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

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.

OBCN isomerization and noble gas insertion compounds of identical valence electron number species: stability and bonding

A series of new noble gas (Ng) insertion compounds of the general type XNgX, XNgY and XNgY+ has been theoretically studied using ab initio and DFT methods herein. We first studied the isomerization process of the OBCN compound, and then investigated the bonding properties and stability of the compounds formed by inserting Ng into the single bond of the three low energy isomers by high-level ab initio calculations. The OBNgCN compounds are thermochemically stable with respect to all dissociation channels except for the processes of releasing OBCN/OBNC and free Ng. Furthermore, the two dissociation processes OBNgCN → Ng + OBNC and OBNgNC → Ng + OBCN are kinetically prohibited by the relatively high free energy barrier ranging from 22.7 to 31.7 kcal mol-1 except for the OBKrCN and OBKrNC analogues. And the adaptive natural density partitioning (AdNDP) analysis indicated that chemical bonding in OBNgCN compounds is realized via a delocalized 3-center 2-electron (3c-2e) σ-bond in the B-Ng-C moiety and a totally delocalized 5-center 2-electron (5c-2e) σ-bond in the whole O-B-Ng-C-N. Natural bond orbital (NBO) theory, atoms-in-molecules (AIM) and energy decomposition analysis (EDA) based on the molecular wavefunction revealed that the B-Ng bond and Ng-C bond have some covalent character in OBNgCN. In addition, the calculation and detailed bonding analysis on a large number of neutral and monocationic compounds with identical valence electron numbers to OBNgCN demonstrate that the two bonds directly linked to the Ng atoms have covalent properties in neutral compounds, whereas Ng forms one typical covalent bond and one partial covalent and partial ionic bond with the neighboring atoms in the monocationic compounds.

Noble gas inserted compounds of borazine and its derivative B3N3R6: structures and bonding

Quantum chemistry computations were performed at the MP2 and B3LYP levels of theory using the basis sets aug-cc-pVDZ and def2-TZVPPD to study the noble gas (Ng) compounds formed by insertion of a Ng atom (Kr, Xe, Rn) into the B-H/F and N-H/F bonds of inorganic benzene B₃N₃H₆ and its fluorine derivative B₃N₃F₆. The geometrical structures were optimized and vibrational analysis was carried out to demonstrate these structures being local minima on the potential energy surface. The thermodynamic properties of the formation process of Ng compounds were calculated. A series of theoretical methods based on the wavefunction analysis, including NBO, AIM and ELF methods and energy decomposition analysis, was used to investigate the bonding nature of the noble gas atoms and the properties of the Ng compounds. The N-Ng bond was found to be stronger than the B-Ng bond, but the B-Ng bond is of typical covalent character and σ-donation from the Ng atom to the ring B atom makes the predominant contribution towards stability of the B-Ng bond. NICS calculation shows that these Ng-containing compounds are of weak π-aromaticity.

Noble gas hydrides in the triplet state: HNgCCO+ (Ng = He, Ne, Ar, Kr, and Xe)

Motivated by the very recent investigations of neutral noble gas compounds in the open-shell configuration, we explored a new series of noble gas hydrides in the triplet state. The possible existence of noble gas-inserted ketenyl cations, HNgCCO+ (Ng = He, Ne, Ar, Kr, and Xe), in their triplet electronic state has been predicted by various ab initio quantum chemical techniques. Density functional theory (DFT), second-order Møller-Plesset perturbation theory (MP2), and coupled-cluster theory (CCSD(T)) based methods have been employed to investigate the structures, energetics, harmonic vibrational frequencies, and charge distribution analysis of these ions. The aforementioned ions have been 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 minima products (Ng + HCCO+). Nevertheless, each of the predicted HNgCCO+ ions is connected to the global minima products through a transition state with a finite barrier height on the potential energy surface, which confirms the kinetic stability of the metastable species. Detailed analysis of the optimized structural parameters, energetics, and harmonic vibrational frequencies of the predicted species clearly indicated that a strong covalent bond exists between H and Ng atoms, while a comparatively weak interaction is found between Ng and C atoms. Moreover, charge distribution and atoms-in-molecules (AIM) analysis strongly concurred with the above inferences and also suggested that the predicted metastable ions should exist essentially in the form of [HNg]+[CCO] complex. These results ultimately indicate that these predicted species may be prepared and characterized by suitable experimental technique(s) under a cryogenic environment.

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.

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

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.

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.

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.

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.