Ab initio calculations of relativistic and electron correlation effects in polyatomics using the universal Gaussian basis set: XeF2

Ab initio accurate all-electron relativistic molecular orbital Dirac–Fock self-consistent field calculations are reported for the linear symmetric XeF₂ molecule at various internuclear distances with our recently developed relativistic universal Gaussian basis set. The nonrelativistic limit Hartree–Fock calculations were also performed for XeF₂ at various internuclear distances. The relativistic correction to the electronic energy of XeF₂ was calculated as ～ ?215 hartrees (?5850 eV) by using the Dirac–Fock method. The dominant magnetic part of the Breit interaction correction to the nonrelativistic interelectron Coulomb repulsion was included in our calculations by both the Dirac–Fock–Breit self-consistent field and perturbation methods. The calculated Breit correction is ～6.5 hartrees (177 eV) for XeF₂. The relativistic Dirac–Fock as well as the nonrelativistic HF wave functions predict XeF₂ to be unbound, due to neglect of electron correlation effects. These effects were incorporated for XeF₂ by using various ab initio post Hartree–Fock methods. The calculated dissociation energy obtained using the MP 2(full) method with our extensive basis set of 313 primitive Gaussians that included d and f polarization functions on Xe and F is 2.77 eV, whereas the experimental dissociation energy is 2.78 eV. The calculated correlation energy is ～ ?2 hartrees (?54 eV) at the predicted internuclear distance of 1.986 Å, which is in excellent agreement with the experimental Xe—F distance of 1.979 Å in XeF₂. In summary, electron correlation effects must be included in accurate ab initio calculations since it has been shown here that their inclusion is crucial for obtaining theoretical dissociation energy (D_e) close to experimental value for XeF₂. Furthermore, relativistic effects have been shown to make an extremely significant contribution to the total energy and orbital binding energies of XeF₂. © 1995 John Wiley & Sons, Inc.     

Electron correlation and relativistic effects in xenon tetrafluoride

Ab initio all-electron fully relativistic Dirac–Fock self-consistent field and Dirac–Fock–Breit calculations are reported for the XeF₄ molecule at various internuclear distances assuming the experimental D_4h geometry with our recently developed relativistic universal Gaussian basis set. The nonrelativistic limit Hartree–Fock calculations were also performed for XeF₄ at various internuclear distances. The calculated relativistic correction to the total energy of molecule at the Dirac–Fock level is ～ ?5856 eV, whereas the magnetic part of the Breit correction to the electron-electron interaction is calculated as ～ 177 eV. The electron correlation effects were included in the nonrelativistic Hartree–Fock calculations using the second-order Møller-Plesset (MP 2) theory, and the calculated correlation energy for XeF₄ is ?71 eV. The basis-set superposition error (BSSE ) was estimated by using the counterpoise method for Xe and F. The inclusion of both the relativistic and electron correlation effects in the calculated total energies of F, Xe, and XeF₄ predicts the Xe—F bond length and dissociation energy of XeF₄ as 1.952 Å and 5.59 eV, respectively, which are in excellent agreement with the experimental values of 1.953 Å and 5.69 eV, respectively, for XeF₄. The contribution of the electron correlation and relativistic effects to the dissociation energy of XeF₄ is 8.11 and 0.05 eV, respectively. The Breit interaction, however, contributes only 0.02 eV to the dissociation energy of XeF₄. Electron correlation is most significant for the prediction of an accurate value of dissociation energy, whereas relativistic effects are very important for the prediction of spin-orbital splitting as well as the energies of the orbitals, especially the inner orbitals of XeF₄. © 1995 John Wiley & Sons, Inc.     

Relativistic all-electron Dirac-Fock-Breit calculations on xenon fluorides (XeFn,n = 1, 2, 4, 6)

The MOLFDIR package of programs is used to perform fully relativistic all-electron Dirac-Fock and Dirac-Fock-Breit calculations for the the XeF_n (n = 1, 2, 4, 6) molecules assuming experimental symmetries. The Xe-F bound length for XeF₂, XeF₄, and XeF₆ is optimized and the total ground-state energies are reported. The variation of the relativistic energy and the Breit correction with the internuclear distance is plotted. The role of relativistic corrections in the proper prediction of the Xe-F distance and the dissociation energy of the molecule is discussed. The problem of the reduction of the number of scalar two-electron integrals is studied. Our results illustrate the possibilities, difficulties, and limitations of the finite basis Dirac-Fock calculations for polyatomic molecules of different symmetries. © 1997 by John Wiley & Sons, Inc.     

Modification of ultra‐high‐molecular weight polyethylene by various fluorinating routes

Chemical–physical properties of ultra‐high‐molecular weight polyethylene (UHMWPE) treated by direct fluorination, direct fluorination accompanied with UV irradiation, by XeF₂ and by TbF₄, were tested by FTIR spectroscopy, visible spectroscopy, 19F and 13C NMR, scanning electron microscopy, XRD, and EPR. Surface energy measurements were carried out. The direct fluorination of UHMWPE is a diffusion‐controlled process, but treatment with XeF₂ is a kinetically controlled one. Direct fluorination and direct fluorination accompanied with UV irradiation results mainly in a formation of ? CF₂? groups. On the contrary, ? CHF? groups are prevailing in UHMWPE treated with XeF₂ and TbF₄. Surface texture of UHMWPE treated with XeF₂ and with F₂ is quite different. Direct fluorination results in a higher polarity of the polymer surface when compared with treatment with XeF₂. For the case of direct fluorination, both long‐lived peroxy and fluoroalkylradicals are formed. For the case of treatment with XeF₂, only fluoroalkylradicals were detected. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49:3559–3573, 2011     

VUV spectra of the xenon fluorides

The absorption spectra of gaseous XeF₂, XeF₄, and XeF₆ have been accurately measured in the photon energy range from 6 to 35 eV with the use of the synchrotron radiation of DESY. The vibrational structure of several Rydberg transitions could be resolved. The spectra are interpreted and most of the structures could be assigned. From these data, information about the ionized species is obtained. The assignment of the first two IP's of XeF₄ is corrected.     

Fluorolactonization of norbornenecarboxylic acids and their methyl esters with F-TEDA-BF4 and XeF2

The selective fluorolactonization was achieved by treatment of cis-5-norbornene-2,3-endo-dicarboxylic acid or its monomethyl and dimethyl esters with F-TEDA-BF₄ or XeF₂. The reactions of 5-norbornene-endo-2-carboxylic acid and its monomethyl ester with F-TEDA-BF₄ or XeF₂ proceed in a non-selective manner to give fluorolactonization, addition and rearrangement products. The basic factor responsible for selectivity of the fluorolactonization is the presence of two endo-oriented carboxyl groups in the substrate molecule. The electrophilicity and type of the fluorinating agent is of secondary importance in this regard. It is postulated that the fluorolactonization of norbornenecarboxylic acids and their methyl esters with F-TEDA-BF₄ or XeF₂ is realized mainly via “open” fluoronorbornyl carbocation intermediates which in the reaction with XeF₂ are postulated as the tight ion pairs.     

Vibrational spectra and structural features of noble gas fluorides in cryogenic and nonaqueous solutions

Data on the vibrational spectra of noble gas fluorides in the gas phase and in cryogenic and nonaqueous solutions are considered in detail. Based on analysis of the IR spectra of xenon fluorides dissolved in liquid Kr and Xe, it is concluded that the XeF₆ molecule possesses the geometry of a distorted octahedron withC _3v symmetry. The contours of spectral lines of totally symmetric stretching modes in the Raman spectra of noble gas fluorides in nonaqueous solutions are considered; the mechanisms of formation contours of these lines, the dynamic parameters of XeF _n (n=2, 4, 6) and KrF₂, and the characteristic times of intramolecular rearrangements in the nonrigid XeF₆ molecule are analyzed. It is concluded that in the XeF₂-HF and XeF₆-HF systems, a number of associates and ionic clusters are formed due to the donor-acceptor interaction of the Lewis bases and acids. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 560–582, April, 1998.     

Interaction of He Atoms with XeF2 Observed in Crossed Molecular Beams

The interactional shape of XeF₂ with respect to energy and distance was observed by He atom scattering in molecular beam experiments. The heterogeneous second virial coefficient and the binary coefficient of diffusion were calculated from the resulting interaction potential.     

Syntheses and Structures of F6XeNCCH3 and F6Xe(NCCH3)2

Acetonitrile and the potent oxidative fluorinating agent XeF₆ react at ?40 °C in Freon‐114 to form the highly energetic, shock‐sensitive compounds F₆XeNCCH₃ ( 1 ) and F₆Xe(NCCH₃)₂?CH₃CN ( 2 ?CH₃CN). Their low‐temperature single‐crystal X‐ray structures show that the adducted XeF₆ molecules of these compounds are the most isolated XeF₆ moieties thus far encountered in the solid state and also provide the first examples of Xe^VI? N bonds. The geometry of the XeF₆ moiety in 1 is nearly identical to the calculated distorted octahedral (C_3v) geometry of gas‐phase XeF₆. The C_2v geometry of the XeF₆ moiety in 2 resembles the transition state proposed to account for the fluxionality of gas‐phase XeF₆. The energy‐minimized gas‐phase geometries and vibrational frequencies were calculated for 1 and 2 , and their respective binding energies with CH₃CN were determined. The Raman spectra of 1 and 2 ?CH₃CN were assigned by comparison with their calculated vibrational frequencies and intensities.     

XeF4 as a Ligand for a Metal Ion

Noble molecule : [Mg(XeF₂)(XeF₄)](AsF₆)₂ is the first coordination compound in which XeF₄ acts as a ligand to a metal center. It is also the first known compound, in which XeF₂ and XeF₄ are simultaneously coordinated to the same metal center (see structure; purple Xe, green F, gray Mg, yellow As).

     

ChemInform Abstract: A Raman Spectroscopic Study of the XeOF4/XeF2 System and the X‐Ray Crystal Structure of α‐XeOF4·XeF2.

The interaction of XeF₂ with excess XeOF₄ leads to the formation of a mixture of α‐XeOF₄·XeF₂ and β‐XeOF₄·XeF₂.     

On the existence of the trifluoroxenate (II) ION,XeF3-: Comments on “the ‘base catalyzed’ fluorination of SO2 by XeF2”

Conflicting data on the existence of the trifluoroxenate (II) ion, XeF₃^-, is analyzed. In particular, lack of isotope exchange and new spectroscopic lines in XeF₂ + F^- reactions, negative ion mass spectra of xenon fluorides and the “‘Base Catalyzed’ Fluorination of SO₂ by XeF₂” are discussed.     

A Raman spectroscopic study of the XeOF4/XeF2 system and the X-ray crystal structure of α-XeOF4·XeF2

The mixed oxidation state complexes, α-XeOF₄·XeF₂ and β-XeOF₄·XeF₂, result from the interaction of XeF₂ with excess XeOF₄. The X-ray crystal structure of the more stable α-phase shows that the XeF₂ molecules are symmetrically coordinated through their fluorine ligands to the Xe(VI) atoms of the XeOF₄ molecules which are, in turn, coordinated to four XeF₂ molecules. The high-temperature phase, β-XeOF₄·XeF₂, was identified by low-temperature Raman spectroscopy in admixture with α-XeOF₄·XeF₂; however, the instability of the β-phase precluded its isolation and characterization by single-crystal X-ray diffraction. The Raman spectrum of β-XeOF₄·XeF₂ indicates that the oxygen atom of XeOF₄ interacts less strongly with the XeF₂ molecules in its crystal lattice than in α-XeOF₄·XeF₂. The ¹⁹F and ¹²⁹Xe NMR spectra of XeF₂ in liquid XeOF₄ at −35 °C indicate that any intermolecular interactions that exist between XeF₂ and XeOF₄ are weak and labile on the NMR time scale. Quantum-chemical calculations at the B3LYP and PBE1PBE levels of theory were used to obtain the gas-phase geometries and vibrational frequencies as well as the NBO bond orders, valencies, and NPA charges for the model compounds, 2XeOF₄·XeF₂, and XeOF₄·4XeF₂, which provide approximations of the local XeF₂ and XeOF₄ environments in the crystal structure of α-XeOF₄·XeF₂. The assignments of the Raman spectra (−150 °C) of α- and β-XeOF₄·XeF₂ have been aided by the calculated vibrational frequencies for the model compounds. The fluorine bridge interactions in α- and β-XeOF₄·XeF₂ are among the weakest for known compounds in which XeF₂ functions as a ligand, whereas such fluorine bridge interactions are considerably weaker in β-XeOF₄·XeF₂.     

DVM-Xα calculations on the electronic structure of the xenon fluorides XeFn : n = 2, 4, 6

The ionization potentials of the XeF₂, XeF₄ and XeF₆ molecules are calculated by the discrete variational Xα-method. The results of the calculations are used for an interpretation of the experitnental PES and XPS of these compounds. Reasonable agreement is found between the theoretical estimates and data obtained from absorption spectroscopy.     

Radical additions of xenon difluoride to cis- and trans-1-phenylpropenes: comparison with trichloramine and iodobenzene dichloride

We would like to report data which support a free radical pathway for reaction of xenon difluoride (XeF₂) with alkenes in organic solvent. Radical intermediates have been proposed for reaction of XeF₂ to double bonds. For example, a radical pathway was suggested for the gas phase reaction of XeF₂ to ethylene and propene [1]. Zupan speculated on a radical cation pathway for the acid catalyzed reaction of XeF₂ with alkenes but gave no experimental evidence for this mechanism [2,3]. Radical cation intermediates were demonstrated for the reaction of XeF₂ to aromatics by Filler [4]. Acid catalyzed ionic reactions to unsaturated hydrocarbons have been reviewed [5].Zupan and Pollak have shown that alkenes do not react in aprotic solvent with XeF₂ at low concentrations of alkene unless acid catalyst is present [3]. However, we observed that illumination of a dilute solution of $\text{cis-}$ or $\text{trans}$-1-phenylpropenes (I) or (II) in methylene chloride at 0° with a 270 watt sunlamp produced IIIa and IIIb in less then two hours (Table). Furthermore, at high concentration of (I) and (II), a spontaneous reaction occurred in the dark between XeF₂ and these styrenes. The reaction conditions for both of these reactions imply a radical mechanism — the latter a molecule-induced pathway.     

Electrical conductivities and degrees of ionic dissociation of 1:1 and 1:2 adducts of xenon difluoride with antimony,tantalum and niobium pentafluorides in the molten state

Electrical conductivities of [XeF₂.MF₅] and [XeF₂.2MF₅] (M = Sb, Ta, Nb) have been measured. These, together with viscosity measurements on [XeF₂.SbF₅], which has the highest specific conductivity, leads to a value of the order of 11% for the degree of dissociation of the compounds near their melting points.     

On the synthesis of xenon(II) fluorostannates(IV)

The reaction between tin difluoride and an excess of xenon difluoride at 140°C yields two new xenon(II) fluorostannates(IV): 3XeF_2^·4SnF₄ and XeF_2^·2SnF₄. The 3:4 compound can be written as a molecular adduct of XeF₂ and the 1:2 compound. On the basis of vibrational spectra, the 1:2 compound can be formulated as a XeF⁺ salt with a polymeric anion.     

Fluorodecarboxylation, rearrangement and cyclisation: the influence of structure and environment on the reactions of carboxylic acids with xenon difluoride

The reactions of structurally diverse carboxylic acids with XeF₂ in both CH₂Cl₂/Pyrex^® and CH₂Cl₂/PTFE have been studied. Pyrex^® appears to be a very effective heterogeneous catalyst for an electrophilic mode of reaction of polarised XeF₂, leading to rearrangement, cyclisation and cationic products. In CH₂Cl₂/PTFE, fluorodecarboxylation is the main mode of reaction, in accordance with previous studies, and may occur via a SET reaction of unpolarised XeF₂.     

Mass spectrometry of graphite intercalation compounds of binary fluorides of xenon,xenon oxide tetrafluoride and arsenic pentafluoride

Thermal decomposition of the intercalates of XeF₆, XeF₄, XeOF₄ and AsF₅ in graphite has been studied using a molecular beam source mass spectrometer. The product of the hydrolysis of the intercalate of XeF₆ has also been examined. The species liberated at low temperatures (T < 150°C) may be either the ones originally intercalated (XeOF₄, AsF₅) or the next lower oxidation state (XeF₄ from XeF₆, and XeF₂ from XeF₄. At higher temperatures (200-400°C) the intercalated XeF₄, XeF₂ or XeF₄ attack the graphite lattice, and evolve large quantities of xenon, and subsequently fluorocarbons and/or carbonyl fluoride. In contrast, the intercalate of AsF₅ evolves AsF₅ as the dominant gas over most of the temperature range, with a much lower degree of fluorination of the graphite lattice. The hydrolysis product of the XeF₆ intercalate was similar to the intercalate of XeF₄, but the evidence indicates that the hydrolysis proceeded well beyond XeOF₄. The extent of attack upon the graphite lattice correlates well with the oxidizing or fluorinating ability of the intercalated compound.     

Molecular CsF5 and CsF2+

D_5h star‐like CsF₅, formally isoelectronic with known XeF₅^? ion, is computed to be a local minimum on the potential energy surface of CsF₅, surrounded by reasonably large activation energies for its exothermic decomposition to CsF+2 F₂, or to CsF₃ (three isomeric forms)+F₂, or for rearrangement to a significantly more stable isomer, a classical Cs⁺ complex of F₅^?. Similarly the CsF₂⁺ ion is computed to be metastable in two isomeric forms. In the more symmetrical structures of these molecules there is definite involvement in bonding of the formally core 5p levels of Cs.