Xe Complexes Research Articles

Bonding Nature between Noble Gases and Small Gold Clusters.

Noble gases are usually seen as utterly inert, likewise gold, which is typically conceived as the noblest of all metals. While one may expect that noble gases bind to gold via dispersion interactions only, strong bonds can be formed between noble gas atoms and small gold clusters. We combine mass spectrometry, infrared spectroscopy, and density functional theory calculations to address the bonding nature between Aun+ (n ≤ 4) clusters and Ar, Kr, and Xe. We unambiguously determine the geometries and quantitatively uncover the bonding nature in AunNgm+ (Ng = Ar, Kr, Xe) complexes. Each Au cluster can form covalent bonds with atop bound noble gas atoms, with strengths that increase with the noble gas atomic radius. This is demonstrated by calculated adsorption energies, Bader electron charges, and analysis of the electron density. The covalent bonding character, however, is limited to the atop-coordinated Ng atoms.

New infrared spectra of CO2–Xe: modelling Xe isotope effects, intermolecular bend and stretch, and symmetry breaking of the CO2 bend

The infrared spectrum of the weakly bound CO2–Xe complex is studied in the region of the carbon dioxide ν3 fundamental vibration (≈2350 cm−1), using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. The Xe isotope dependence of the spectrum is modelled by scaling the vibrational and rotational parameters, with the help of previous microwave data. The scaling model provides a good simulation of the observed broadening and (partial) splitting of transitions in the fundamental band, and it is essential for understanding the intermolecular bending combination band where some transitions are completely split by isotope effects. The combination band is influenced by a significant bend–stretch Coriolis interaction and by the relatively large Xe isotope dependence of the intermolecular stretch frequency. The weak CO2–Xe spectrum corresponding to the (0111) ← (0110) hot band of CO2 is also detected and analysed, providing a measurement of the symmetry breaking of the CO2 bending mode induced by the nearby Xe atom. This in-plane/out-of-plane splitting is determined to be 2.14 cm−1.

Intermolecular dynamics of NH3-rare gas complexes in the ν2 umbrella region of NH3 investigated by rovibrational laser jet-cooled spectroscopy and ab initio calculations.

High resolution jet-cooled spectroscopy experiments have been realized to investigate the intermolecular dynamics of van der Waals (vdW) heterodimers between NH3 and rare gas (Rg) atoms in the ν2 umbrella mode region of NH3. With respect to a previous study dedicated to NH3-Ar [Asselin et al. Mol. Phys. 116, 3642 (2018)], the sensitivity and spectral resolution of our laser spectrometer coupled to a pulsed supersonic jet have been significantly improved to derive more accurate excited state spectroscopic parameters from rovibrational analyses. In addition, we calculated the ground and ν2 excited vibration-rotation-tunneling (VRT) states of these complexes on the four-dimensional ab initio potential energy surfaces from Loreau et al. [J. Chem. Phys. 141, 224303 (2014), ibid. 143, 184303 (2015).] Transition frequencies and intensities of the allowed ν2 = 1 ← 0 transitions obtained from the calculated energy levels and wave functions agree well with the experimental data and are helpful in their analysis. By means of a pseudodiatomic model with the assumption of weak Coriolis coupling, the rovibrational analysis of both the Πe/f(j = 1,k = 0) ←Σf(j = 0,k = 0) and Σf(j = 1,k = 0) ←Σf(j = 0,k = 0) transitions in ortho NH3-Rg (Rg = Ne, Ar, Kr, Xe) complexes enabled us to determine reliable excited state parameters and derive accurate values of the effective vdW bond length Reff, force constant ks, and vdW stretching frequency νs. Comparison between the experimental structural parameters and those from the ab initio calculated VRT levels shows good agreement for NH3-Ne, NH3-Ar and NH3-Kr, and a similar variation of Reff, ks, and νs with the polarizability of Rg in the ground and ν2 excited states. Anomalously small values of νs and ks derived for NH3-Xe in the Πe/f(j = 1,k = 0) state suggest that the applied model is not valid in this case, due to the presence of another state coupling to the perturbed Πf state. Such a state could not be found, however.

Ab initio relativistic potential energy surfaces of benzene-Xe complex with application to intermolecular vibrations.

The benzene-Xe (BXe) complex in its electronic ground state is studied using ab initio methods. Since this complex contains the heavy Xe atom, the relativistic effects cannot be neglected. We test two different approaches that describe the scalar relativistic effects in the framework of the coupled-cluster level of theory with single, double, and perturbative triple excitations, used for the interaction energy calculations. The first one is based on the small core pseudopotential (PP), and the second one is based on the explicit treatment of scalar relativistic effects using the Douglas-Kroll-Hess (DKH) Hamiltonian. A few basis sets are tested with the PP and DKH, and for each one, the analytical potential energy surface (PES) is constructed. It is shown that the difference between PESs determined with PP and DKH methods is small, if the orbitals of the 4d subshell in Xe are correlated. We select the most appropriate approach for the calculation of the potential energy surface of BXe, with respect to accuracy and computational cost. The optimal level of theory includes a small Dunning's basis set for the benzene monomer and a larger PP basis set for Xe supplemented by midbond functions. The PES obtained using such an approach provides a reasonable accuracy when compared to the empirical one derived from the microwave spectra of BXe. The empirical and the theoretical values of intermolecular vibrational energies agree within 0.5 cm-1 up to second overtones. The vibrational energy level pattern of BXe is characterized by a distinct polyad structure.

Theoretical Investigation on H2O2-Ng (He, Ne, Ar, Kr, Xe, and Rn) Complexes Suitable for Stereodynamics: Interactions and Thermal Chiral Rate Consequences.

Although molecular collisions of noble gases (Ng) can be theoretically used to distinguish between the enantiomers of hydrogen peroxide - H2O2 (HP), little is known about the effects of HP-Ng interactions on the chiral rate. In this work, the chiral rate as a function of temperature (CRT) between enantiomeric conformations of HP and Ng (Ng=He, Ne, Ar, Kr, Xe, and Rn) are presented at MP2(full)/aug-cc-pVTZ level of theory through a fully basis set superposition error (BSSE) corrected potential energy surface. The results show that: (a) the CRT is highly affected even at a small decrease in the height of trans-barrier; (b) its smallest values occur with Ne for all temperatures between 100 and 4,000 K; (c) that the decrease of CRT shows an inverse correlation with respect to the average valence electron energy of the Ng and (d) Ne and He may be the noble gases more suitable for study the oriented collision dynamics of HP. In addition to binding energies, the electron density ρ and its Laplacian ∇2ρ topological analyses were also performed within the atoms in molecules (AIM) theory in order to determine the nature of the HP-Ng interactions. The results of this work provide a more complete foundation on experiments to study HP's chirality using Ng in crossed molecular beams without a light source.

Noble Gas-Tungsten Peroxide Complexes in Noble Gas Matrixes: Infrared Spectroscopy and Density Functional Theoretical Study.

The matrix isolation infrared spectroscopic and quantum chemical calculation results indicate that tungsten oxo and mono-superoxide, WO3 and (η2-O2)WO2, coordinate noble gas atoms in forming noble gas-tungsten oxide complexes. The results showed that both WO3 and (η2-O2)WO2 oxides can coordinate one Ar or Xe atom in solid noble gas matrixes; otherwise, tungsten mono- and dioxides cannot. Hence, the WO3 and (η2-O2)WO2 molecules trapped previously in solid argon noble gas matrixes should be regarded as the WO3(Ar) oxide and (η2-O2)WO2(Ar) peroxide complexes. When annealing, the lighter Ar atom can be replaced by a heavier xenon atom to form WO3(Xe) and (η2-O2)WO2(Xe) complexes. What's more, upon UV photolysis, both Ar and Xe atoms can be replaced by oxygen to form a tungsten disuperoxide (η2-O2)2WO2 complex. The binding energies were predicted to be 25.7, 16.6, 9.4, 14.7, and 8.1 kcal/mol for the (η2-O2)2WO2, WO3(Xe), WO3(Ar), (η2-O2)WO2(Xe), and (η2-O2)WO2(Ar) complexes at the CCSD(T)//M06-2X-D3//def2-TZVP/DGDZVP/SDD level. The substitution law, O2 > Xe > Ar, can be interpreted according to the chemical reaction energies calculated to be -6.6 and +11.0 kcal/mol, respectively, for the equation formulas Xe + (η2-O2)WO2(Ar) = (η2-O2)WO2(Xe) + Ar and O2 + (η2-O2)WO2(Xe) = (η2-O2)2WO2 + Xe at the same level.

Boron Nanowheels with Axles Containing Noble Gas Atoms: Viable Noble Gas Bound M©B10- Clusters (M=Nb, Ta).

The viability of noble gas axled boron nanowheels Ngn M©B10- (Ng=Ar-Rn; M=Nb, Ta; n=1, 2) is explored by ab initio computations. In the resulting Ng2 -M complexes, the Ng-M-Ng nanorod passes through the center of the B10- ring, providing them with an inverse sandwich-like structure. While in the singly Ng bound analogue, the Ng binding enthalpy Hb at 298 K ranges from 2.5 to 10.6 kcal mol-1 , in doubly Ng bound cases it becomes very low for the Ng2 M©B10- →Ng+NgM©B10- dissociation channel, except for the case of Rn, for which the corresponding Hb values are 3.4 (Nb) and 4.0 kcal mol-1 (Ta). For a given Ng, Ta has slightly higher Ng-binding ability than Nb. The corresponding free-energy changes indicate that these systems, particularly the Xe and Rn complexes, are good candidates for experimental realization in a low-temperature matrix. The Ng-M bonds were found to be covalent in nature, as reflected in their large Wiberg bond indices, formation of a 2c-2e σ orbital between Ng and M centers in natural bond orbital and adaptive natural density partitioning (AdNDP) analyses, and the short Ng-M distances. Energy decomposition analysis and a study on the natural orbitals for chemical valence show that the Ng-M contact is supported mainly by the orbital and electrostatic interactions, with almost equal contributions. Although both the Ng→M σ donation and Ng←M π backdonation play roles in the origin of orbital interaction, the former is significantly dominant over the latter. Further, AdNDP analysis indicates that the doubly aromatic character (both σ and π) in MB10- clusters is not perturbed by the interaction with Ng atoms.

A Noncovalent Binding Strategy to Capture Noble Gases, Hydrogen and Nitrogen.

A molecular design strategy to develop receptor systems for the entrapment of noble gases, H2 and N2 is described using M06L-D3/6-311++G(d,p)//M06L/6-311++G(d,p) DFT method. These receptors made with two-, three-, four- and five-fluorinated benzene cores, linked with methelene units viz. RI , RII , RIII and RIV as well as the corresponding non-fluorinated hydrocarbons viz. RIH , RIIH , RIIIH and RIVH show a steady and significant increase in binding energy (Eint ) with increase in the number of aromatic rings in the receptor. A stabilizing "cage effect" is observed in the cyclophane type receptors RIV and RIVH which is 26-48% of total Eint for all except the larger sized Kr, Xe and N2 complexes. Eint of RIV …He, RIV …Ne, RIV …Ar, RIV …Kr, RIV …H2 and RIV …N2 is 4.89, 7.03, 6.49, 6.19, 8.57 and 8.17 kcal/mol, respectively which is 5- to9-fold higher than that of hexafluorobenzene. Similarly, compared to benzene, multiple fold increase in Eint is observed for RIVH receptors with noble gases, H2 and N2 . Fluorination of the aromatic core has no significant impact on Eint (∼ ±0.5 kcal/mol) for most of the systems with a notable exception of the cage receptor RIV for N2 where fluorination improves Eint by 1.61 kcal/mol. The Eint of the cage receptors may be projected as one of the highest interaction energy ranges reported for noble gases, H2 and N2 for a neutral carbon framework. Synthesis of such systems is promising in the study of molecules in confined environment. © 2018 Wiley Periodicals, Inc.

Theoretical investigation of the weak interactions of rare gas atoms with silver clusters by resonance Raman spectroscopy modeling

AbstractThe interactions of rare gas atoms (Rg = Ar, Kr, and Xe) with small neutral and cationic silver clusters have been investigated by density functional methods and the effect of these weak interactions on the resonance Raman spectra of the complexes has been evaluated. The resonance Raman technique that depends on the properties of ground and excited state, seems deeply sensitive to the weak rare gas–metal cluster interactions, and the use of inert gases has been proven to be an excellent approach to recognize the ability of this technique to detect extremely weak interactions. In this work, for , and complexes the IR, normal and resonance Raman spectra have been calculated and the effect of rare gas–cluster stretching vibration ( ) on the pattern and the relative intensities of different spectra have been investigated. The resonance Raman spectra for the weakly interacted complexes (with the interaction energies less than −2.0 kcal/mol) exhibit the vibration with the detectable intensity that its intensity increases by going from Ag6–Ar to Ag6–Xe complex. Moreover, the resonance Raman spectra (based on the excited state gradient approximation) for high intensity nearly degenerate excited states, proved the effect of accumulation of the excited state charge density on the relative intensity of vibration.

Unprecedented Enhancement of Noble Gas-Noble Metal Bonding in NgAu3+ (Ng = Ar, Kr, and Xe) Ion through Hydrogen Doping.

Behavior of gold as hydrogen in certain gold compounds and a very recent experimental report on the noble gas-noble metal interaction in Ar complexes of mixed Au-Ag trimers have motivated us to investigate the effect of hydrogen doping on the Ng-Au (Ng = Ar, Kr, and Xe) bonding through various ab initio based techniques. The calculated results show considerable strengthening of the Ng-Au bond in terms of bond length, bond energy, stretching vibrational frequency, and force constant. Particularly, an exceptional enhancement of Ar-Au bonding strength has been observed in ArAuH2+ species as compared to that in ArAu3+ system, as revealed from the CCSD(T) calculated Ar-Au bond energy value of 32 and 72 kJ mol-1 for ArAu3+ and ArAuH2+, respectively. In the calculated IR spectra, the Ar-Au stretching frequency is blue-shifted by 65% in going from ArAu3+ to ArAuH2+ species. Similar trends have been obtained in the case of all Ar, Kr, and Xe complexes with Ag and Cu trimers. Among all the NgM3-kHk+ complexes (where k = 0-2), the strongest binding in NgMH2+ complex is attributed to significant enhancement in the covalent characteristics of the Ng-M bond and considerable increase in charge-induced dipole interaction, as shown from the topological analysis.

An ab initio electronic density study of the CH4–Ar, CH4–Xe, CH4–H2O and CH4–H2S complexes: insights into the nature of the intermolecular interaction

The main point of this paper concerns the theoretical characterisation of the effects induced by the intermolecular interaction on the electron density upon the formation of CH4-H2X (X=O,S) and CH4–Ng (Ng=Ar,Xe) complexes. The work has been stimulated by recent molecular scattering beams experiments, which point out differences in both strength and anisotropy of the intermolecular potential between CH4–H2X respect to reference CH4–Ng systems. Herein, attention is focused on the electronic charge polarisation and particularly charge transfer (CT) effects between involved partners, directly related to the topology of the full potential energy surface. The modification of electron density and the occurrence of CT have been evaluated via the charge displacement function worked out by high level ab initio calculations. Moreover, in the case of a specific configuration of CH4–H2O system, we define the leading interaction components, including their relative stabilising role and test our intermolecular potential model with reference to ab initio calculations. The results obtained indicate that CT clearly affects the strength and the anisotropy of CH4–H2O complex, and covers a minor and negligible role for CH4–H2S and the noble gas complexes, respectively.

H2O2–Ng dynamics predictions using an accurate potential energy surface

ABSTRACTBased on ab initio calculations, our research group has built an analytical ground-state potential energy surface (PES) for hydrogen peroxide– noble gas (Ng) interactions, such as H2O2–He, H2O2–Ne, H2O2–Ar, H2O2–Kr, and H2O2–Xe complexes. From this PES, it was verified that the Ng presence does not affect the equilibrium values of the H2O2 dihedral angles. This happens because the H2O2 intramolecular barriers have much higher energies than the atom–bond interaction within these complexes. From this point of view, it is indeed reasonable to consider the H2O2 system as a rigid rotor, frozen at its equilibrium configuration. We present in this work the torsional motion for the H2O2 isolated system, the vibration–rotation energy levels and spectroscopic constants for hydrogen peroxide–noble gas by using the aforementioned PES. The predicted H2O2 torsional motions are in good agreement with both theoretical and experimental results available in the literature. Regarding H2O2–Ng ro-vibrational energies and spectroscopic constants, it is the first time that these calculations are presented in the literature. The current theoretical predictions are expected to be useful in the future experimental investigations.

Novel cations of xenon trifluoroborazine complexes: Structures, reactivities, and natural bonding orbital analysis

The structural isomers of cations of xenon trifluoroborazine complexes were investigated by B3LYP method of density functional theory. The aug-cc-PVTZ basis set was applied to H, B, N, and F atoms, and Def2-PVTZ to Xe atom. The DFT results showed that all Xe complexes of trifluoroborazines correspond to real minima in potential energy surface. The calculations also demonstrated the ZPE correction is fairly important to the total electronic energy of Xe complexes. The natural bonding analysis of donor–acceptor interactions indicated remarkably powerful interactions. All donor natural orbitals were core orbitals of Xe atom, and acceptor natural orbitals were post-valence, unoccupied valence, and π* natural orbitals of atoms/bonds of trifluoroborazine. The DFT calculated global reactivity indexes verified xenon trifluoroborazine complexes more electronegative structures with softer nature, and with considerably more electrophilic characteristics than the corresponding trifluoroborazines.

Matrix-Isolation Studies of Noncovalent Interactions: More Sophisticated Approaches

Noncovalent interactions are crucial for many physical, chemical, and biological phenomena. Matrix isolation is a powerful method to study noncovalent interactions, including hydrogen-bonded species, and it has been extensively used in this field. However, there are difficult situations, such as in the case of species that are impossible to prepare in the gas phase. In this article, we describe some advanced approaches allowing studies of complexes that are problematic for the traditional methods. Photolysis of a suitable precursor in a matrix can lead to a large concentration of 1:1 complexes, which are otherwise very difficult to prepare (e.g., the H2O···O complex). Photolysis of species combined with annealing can lead to complexes of molecules with mobile atoms (e.g., the same H2O···O complex). Simultaneous photolysis of two species combined with annealing can produce complexes of radicals via reactions of the photogenerated complexes with mobile atoms (e.g., the H2O···HCO complex). Interaction of noble-gas (Ng) hydrides with other species is another topic (e.g., the N2···HArF complex) and very large blue shifts of the H-Ng stretching modes are normally observed for these systems. Complexes and dimers of the higher-energy conformer of formic acid have been prepared by using selective vibrational excitation of the ground-state conformer. The higher-energy conformer of formic acid can be efficiently stabilized in the complexes with strong hydrogen bonding. We also consider some problematic cases when the changes in the vibrational frequencies of the 1:1 complexes are very small (e.g., the phenol···Xe complex) and when the complex formation is prevented by strong solvation in the matrix (e.g., species in solid xenon).

Interaction of aromatic compounds with xenon: spectroscopic and computational characterization for the cases of p-cresol and toluene.

We have investigated noncovalent interactions of two aromatic compounds (toluene and p-cresol) with Xe atoms by using infrared spectroscopy in a Ne matrix and quantum chemical calculations. The present results show that the methyl group of these molecules is a sensitive probe of the interaction with Xe. We have used the molecules with the deuterated methyl group, possessing a relatively simple spectrum, which allows us to detect characteristic vibrational shifts in the complexes, in which a Xe atom interacts with the aromatic π electron system (π structure). For the p-cresol···Xe complex, we also observed evidence of the 1:1 H-bonded structure. The amount of the H-bonded structure of the cresol···Xe complex is relatively small, which agrees with the calculated interaction energies (stronger interaction for the π structure). The bands of the 1:1 complexes of p-cresol and toluene with Xe appear at low Xe concentration and their intensities relative to the monomer bands are nearly proportional to the Xe/Ne concentration ratio. For the p-cresol-Xe system, additional OH stretching bands appear at higher Xe concentrations, which are suitable for the complexes with several Xe atoms. The π structures studied in this work can probably be formed in the case of aromatic amino acids, for which these simple aromatic compounds are useful models.

Vibrational spectra and structures of bare and Xe-tagged cationic Si(n)O(m)⁺ clusters.

Vibrational spectra of Xe-tagged cationic silicon oxide clusters Si(n)O(m)(+) with n = 3-5 and m = n, n ± 1 in the gas phase are obtained by resonant infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory calculations. The Si(n)O(m)(+) clusters are produced in a laser vaporization ion source and Xe complexes are formed after thermalization to 100 K. The clusters are subsequently irradiated with tunable light from an IR free electron laser and changes in the mass distribution yield size-specific IR spectra. The measured IRMPD spectra are compared to calculated linear IR absorption spectra leading to structural assignments. For several clusters, Xe complexation alters the energetic order of the Si(n)O(m)(+) isomers. Common structural motifs include the Si2O2 rhombus, the Si3O2 pentagon, and the Si3O3 hexagon.

Density Functional (B3LYP)and the Second–Order Møller–Plesset (MP2) Theoretical Method Investigate the Geometric Configurations of the D…CO (D=He, Ne, Ar, Kr and Xe) Complexes

Density functional (B3LYP)and the second–order Møller–Plesset (MP2) theoretical method with differentbasis sets are used to investigate the geometricconfigurations of the D…CO (D=He, Ne, Ar, Kr andXe) complexes. The results showed that C end of the CO molecule can close and interact with D atom and formstable van der Waals complex, so does the O end of the CO molecule. It issuggested that the interaction between CO and D atom is not electrostaticinteraction in nature. The harmonic frequency analysesand Mulliken charge distributions of five complexes were performed at the MP2/aug-cc-pvtz/DGDZVPlevel.

Environmental effects on noble-gas hydrides: HXeBr, HXeCCH, and HXeH in noble-gas and molecular matrices

Noble-gas hydrides HNgY (Ng is a noble-gas atom and Y is an electronegative group) are sensitive probes of local environment due to their relatively weak bonding and large dipole moments. We experimentally studied HXeBr in Ar, Kr, and N2 matrices, HXeCCH in Ne and N2 matrices, and HXeH in an N2 matrix. These are the first observations of noble-gas hydrides in an N2 matrix. An N2 matrix strongly increases the H-Xe stretching frequency of HXeBr and HXeCCH with respect to a Ne matrix, which is presumably due to a strong interaction between the HNgY dipole moment and quadrupole moments of the surrounding lattice N2 molecules. The spectral shift of HXeBr in an N2 matrix is similar to that in a CO2 matrix, which is a rather unexpected result because the quadrupole moment of CO2 is about three times as large as that of N2. The H-Xe stretching frequencies of HXeBr and HXeCCH in noble-gas matrices show a trend of ν(Ne) < ν(Xe) < ν(Kr) < ν(Ar), which is a non-monotonous function of the dielectric constants of the noble-gas solids. The MP2(full) calculations of HXeBr and HXeCCH with the polarizable continuum model as well as the CCSD(T) calculations of the HXeBr···Ng and HXeCCH···Ng (Ng = Ne, Ar, Kr, and Xe) complexes cannot fully explain the experimental observations. It is concluded that more sophisticated computational models should be used to describe these experimental findings.

How to Make the σ0π2 Singlet the Ground State of Carbenes

Successful strategies have previously been developed to stabilize the σ(2)π(0) singlet states of carbenes, relative to σ(1)π(1) triplet states. However, little or no attention has been paid to the stabilization of the σ(0)π(2) singlet states. We present two simple strategies to stabilize the σ(0)π(2) singlet states of carbenes, relative to both the σ(2)π(0) singlet and σ(1)π(1) triplet states. These strategies consist of destabilization of the carbene σ orbital by two, adjacent, sp(2) nitrogen lone pairs of electrons and stabilization of the carbene 2p-π orbital by incorporating it into a five-membered ring, containing two double bonds, or into a six-membered ring, containing two double bonds and a sixth atom that has a low-lying empty π orbital. B3LYP, CASPT2, and CCSD(T) calculations have been performed in order to assess the success of these strategies in creating derivatives of cyclopenta-2,4-dienylidene and cyclohexa-2,5-dienylidene with σ(0)π(6) singlet ground states. Differences between the calculated geometries and binding energies of the Xe complexes of the σ(0)π(6) singlet ground state of 2,5-diazacyclopentadienylidene (5) and the σ(2)π(0) singlet states of CH2 and CF2 are discussed.

Hydrogen bonding to xenon: A comparison with neon, argon and krypton complexes

H-bonding-like interactions between AH acids and Ne, Ar, Kr and Xe are examined by analysis of predicted A–H⋯Rg geometry, energy, A–H stretching vibration (CCSD(T) level) as well as assumed proton affinitiy, pKa, polarizability and chemical hardness of the complex components. The Kr and Xe systems are described as mostly the acid–base contacts and reveal properties of typical H-bonded complexes. These contacts are also influenced by structural factors. Properties of the Ne contacts are qualitatively different. The A–H⋯Xe complexes can be divided into stronger and weaker ones using the 129Xe chemical shift as the criterion.