Effects of subsurface Na,H and C on the bonding of carbon to nickel surfaces

This paper reports the results of a theoretical study of Na, H and C subsurface atomic species in nickel and demonstrates how these interstitial atoms influence the reactivity of the Ni(111) surface and the structure of carbon species adsorbed on the surface. The benzene molecule, C₆H₆, in planar and nonplanar geometries, is used to probe bonding at the surface. Adsorption energies are calculated by ab initio configuration interaction techniques modelling the surface as an embedded cluster. Adsorption energies of planar C₆H₆ at the most stable, three-fold, adsorption site are 18 kcal/mol for the Ni(111) surface, and 10, 19 and 44 kcal/mol in the presence of the Na, H and C interstitials, respectively. The energies required for the planar to puckered distortion are 99 kcal/mol on Ni(111), 69 kcal/mol with the Na interstitial, 83 kcal/mol with H, and 134 kcal/mol with C compared to 198 kcal/mol for distortion of C₆H₆ in the gas phase. The possible relevance of these results to the nucleation of diamond on nickel are discussed. The results indicate that subsurface Na stabilizes tetrahedrally bonded carbon subunits of the diamond structure while subsurface C may make it easier for the overlayer to revert to a planar graphite structure.     

The study of lithium fast ion conductors of Li3xLa0.67−xScyTi1−2yNbyO3 system

Perovskite-type lithium fast ion conductors of Li_3xLa_0.67−xSc_yTi_1−2yNb_yO₃ system were prepared by solid state reaction. X-Ray powder diffraction shows that perovskite solid solution form in the ranges of x=0.10, y≤0.10. AC impedance measurements indicate that the bulk conductivities and the total conductivities are of the order of 10⁻⁴ S·cm⁻¹ and 10⁻⁵ S·cm⁻¹ at 25 °C respectively. The compositions have low bulk activation energies of about 17 kJ/mol in the temperature ranges of 298 – 523 K and total activation energies of about 37 kJ/mol in the temperature ranges of 298 – 523 K.     

Reactions and anion desorption induced by low-energy electron exposure of condensed acetonitrile

Thermal desorption spectrometry (TDS) and electron stimulated desorption (ESD) are employed to investigate mechanisms responsible for the formation of C₂H₆ in electron irradiated multilayer films of acetonitrile (CH₃CN) at 30 K. Using a high sensitivity time-of-flight mass spectrometer, we observe the ESD of anionic fragments H⁻, CH₂ ⁻, CH₃ ⁻ and CN⁻. Desorption occurs following dissociative electron attachment (DEA) via several negative ion resonances in the 6 to 14 eV energy range and correlates well with a “resonant” structure seen in the TDS yield of C₂H₆ (i.e., at mass 30 amu). It is proposed that C₂H₆ is formed by the reactions of CH₃ radicals generated following DEA to CH₃CN which also yields CN⁻. Between 2 and 5 eV, a second resonant feature is seen in the C₂H₆ signal. While DEA is observed in the gas phase at these energies, no anion desorption occurs since anionic fragments likely have insufficient kinetic energy to desorb. Since the CH₂ ⁻ ion has not been observed in gas-phase measurements, we propose that it is formed, along with HCN (that is detected in TDS) when dissociation into CH₃ ⁻ and CN is hindered by adjacent molecules.     

Hydrogen bond and internal rotations barrier: DFT study on heavier group‐14 analogues of formamide

A theoretical study on heavier group‐14 substituting effect on the essential property of formamide, strong hydrogen bond with water and internal rotational barrier was performed within the framework of natural bond orbital (NBO) analysis and based on the density functional theory calculation. For heavier group‐14 analogues of formamide (YHONH₂, Y = Si, Ge and Sn), the n_N–π_Y=O conjugation strength does not always reduce as Y becomes heavier, for example, silaformamide and germaformamide have similar strength of delocalization. Heavier formamides prefer being H‐bond donors to form FYO–H₂O complexes to being H‐bond acceptors to form FYH–H₂O complexes. The NEDA analysis indicates that H‐bond energies of FYO–H₂O complexes increase as moving down group 14 due to concurrently stronger charge transfer (CT) and electrostatic attraction and for the FYH–H₂O complexes H‐bond strengths are similar. The model of CTs from FYO to H₂O differs from that at FYH–H₂O complexes, which are contributed not only by aligning lone‐pair orbital of O but also by another lone‐pair orbital. At two lowest lying excited states (the triplet and S₁ excited states), formamide and its heavier analogues form double H‐bonds with H₂O molecule at the same time. The barrier heights of internal rotation become gradually low from C to Sn, formamide (15.73 kcal/mol) > silaformamide (11.73 kcal/mol) > germaformamide (9.45 kcal/mol) > stannaformamide (7.50 kcal/mol) at the CCSD(T)/aug‐cc‐pVTZ//B3LYP/cc‐pVTZ level. NBO analysis indicates that the barrier does not only come from the n_N→π*_YO conjugation, and for heavier analogues of formamide, the n_N→σ*_YO hyperconjugation effect and steric effect considerably contribute to the overall rotational barrier. Copyright © 2013 John Wiley & Sons, Ltd.     

Photophysical Properties of Luminescent Quaternary Lanthanide Molecular Hybrid Systems with Chemical Bonds from the Cooperative Design and Assembly of Structure and Function

Two long chain aliphatic acyl chlorides (dodecanoyl chloride (C₁₀H₁₉OCl, abbreviated as DC) and stearoyl chloride (C₁₈H₃₅Ocl, abbreviated as SC)) were modified by means of the amidation reaction with crosslinking molecules (N-aminopropyl-triethoxylsiliane, (APES, H₂N(CH₂)₃Si(OC₂H₅)₃)) and afford two kinds of structural molecular bridge DC (SC)− APES with double reactivity. Subsequently, according to the principle of coordination chemistry, ternary lanthanide (terbium and europium) molecular complex systems with two molecular bridges DC (SC)− APES and 1,10-phenanthroline (phen) of were successfully assembled. Then the modified molecular bridges behave as structural ligands to form the covalent bond Si− O network with matrix precursor (tetraethoxysilane, TEOS) through a sol-gel process (cohydrolysis and copolycondensation process), resulting in a novel quaternary molecular hybrid material (so called as phen-Tb(Eu)−DC(SC)− APES) with strong chemical bonds (N− Tb(Eu)− O coordination bonds and Si− O covalent bonds). And phen behaves as functional ligand to sensitize the luminescence of terbium or europium ions through the effective intramolecular energy transfer process, which gives rise to the characteristic emission of metal ion.     

基质隔离红外光谱结合理论计算研究第五族金属原子和硫化氢反应

利用基质隔离红外光谱结合理论计算,研究了激光溅射获得的第五族金属原子和硫化氢分子的反应. 结果表明金属原子插入H₂S的H-S化学键形成HMSH分子(M=V,Nb,Ta). 对Nb和Ta该HMSH分子重排为H₂MS分子. HMSH分子和H₂S进一步反应生成H₂M(SH)₂分子. 通过D₂S和H₂³⁴S同位素标定确定了产物的分子结构,同时我们用DFT(B3LYP和BPW91)理论计算预测了产物分子的能量、结构和振动频率. 通过DFT IRC计算研究了第五族金属原子和₂S分子的反应机理. HVSH分子通过光照解离为VS和H₂,然后通过退火可以发生VS和H₂复合反应. 计算表明HVSH释放H₂需要16.9 kcal/mol的活化能及吸热13.5 kcal/mol.     

Diffusion of Li ion in graphite cluster model at 800 K: a direct molecular orbital dynamics study

Using the hydrogen terminated planar cluster model, C₅₄H₁₈, the stabilization site of Li⁺ ion was determined by the unrestricted Hartree-Fock (UHF) AM1 energy gradient method. Six kinds of stabilization sites are considered, suggesting that the Li⁺ ion is rather stable at the two distinct sites in the bulk where the potential energy difference between them is 2.0 kcal/mol. For the Li⁺ ions stabilized at these two sites, the diffusion processes were simulated at 800 K through the direct molecular orbital dynamics procedure which was newly developed by one of the present authors. No jumping diffusion occurs with Li⁺ ions among the stabilization sites, but they diffuse along the outline of the cluster model with the fluctuations. It takes 2.0 ps for a Li⁺ ion to diffuse from the lower potential site to another equivalent site. On the other hand, it takes 0.7 ps to move from the higher potential site to the unstable circumference site composed of corner (armchair edge) carbon atoms. As the result, the diffusivity is approximated as 10⁻⁸-10⁻⁷ m²/s.     

Chemisorption of hydrogen on titanium: Embedding theory and comparisons with small clusters

The chemisorption of H₂ on Ti(0001) is treated using an ab initio CI theory for the surface region. Dissociation of H₂ occurs above the surface but more stable 3-fold coordination sites lie closer to the surface at ～ 1.3 Å. Adsorption in adjacent 3-fold sites is less stable than in separated sites sharing only one surface atom. The calculated adsorption energy of 45 kcal/mol H₂ compares favorably with experiment. Bonding involves mainly the 4s electrons of the metal leading to hydridic hydrogens and a polarized lattice electron distribution, but d bonding and correlation effects significantly increase the binding energy. Calculations on small metal clusters also show dissociative adsorption but much larger hydrogen binding energies are obtained.     

Comparative Raman study of the Ti complex Cp2Ti(η2-C60) · C6H5CH3 and TixC60 films

Raman spectra from the first Ti fullerene complex Cp ₂Ti(η²-C₆₀) · C₆H₅CH₃ are presented. Compared to spectra of pure C₆₀, the spectra of the Ti complex exhibit a number of new peaks due to the symmetry lowering for C₆₀. The A _g(2) mode is downshifted by 12 cm⁻¹ compared to C₆₀, which corresponds to a charge transfer of one electron per Ti-C₆₀ bond. This value (6 cm⁻¹ for one transferred electron) is identical to the downshift of the A _g(2) mode in alkali metal fullerides with ionic bonding. The spectra of Cp ₂Ti(η²-C₆₀) · C₆H₅CH₃ were compared to the spectra of evaporated Ti_xC₆₀ films. The A _g(2) mode in Ti₄C₆₀ showed a downshift of about 25 cm⁻¹ compared to pure C₆₀, which corresponds to a charge transfer of one electron per Ti atom; this is similar to the ionic alkali metal fullerides and different from η²-C₆₀-type bonding. From Fizika Tverdogo Tela, Vol. 44, No. 3, 2002, pp. 483–485. Original English Text Copyright ? 2002 by Talyzin, Jansson, Usatov, Burlakov, Shur, Novikov. This article was submitted by the authors in English.     

Pyrophosphate Selective Recognition in Aqueous Solution Based on Fluorescence Enhancement of a New Aluminium Complex

A novel and simple fluorescence enhancement method for selective pyrophosphate(PPi) sensing was proposed based on a 1:1 metal complex formation between bis(8-hydroxy quinoline-5-solphonat) chloride aluminum(III) (Al(QS)₂Cl), (L) and PPi in aqueous solution. The linear response range covers a concentration range of 1.6 × 10⁻⁷ to 1.0 × 10⁻⁵ mol/L of PPi and the detection limit of 2.3 × 10⁻⁸ mol/L. The association constant of L-PPi complex was calculated 2.6 × 10⁵ L/mol. L was found to show selectively and sensitively fluorescence enhancement toward PPi over than I₃^-, NO₃^-, CN⁻, CO₃²⁻, Br⁻, Cl⁻, F⁻, H₂PO4⁻ and SO₄²⁻, which was attributed to higher stability of inorganic complex between pyrophosphate and L.     

Reactions C<Subscript>2</Subscript>H<Subscript>2</Subscript> + OH and C<Subscript>2</Subscript> + H<Subscript>2</Subscript>O: Ab initio study of the potential energy surfaces

The stationary points of the potential energy surfaces for the reactions C₂H₂ + OH and C₂ + H₂O are calculated using density functional theory and the coupled cluster method. The relative energies and geometric parameters of the stable intermediates and transition states are in good agreement with the results of independent studies. In most cases, the relative energies differ from the earlier published values by no more than 3 kcal/mol, whereas the rotational constants, by 1–2%. The mechanism of the reaction CCOH₂ → C₂ + H₂O is studied in detail. The possible sources of errors in the calculation methods are examined.     

Proton transfer reactions of hydrazine‐boranes

Hydrazine‐borane and hydrazine‐diborane contain, respectively, 15.4 and 16.9 wt% of hydrogen and are potential materials for hydrogen storage. In this work we present the gas‐phase complexation energies, acidities, and basicities of hydrazine‐borane and hydrazine‐bisborane calculated at MP2/6‐311 + G(d,p) level. We also report the release of dihydrogen from both protonated complexes (ΔG_{hydrazine‐borane} = ?20.9 kcal/mol and ΔG_{hydrazine‐bisborane} = ?27.2 kcal/mol) which is much more exergonic than from analogues amine‐boranes. The addition of the first BH₃ to the hydrazine releases 17.1 kcal/mol, and the second addition releases 15.8 kcal/mol. The attachment of BH₃ also increases the N―H acidity of hydrazine by 46.3 kcal/mol. It was found that the B―H deprotonation leads to intramolecular rearrangement. The basicity values for hydrazine‐borane and ‐bisborane are 180 and 172.8 kcal/mol, respectively. For both complexes the protonation centres are located at the boron moiety. The protonated structure of hydrazine‐bisborane is cyclic and can be described as H₂ captured between a negatively charged B―H hydrogen and positive boron (B―H??H2??B). Atoms in molecules analysis are used to investigate bond paths in concerning structures. Copyright © 2015 John Wiley & Sons, Ltd.     

The influence of structural defects on the adsorption of simple molecules (H2, C2H2, C2H4, C2H6, CO,NO) on rhenium single crystals

Using Thermal Programmed Desorption (TPD), Low Energy Electron Diffraction (LEED) and Auger Electron Spectroscopy (AES) we have studied the adsorption of hydrogen-containing molecules (H₂, C₂H₂, C₂H₄, C₂H₆) and oxygen-containing molecules (CO and NO) on two vicinal planes of the Re(0001) surface. The two surfaces are designated thus: ReS ¦14(0001)(101&#x0304;1)¦, ReS |6(0001)(167&#x0304;1) | . The structural defects have little effect on the adsorption of hydrogen and the hydrocarbons. They are more influential in the case of the oxygen-containing molecules. This is particularly true for CO; on the kink sites the CO molecules can completely dissociate whereas only a partial dissociation is possible on the steps. These results should be viewed in relation to the strong bond energy between carbon and oxygen in a CO molecule of 256 kcal/mole and the great affinity of oxygen for rhenium; E_Re?O = 127 kcal/mole.     

The hydrogenated aluminium trimer: a theoretical examination of the formation and interconversion pathways

Five doublet isomers of the Al₃H₂ cluster lying within a narrow range of 5 kcal/mol, along with the isomerization transition states connecting them, have been located with the coupled-cluster CCSD(T) and DFT methods. The two most stable doublet structures, the C_2v planar including the two Hs bound terminally and C₁ non-planar showing one H in terminal site and the other in threefold site are found to be essentially degenerate. Although the reaction of Al₃ with H₂ to yield Al₃H₂ is found to be significantly exothermic, by 23.5 kcal/mol, this hydrogenation is impeded by a considerable kinetic barrier of 16 kcal/mol. Our result is consistent with the observed lack of reactivity of Al_n towards H₂(D₂) for n=3 under thermal conditions [3]. The quartet Al₃H₂ isomers are predicted to lie 16–21 kcal/mol higher in energy than the doublet analogues. Further dimerization of Al₃H₂ to form Al₆H₄ has also been examined. Electronic supplementary material Supplementary Online Material     

Infrared spectra and stability of CO and H2O sorption over Ag-exchanged ZSM-5 zeolite: DFT study

The infrared spectra and stability of CO and H₂O sorption over Ag-exchanged ZSM-5 zeolite were investigated by using density function theory (DFT). The changes of NBO charge show that the electron transfers from CO molecule to the Ag⁺ cation to form an σ-bond, and it accompanies by the back donation of d-electrons from Ag⁺ cation to the CO (π*) orbital as one and two CO molecules are adsorbed on Ag-ZSM-5. The free energy changes ΔG, −5.55 kcal/mol and 6.52 kcal/mol for one and two CO molecules, illustrate that the Ag⁺(CO)₂ complex is unstable at the room temperature. The vibration frequency of C-O stretching of one CO molecule bonded to Ag⁺ ion at 2211 cm⁻¹ is in good agreement with the experimental results. The calculated C-O symmetric and antisymmetric stretching frequencies in the Ag⁺(CO)₂ complex shift to 2231 cm⁻¹ and 2205 cm⁻¹ when the second CO molecule is adsorbed. The calculated C-O stretching frequency in CO-Ag-ZSM-5-H₂O complex shifts to 2199 cm⁻¹, the symmetric and antisymmetric O-H stretching frequencies are 3390 cm⁻¹ and 3869 cm⁻¹, respectively. The Gibbs free energy change (ΔGH₂O) is −6.58 kcal/mol as a H₂O molecule is adsorbed on CO-Ag-ZSM-5 complex at 298 K. The results show that CO-Ag-ZSM-5-H₂O complex is more stable at room temperature.     

The mechanism of formation of the hydroperoxyl radical in the CF<Subscript>3</Subscript>COOH + <Superscript>3</Superscript>O<Subscript>2</Subscript> system: a quantum-chemical study

Ab initio quantum-chemical calculations of the (CF₃CO₂H₂⁺…³O₂) and (CF₃CO₂⁻…³O₂) complexes were performed by the MP2 method. It was found that these complexes were characterized by low complex formation energies, of 2.97 and 1.72 kcal/mol, respectively. According to the MP2(full)/6-311++G(d, p) calculation data, the bridge stabilization of oxygen by linking with both the CF₃CO₂H₂⁺ cation and CF₃CO₂⁻ anion is much more favorable energetically. A study of the potential energy surface of the joint molecular system (CF₃CO₂H₂⁺…³O₂…CF₃CO₂⁻) shows that proton experiences activationless transfer from the cation to the ³O₂ molecule accompanied by electron transfer from the CF₃COO⁻ anion. An analysis of spin density distribution shows that two radicals are stabilized in the (CF₃CO₂….OOH….O=C(OH)CF₃) complex in the triplet state observed on the potential energy surface.     

Quantum-chemical modeling of structural,electronic, and spin characteristics of NV centers in nanostructured diamond: Surface effect

The effect of the surface of diamond on atomic, electronic, and spin properties of diamond nanocrystals containing single nitrogen-vacancy defects ([NV]⁻ centers) is studied. The surface was modeled with clusters C₃₃H₃₀[NV]⁻, C₆₆H₇₂[NV]⁻, which were constructed based on bulk clusters C₃₃H₃₆[NV]⁻ and C₆₉H₈₄[NV]⁻, respectively. In all cases, clusters in the triplet state S = 1 are considered with the cluster charge being −1. The geometric structure of clusters is optimized using the principle of minimization of the total energy of the system; then, the electronic and spin characteristics of clusters are calculated by the density functional theory. The isotropic and anisotropic hyperfine interaction constants of the electron spin of the NV center with the nuclear spin of the nitrogen atom and ¹³C atoms located at different sites in the cluster are calculated. It is found that, in contrast to bulk clusters with [NV]-centers in which the spin density is mainly localized at the three carbon atoms that are the nearest neighbors of the vacancy of the center, upon arrangement of the NV center in the immediate proximity to the surface, the spin density is redistributed such that it is mainly localized at the three carbon atoms that are the nearest neighbors of the nitrogen atom of the center and at C atoms that form the first atomic layer of the (111) surface of the nanocrystal.     

Organic superalkalis with closed-shell structure and aromaticity

Benzene (C₆H₆) and polycyclic hydrocarbons such as naphthalene (C₁₀H₈), anthracene (C₁₄H₁₀) and coronene (C₂₄H₁₂) are well known aromatic organic compounds. We study the substitution of Li replacing all H-atoms in these hydrocarbons using density functional method. The vertical ionisation energy of such lithiated species, i.e. C₆Li₆, C₁₀Li₈, C₁₄Li₁₀ and C₂₄Li₁₂ ranges 4.24–4.50 eV, which is lower than the ionisation energy (IE) of Li atom. Thus, these species may behave as superalkalis due to their lower IE than alkali metal. However, these lithiated species possess planar and closed-shell structure, unlike typical superalkalis. Furthermore, all Li-substituted species are aromatic although their degree of aromaticity is reduced as compared to corresponding hydrocarbon analogues. We have further explored the structure of C₆Li₆ as star-like, unlike its inorganic analogue B₃N₃Li₆, which appears as fan-like structure. We have also demonstrated that the interaction of C₆Li₆ with a superhalogen (such as BF₄) is similar to that of a typical superalkali (such as OLi₃). This may further suggest that the proposed lithiated species may form a new class of closed-shell organic superalkalis with aromaticity.     

Physisorption and dissociative chemisorption of H2 on sub-nanosized Al$_{13}^{-}$ anion cluster: ab initio study

We have studied the interaction of Al₁₃^-_{13}^{-} anion cluster with H₂. Both the long range interaction and dissociative adsorption have been examined using the established correlated ab initio methods, MP2 and CCSD(T), in conjunction with the augmented correlation consistent basis sets up to aug-cc-pVTZ. The formation of the weakly bound (physisorbed) end-on anion complex Al₁₃^-_{13}^{-}...H₂ is predicted for the interacting Al...H distances of 3.95 ? with the H-H axis pointing towards the ‘hollow’ site of Al₁₃^-_{13}^{-} and binding energy (D_e)D_{e}) of 0.7 kcal/mol at the estimated complete basis set (CBS) limit of CCSD(T). The barrier height for H₂ dissociation on Al₁₃^-_{13}^{-} of 41.6 (42.9) kcal/mol calculated at the ZPVE-corrected CCSD(T)/aug-cc-pVTZ (estimated CCSD(T)/CBS) level is at least twice as large as that evaluated by us for a dissociative adsorption of H₂ on an open-shell Al₁₃ neutral cluster. To our knowledge, this report presents the first “benchmark” quality study of the physisorption and dissociative chemisorption of molecular hydrogen on Al₁₃^-_{13}^{-} anion cluster.     

Factor group theoretical analysis of fundamental vibrations of the H2AsO 4? anion in (C6H9N2)H2AsO4 single crystal

Fundamental (lattice, rotational, and intermolecular) vibrations of the H₂AsO₄⁻ anion in (C₆H₉N₂)H₂AsO₄ crystal are calculated using the correlation theorem based on the group theory. The correlation between anionic site of symmetry C _s and the factor group D _2h of the crystal yields 12 modes for both lattice and rotational vibrations. The infrared and Raman spectra of these modes do not coincide. Addition of two hydrogen atoms to AsO₄⁻ ion yields two As-OH bonds in the H₂AsO₄⁻ anion. As a result, the molecular symmetry is reduced from T _d to C _2υ . The free H₂AsO₄⁻ anion having C _2υ symmetry gives in total 15 fundamental normal vibrations. Under the crystal field splitting effects, the number of intermolecular vibrations for the anion in infrared and Raman spectra is calculated to be 56 active vibrations. The calculated fundamental vibrationsmanifest themselves as the main features in an experimental infrared spectrum.