Synthesis and characterization of tetramethylammonium trifluorosulfate

[Me₄N]⁺[SO₂F₃]^?, the first example of a [SO₂F₃]^? salt, has been prepared from Me₄NF and SO₂F₂. The colorless, microcrystalline solid was characterized by its infrared and Raman spectra. The trigonal bipyramidal structure of C_2v symmetry of the [SO₂F₃]^? anion is predicted by ab initio calculations. Two oxygen atoms with d(SO)=143.2 pm and one fluorine atom with d(SF)=157.9 pm occupy the equatorial plane. The two fluorine atoms in the axial position with d(SF)=168.5 pm are repulsed by the two oxygen atoms forming a bent axis with ?(F_axSF_ax)=165.2°.     

The unusual chemical equilibria F3SSF ⇌ 2 SF2 and CF3SF2SCF3 ⇌ 2CF3SF

In order to understand more about the instability of sulfur difluoride, we have investigated the chemical interrelations between each of the monomers SF₂ and CF₃SF and the corresponding dimers F₃SSF and CF₃SF₂SCF₃. Thus we have found that SF₂ and CF₃SF exist in chemical equilibria with their dimers. These equilibria are unusual because they involve two different bonds (SF and SS). The equilibrium constants and dissociatíon enthalpies have been determined by i.r. and mass spectroscopic measurements.

The equilibrium between F₃SSF and SF₂ is disturbed by a decomposition reaction of these compounds yielding SF₄ and SSF₂. In both systems (1) and (2) the achievement of the equilibrium is comparatively slow at ?30 to 30 °C. The rates for dissociation and decomposition are strongly surface-dependent and the kinetics of the two processes have been studied separately. Under favorable conditions the half-lives at 298 K for the dissociation of F₃SSF and CF₃SF₂SCF₃ are found to be ca. 8.h and ca. 2 h, respectively, and for the decomposition of SF₂ to SF₄ and SSF₂ and CF₃SF to CF₃SF₃ and CF₃SSCF₃ (p?13 mbar) the values are ca. 10 h and 1 year respectively.     

Structure of tetracoordinated sulphur compounds. Model calculations on SH4 and SF2H2

The structure of the hypothetical sulphuranes SH₄ and SF₂H₂ is investigated through ab initio LCAO MO SCF calculations. In contrast to a recent report the structure of lowest energy for SH₄ is of C_4V symmetry. For SF₂H₂ a structure of C_2V symmetry with axiai fluorine atoms is predicted. These results have been rationalized on the basis of perturbation theory.     

ChemInform Abstract: The cis Influence of Bromine in SF5Br. A Combined Electron Diffraction-Microwave Study.

The results obtained from the electron diffraction study of the gas phase molecular structure of SF₅Br demonstrate a small cis influence of Br on the SF₅ group, i.e., the equatorial bonds (cis to Br) are affected more strongly by the substituent than the axial bond.     

A molecular orbital study of bond energies in compounds of sulfur and fluorine

CNDO/2 molecular orbital theory is employed in a study of the binding energies of the molecules SF, SF₂, SF₄, SF₆, their cations and anions, and of the molecules SSF₂, FSSF and S₂F₁₀. Computed energies, when rescaled according to energy partitioning concepts, compare favorably with available experimental data. Ionization energies and electron affinities are calculated for SF, SF₂, SF₄ and SF₆.

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Zusammenfassung Mit Hilfe der CNDO/2 Theorie werden die Bindungsenergien der SF, SF₂, SF₄ und SF₆ Moleküle, von deren positiven und negativen Ionen und von SSF₂, FSSF und S₂F₁₀ berechnet. Die berechneten Energien stimmen gut mit experimentellen Daten überein, wenn sie nach Energieaufteilungsprinzipien wiederberechnet werden. Ferner werden die Ionisierungsenergien und Elektronenaffinitäten für SF, SF₂, SF₄ und SF₆ angegeben.

     

Theoretical determination of molecular structure and conformation: Part X. Geometry and puckering potential of azetidine, (CH2)3NH,combination of electron diffraction and ab initio studies

Restricted Hartree—Fock calculations on 21 planar and puckered conformers of azetidine have been done employing a split valence basis augmented by d functions. Complete geometry optimizations have been performed for eight conformers. In this way the puckering potential of azetidine is explored over the range ?40° < ø (puckering angle) < 40°, for both sp³ and sp² hybridization of the nitrogen atom. In its equatorial form, azetidine is slightly more puckered than cyclobutane. This is because of a decrease of van der Waals' repulsion between H atoms. Charge effects lead to destabilization of the axial forms. There is only moderate coupling between puckering and methylene group rocking. Previously published electron diffraction (ED) data are reinvestigated using vibrational corrections and information from the ab initio calculations. On the basis of this MO constrained ED (MOCED) analysis a puckering angle φ = 35.1(1.8)° is found. Observed r_g and r_e bond distances are compared with ab initio values.     

Matrix Isolation and IR spectroscopy of stannylenes (CH3)2Sn and (CD3)2Sn

Free stannylenes Me₂Sn and (CD₃)₂Sn, generated thermally from the cyclic hexamers or by microwave discharge from Me₂SnH₂, are isolated by Argon matrix technique. All IR bands could be attributed to the important molecular vibrations by normal coordinate analysis. As shown by ab initio SCF calculations, Me₂Sn has a singlet groud state, the angle CSnC is 95.3°, the CSn bond length is 2.203 Å.     

Structure and conformation of cyclobutylsilane: an electron diffraction and ab initio study

A gas electron diffraction study of cyclobutylsilane results in a mixture of equatorial and axial conformers, with the equatorial confomer slightly more stable (Δ G = 0.8 ± 0.4 kJ mol⁻¹). The cyclobutyl ring is distorted with the adjacent bonds longer (C₁---C₂ = 1.573 (4) Å) than the opposite bonds (C₂---C₃ = 1.557 (4) Å). The experimental values for the energy difference between the two conformers and for the geometric parameters are reproduced very well by ab initio calculations. The importance of silicon 3d orbitals in the interpretation of ring distortion is ambiguous, but on the basis of the ab initio calculations the participation of silicon 3d functions is negligible.     

Chalkogenfluoride in niedrigen Oxydationsstufen. V. Die ungewöhnlichen chemischen Gleichgewichte F3S?SF ⇌ 2SF2 und CF3SF2?SCF3 ⇌ 2 CF3SF

Lower Chalcogen Fluorides V. Unusual Chemical Equilibria F₃S? SF ? 2 SF₂ and CF₃SF₂? SCF₃ ? 2 CF₃SF SF₂ and CF₃SF form unusual chemical equilibria with their dimers F₃SSF and CF₃SF₂ SCF₃ involving two different bonds (SF and SS). The equilibrium between F₃SSF and SF₂ is disturbed by a decomposition reaction of these compounds yielding SF₄ and SSF₂ · K_p (298) = 2.5 · 10^?3atm, ΔH°₂₉₈ = 68.5 kJ/mol for the system F₃SSF ? 2SF₂ and K_p(298) = 1.3 × 10³ atm, δH₂₉₈ = 42.5 kJ/mol for the system CF₃SF₂SCF₃ ? 2CF₃SF have been determined as the equilibrium constants and the dissociation enthalpies. In both systems kinetic hindrance delays the achievement of the equilibrium. The rates for dissociation and decomposition are strongly surface dependent. Under favourable conditions the half-lives at 298 K for the dissociation of F₃SSF and CF₃SF₂SCF₃ are found to be ca. 8 h and ca. 2 h respectively, and for the decomposition of SF₂ and CF₃SF (p ～ 13 mbar) the values are ca. 10 h and 1 year respectively.     

S42+ and S42− : an ab initio study

The structures of S₄²⁺ and S₄^2? have been investigated by ab initio calculations using the GAUSSIAN 70 system of programs and the 44-31G basis set. Electronic singlet states of the square form and three possible conformations of the chain structure were examined for both ions, and the singlet rectangle form of S₄^2? was also investigated. The anti chain form of S₄²⁺ was found to be 78.3 kJ mol^? more stable than the square form, in contrast to previous experimental data. S₄^2?is predicted to adopt the chain structure with the anti conformation.     

The structure of trimethoxymethane in the gas phase,an electron diffraction,ab initio and molecular mechanics study

The structure of trimethoxymethane in the gas phase was studied by electron diffraction, ab initio molecular orbital calculations and molecular mechanics. The molecule was found to exist almost exclusively as an asymmetric all-staggered TGG conformer. The electron diffraction structural parameters (r_g distances, r_α angles) as obtained from geometrically consistent r_α-refinements are: r(C-O) central 1.382(6) Å, r(C-O) terminal 1.418(6) Å, r(C-H) 1.112(1) Å, ∠(O-C-O) in the gauche—gauche chain 115.0(1.0)°, in the gauche-anti chains 109.2(0.6)° ∠(C-O-C) 114.3(0.6)°, ∠(O-C-H)_Me 109.9(0.3)°, methyl torsion 68(6)°. The structure is adequately reproduced by molecular mechanics calculations applying Allinger's force field. The structures of methoxymethanes can be explained in terms of the anomeric effect. This is confirmed by ab initio calculations.     

The <Emphasis Type="Italic">r</Emphasis><Subscript>0</Subscript> structural parameters of equatorial and axial chlorocyclobutane,conformational stability from temperature dependent infrared spectra of xenon solutions,and vibrational assignments

Variable temperature (?55 to ?100 °C) studies of the infrared spectra (4,000–400 cm^?1) of chlorocyclobutane, c-C₄H₇Cl, dissolved in liquid xenon have been carried out. The infrared spectrum (4,000–100 cm^–1) of the gas has also been recorded. For this puckered ring molecule the enthalpy difference between the more stable equatorial conformer and the axial form, has been determined to be 361 ± 17 cm^?1 (4.32 ± 0.20 kJ/mol). This stability order is consistent with that predicted by ab initio calculations but the ?H is much lower than the average energy value of 646 ± 73 cm^?1 obtained from the MP2 ab initio calculations or 611 ± 28 cm^?1 from the B3LYP density functional theory calculations. The percentage of the axial conformer present at ambient temperature is estimated to be 15 ± 1%. By utilizing previously reported microwave rotational constants for both conformers combined with ab initio MP2(full)/6–311+G(d,p) predicted structural values, adjusted r ₀ parameters have been obtained. The determined heavy atom structural parameters for the equatorial conformer are: the distances C–Cl = 1.783(5), C₁–C₄ = 1.539(3), C₄–C₆ = 1.558(3) Å, and angles ∠C₆C₄C₁ = 86.9(5), ∠C₄C₁C₅ = 89.7(5)°, and for the axial conformer are: the distances C–Cl = 1.803(5), C₁–C₄ = 1.547(3), C₄–C₆ = 1.557(3) Å, and angles ∠C₆C₄C₁ = 86.3(5), ∠C₄C₁C₅ = 88.9(5) and the puckering angles for the equatorial and axial conformers are 30.7(5)° and 22.3(5)°, respectively. The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for both conformers from MP2(full)/6-31G(d) ab initio calculations and compared to experimental values where available. The results are discussed and compared to the corresponding properties of some similar molecules.     

The structure of propadienone (CH2CCO)

A complete r_o structure has been obtained for propadienone (CH₂CCCO) with the aid of ab initio molecular-orbital calculations. The effect of electron correlation has been investigated using third order Møller-Plesset perturbation theory. The molecule is found to be planar bent (CCC145°) and the calculated structure yields rotational constants which are in good agreemant with experimental values.     

An improved electron diffraction—microwave and molecular orbital study of the structure of SF5Cl

A new study of the structure of SF₅Cl is reported. Previously-obtained electron diffraction data have been corrected for multiple scattering, and newly-reported microwave rotational constants have been combined in the analysis. Structural parameters, with estimated limits of error, were found to be r_g (S-Cl) 2.055(1) Å, r_g (S-F)_mean 1.570(1) Å, r_g (S-F_ax) - r_g(S-F_eq) 0.001(8) Å, r_g(S-F_eq) 1.571(3) Å, r_g (S-F_ax) 1.571(8) Å, ∠α Cl-S-F_eq 90.4(0.1)°. The new data are more self-consistent than was previously the case. Ab initio molecular calculations using three different basis sets are reported and discussed.     

Calculation of the equilibrium conformation of HN3

An ab initio LCAO MO SCF series of calculations has been carried out on the ground state of HN₃ for a number of different geometries. The results indicate that the N₃ group is non-linear with an NNN bond angle near 8°. A re-analysis of infrared and microwave data may be required since previous analyses have been based on a linear N₃ geometry.     

The structure of the metallated iridium complex [(C8H12)Ir{P(OC6H3Me)(OC6H4Me)2} {P(OCH2)3CMe}]

The crystal structure of [(C₈H₁₂)$\text{Ir{P(OC}$₆H₃Me)(OC₆H₄Me)₂} {P(OCH₂)₃CMe}] has been determined. a 18.32, b 18.98, c 9.35 Å, U 3251 ų, Pn2_1^a, Z = 4, R = 0.048, 2541 observed data.The coordination about the iridium atom is distorted trigonal bipyramidal; the two phosphorus atoms are equatorial, the σ-bonded carbon is axial, and the bidentate cyclooctadiene is bonded axialequatorial. The IrC(axial) bonds are longer than the IrC(equatorial) bonds: 2.22, 2.26; 2.17, 2.19 Å. The IrC(σ) bond length is 2.19 Å, not significantly different from the formally π-bonded C to Ir distances. The IrP lengths of 2.201 and 2.240 Å and the PIrP angle of 108.7° are normal. The longer IrP bond is in the five-membered chelate ring. The inertness to substitution is discussed.     

Ab initio calculation of the electronic structure and the barrier to pyramidal inversion for H3S+

The electronic structure of H₃S⁺ is examined by ab initio MO calculations (STO 3G) and is compared with those of other XH₃ type molecules. The barrier to pyramidal inversion and the proton affinity of H₂S are calculated to be 34.8 and 225.05 kcal/mol respectively. Computations are made with respect to a model A₃S⁺ which is employed to discuss the barrier to pyramidal inversion of H₃S⁺, where A corresponds to an electromagnetive substituent or an electron donating one.     

Experimental and theoretical structural study of 2,9-bis-(4-fluorophenyl)-azaadamantan-4-one ethylene ketal

The title ethylene ketal 1, C₂₃H₂₃F₂NO₂, has a tricyclic azaadamantane cage with aryl rings (4-fluorophenyl) substituted at the 2 and 9 positions. Rings A (C11-C16) and B (C17-C22) are attached to atoms C2 and C9 in axial and equatorial positions, respectively; and the presence of the five-membered 1,3-dioxolane ring attached to atom C4. The structural analysis of the title was carried out by experimental (single crystal X-ray diffraction and NMR) and confirmed by theoretical calculations (ab initio RHF, DFT and NMR-DFT-GIAO).     

A full dimensional direct ab initio dynamics study of the electron capture by SF6

The dynamics of electron capture by sulfur hexafluoride (SF₆) have been investigated by means of full dimensional direct ab initio dynamics calculations at the HF/6-311G(d)+sp (a diffuse sp-function is further added to sulfur atom) level. A rigid SF₆ structure and narrow Franck–Condon region for electron capture was assumed in choosing initial conditions for the trajectories. The direct ab initio dynamics calculations for the electron capture processes by SF₆ indicated that the SF⁻₆ ion formed by the vertical electron attachment to SF₆ decomposes into SF⁻₅ and F via short-lived complex formation (SF⁻₆). The lifetime of SF⁻₆ was distributed from 0.1–0.2 ps, which is quite short as lifetime of the intermediate complex. The dynamics calculations showed that 12% of the total available energy is partitioned into the relative translational mode between SF₅⁻ and F. The effect of solid phase on the dynamics has been examined by introducing a model bath-relaxation time for energy dispersion. There was a possibility that the SF₆⁻ anion exists in solid phase. The mechanism of the electron capture by SF₆ in gas phase and in solid phase was discussed on the basis of the results.     

A critical review of the chemical kinetics of SF4, SF5, and S2F10 in the gas phase

The gas phase chemical kinetics of SF₄, SF₅, and S₂F₁₀ are reviewed with particular emphasis on relevance to the general problem of the dielectric breakdown of SF₆. Specific reaction systems treated are SF₄ + F₂, SF₅ + SF₅, and the pyrolysis of S₂F₁₀. Computer modeling calculations were carried out to arrive at the best estimates of rate parameters. Based on the results of these calculations, sets of recommended rate parameters are provided. The major discrepancies and problems in establishing the kinetic data base are described. Thermochemical consequences of different model calculations are given.