Stability analysis of the neutral noble gas molecules FNgX and their anions FNgX− (Ng = He,Ar, Kr; X = O,S)

The structural stability and bonding energies of the neutral noble gas molecules FNgX and their anions FNgX^? (Ng = He, Ar, Kr; X = O, S) are discussed at the CCSD(T)/aug‐cc‐pVnZ (n = D, T) levels. Results reveal that only two neutral FKrX molecules are stable, whereas their FHeX and FArX counterparts are not. All their anions are stable and the stability mainly derives from the contribution of the extra electron, i.e., the attachment of the electron greatly enhances the orbital interactions of two bonds, F? Ng and Ng? X. Different from the anion counterparts, the electrostatic interaction energy plays a crucial role in the FKrX stability. Compared with those unstable FHeX and FArX counterparts, the enough charge distribution over each atom of FKrX ensures the effective bonding between F and Kr, and between Kr and X, consequently strengthen the stability of the neutral FKrX (X = O, S) structures. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

A noble interaction: An assessment of noble gas binding ability of metal oxides (metal = Cu,Ag, Au)

An in silico study is performed on the structure and the stability of noble gas (Ng) bound MO complexes (M = Cu, Ag, Au). To understand the stability of these Ng bound complexes, dissociation energies, dissociation enthalpy, and dissociation free energy change are computed. The stability of NgMO is also compared with that of the experimentally detected NgMX (X= F, Cl, Br). It is found that MO has lower Ng binding ability than that of MX. All the dissociation processes producing Ng and MO are endothermic in nature and for the Kr‐Rn bound MO (M = Cu, Au), and Xe and Rn bound AgO cases, the corresponding dissociation processes are turned out to be endergonic in nature at standard state. The Wiberg bond indices of Ng? M bonds and Ng→M electron transfer gradually increase from Ar to Rn and for the same Ng they follow the order of NgAuO > NgCuO > NgAgO. Energy decomposition analysis shows that the Ng? M bonds in NgMO are partly covalent and partly electrostatic in nature. Electron density analysis further highlights the partial covalent character in Ng? M bonds. © 2016 Wiley Periodicals, Inc.     

Bonding of multiple noble-gas atoms to CUO in solid neon: CUO(Ng)n (Ng=Ar, Kr, Xe; n=1, 2, 3, 4) complexes and the singlet-triplet crossover point

Laser-ablated U atoms co-deposited with CO in excess neon produce the novel CUO molecule, which forms distinct Ng complexes (Ng=Ar, Kr, Xe) with the heavier noble gases. The CUO(Ng) complexes are identified through CO isotopic and Ng reagent substitution and comparison to results of DFT frequency calculations. The U[bond]C and U[bond]O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from neon matrix (1)Sigma(+) CUO values, which indicates a (1)A' ground state for the CUO(Ng) complexes. The CUO(Ng)(2) complexes in excess neon are likewise singlet molecules. However, the CUO(Ng)(3) and CUO(Ng)(4) complexes exhibit very different stretching frequencies and isotopic behaviors that are similar to those of CUO(Ar)(n) in a pure argon matrix, which has a (3)A" ground state based on DFT vibrational frequency calculations. This work suggests a coordination sphere model in which CUO in solid neon is initially solvated by four or more Ne atoms. Up to four heavier Ng atoms successively displace the Ne atoms leading ultimately to CUO(Ng)(4) complexes. The major changes in the CUO stretching frequencies from CUO(Ng)(2) to CUO(Ng)(3) provides evidence for the crossover from a singlet ground state to a triplet ground state.     

Noble gas-actinide complexes of the CUO molecule with multiple Ar,Kr, and Xe atoms in noble-gas matrices

Laser-ablated U atoms react with CO in excess argon to produce CUO, which is trapped in a triplet state in solid argon at 7 K, based on agreement between observed and relativistic density functional theory (DFT) calculated isotopic frequencies ((12)C(16)O, (13)C(16)O, (12)C(18)O). This observation contrasts a recent neon matrix investigation, which trapped CUO in a linear singlet state calculated to be about 1 kcal/mol lower in energy. Experiments with krypton and xenon give results analogous to those with argon. Similar work with dilute Kr and Xe in argon finds small frequency shifts in new four-band progressions for CUO in the same triplet states trapped in solid argon and provides evidence for four distinct CUO(Ar)(4-n)(Ng)(n) (Ng = Kr, Xe, n = 1, 2, 3, 4) complexes for each Ng. DFT calculations show that successively higher Ng complexes are responsible for the observed frequency progressions. This work provides the first evidence for noble gas-actinide complexes, and the first example of neutral complexes with four noble gas atoms bonded to one metal center.     

Investigating the nature of intermolecular and intramolecular bonds in noble gas containing molecules

This article presents a theoretical study on a number of selected noble gas containing systems of the general formula FNgR and NgR (Ng = He, Ne, Ar, Kr, Xe and R = CH₃, CN, CCH, BO, BNH, H, BeO, and AuF). The principal structures, bond energies, spectroscopic, and electronic properties of 28 noble gas containing molecules were investigated using density functional theory at the BMK level. Quantum theory of atoms in molecules, natural bond orbital, and several other analysis methods have been used to provide more insight into the nature of noble gas bonds. Although both F? Ng and Ng? R bonds in the investigated molecules are assigned to have partially covalent and partially electrostatic nature, the covalent character is dominant in Ng? R bonds. In the second part, the intermolecular interactions between FNgR molecules and hydrogen fluoride are overviewed with emphasis on the hydrogen bonding through the fluorine side of noble gas molecule with hydrogen of HF. The calculated interaction energies were found to decrease in magnitude going down the noble gas series. For all noble gases, the strongest hydrogen bond has been observed in the case R=CH₃. On the contrary, using R=CN in the FNgR moiety weakens the interaction strength. © 2014 Wiley Periodicals, Inc.     

Bonding analysis for NgAuOH (Ng = Kr,Xe)

Noble‐gas‐noble‐metal hydroxides NgAuOH (Ng = Kr, Xe) are investigated at the MP2 theoretical level. All species are found to be in Cs symmetry with an approximate linear Ng? Au? O moiety. The noble‐gas‐noble‐metal bond lengths are comparable with covalent limits, and the corresponding binding energies have been computed to be 59.6 and 83.4 kJ/mol for KrAuOH and XeAuOH, respectively. Except the charge‐induced dipole contribution to the binding energies, the remainder could be ascribed to the higher‐order charge‐induction energies, dispersion energies, the contributions of multipole moments on AuOH and covalent effects. The title species are sufficiently chemical bound and are expected to be stable species theoretically. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

M + Ng potential energy curves including spin-orbit coupling for M = K, Rb, Cs and Ng = He, Ne, Ar

The X(2)Σ(1/2)(+), A(2)Π(1∕2), A(2)Π(3∕2), and B(2)Σ(1/2)(+) potential energy curves and associated dipole matrix elements are computed for M + Ng at the spin-orbit multi-reference configuration interaction level, where M = K, Rb, Cs and Ng = He, Ne, Ar. Dissociation energies and equilibrium positions for all minima are identified and corresponding vibrational energy levels are computed. Difference potentials are used together with the quasistatic approximation to estimate the position of satellite peaks of collisionally broadened D2 lines. The comparison of potential energy curves for different alkali atom and noble gas atom combinations is facilitated by using the same level of theory for all nine M + Ng pairs.     

Insertion of noble-gas atom (Kr and Xe) into noble-metal molecules (AuF and AuOH): are they stable?

The structure and the stability of a new class of insertion compounds of noble-gas atoms of the type AuNgX (Ng=Kr, Xe and X=F, OH) have been investigated theoretically through ab initio molecular-orbital calculations. All the species are found to have a linear structure with a noble-gas-noble-metal bond, the distance of which is comparable to covalent bond length except the AuKrOH system, for which it lies in between the covalent and van der Waals limits. The dissociation energies corresponding to the lowest-energy fragmentation products, AuX+Ng have been computed to be -166.2, -276.0, -194.4, and -257.6 kJ/mol for AuXeF, AuKrF, AuXeOH, and AuKrOH, respectively, at the MP2 level of theory. The respective barrier heights corresponding to the bent transition states (Au-Ng-X bending mode) have been calculated to be 119.1, 74.9, 160.7, and 141.6 kJ/mol. However, three of these species are found to be metastable in their respective potential-energy surface, and the dissociation energies corresponding to the Au+Ng+X fragments have been calculated to be 112.9, 3.0, and 18.7 kJ/mol for AuXeF, AuKrF, and AuXeOH, respectively, at the same level of theory. An analysis of the nature of interactions involved in the Au-Ng-X systems has been performed using Bader's topological theory of atoms-in-molecules (AIM). Geometric as well as energetic considerations along with AIM results suggest a partial covalent nature of Au-Ng bonds in these systems. This work might have important implications in the preparation of a new class of insertion compounds of noble-gas atoms containing noble-gas-noble-metal bond.     

Theoretical prediction of noble-gas compounds: Ng-Pd-Ng and Ng-Pt-Ng

Following our recent study on Ng-Pt-Ng (Ng=Ar,Kr,Xe) [J. Chem. Phys. 123, 204321 (2005)], the binding of noble-gas atoms with Pd atom has been investigated by the ab initio coupled cluster CCSD(T) method with counterpoise corrections, including relativistic effects. It is shown that two Ng atoms bind with Pd atom in linear geometry due to the s-d(sigma) hybridization in Pd where the second Ng atom attaches with much larger binding energy than the first. The binding energies are evaluated as 4.0, 10.2, and 21.5 kcalmol for Ar-Pd-Ar, Kr-Pd-Kr, and Xe-Pd-Xe, respectively, relative to the dissociation limit, Pd ((1)S)+2Ng. In the hybrid Ng complexes, the binding energies for XePd and Ng (=Ar,Kr) are evaluated as 4.0 and 6.9 kcalmol for XePd-Ar and XePd-Kr, respectively. The fundamental frequencies and low-lying vibrational-rotational energy levels are determined for each compound by the variational method, based on the three-dimensional near-equilibrium potential energy surface. Results of vibrational-rotational analyses for Ng-Pt-Ng (Ng=Ar,Kr,Xe) and Xe-Pt-Ng (Ng=He,Ne,Ar,Kr) compounds are also given.     

On the noble-gas-induced intersystem crossing for the CUO molecule: experimental and theoretical investigations of CUO(Ng)n (Ng = Ar, Kr, Xe; n = 1, 2, 3, 4) complexes in solid neon

Uranium atoms excited by laser ablation react with CO in excess neon to produce the novel CUO molecule, which forms distinct Ng complexes (Ng = Ar, Kr, Xe) when the heavier noble gases are added. The CUO(Ng) complexes are identified through CO isotopic and Ng substitution on the neon matrix infrared spectra and by comparison to DFT frequency calculations. The U-C and U-O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from frequencies for the (1)Sigma(+) CUO ground state, which identifies singlet ground state CUO(Ng) complexes. In solid neon the CUO molecule is also a complex CUO(Ne)(n), and the CUO(Ne)(n-1)(Ng) complexes are likewise specified. The next singlet CUO(Ne)(x)(Ng)(2) complexes in excess neon follow in like manner. However, the higher CUO(Ne)(x)(Ng)(n) complex (n = 3, 4) stretching modes approach pure argon matrix CUO(Ar)(n) values and isotopic behavior, which are characterized as triplet ground state complexes by DFT frequency calculations. This work suggests that the singlet-triplet crossing occurs with 3 Ar, 3 Kr, or 4 Xe and a balance of Ne atoms coordinated to CUO in the neon matrix host.     

Theoretical study of Pt-Ng and Ng-Pt-Ng (Ng=Ar,Kr,Xe)

We have investigated the binding of noble-gas (Ng) atoms (Ng=Ar,Kr,Xe) with Pt atom by the ab initio coupled-cluster CCSD(T) method, taking into account the relativistic effects. It is shown that two Ng atoms can bind with Pt atom in linear geometry in the singlet lowest state where the second Ng atom attaches to Pt with the larger binding energy than the first Ng atom. The binding energy is evaluated as 8.2, 17.9, and 33.4 kcal/mol for Ar-Pt-Ar, Kr-Pt-Kr, and Xe-Pt-Xe, respectively, relative to the triplet ground state of the dissociation limit Pt ((3)D)+2Ng. The present results indicate that these Ng-Pt-Ng compounds are possible new gas-phase or matrix species.     

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

Noble gas anions of general formula FNgBN- (Ng = He-Xe) have been investigated by MP2, coupled-cluster, and multireference-CI calculations with correlation-consistent basis sets. These species reside in deep wells on the singlet potential energy surface and are thermodynamically stable with respect to the loss of F, F-, BN, and BN-. They are unstable with respect to Ng + FBN-, but at least for Ng = Ar, Kr, and Xe, the involved energy barriers are high enough to suggest their conceivable existence as metastable species. The stability of FNgBN- arises from the strong F--stabilization of the elusive NgBN. The character of the boron-noble gas bond passes from purely ionic for FHeBN- and FNeBN- to covalent for FXeBN-.     

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.     

Energetics, structure, and electron detachment spectra of calcium and zinc neutral and anion clusters: a density functional theory study

A hybrid density functional approach with very large basis sets was used for studying Ca2 through Ca19 and Zn3 through Zn11 neutral clusters and their cluster anions. Energetics, structure, and vibrational analysis of all these neutral clusters and cluster anions are reported. The calculated electron affinities are in excellent agreement with experiment displaying a characteristic kink at Ca10 and Zn10. This kink occurs because the 10-atom neutral cluster is very stable whereas the cluster anion is not. Additionally, the electron detachment binding energies (BEs) up to Ca6(-) and Zn6(-) were identified by analyzing the ground and excited states of the cluster anions and of their corresponding size neutral clusters. The theoretical BE is in very good agreement with experiment for both calcium and zinc cluster anions. The three main peaks in the spectrum correspond to BEs from the ground state of the cluster anion (doublet) to the ground state of the neutral cluster (singlet) and to the first triplet and quintet excited states of the neutral cluster. The calculated energy gap from the lowest BE peak to the second peak is in excellent agreement with experiment. The calculation reproduces very well the energy gap observed in Ca4(-) and Zn4(-), which is larger than those for other sizes and is indicative of the strong stability of the anion and neutral tetramers.     

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12Cl11]−

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 [B₁₂Cl₁₁]⁻ spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of “superelectrophilic” dications. [B₁₂Cl₁₁Ng]⁻ 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 [B₁₂Cl₁₁]⁻ anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B₁₂Cl₁₁CO]⁻ and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B₁₂Cl₁₁]⁻ 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 [C₆H₅]⁺. This introduces the new chemical concept of “dipole-discriminating electrophilic anions.”     

BX4- and AlX4- superhalogen anions (X = F, Cl, Br): an ab initio study

The vertical electron detachment energies (VDEs) of 30 MX 4 (-) (M = B, Al; X = F, Cl, Br) anions were calculated at the OVGF level with the 6-311+G(3df) basis sets. The largest vertical electron binding energy was found for the AlF 4 (-) system (9.789 eV). The strong VDE dependence on the symmetry of the species, ligand type, ligand-central atom distance, and bonding/nonbonding/antibonding character of the highest occupied molecular orbital was observed and discussed.     

Theoretical predictions of the nitrogen heterocyclic compounds with metal and noble gas (metal = Cu,Ag, Au)

Here, we report a new type of Ng-containing compounds formed between the Ng-M group and nitrogen heterocyclic compounds, (CH₂)_nHNCuNg⁺ (n = 2, 3), (CH)₄NMNg, and (CH)₅NCuNg⁺ (M = Cu, Ag, Au; Ng = Ar, Kr, Xe). Quantum chemistry computations were carried out to optimize their geometric structures and calculate the dissociation energies, dissociation enthalpy, and dissociation free energy change. The stability of these Ng-bonding complexes was inspected by investigating the three dissociation processes of the these compounds into (a) Ng, M, and nitrogen heterocycle C_nN; (b) C_nN + MNg⁺; and (c) C_nNM + Ng, which are all endothermic and nonspontaneous, these dissociation processes are also turned out to be endergonic in nature at standard state. The natural bond orbital, atoms in molecules, and energy decomposition analysis based on the molecular wavefunction show that the M-Ng and M-N bonds have some covalent and electrostatic characters.     

Photoelectron spectroscopic study of the hydrated nucleoside anions: Uridine(-)(H(2)O)(n=0-2), cytidine(-)(H(2)O)(n=0-2), and thymidine(-)(H(2)O)(n=0,1)

The hydrated nucleoside anions, uridine(-)(H(2)O)(n=0-2), cytidine(-)(H(2)O)(n=0-2), and thymidine(-)(H(2)O)(n=0,1), have been prepared in beams and studied by anion photoelectron spectroscopy in order to investigate the effects of a microhydrated environment on parent nucleoside anions. Vertical detachment energies (VDEs) were measured for all eight anions, and from these, estimates were made for five sequential anion hydration energies. Excellent agreement was found between our measured VDE value for thymidine(-)(H(2)O)(1) and its calculated value in the companion article by S. Kim and H. F. Schaefer III.     

Relative energy of organic compounds IV. Radicals,carbocations, and carbanions

The structure-dependent energies of organic radicals, cations, and anions are deduced from their calculated relative enthalpies and are compared to the relative enthalpies of their parent compounds. The use of relative enthalpies to express the relative energies of organic radicals, cations, and anions proved to be as fruitful as in the case of their parent organic compounds. The same energy-determining structural factors may have stronger, weaker, or even opposite effects in the radicals, cations, or anions than those in their parent molecules.     

How strong is the interaction between a noble gas atom and a noble metal atom in the insertion compounds MNgF (M=Cu and Ag, and Ng=Ar, Kr, and Xe)?

Ab initio molecular orbital calculations have been carried out to investigate the structure and the stability of noble gas insertion compounds of the type MNgF (M=Cu and Ag, and Ng=Ar, Kr, and Xe) through second order Moller-Plesset perturbation method. All the species are found to have a linear structure with a noble gas-noble metal bond, the distance of which is closer to the respective covalent bond length in comparison with the relevant van der Waals limit. The dissociation energies corresponding to the lowest energy fragmentation products, MF+Ng, have been found to be in the range of -231 to -398 kJ/mol. The respective barrier heights pertinent to the bent transition states (M-Ng-F bending mode) are quite high for the CuXeF and AgXeF species, although for the Ar and Kr containing species the same are rather low. Nevertheless the M-Ng bond length in MNgF compounds reported here is the smallest M-Ng bond ever predicted through any experimental or theoretical investigation, indicating strongest M-Ng interaction. All these species (except AgArF) are found to be metastable in their respective potential energy surface, and the dissociation energies corresponding to the M+Ng+F fragments have been calculated to be 30.1-155.3 kJ/mol. Indeed, in the present work we have demonstrated that the noble metal-noble gas interaction strength in MNgF species (with M=Cu and Ag, and Ng=Kr and Xe) is much stronger than that in NgMF systems. Bader's [Atoms in molecules-A Quantum Theory (Oxford University Press, Oxford, 1990)] topological theory of atoms in molecules (AIM) has been employed to explore the nature of interactions involved in these systems. Geometric as well as energetic considerations along with AIM results suggest a partial covalent nature of M-Ng bonds in these systems. The present results strengthen our earlier work and further support the proposition on the possibility of experimental identification of this new class of insertion compounds of noble gas atoms containing noble gas-noble metal bond.