Low-temperature Raman Spectroscopy Research Articles

Chromium(VI) Oxyfluoride Dianions, [Cr2 O4 F6 ]2- and [CrO2 F4 ]2- ; Syntheses and Structures of [XeF5 ]2 [Cr2 O4 F6 ], [XeF5 ]2 [Cr2 O4 F6 ] ⋅ nX (X=HF, n=4; X=XeOF4 , n=2), and [XeF5 ][Xe2 F11 ][CrO2 F4 ].

The fluorobasic character of the strong oxidative fluorinator, XeF6 , and the oxidative resistance of the [XeF5 ]+ and [Xe2 F11 ]+ cations have been exploited for the syntheses of several novel Cr(VI) dianion salts. The reactions of XeF6 and CrO2 F2 in anhydrous HF and by direct fusion of the reactants in melts have yielded the first dinuclear Cr(VI) oxyfluoro-dianion salts, [XeF5 ]2 [Cr2 O4 F6 ], [XeF5 ]2 [Cr2 O4 F6 ] ⋅ 4HF, [XeF5 ]2 [Cr2 O4 F6 ] ⋅ 2XeOF4 , and mononuclear Cr(VI) oxyfluoro-dianion salt, [XeF5 ][Xe2 F11 ][CrO2 F4 ]. The salts were structurally characterized by low-temperature (LT) single-crystal X-ray diffraction (SCXRD) and LT Raman spectroscopy. The [CrO2 F4 ]2- and [Cr2 O4 F6 ]2- dianions have distorted octahedral cis-dioxo Cr(VI) coordination spheres in which two F-atoms are trans to one another and two F-atoms are trans to O-atoms, where the [Cr2 O4 F6 ]2- dianion is the fluorine-bridged dimer of the [CrO2 F3 ]- anion. Quantum-chemical calculations were used to obtain the energy-minimized, gas-phase geometries, and the calculated vibrational spectra of the gas-phase dianions and their ion-pairs, which were used to aid in the vibrational frequency assignments of the crystalline salts. NBO and MEPS analyses and SCXRD show these salts are comprised of intimate ion-pairs in which their cations and anions interact through primarily electrostatic Xe- - -F σ-hole bonds.

Significant phonon assignments in multiferroic BiFeO3 single crystal

In the present work, the technique of Back Scattering Micro-Raman was employed at low and room temperatures in order to examine all the possible phonon vibration modes present in a crystal of BiFeO3(BFO). The observation & identification of all E (TO), E (LO), A1 (TO), and A1 (LO) normal modes was sucessfully accomplished. The low temperature Raman spectroscopy measurements showed two one-magnon branches, σ-magnon at 20.06 cm−1 and γ-magnon at 26.93 cm−1. The spectral characteristics of the three A1 (LO) modes were observed at roughly 176.63 cm−1, 225.93 cm−1 and 505.53 cm−1, exhibiting low intensity longitudinal optical modes. The observed peaks at 145.34 cm−1, 223.92 cm−1, 292.54 cm−1, and 552.18 cm−1 were identified and categorized as A1 (TO) modes. E (TO) peaks were observed at 73.30 cm-1, 131.94 cm-1, 239.35 cm-1, 265.04 cm-1, 278.45 cm-1, 349.95 cm-1, 374.69 cm-1, 441.04 cm-1, 522.99 cm-1. In addition, E(LO) peaks were observed at 80.76 cm-1, 175.03 cm-1, 241.59 cm-1, 275.42 cm-1, 346.92 cm-1, 371.34 cm-1, 419.38 cm-1, and 469.65 cm-1.

Configuration of the dimolybdate in salt inclusion type of compounds, Cs2Mo2O7 ⋅ CsX (X=Cl, Br, and I)

AbstractCs2Mo2O7 ⋅ CsI is obtained as a member of the series Cs2Mo2O7 ⋅ CsX with X=Cl, Br, and I from the synthesis of Cs2MoO4 with MoO3 and CsX. At room temperature, the compounds crystallize in the space group P63/mmc with the dimolybdate, [Mo2O7]2−, in a linear and eclipsed conformation. Low temperature Raman spectroscopy and low temperature X‐ray diffraction were used to investigate the effect of the hetero‐honeycomb lattice on the bridging angle of the dimolybdate. For X=Cl, a phase transition occurs below 150 K (P63/mmc → Cmcm). The phase transition relates to a lock‐in that involves bending of the (Mo−O−Mo) bridge. For the Pearson softer iodide compound, no phase transition is observed down to 4 K; thus, the linear configuration remains stable. Specific heat data and their evaluation in terms of phonon contributions are given.

XeF2 Coordination Complexes of the [BrO2]+ Cation, [O2Br(FXeF)n][AsF6] (n = 1, 2) and [O2Br(FXeF)2][SbF6]; Their Syntheses and Structural Characterizations.

The syntheses and structural characterizations of the first XeF2 coordination complexes of the [BrO2]+ cation are described. The reactions of [BrO2][PnF6] (Pn = As, Sb) with XeF2 in anhydrous HF solvent yield the salts [O2Br(FXeF)n][AsF6] (n = 1, 2) and [O2Br(FXeF)2][SbF6], which were characterized by low-temperature (LT) Raman spectroscopy and single-crystal X-ray diffraction (SCXRD). The XeF2 ligands and [PnF6]- coordinate to the Lewis acidic [BrO2]+ cation through primarily electrostatic BrV---FXe σ-hole bonds that result from coordination of the F atoms into regions of high positive electrostatic potential on the Br(V) atom and have bond trajectories that avoid the stereoactive valence electron lone-pair of Br(V). The complexes and their structural characterizations by LT Raman spectroscopy and SCXRD significantly extend the coordination chemistry of Br(V) and provide rare examples of a noble-gas difluoride coordinated to a strong oxidant main-group Lewis acid center.

Interaction Modes between SF4 and Ketones; Study of Intermediates in Deoxofluorination Reactions.

Interactions between ketones and SF4 are studied for the simplest ketone, acetone, and the bulky polycyclic 2-adamantanone. Acetone forms the 1:2 adduct SF4·[O=C(CH-3)2]2, as well as the dimeric 1:1 adducts [SF4·O=C(CH-3)2]2 as identified by low-temperature Raman spectroscopy and, for the latter, X-ray crystallography. In both adducts, SF4 acts as a double chalcogen-bond donor to two keto groups. In contrast 2-adamantanone does not form an isolable solid adduct with SF4; in the presence of HF, however, it forms SF4·O=C10H14O·HF, which comprises chains with weak S---O and S---FH chalcogen bonds in the crystal structure. Sulfur tetrafluoride in this compound is readily lost at -85 °C, leading to the isolation of C10H14O·HF at low temperature. Density functional theory (DFT) calculations aid in vibrational assignments and serve to describe the interactions of the keto group with SF4 and HF, as well as interactions between SF4 with HF. It is found that separate and combined CO---HF and CO---SF4 chalcogen bonds do not polarize the C=O group to any significant degree.

Lattice dynamics and in-plane antiferromagnetism in MnxZn1−xPS3 across the entire composition range

Antiferromagnetic MnPS${}_{3}$ and diamagnetic ZnPS${}_{3}$ belong to a family of two-dimensional compounds that exhibit a rich variety of magnetic ordering. Low-temperature Raman spectroscopy and SQUID magnetometer measurements are performed on both compounds and their alloy in order to evaluate a possible Jahn-Teller distortion as well as to reveal magnetic and alloy signatures. With the aid of first-principles calculations, a description of the lattice dynamics of the system is presented, together with the magnetic phase diagram across the entire compositional range.

Characterizing cellular membrane partitioning of DMSO using low-temperature Raman spectroscopy.

Additives that help cells survive the stresses of freezing and thawing are known as cryoprotective agents (CPAs). Two different types of CPAs have been identified: penetrating and non-penetrating. Common penetrating CPAs include dimethylsulfoxide (DMSO) and glycerol. The location of a CPA (intracelluar or extracellular) is important for understanding the molecular mechanisms of action for the agent. Low-temperature Raman spectroscopy is a label-free method of detecting the location of CPAs at low temperature with high spatial resolution and chemical specificity. To this end, cells cryopreserved in DMSO using a variety of cooling rates and DMSO concentrations and imaged using Raman spectroscopy were analyzed using automated image analysis to determine the partitioning ratio (concentration of DMSO outside/concentration of DMSO inside the cell). The partitioning ratio was roughly 1 for Jurkat cells frozen at 1°C/min in varying concentrations of DMSO with the exception of 1% DMSO which had a partitioning ratio of 0.2. The partitioning ratio increased from 1 to 1.3 as the cooling rate increased from 1°C to 5°C/min. Different cell types, specifically sensory neurons cells and human induced pluripotent stem cells, exhibited differences in partitioning ratio when frozen in 10% DMSO and 1°C/min suggesting that differences in freezing response may result from differences in solute partitioning. The presence of intracellular ice changed the distribution of DMSO inside the cell and also the partitioning ratio.

Hydrothermal assisted synthesis of hierarchical SnO2 micro flowers with CdO nanoparticles based membrane for energy storage applications

Hierarchical nanostructures with appropriate morphology and surface functionalities are highly desired to achieve an optimized electrochemical property for active electrode materials. This work renders the facile hydrothermal synthesis of CdO, SnO2, and CdO–SnO2 nanocomposite, and their capacitive performance was tested. The formation of the pure samples and their composite was committed by low-temperature Raman spectroscopy and x-ray diffraction studies which revealed the tetragonal and cubic structures of CdO and SnO2 powder samples with good crystallinity and purity. The morphological postmortem reveals the formation of nanoparticles morphology of CdO with a highly smooth surface appearance. Besides, the SnO2 illustrates the morphology of the micro flowers composed of ultrathin nanosheets. More specifically, the electrochemical properties indicate the pseudocapacitive charge storage mechanism based on cyclic voltammetry and chronopotentiometry analysis. The CdO–SnO2 composite electrode displayed a higher capacitance due to additional pores/space offered for active sites and continuously allowed electrolyte ions to interact with the inner/outer surface of the electrode. These exciting findings led us to design and fabricate battery hybrid supercapacitors (BHSC) from CdO–SnO2, and activated carbon (AC), referred to as CdO–SnO2//AC BHSC, attains a high power delivery (5717 W/kg), and a maximum energy density of 42 Wh/kg at low discharge rate. Noteworthy, a stable cycling performance was obtained with only 91.3% retention after 8000 cycling at a large discharge current of 10 A/g, denoting the magnificent durability of the active electrode material.

Electrochemical properties of carbonized bentonite

Organomodified bentonites were obtained by modification of bentonite clay from local mine Bogovina, with four different alkylammonium ions in the amounts that correspond to cation exchange capacity. Carbonized bentonites, obtained by pyrolyzing the organomodified bentonites in the flow of nitrogen, were characterized using XRD, low-temperature N2 physisorption and Raman spectroscopy. Structural and textural properties of carbonized bentonites depended on the arrangement of alkylammonium cations in the paternal organomodified bentonite, while the Raman spectroscopy confirmed the presence of amorphous carbon. The obtained carbonized bentonites were used for modification of the carbon paste electrode. The modified electrodes were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The electrosorption of chloride and sulfate anions on carbonized bentonites was studied by chronocoulometry. The results were interpreted in the terms of surface groups and textural properties of the carbonized bentonites.

Nickel doped bismuth sulfide nanomaterials: Synthesis, characterization, and enhancement of anti-microbial activity

This study aims to evaluate the minimum inhibitory concentration (MIC) of pristine Bi2S3 and Ni-doped Bi2S3 nanostructures for their anti-microbial study. The nanostructures were synthesized by the reverse micelle method using the AOT/Water/Cyclohexane ternary system. As per our knowledge, the current study shows the lowest value of MIC compared to reported work for pristine Bi2S3 against Staphylococcus Aureus and Bacillus Subtilis pathogens. The compositional, structural, morphological, optical, and vibrational properties of synthesized Bi2S3 and Ni-doped Bi2S3 nanomaterials were investigated using EDAX, X-ray diffraction, HR-TEM, DLS, diffuse UV–Vis reflectance spectroscopy, room temperature, and low-temperature Raman spectroscopy, respectively. Finally, the anti-microbial activity of synthesized nanostructures against four different pathogens was examined using the broth dilution method in terms of MIC value. The result of MIC reports that pristine Bi2S3 and Ni-doped Bi2S3 nanomaterials have a strong anti-microbial effect for two Gram-negative Serratia Marcescens and Pseudomonas Aeruginosa compared to two Gram-positive Staphylococcus Aureus and Bacillus Subtilis micro-organisms.

Solvent effect on the NO2 sensing properties of multi-walled carbon nanotubes

This article is devoted to the investigation of the influence of the solvent on sensing properties, such as response and recovery rate, of chemiresistive gas sensors. Multi-walled carbon nanotubes were used as an active material for the sensors. The initial material was investigated by scanning electron spectroscopy and transmission electron microscopy, low-temperature nitrogen adsorption, Raman spectroscopy, and X-ray diffraction. The active material was produced by drop casting. Different polar solvents (acetone and ethanol) were used for suspension preparation. Textolite with copper contacts on the edges of one side was used as a sensor substrate. The gas sensing properties (the response and the recovery time) were investigated in the range of 100–500 ppm NO2 at room temperature. The films made using different solvent suspensions showed high sensitivity and rapid recovery rate to nitrogen dioxide. It was found that the method of film preparation has an effect on the measured sensing properties. The films prepared using different suspensions possessed different properties: the film made from the acetone suspension had the response values from 8.49% to 20.26%, and the recovery values from 0.06%/min to 0.16%/min. The response of the film made from the ethanol suspension increased , being from 12.25% to 23.63%; the recovery rate were also increased (from 0.19%/min to 0.39%/min).

Photocatalytic and antibacterial activity of Yttrium doped TiO2 nanostructure

In this study, TiO2 nanostructures were doped with Yttrium (Y) at various doping concentrations using a low-cost approach called chemical co-precipitation, and then used for photocatalysis and antibacterial activity application. The effects of yttrium doping on TiO2 nanostructure properties such as crystal structure, chemical impurities, and optical features were investigated using EDAX, XRD, TEM, SAED, RAMAN, UV–Vis, and PL techniques. X-ray diffraction (XRD) confirmed the presence of the Rutile tetragonal crystalline phase in both pure and Y doped-TiO2 nanostructure. TEM images of synthesised nanomaterials depict typical nanoellipsoid morphology. UV–Vis absorption spectroscopy revealed that due to doping, the optical band gap was reduced from 3.28 eV to 3.11 eV. Low temperature Raman spectroscopy was used to determine variations in the isobaric Gruneisen parameter for both pure and Y doped materials. The photocatalytic activities of samples were evaluated by the photodegradation of methyl blue (MB) aqueous solution under 250 W UV lamp irradiation. The photodegradation efficiency of TiO2 has been found to vary with Y doping, despite 6% Y doped TiO2 nanostructure are most efficient than other samples. Furthermore, antibacterial analysis indicated that the doping exhibits excellent antibacterial properties when evaluated against E. coli culture.

Structural stability of orthorhombic DyScO3 under extreme conditions of pressure and temperature

In the present work, the effect of elevated pressure and lowered temperature on the structural and vibrational stability of dysprosium scandate (${\mathrm{DyScO}}_{3}$) is studied via high-pressure synchrotron x-ray diffraction (HPXRD) and high-pressure (HP) and low-temperature Raman spectroscopy. A solid-state reaction route is employed to synthesize the material with a crystallite size of 92 nm, which at ambient conditions exhibits an orthorhombic phase with the space group $Pbnm$ (62). HPXRD results reveal excellent phase stability of the material, with the ratio of the polyhedral volumes and the compressibility for the ${\mathrm{DyO}}_{12}$ and ${\mathrm{ScO}}_{6}$ polyhedra to be around 4.26 and 1 for the entire applied pressure range of up to 40 GPa. Interestingly, the combination of HPXRD and HP Raman measurements signals a change in the preferred orientations in the crystalline structure with the increased pressure, while keeping the structure stable. The bulk modulus of the material is estimated to be 189.4 GPa from the HPXRD data and is further used to estimate the mode Gr\"uneisen parameter (\ensuremath{\gamma}) for various Raman modes. The behavior of phonon frequency with varying temperature is explained by considering the anharmonic effects, i.e., lattice expansion and perturbation in the Hamiltonian, with an increase in temperature. Furthermore, the implicit and explicit anharmonicity contributions were calculated to elucidate the phonon decay mechanisms. Our results offer valuable insights relating to the behavior of this intriguing class of materials under extreme conditions and lays the foundation for further exploration.

Nanoscale Heating of an Ultrathin Oxide Film Studied by Tip-Enhanced Raman Spectroscopy

We report on the nanoscale heating mechanism of an ultrathin ZnO film using low-temperature tip-enhanced Raman spectroscopy. Under the resonance condition, intense Stokes and anti-Stokes Raman scattering can be observed for the phonon modes of a two-monolayer (ML) ZnO on an Ag(111) surface, enabling us to monitor local heating at the nanoscale. It is revealed that the local heating originates mainly from inelastic electron tunneling through the electronic resonance when the bias voltage exceeds the conduction band edge of the 2-ML ZnO. When the bias voltage is lower than the conduction band edge, the local heating arises from two different contributions, namely direct optical excitation between the interface state and the conduction band of 2-ML ZnO or injection of photoexcited electrons from an Ag tip into the conduction band. These optical heating processes are promoted by localized surface plasmon excitation. Simultaneous mapping of tip-enhanced Raman spectroscopy and scanning tunneling spectroscopy for 2-ML ZnO including an atomic-scale defect demonstrates visualizing a correlation between the heating efficiency and the local density of states, which further allows us to analyze the local electron-phonon coupling strength with ∼2  nm spatial resolution.

UV-Activated NO2 Gas Sensing by Nanocrystalline ZnO: Mechanistic Insights from Mass Spectrometry Investigations

In this work, the photostimulated processes of O2 and NO2 molecules with the surface of ZnO under UV radiation were studied by in situ mass spectrometry in the temperature range of 30–100 ∘C. Nanocrystalline needle-like ZnO was synthesized by decomposition of basic zinc carbonate at 300 ∘C, and the surface concentration of oxygen vacancies in it were controlled by reductive post-annealing in an inert gas at 170 ∘C. The synthesized materials were characterized by XRD, SEM, low-temperature nitrogen adsorption (BET), XPS, Raman spectroscopy, and PL spectroscopy. Irradiation of samples with UV light causes the photoabsorption of both O2 and NO2. The photoadsorption properties of ZnO are compared with its defective structure and gas-sensitive properties to NO2. A model of the sensor response of ZnO to NO2 under UV photoactivation is proposed.

Charge Transfer-Mediated Dramatic Enhancement of Raman Scattering upon Molecular Point Contact Formation.

Charge-transfer enhancement of Raman scattering plays a crucial role in current-carrying molecular junctions. However, the microscopic mechanism of light scattering in such nonequilibrium systems is still imperfectly understood. Here, using low-temperature tip-enhanced Raman spectroscopy (TERS), we investigate how Raman scattering evolves as a function of the gap distance in the single C60-molecule junction consisting of an Ag tip and various metal surfaces. Precise gap-distance control allows the examination of two distinct transport regimes, namely tunneling regime and molecular point contact (MPC). Simultaneous measurement of TERS and the electric current in scanning tunneling microscopy shows that the MPC formation results in dramatic Raman enhancement that enables one to observe the vibrations undetectable in the tunneling regime. This enhancement is found to commonly occur not only for coinage but also transition metal substrates. We suggest that the characteristic enhancement upon the MPC formation is rationalized by charge-transfer excitation.

Ring Opening and Closure Reactions of β‐Propiolactone in the Superacids HF/MF5 (M=Sb, As)

AbstractTransformations of β‐propiolactone in the binary superacidic systems HF/MF5 (M=Sb, As) were investigated at different temperatures. Salts of monoprotonated 3‐hydroxypropanoyl fluoride [H2O(CH2)2C(O)F][SbF6] (1) and [H2O(CH2)2C(O)F][AsF6] (2) were obtained by performing the reactions at temperatures lower than −40 °C. In contrast, temperatures higher than −40 °C yield the respective salts [C9H15O6][SbF6]3 (3) and [C9H15O6][AsF6]3 (4) containing a cyclic trication. The protonated species of β‐propiolactone was not observed. All salts were characterized by low temperature Raman and IR spectroscopy. In addition, single‐crystal X‐ray analyses were performed for (1) and (3). For both cations the existence of a cationic acyl species as a reactive intermediate in the form of [HO(CH2)2CO][MF6] is assumed. The formation of the acyl cation, based on protonated β‐propiolactone, was investigated by quantum chemical calculations on the MP2/aug‐cc‐pVTZ level of theory.

Syntheses and Characterizations of the Mixed Noble-Gas Compounds, [FKrII FXeII F][AsF6 ]⋅0.5 KrII F2 ⋅2 HF, ([KrII 2 F3 ][AsF6 ])2 ⋅XeIV F4 , and XeIV F4 ⋅KrII F2.

Reaction of [XeF][AsF6 ] with excess KrF2 at -78 °C in anhydrous HF (aHF) solvent has yielded the first mixed KrII /XeII noble-gas compound, [FKrFXeF][AsF6 ] ⋅0.5 KrF2 ⋅2 HF, a salt of the [FKrFXeF]+ cation. The potent oxidative fluorinating properties of KrII fluoride species resulted in oxidation of XeII to XeIV in aHF at -60 °C to form the mixed KrII /XeIV cocrystals, ([Kr2 F3 ][AsF6 ])2 ⋅XeF4 and XeF4 ⋅KrF2 . Further decomposition at 22 °C resulted in oxidation of XeIV to XeVI to give the recently reported KrII /XeVI complexes, [F5 Xe(FKrF)n ][AsF6 ] (n=1, 2), [F5 Xe][AsF6 ], and a new KrII /XeVI complex, [(F5 Xe)2 (μ-FKrF)(AsF6 )2 ], which was characterized by low-temperature (LT) Raman spectroscopy. The [FKrFXeF][AsF6 ]⋅0.5 KrF2 ⋅2 HF, ([Kr2 F3 ][AsF6 ])2 ⋅XeF4  , and XeF4 ⋅KrF2 compounds were characterized by LT Raman spectroscopy and single-crystal X-ray diffraction. Quantum-chemical calculations were used to assess the bonding in [FKrFXeF]+ , [Kr2 F3 ]+ , and [Xe2 F3 ]+ and to aid in their vibrational assignments.

Syntheses and Characterizations of the Mixed Noble‐Gas Compounds, [FKrIIFXeIIF][AsF6]⋅0.5 KrIIF2⋅2 HF, ([KrII2F3][AsF6])2⋅XeIVF4, and XeIVF4⋅KrIIF2

AbstractReaction of [XeF][AsF6] with excess KrF2 at −78 °C in anhydrous HF (aHF) solvent has yielded the first mixed KrII/XeII noble‐gas compound, [FKrFXeF][AsF6] ⋅0.5 KrF2⋅2 HF, a salt of the [FKrFXeF]+ cation. The potent oxidative fluorinating properties of KrII fluoride species resulted in oxidation of XeII to XeIV in aHF at −60 °C to form the mixed KrII/XeIV cocrystals, ([Kr2F3][AsF6])2⋅XeF4 and XeF4⋅KrF2. Further decomposition at 22 °C resulted in oxidation of XeIV to XeVI to give the recently reported KrII/XeVI complexes, [F5Xe(FKrF)n][AsF6] (n=1, 2), [F5Xe][AsF6], and a new KrII/XeVI complex, [(F5Xe)2(μ‐FKrF)(AsF6)2], which was characterized by low‐temperature (LT) Raman spectroscopy. The [FKrFXeF][AsF6]⋅0.5 KrF2⋅2 HF, ([Kr2F3][AsF6])2⋅XeF4 , and XeF4⋅KrF2 compounds were characterized by LT Raman spectroscopy and single‐crystal X‐ray diffraction. Quantum‐chemical calculations were used to assess the bonding in [FKrFXeF]+, [Kr2F3]+, and [Xe2F3]+ and to aid in their vibrational assignments.

Syntheses and Structural Characterizations of the Cl(V) Coordination Complex, [O2Cl(FXeF)2][AsF6], and β-[ClO2][AsF6]

The synthesis and structural characterization of the first Cl(V) coordination complex of XeF2, [O2Cl(FXeF)2][AsF6], is described. The reaction of α-[ClO2][AsF6] with XeF2 at −78 °C in anhydrous HF (aHF) solvent yields [O2Cl(FXeF)2][AsF6], a rare example of noble-gas difluoride coordination to a main-group Lewis acid center. The low-temperature (LT) phase of β-[ClO2][AsF6] was obtained by recrystallization of α-[ClO2][AsF6] from aHF solvent at –10 °C. The compounds were characterized by LT single-crystal X-ray diffraction and LT Raman spectroscopy. Quantum-chemical calculations were carried out for the model gas-phase ([O2Cl(FXeF)2][AsF6]2)− anion to aid in the assignments of fundamental vibrational frequencies and 35/37Cl isotope shifts for [O2Cl(FXeF)2][AsF6] and to assess its chemical bonding by use of an NBO analysis. The [O2Cl(FXeF)2]+ cations and [AsF6]− anions of [O2Cl(FXeF)2][AsF6] are intimate ion-pairs with secondary Cl---FAs and Cl---FXe bonds that are significantly shorter than the sums of the Cl and F van der Waals radii, and are consistent with noncovalent σ-hole bonding. MEPS and NBO analyses were also carried out for the gas-phase [XO2]+ (X = Cl, Br, I) cations.