Far-infrared spectra of ring compounds: A semi-rigid model for the ring-puckering vibration in some pseudo-four-membered ring molecules

Malloy, Thomas B.

doi:10.1016/0022-2852(72)90260-3

Cited by 109 publications

(23 citation statements)

References 33 publications

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“…Thus, the tetrahedral Co atoms in Co9S8 have Co-S distances of 2.13 and 2.23 hi and square-planar Co coordination complexes have Co-S distances of 2.15-2.17 A,44 while for 5-fold sulfur coordinated square-pyramidal Co complexes four short Co-S distances in the range of 2.14-2.21 hi and one long Co-S distance of about 2. 4 8, have been measured.45 Evidently, there is a conflict between the Co-S coordination distances and coordination numbers of the Co-Mo-S/C and Co-Mo/C catalysts. Since the reliability of distances measured by EXAFS is much higher than that of coordination numbers, and also since the reliability of the measured distances is good enough to be able to distinguish between 4-and 5-fold S coordination on the one hand and 6-fold S coordination on the other hand, we feel that the only way to resolve this discrepancy is to assume that the cobalt atoms have a distorted 6-fold coordination.…”

Section: Discussionmentioning

confidence: 97%

EXAFS determination of the structure of cobalt in carbon-supported cobalt and cobalt-molybdenum sulfide hydrodesulfurization catalysts

Bouwens¹,

Veen²,

Koningsberger³

et al. 1991

J. Phys. Chem.

209

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The structure of the cobalt present in carbon-supported Co and Co-Mo sulfide catalysts was studied by means of X-ray absorption spectroscopy at the Co K-edge and by X-ray photoelectron spectroscopy (XPS). Thiophene hydrodesulfurization activities were used to measure the catalytic properties of these catalysts. By comparison of the EXAFS and XANES spectra of the catalysts with those of c 0 9 s S and Cos2 model compounds, it was concluded that all Co atoms in a catalyst prepared with nitrilotriacetic acid as complexing agent were in the "Co-Mo-S" state, while the Co atoms in a conventionally prepared catalyst were partly present in a CO$8-like structure and partly in a "Co-Mo-S" structure. The Co atoms in the To-Mc-S" state have a distorted 5-to 6-fold sulfur coordination, and on the average, every Co atom is in contact with two Mo atoms at a distance of 2.80 A. On the basis of these data, the most likely position for the Co atoms is in front of the square sulfur faces of the MoS6 trigonal prisms along the edges of the MoS, crystallites with two additional sulfur atoms or H2S molecules attached. The Co atoms in the sulfided Co/C catalyst have Co-S and Co-Co coordinations as in c 0 9 s g , although the sulfur coordination number is higher. IntroductionCobalt-or nickel-promoted molybdenum sulfide catalysts supported on alumina are extensively used in the hydrotreatment of petroleum feedstocks. The increasing need for efficient removal of sulfur, nitrogen, and metal contaminants has led to a continuous drive to clarify the structure and the related catalytic activity of these complex catalyst systems. Especially the role and the chemical state of the promoter cobalt and nickel atoms in the sulfided catalysts is a subject of great interest, and numerous studies have been devoted to it.'v2 The introduction of in situ Mossbauer emission spectroscopy (MES) provided for the first time direct information regarding the nature of the cobalt phases present in a working Co-Mo hydrodesulfurization (HDS) catalyst. With the use of MES, Topsere et al.3 and Wivel et aL4 showed that most of the cobalt atoms are situated at MaS2 crystallite edges in a so-called "Co-Mo-S" structure and that this structure governs almost completely the HDS activity. However, the precise local structure of the cobalt promoter atoms is still unknown. Also, the high specific activity of the "Co-Mo-S" structure is not understood. In this respect, it has not been established whether the cobalt atoms are the active sites or whether the neighboring molybdenum atoms also play a direct role in the catalytic activit y . 5-7Detailed information on the chemical state of the cobalt atoms was obtained by Ledoux et al. with the use of 59C0 NMR.8 They argued that the promotion effect of cobalt was correlated with the concentration of cobalt sites having a distorted tetrahedral symmetry and that these sites were stabilized by so-called "rapid octahedral" cobalt atoms acting as a glue between the tetrahedral cobalt sites and the MoS, phase. Although the "rapid octahe...

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Section: Discussionmentioning

confidence: 97%

EXAFS determination of the structure of cobalt in carbon-supported cobalt and cobalt-molybdenum sulfide hydrodesulfurization catalysts

Bouwens¹,

Veen²,

Koningsberger³

et al. 1991

J. Phys. Chem.

209

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“…Cyclopentene is thus typically the most thoroughly studied example of a pseudo-four-membered-ring molecule characterized by a double-minimum potential function describing low-frequency puckering vibrations. A number of experiments employing far-infrared [1,[3][4][5], mid-infrared, [6][7][8][9][10][11][12][13][14][15][16][17], Raman [14][15][16][17][18][19][20][21][22][23][24], and microwave [25][26][27] spectroscopy, electron diffraction [28], and various theoretical analyses [29][30][31][32][33][34][35][36][37] indicate that cyclopentene has a non-planar equilibrium structure of C s symmetry, with the carbon atom opposite to the double bond being tilted out of the plane of the four other carbon atoms. Cyclic unsaturated hydrocarbons such as cyclopentene (C 5 H 8 ) have been widely used for the making of ordered organic monolayer films on semiconductor surfaces of crystalline silicon (Si) [38][39][40]…”

Section: Introductionmentioning

confidence: 99%

Study of the photoelectron and electron momentum spectra of cyclopentene using benchmark Dyson orbital theories

Huang

Ning

Deng

et al. 2008

Phys. Chem. Chem. Phys.

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Abstract:A complete study of the valence electronic structure and related electronic excitation properties of cyclopentene in its C s ground state geometry is presented. Ionization spectra obtained from this compound by means of photoelectron spectroscopy (He I and He II) and Electron Momentum Spectroscopy have been analyzed in details up to electron binding energies of 30 eV using one-particle Green's function (1p-GF) theory along with the outer-valence (OVGF) and the third-order algebraic diagrammatic construction [ADC(3)] schemes. The employed geometries derive from DFT/B3LYP calculations in conjunction with the aug-cc-pVTZ basis set, and closely approach the structures inferred from experiments employing microwave spectroscopy or electron diffraction in the gas phase. The 1p-GF/ADC (3) calculations indicate that the orbital picture of ionization breaks down at binding energies larger 2 than ~17 eV in the inner-valence region, and that the outer-valence 7a′ orbital is also subject to a significant dispersion of the ionization intensity over shake-up states. This study confirms further the rule that OVGF pole strengths smaller than 0.85 foretell a breakdown of the orbital picture of ionization at the ADC(3) level. Spherically averaged (e, 2e) electron momentum distributions at an electron impact energy of 1200 eV that were experimentally inferred from an angular analysis of EMS intensities have been interpreted by comparison with accurate simulations employing ADC(3) Dyson orbitals. Very significant discrepancies were observed with momentum distributions obtained from several outer-valence ionization bands using standard Kohn-Sham orbitals.

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“…When we attempted to include in the fitting process a kinetic term of the form g"'pq2p, q the dimensionless coordinate, p its conjugate momentum, and g"' the coefficient of q 2 in the expansion of the reduced mass in terms of the deformation coordinate used as a fitting parameter, the deviations were reduced only marginally with the trend remaining, even if g"' was optimized to yield the best fitting potential constants. In contrast, remarkable improvements in the fit have been demonstrated by just such a procedure in several other instances (19,20). While anharmonic contributions from the kinetic energy may well play a role also in the present cases, they evidently are difficult to quantify.…”

Section: Discussionmentioning

confidence: 74%

The far-infrared spectra and the ring inversion vibrations of a series of methylenecyclohexanes

Wieser¹,

Smithson²,

Ibrahim³

et al. 1984

Can. J. Chem.

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, 1565 (1984). The far-infrared spectra in the region of 50 to 400 cm-' are reported for the vapours of methylenecyclohexane and the related compounds 4-methylenetetrahydro-4H-pyran, 4-methylenetetrahydro-4H-thiopyran and 3-methylenetetrahydro-4H-pyran. The absorptions are assigned to the three out-of-plane deformations of the six-membered rings. The observed series of Q branches are ascribed to combination sequences involving the three modes. The lowest wavenumber sequence in each compound is believed to arise from a vibration which if completely executed would take the chair conformation to its equivalent via an inversion through the planar form. With the use of a one-dimensional Hamiltonian incorporating a quadratic-quartic double minimum potential function, barriers to planarity for the rings are estimated. The similarities between these compounds and the corresponding ketones are discussed. 1565 (1984). On rapporte les spectres infrarouges lointains, dans la region allant de 50 a 400 cm, des vapeurs du mCthyltnecyclohexane et de composCs apparent&, les m6thyltne-4 tetrahydro 4H-pyranne, mkthyltne-4 tetrahydro 4H-thiopyranne et mkthylkne-3 tetrahydro 4H-pyranne. On a attribuC les absorptions aux trois deformations hors du plan des cycles a 6 chainons. On a attribut les shies de branches Q observtes h des series de combinaisons qui font intervenir les trois modes. On pense que la sCrie de combinaisons apparaissant aux plus faibles longueurs d'onde, dans le cas de chacun des composes, provient d'une vibration qui, si elle h i t complttement executte, transformerait la conformation chaise en son equivalent par I'intermCdiaire d'une inversion en passant par la forme planaire. On a CvaluC les barritres a la plankite du cycle en utilisant un Hamiltonien unidimensionel incorporant une fonction de potentiel quadratique-quartique a double minima. On discute des ressemblances entre ces composes et les cetones correspondantes.

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Far-infrared spectra of ring compounds: A semi-rigid model for the ring-puckering vibration in some pseudo-four-membered ring molecules

Cited by 109 publications

References 33 publications

EXAFS determination of the structure of cobalt in carbon-supported cobalt and cobalt-molybdenum sulfide hydrodesulfurization catalysts

EXAFS determination of the structure of cobalt in carbon-supported cobalt and cobalt-molybdenum sulfide hydrodesulfurization catalysts

Study of the photoelectron and electron momentum spectra of cyclopentene using benchmark Dyson orbital theories

The far-infrared spectra and the ring inversion vibrations of a series of methylenecyclohexanes

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