The CNDO approximation in the Green's function method for VIP calculation

By introducing a CNDO adapted approximation into an appropriate irreducible interaction part a simple formula for calculation of vertical ionization potentials (VIP's) is derived. The method is applied to the molecules F₂, HF, C₂F₄, CH₂F₂, BF₃, CH₃F, CF₄.     

F3SiSH and (F3Si)2S: Conflicting Observations Resolved by Unambiguous Syntheses

The reaction between liquid F₃SiI and red HgS mainly yields the disilylsulfane (F₃Si)₂S and, in smaller amounts, hitherto unknown (F₃SiS)₂SiF₂. These fluorosilylsulfanes have different thermal stabilities. (F₃Si)₂S is a versatile precursor for F₃Si derivatives, and at ambient temperature it is stable, while (F₃SiS)₂SiF₂ decomposes rapidly. F₃SiSH has been obtained, along with F₃SiBr, by selective cleavage of one of the Si–S bonds in (F₃Si)₂S with HBr in the liquid phase and was for the first time unambiguously characterized. Contrary to previous reports, (F₃Si)₂O rather than (F₂SiS)₂ is formed when SiF₄ is passed over SiS₂ at 1298 K in a quartz tube. Raman and infrared spectra of (F₃Si)₂S, F₃SiSH and its deuterated derivative F₃SiSD have been measured and assigned to vibrational fundamentals. Multinuclear NMR spectra have been recorded.     

On the nature of interactions in the F2OXe…NCCH3 complex: Is there the Xe(IV)?N bond?

Nature of the bonding in isolated XeOF₂ molecule and F₂OXe^…NCCH₃ complexes have been studied in the gas phase (0 K) using Quantum Chemical Topology methods. The wave functions have been approximated at the MP2 and DFT levels of calculations, using the APFD, B3LYP, M062X, and B2PLYP functionals with the GD3 dispersion correction. The nature of the formal Xe?O bond in the XeOF₂ monomer depends on the basis set used (all‐electron vs. the ecp‐28 approximation for Xe). Within the all‐electron basis set approach the bond is represented by two bonding attractors, V_{i = 1,2}(Xe,O), with total population of about 1.06e and highly delocalized electron density in both bonding basins. No bonding basins are observed using the ecp‐28 approximation. These results shows that the nature of xenon–oxygen is complicated and may be described with mesomeric equilibrium of the Lewis representations: Xe⁽⁺⁾O^(?) and Xe^(–)O⁽⁺⁾. For both the xenon–oxygen and xenon–fluorine interactions the charge‐shift model can be applied. The F₂OXe^…NCCH₃ complex exists in two structures: “parallel,” stabilized by non‐covalent C^…O and Xe^…N interactions and “linear” stabilized by the Xe^…N interaction. Topological analysis of ELF shows that the F₂OXe^…NCCH₃ molecule appears as a weakly bound intermolecular complex. Intermolecular interaction energy components have also been studied using Symmetry Adapted Perturbation Theory. © 2016 Wiley Periodicals, Inc.     

The mass spectra of some pentafluorophenylthio derivatives

Ionic fragmentations induced by electron-impact on compounds of the type C₆F₅SX (X ? H, CH₃, COCH₃, Cl, C₆F₅) and (C₆F₅S)₂, (C₆F₅S)₂Hg, (C₆F₅S)₃As and (C₆F₅SCH₂)₂ have been studied. Principal features of the mass spectra are reported. The [C₆F₅S]⁺ ion (m/e 199) is predominant and its mode of fragmentation has been deduced. The precursor ions for m/e 199 have been examined in (C₆F₅)₂S, (C₆F₅S)₂, (C₆F₅S)₂Hg, (C₆F₅S)₃As and C₆F₅SCl. Ion kinetic energy spectra of (C₆F₅)₂S, (C₆F₅S)₂, (C₆F₅S)₂Hg and C₆F₅SCl have been recorded, and all contain peaks corresponding to the fragmentation of the [C₆F₅S]⁺ ion.     

The electronic and geometric structures of some xenon oxyfluorides

The modified Wolfsberg-Helmholz approximation has been applied to calculate the MO eigenvectors and eigenvalues for several xenon oxyfluorides. Structural properties for XeOF₂, XeO₂F₂ and XeOF₄ have been rationalized and predicted based on the nodal characters of the highest filled MO('s). Results show that XeOF₂ should have C_2vsymmetry with angle OXeF less than 90°. For XeO₂F₂, the OXeO angle is predicted to be less than 120° while the FXeF angle on the side of the oxygens is less than 180°. According to this model, XeOF₄ has C_4vsymmetry with angle OXeF greater than 90°. In addition, the relative bond lengths in these systems have been commented upon. Except for XeOF₄, the exact structures of the other two remain unknown. These results seem to imply that double bond and lone pair are of similar bulkiness in the coordination sphere and that the Pauli force in the valence-shell-electron-pair-repulsion model and nodal repulsion are intimately related.     

Graphical representation of the state of orientation of polymer systems

The orientation distribution function for noncrystalline structural units in polymer systems cannot be determined completely from any experimental source; only the second and/or fourth moments of the distribution function, i.e., the second and/or fourth orders of the generalized orientation factors F_lm^j, can be evaluated. It is there-fore necessary to estimate the distribution function from F_2m^j and F_4m^j. In this paper, a graphical representation of the state of orientation is first discussed in terms of plots of F₄₀^j against F₂₀^j for several types of distribution functions for uniaxial orientation. These are three types of extreme concentration of the distribution at particular polar angles θ₀ given by θ₀ = 0, 0<θ₀<π/2, and θ₀ = π/2; five types of rather realistic distributions having single maxima at θ_j = 0, θ₀, π/2 and double maxima at θ_j = 0, π/2, and a single minimum at θ_j = θ₀; and four types of more realistic distributions including Kratky's floating rod model in an affine matrix. Second, estimation of the distribution function for uniaxial orientation from F₄₀^j and F₂₀^j is discussed quantitatively in terms of the mean-square error by three approximation methods: (a) expansion of the distribution function in finite series of spherical harmonics through the fourth order, (b) approximation of the distribution function as a composite of two components, random orientation and a particular orientation distribution given by N_a (cos²θ_j)^a, N_a being a constant, and (c) approximation of the distribution function by N_a (cos²θ_j)^a alone. It is concluded that when the orientation distribution is sharp, estimation by the second method of approximation gives a smaller error than the first.     

Stark effect on the spin coherence of phosphorescent F2+2 defects in calcium oxide

Using techniques for the optical detection of spin coherence, we have studied the Stark effect for the F²⁺₂ (CaO) center in its photo-excited ³B₁ state at 1.2 K. Electric-field induced inhomogeneous broadening of the T_x → T_z spin transition (at 1870 MHz), linearly dependent on the electric field strength, can be deduced. The results are related to random variations in the local crystal field of the F²⁺₂ defects.     

Well‐Defined CuC2F5 Complexes and Pentafluoroethylation of Acid Chlorides

Four new well‐defined Cu^I complexes bearing a C₂F₅ ligand have been prepared and fully characterized: [(Ph₃P)₂CuC₂F₅] ( 2 ), [(bpy)CuC₂F₅] ( 3 ), [(Ph₃P)Cu(phen)C₂F₅] ( 4 ), and [(IPr*)CuC₂F₅] ( 5 ). X‐ray structures of all four have been determined, showing that the C₂F₅‐ligated Cu atom can be di‐ ( 5 ), tri‐ ( 2 and 3 ), and tetracoordinate ( 4 ). The mixed phen‐PPh₃ complex 4 is a highly efficient fluoroalkylating agent for a broad variety of acid chlorides. This high‐yielding transformation represents the first general method for the synthesis of RCOC₂F₅ from the corresponding RCOCl.     

Improved Iterative Version of the Coats-Redfern Method to Evaluate Non-Isothermal Kinetic Parameters

An improved version of the Coats-Redfern method of evaluating non-isothermal kinetic parameters is presented. The Coats-Redfern approximation of the temperature integral is replaced by a third-degree rational approximation, which is much more accurate. The kinetic parameters are evaluated iteratively by linear regression and, besides the correlation coefficient, the F test is suggested as a supplementary statistical criterion for selecting the most probable mechanism function. For applications, both non-isothermal data obtained by theoretical simulation and experimental data taken from the literature for the non-isothermal dehydration of Mg(OH)₂ have been processed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Transmission of electronic effects in certain ployenes

The effect of substituent variation in compounds of the general type R(CHCH)_nCHO (1) or p-RC₆H₄ (CHCH)_nCHO (2) on the stretching vibrations of the CHO group (ν_co), the dipole moments (μ), the long wave maxima (λ_max), and the halfwave potentials (E_{$\text{1}\text{2}$}) for the polarographic reduction of the CHO group have been studied as well as the influence of variation of substituent R on the rate constants (k) of the alkaline hydrolysis of polyenic esters R(CHCH)_nCOOEt (3). A linear relationship between the σ⁺, σ_c⁰ or σ_c⁺ values and the experimental values of ν_co, μ, gl_max, E_{$\text{1}\text{2}$} and k has been established, which indicates the importance of the mesomeric mechanism of the transmission of electronic effects through the chain of conjugated double bonds in compounds 1, 2 and 3. Transmission coefficients (π′) for one (π′_1F), two (π′_2F), three (π′_2F), and four (π′_4F) double bonds were calculated, and it was found that these values are bound together by the ratio: (π′_1F):(π′_2F):(π′_3F):(π′_4F) = (π′_1F):(π′_1F)²:(π′_1F)³:(π′_1F⁴, i.e. the influence of substituents R is decreased m a geometrical progression when the number of double bonds increases. The distribution of the electronic density in 1 was calculated by the LCAO SCF method in the Pariser-Parr-Pople approximation, and it was found that the π-electronic density values at the O atoms of the CHO group correlates well with σ_c⁰ constants and the calculated values of π′_1F, π′_2F, and π′_3F are bound together by the above ratio.     

Synthesis and coordination chemistry of perfluoroalkyl-derivatised β-diketonates

A series of fluorinated β-diketones, R_fC(O)CH₂C(O)R_f′ (R_f=C₆F₁₃, R_f′=CF₃; R_f=R_f′=C₆F₁₃, C₇F₁₅), have been prepared in reasonable yields by a two-step synthesis. On reaction with appropriate metal substrates, deprotonation and concurrent coordination of the perfluoroalkyl-derivatised β-diketonate ligands affords a range of fluorous metal complexes which have been characterised by elemental analysis, mass spectrometry, IR and NMR spectroscopies. The structures of [Cu(L-L)₂(H₂O)₂] {L-L=CF₃C(O)CHC(O)C₆F₁₃, C₆F₁₃C(O)CHC(O)C₆F₁₃} and [Cu(PPh₃)₂{C₇F₁₅C(O)CHC(O)C₇F₁₅}] have been determined by single-crystal X-ray diffraction.     

Some reactions of copper(I) pentafluorothiophenolate

Copper(I) pentafluorothiophenolate, CuSC₆F₅ reacted with a number of acyl and alkyl halides in either $\text{n}$-hexane or DMF. The products RCH₂SC₆F₅ (R = Me, Ph, C₆F₅S, C₆F₅SCH₂), Ph₂CHSC₆F₅, R₃CSC₆F₅(R =Me, Ph) and RCOSC₆F₅ (R = Me, C₆F₅) have been characterized and their spectra, particularly NMR spectra (H1, C13, F19) have been examined.     

Syntheses of polyfluorophenylcobalt(III) schiff base complexes using organothallium reagents

The complexes RCo(acacen) [R = C₆F₅, p-HC₆F₄, or o-HC₆F₄; H₂acacen = N,N′-ethylenebis(acetylacetonimine)] and RCo(salen) [R = C₆F₅ or p-HC₆F₄; H₂salen = N,N′-ethylenebis(salicylaldimine)] have been prepared by reaction between Co(acacen) or Co(salen) and the appropriate bromobis(polyfluorophenyl)thallium(III) compounds, and have been isolated as pyridinates. Spectroscopic evidence for formation of C₆F₅Co(salophen) [H₂salophen = _N,N′-o-phenylenebis(salicylaldimine)] has also been obtained. The reactivity of the thallium compounds increased in the sequence Ph₂TlBr ? (o-HC₆F₄)2TlBr < (p-HC₆F₄)₂TlBr < (C₆F₅)₂TlBr, and of the cobalt complexes in the sequence Co(salophen) < Co(salen) < Co(acacen). Possible mechanisms are discussed.     

A gas-phase anionic analog of the wittig reaction. An ion cyclotron resonance study of the gas-phase ion chemistry of silyl carbanions

Gas-phase ion–molecule reactions of a variety of fluorosilyl carbanions with compounds containing double bonds to oxygen, X?O, have been examined using pulsed ion cyclotron resonance spectroscopy. The predominant reaction channel observed for species not containing acidic hydrogens is a Wittig-like process involving Si? O bond formation and elimination of X?CH₂ species. The gas-phase acidity of F₃Si(CH₃) has been determined and those of F₂Si(CH₃)₂ and FSi(CH₃)₃ have been estimated. From the fluoride transfer reactions of F₃SiCH₂^? the fluoride affinity of F₂Si?CH₂ has been estimated and limits on the π bond strength in this silaethene obtained. Potential analytical applications of the Wittig reactivity have been discussed.     

Reactions of 3-(Polyfluoroalkyl)propane-1,2,3-trione-2-oximes with Diaminoarenes

Novel quinoxaline derivatives have been synthesized via the reaction of 3-trifhioromethyl-1,2,3-propanetrione-2-oximes with 1,2-diaminobenzene or 2,3-diaminonaphthalene: 2-trifluoromethyl-3-aroylquinoxaline and 2-trifluoromethyl-3-aroylbenzo[g]quinoxaline. Under similar conditions, 3-R^F-1,2,3-propanetrione-2-oximes [R^F = C₃F₇, H(CF₂)₄, C₄F₉, and C₆F₁₃] with the same diaminoarenes have given a mixture of the condensation and fragmentation products in different ratios. The structure of (4-methylphenyl)[3-(tri-fluoromethyl)benzo[g]quinoxalin-2-yl]methanone has been elucidated by means of X-ray diffraction analysis.

     

Reactions of Pentafluorobenzenesulfanylamines (C6F5S)nNH3–n,n = 1, 2, 3 and the Structure of (C6F5S)3N

The crystal structure of (C₆F₅S)₃N has been examined. The compounds (C₆F₅S)₂NX, X = SiMe₃ and ½ Hg have been prepared from (C₆F₅S)₂NH and characterised. In a number of other reactions, such as oxidation and irradiation, the S? N bond in (C₆F₅S)₂NH was readily fractured, forming the disulfide, (C₆F₅S)₂. The compound (C₆F₅S)₃N has been found to be unreactive. Details of the mass and ¹³C NMR spectra of (C₆F₅S)_nNH_3–n, n = 1, 2, 3 are reported.     

Coordination chemistry of higher oxidation states. 10 [1]. Oxofluoroanions of osmium(VIII) [OsO4F2]2− and [OsO3F3]−

Trioxotrifluoroosmates(VIII) M[OsO₃F₃] (M = Cs, Rb, K) have been prepared by direct combination of OsO₃F₂ and the appropriate alkali fluoride MF. The reaction of OsO₄ with M′F (M′ = Cs, Rb) in aqueous solution produces the tetraoxodifluoroosmates(VIII) M′₂[OsO₄F₂]. On the basis of their vibrational spectra the assignment of a $\text{fac}$ (C_3v) structure to [OsO₃F₃]^? and a $\text{cis}$ (C_2v) to [OsO₄F₂]^2? is proposed. The electronic spectra of the anions have been recorded and are interpreted using the optical electronegativity concept.     

Structure and conformation in molecular peroxides

Molecular structures and energies have been calculated in the MINDO approximation for fifteen neutral and anionic peroxides: fully optimized torsional potential functions have been calculated for twelve of these, and torsional potential functions, subject to constrained optimizations, for a further two peroxides. Bond dissociation energies D(R₁O—OR₂) were also calculated. Equilibrium structures and energies were calculated for the polyoxo species H₂O_n, HO_nF, F₂O_n, HO_n and FO_n (n ? 4), and a complete set of bond dissociation energies derived for H₂O_n, HO_nF, and F₂O_n.     

Stark effect study of the 4f66s2 7 F 1, 2, 3, 4, 5, 6 levels of samarium using nonlinear level crossing technique

The nonlinear level crossing technique with parallel electric and magnetic fields was used to investigate the Stark effect of six levels of the ground multiplet 4f⁶6s^{2 7} F in the Sm I-spectrum. The tensor polarizabilities were deduced from the level crossing signals. The variation of the tensor polarizabilities of the levels of the ground multiplet is well reproduced by the LS coupling approximation, which gives an average value of α₂(F)=?0.88(6) kHz/(kV/cm)² for the six measured levels. The experimental results confirm the validity of the central field approximation in the ground configuration of Sm.     

The thiolate anion as a nucleophile Part III. Reactions with various fluorobenzenes

The reactions of the fluorobenzenes, C₆F₅H, o-C₆H₂F₄, m-C₆H₂F₄, p-C₆H₂F₄, 1,3,5-C₆F₃H₃, 1,2,4-C₆F₃H₃, o-C₆F₂H₄, m-C₆F₂H₄, p-C₆F₂H₄ and C₆F₅H with thiolate anion nucleophiles RS^? (primarily MeS^?), have been studied in ethylene glycol/pyridine mixtures as a solvent. Multiple replacement of fluorine atoms was observed in the more highly fluorinated compounds, but in all cases two aromatic fluorine atoms were not replaced. Difluorobenzene and fluorobenzene did not react. The product orientations have been deduced from their NMR spectra. The mass spectra of the isomeric products C₆F₂H₃(SMe), C₆F₃H₂(SMe) and C₆F₂H₂(SMe)₂ have been examined.