimental identification of the FNgCC(-) anions is expected under cryogenic conditions.

Benchmark of density functional theory methods on the prediction of bond energies and bond distances of noble-gas containing molecules

We have tested three pure density functional theory (DFT) functionals, BLYP, MPWPW91, MPWB95, and ten hybrid DFT functionals, B3LYP, B3P86, B98, MPW1B95, MPW1PW91, BMK, M05-2X, M06-2X, B2GP-PLYP, and DSD-BLYP with a series of commonly used basis sets on the performance of predicting the bond energies and bond distances of 31 small neutral noble-gas containing molecules. The reference structures were obtained using the CCSD(T)∕aug-cc-pVTZ theory and the reference energies were based on the calculation at the CCSD(T)∕CBS level. While in general the hybrid functionals performed significantly better than the pure functionals, our tests showed a range of performance by these hybrid functionals. For the bond energies, the MPW1B95∕6-311+G(2df,2pd), BMK∕aug-cc-pVTZ, B2GP-PLYP∕aug-cc-pVTZ, and DSD-BLYP∕aug-cc-pVTZ methods stood out with mean unsigned errors of 2.0-2.3 kcal∕mol per molecule. For the bond distances, the MPW1B95∕6-311+G(2df,2pd), MPW1PW91∕6-311+G(2df,2pd), and B3P86∕6-311+G(2df,2pd), DSD-BLYP∕6-311+G(2df,2pd), and DSD-BLYP∕aug-cc-pVTZ methods stood out with mean unsigned errors of 0.008-0.013 Å per bond. The current study showed that a careful selection of DFT functionals is very important in the study of noble-gas chemistry, and the most recommended methods are MPW1B95∕6-311+G(2df,2pd) and DSD-BLYP∕aug-cc-pVTZ.

Review: gas-phase ion chemistry of the noble gases: recent advances and future perspectives

This review article surveys recent experimental and theoretical advances in the gas-phase ion chemistry of the noble gases. Covered issues include the interaction of the noble gases with metal and non-metal cations, the conceivable existence of covalent noble-gas anions, the occurrence of ion-molecule reactions involving singly-charged xenon cations, and the occurrence of bond-forming reactions involving doubly-charged cations. Research themes are also highlighted, that are expected to attract further interest in the future.

Cationic noble gas hydrides: a theoretical investigation of dinuclear HNgFNgH+ (Ng = He-Xe)

Theoretical calculations at the B3LYP, MP2, and CCSD(T) levels of theory disclose the conceivable existence of cationic noble gas hydrides containing two Ng atoms. These species have a general formula of HNgFNgH(+) (Ng = He-Xe), and are the cationic counterparts of the neutral HNgF. The optimized geometries, harmonic frequencies, and bonding properties point to ion-dipole complexes between a fluoride anion and two covalent H-Ng(+) cations, best formulated as (H-Ng(+))(2)F(-). The HXeFXeH(+) is also isoelectronic with the recently experimentally observed HXeOXeH (Khriachtchev et al. J. Am. Chem. Soc. 2008, 130, 6114-6118). The resulting HNgFNgH(+) are thermochemically stable with respect to dissociation into HNg(+) + HNgF and HNg(+) + H + Ng + F, but are largely unstable with respect to both the loss of HF (with formation of HNg(+) + Ng) and H(2)F(+) (with formation of two Ng atoms). These decompositions pass through bent transition structures, and only the heaviest HArFArH(+), HKrFKrH(+), and HXeFXeH(+) are protected by energy barriers large enough (ca. 10-15 kcal mol(-1)) to support their conceivable metastability. In line with other series of noble gas compounds, the neon cation HNeFNeH(+) is the least stable among the various HNgFNgH(+).