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The adsorption of CO molecules onto small metal clusters was studied using density functional theory (DFT) calculations, and experimental electrochemical and attenuated total reflection-Fourier transform infrared spectroscopic (ATRFTIR) techniques were used to examine CO adsorbed onto nanostructures of similar composition. The adsorption strengths and CO vibrational stretching frequencies were calculated and analyzed for clusters of the form M-CO for all of the period 4, 5, and 6 d-block transition metals. A direct link between the [v.sub.CO] and the population of d orbitals of the metal was observed. All possible binding sites for CO on clusters of the form [Pd.sub.4]-CO, [Pd.sub.2][Pt.sub.2]-CO, and [Pd.sub.2][Au.sub.2]-CO were determined and the corresponding adsorption energies and CO stretching frequencies were examined. Pure Pd and bimetallic PdPt and PdAu nanostructures were fabricated and used as catalysts for the adsorption and electrochemical oxidation of CO. The relative quantities of CO molecules adsorbed to surface of the catalysts decrease in the order of PdPt > Pd > PdAu, consistent with our DFT results. The location of [v.sub.CO] bands of CO adsorbed onto the nanostructured catalysts were determined by means of ATR-FTIR spectroscopy and were found to have values close to that predicted by DFT. This paper shows that DFT calculations on very small metal clusters [M.sub.n]-CO (n ≤ 4) can be a simple but effective way of screening catalysts for their adsorbing properties. Key words: carbon monoxide, nanoparticles, metal clusters, DFT calculations, CO adsorption. On a etudie l'adsorption de molecules de CO sur de petits agregats metalliques en utilisant des calculs theoriques sur la base de la theorie de la fonctionnelle de la densite. D'un point de vue experimental, on a utilise des techniques electrochimiques et de la spectroscopie infrarouge a transformee de Fourier avec reflexion totale attenuee pour etudier l'adsorption du CO sur des nanostructures de compositions semblables. On a calcule et analyse les forces d'adsorption et les frequences d'elongation vibrationnelles du CO pour des agregats de la forme M-CO pour tous les elements de transition des blocs 4, 5 et 6 d. On a observe une relation directe entre la valeur de [v.sub.CO] et la population des orbitales d du metal. On a determine tous les sites de liaison possibles pour le CO sur des agregats de la forme [Pd.sub.4]-CO, [Pd.sub.2][Pt.sub.2]-CO et [Pd.sub.2][Au.sub.2]-CO et on a examine les energies d'adsorption correspondantes et les frequences d'elongation du CO. On a prepare les nanostructures de palladium pur ainsi que les structures bimetalliques PdPd et PdAu et elles ont ete utilisees pour la reaction d'adsorption et d'oxydation electrochimique du CO. Les quantites relatives de molecules de CO adsorbees sur la surface des catalyseurs diminue dans l'ordre PdPt > Pd > PdAu, en accord avec les resultats des calculs a base de la theorie de la fonctionnelle de la densite (TFD). On a determine la position des bandes, vCO, du CO adsorbe sur les catalyseurs a nanostructures en faisant appel a la spectroscopie infrarouge a transformee de Fourier avec reflexion totale attenuee et on a trouve que ces valeurs sont proches de celles predites par les calculs de la TFD. Dans ce travail, on montre que des calculs selon la TFD sur de tres petits agregats metalliques [M.sub.n]-CO (n [less than or equal to] 4) peuvent s'averer etre une methode simple et efficace d'evaluer les proprietes absorbantes de catalyseurs. Mots-cles : monoxyde de carbone, nanoparticules, agregats metalliques, calcules d'apres la theorie de la fonctionnelle de la densite (TFD), adsorption du CO. [Traduit par la Redaction], Introduction Carbon monoxide adsorption on metallic nanoparticles has been extensively investigated because of its importance in the water-gas shift reaction, in emission control, and in fuel cell reactions. (1) In [...]

A new synthetic route to mononitrated oligothiophenes is described, as well as the preparation of halogenated derivatives (Br, I) thereof. An unusual deep red colour is observed and explained, with the aid of DFT calculations, as arising from a significant quinoidal contribution to the molecular structure. The crystal structures of two compounds, H[([C.sub.4][H.sub.2]S).sub.3]N[O.sub.2] and Br([C.sub.4][H.sub.2]S)3N[O.sub.2], are presented. Both compounds have planar sheets held together by intermolecular short contacts (hydrogen bonds and, for the latter, N[O.sub.2] ... Br interactions); the sheets do not directly superimpose, so the effect of the π-stacking is not maximized. Solid-state fluorescence and extended-Huckel band-structure calculations are also presented for these materials. Key words: oligothiophene, organic semiconductor, crystal structure, band structure, nitro-substitution. On decrit une nouvelle methode generale de synthese des oligothiophenes mononitres ainsi que la preparation de leurs derives bromes et iodes. On a observe une couleur rouge fonce inhabituelle et, en se basant sur des calculs de la theorie de la fonctionnelle de la densite (TFD), on suggere qu'elle resulte d'une importante contribution quinonoidale a la structure moleculaire. On a determine les structures cristallines des deux composes H[([C.sub.4][H.sub.2]S).sub.3]N[O.sub.2] et Br[([C.sub.4][H.sub.2]S).sub.3]N[O.sub.2]. Les deux composes se presenten sous la forme de feuillets plans maintenus en place par des contacts intermoleculaires courts (liaisons hydrogenes et, dans le deuxieme cas, interactions N[O.sub.2] ... Br); les feuillets ne sont pas directement superposes et il en resulte que l'effet de superposition π n'est pas maximise. On rapporte aussi les resultats obtenus pour la fluorescence a l'etat solide de ces materiaux ainsi que les calculs etendus de Huckel de leur structure de bande. Mots-cles: oligothiophene, semiconducteur organique, structure cristalline, structure de bande, substitution par un groupe nitro. [Traduit par la Redaction], Introduction Organic materials are carbon-based small molecules or polymers with interesting electronic properties. Two of the most studied organic semiconductors are the oligothiophenes (1-3) and the acenes. (4) The promise [...]

Traditionally, substituents are described not by their intrinsic properties, but by their effect elsewhere in a molecule. However, the quantum theory of atoms in molecules (QTAIM) provides a route to intrinsic substituent descriptors. Ideally, these descriptors would exhibit minimal change as the local environment changes, and hence be considered transferable. Whether this is true is an open question. Here, we evaluated the transferability of QTAIM functional group descriptors for 117 functional groups in a series of 17 substrates to determine whether descriptors obtained using hydrogen as substrate are transferable. The functional group volume has a strong, consistent, linear relationship throughout. All other hydrogen‐based group descriptors exhibit a relatively strong linear relationship with those in carbon‐based substrates and a reasonable linear relationship with those in non‐carbon‐based substrates. Outliers are readily interpretable in terms of substrate induced functional group geometry changes. As expected, directional descriptors lying along the substituent‐substrate axis are the least conserved. [ABSTRACT FROM AUTHOR]

The effects of substitution on the [super 13]C chemical shifts in nitrilimines are examined. The analysis of the [super 13]C chemical shifts has shown that an increase in the dipolar character of nitrilimines has induced a shielding at the carbon nucleus, while an increase in allenic or carbenic character has caused deshielding.

The modern quantum-chemical methods in the form of the B3LYP approach were used to study the lithium hexamethyldisilazide (LiHMDS), a prototypical and relatively simple lithium amide complex. The highest possible degree of aggregation for unsolvated LiHMDS was found to be four and in nonpolar solvents, formation of the LiHDMs dimer from the trimer is thermodynamically preferred which involves an intermediate tetramer.

The [3+2] and [1+2] cycloaddition pathways between ethene and a series of 13 nitrilimines ([R.sub.1]CNN[R.sub.2]) have been examined by density functional theory [PBE0/6-311++G(2df, pd)] calculations. All reactions have low barriers ranging from 14.14 ([R.sub.1] = C[H.sub.3], [R.sub.2] = H) to 1.01 ([R.sub.1] = [R.sub.2] = F) kcal [mol.sup.-1], and large reaction exothermicities consistent with the transient nature of nitrilimines. The [3+2] and [1+2] transition-state structures are very similar, mainly differing in the relative orientation of their fragments and the newly forming C--C bond distance, and exhibit only minor deviations from the structures of the reactants. Both reaction pathways are concerted and asynchronous, but the [1+2] reaction has a greater degree of asynchronicity. Examination of the frontier molecular orbitals reveals that both the [3+2] and [1+2] barrier heights are related to two sets of orbital interactions, with the interaction between the lowest unoccupied molecular orbital [π.sup.NN.sub.5] of nitrilimine and the highest occupied molecular orbital of ethene in common. The second interaction in both cases is carbene-like. A relationship between the weights of the 1,3-dipolar resonance contribution in the various nitrilimines and the corresponding [3+2] barrier heights was not found, but a good correlation could be found between the [1+2] barrier heights and both the 1,3-dipolar and carbene contributions. Inspection of the potential energy surface in the vicinity of the two transition states for the reaction between unsubstituted nitrilimine and ethene suggests that the observed [3+2] product is a result of an initial carbene-like approach of the two fragments followed by a ridge bifurcation that leads to the [3+2] product minimum. Key words: nitrilimines, 1,3-dipole, carbene, [3+2] cycloaddition, [1+2] cycloaddition, density functional theory (DFT). Les reactions de cycloaddition [3+2] et [1+2] entre l'ethene et une serie de treize nitrilimines ([R.sub.1]CNN[R.sub.2]) ont ete etudiees par calculs de theorie de la fonctionelle de densite [PBE0/6-311++G(2df, pd)]. Les reactions sont caraterisees par des barrieres variant de 14,14 ([R.sub.1] = C[H.sub.3], [R.sub.2] = H) a 1,01 ([R.sub.1] = [R.sub.2] = F) kcal [mol-.sup.1] et une forte exothermicite qui reflete la nature transitoire des nitrilimines. La structure des etats de transition, tres proche de celle des reactifs, est tres semblable pour les reactions de cycloaddition [3+2] et [1+2] et ne differe que par l'orientation relative des fragments et par la longueur de la liaison C--C qui se forme au cours de la traction. Les deux chemins de reactions sont concertes et aynchrones, avec une asynchronicite plus prononcee pour la reaction [1+2]. Les orbitales moleculaires frontieres demontrent que les barrieres de reaction [3+2] et [1+2] sont reliees a deux groupes d'interactions orbitalaires qui ont en commun l'interaction entre la plus basse orbitale moleculaire inoccupee [π.sup.NN.sub.5] de la nitrilimine et la plus haute orbitale moleculaire occupre de l'ethene. La seconde interaction est de type carbine pour les deux reactions. Une correlation entre la contribution de la forme de resonance 1,3-dipolaire des nitrilimines et les barrieres de reaction [3+2] correspondantes n'a pu etre trouvee. Par contre, une forte correlation est observre entre les barrieres de reaction [1+2] et les contributions 1,3-dipolaires et carbeniques. L'examen de la surface d'energie potentielle et proximite des deux etats de transition de la traction entre la nitrilimine non-substituee et l'ethene suggere que le produit [3+2] resulte d'une approche initiale des deux fragments de type carbenique, suivie d'une bifurcation a la crete de la surface qui conduit au minimum d'energie potentielle du produit [3+2]. Mots cles : nitrilimines, 1,3-dipolaire, carbene, cycloaddition [3+2], cycloaddition [1+2], theorie de la fonctionelle de densite., Introduction The addition of a 1,3-dipole, a system of three atoms over which four π electrons are distributed, to a dipolarophile, typically an alkene or alkyne, is the most commonly [...]

The use of the PBE0 hybrid density functional theory method in conjunction with the COSMO solvation model allowed us to reproduce, both qualitatively and quantitatively, the experimentally observed conformational compositions of 2-substituted and 2,7-disubstituted methylenecyclohexanes. An analysis revealed several different interactions that influence the overall equilibrium. It was found that the endo (general) anomeric effect plays a significant role in the equilibrium and that the "unsaturation effect" possibly comprises two effects. Key words: conformational analysis, methylenecyclohexanes, anomeric effect, unsaturation effect.

The commonly accepted solid-state polymerization mechanism for the formation of (SN)x from S(sub 2)N(sub 2) is problematic due to a number of low-lying states that dissociate into SN. An alternative mechanism where S(sub 2)N(sub 2) first undergoes a vertical excitation, is proposed.

The electronic structure of molecules is routinely assessed using a number of methodologies including Bader's Quantum Theory of Atoms in Molecules (QTAIM) and Weinhold's Natural Bond Orbital/Natural Resonance Theory (NBO/NRT). Previously these methods were applied to the study of isothiirane; however, the results obtained were incongruous with one another: the QTAIM analysis suggested an acyclic structure while NRT indicated a cyclic structure. The previous results assume the NRT description to be correct despite limitations in the analysis, while Foroutan‐Nejad et al. (Chem. Eur. J. 2014, 20, 10140) employed a multiple molecular graph analysis to resolve the QTAIM discrepancy. In this work, we re‐examine the electronic structure of isothiirane, employing a detailed NRT analysis and the catastrophe theory model originally described by Bader for the study of three‐membered ring systems; additional analysis is performed using NMR tensor calculations and studying substituent effects. A congruous description of the electronic structure of isothiirane and the substituted versions is achieved using all modes of analysis. These results highlight how the careful application of commonly used methodologies can achieve a unified description of electronic structure. © 2018 Wiley Periodicals, Inc. The electronic structure of isothiirane is studied using a combined QTAIM, NRT, 13C NMR tensor, and substituent effect analysis. The inner workings of the analysis tools used are critically evaluated. In opposition to previous analysis, which was in disagreement on the electronic structure, isothiirane is described as a hybrid of a carbene and zwitterion (1,3‐dipole). The given methodology can be used to determine any molecules electronic structure and isothiirane may be a new moiety for use in cycloaddition chemistry. [ABSTRACT FROM AUTHOR]

Multireference CI calculations predict fourteen states of BN2+ to be quasibound, an uncommonly large number for a first-row diatomic, confirming the important role played by the electropositive B atom in stabilizing molecular dications. About two-thirds of the metastable potentials have dissociation barriers (Deff) between 0.59 and 2.25 eV, accommodating several vibrational levels and therefore being kinetically stable. The ground state X 3Σ-, however, might be difficult to study experimentally because it is only weakly bound (Deff=0.23 eV), and its formation via ionization of BN or BN+ has unfavorable Franck–Condon factors (FCF). The 1 5Σ- state is the best candidate for detecting BN2+: Its barrier is the highest (Deff=2.25 eV), sustaining about 30 vibrational levels (with tunneling lifetimes τTυ≊∞ for υ<20), and the ionization FCFs are favorable. The 1 1Δ state might also be detectable since its properties are similar to those of 1 5Σ-. Near equilibrium, most metastable states are described by the configurations 3σ24σ5σ1π2 and 3σ24σ1π3, both having charge distributions B2+N. The adiabatic ionization potential into BN2+ (X 3Σ-) is 21.4 eV for ionization from BN+ (X 4Σ-) and 32.9 eV from BN(X 3Π). The corresponding IPs into 1 5Σ- lie 1.12 eV higher. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: The bonding and energetics in H(S2N2) Y H are analyzed within two models of conductivity. The effective exchange and mixed-valence models for conductivity predict similar geometric changes. The effects of hydrogen capping on the geometries were removed by averaging the central bond lengths and angles in the larger oligomers. The extrapolated singlet–triplet energy gap, predicted to be between 2.44 and −2.54kcalmol−1 for the polymer, accounts for conductivity along the chain axis, the suppression of a Peierls instability and the failure to synthesize single strand (SN) X . Extrapolated values for the ionization potential, between 5.61 and 5.17eV, electron affinity, between 3.40 and 4.08eV, and disproportionation energy, between 2.14 and 0.98eV, are consistent with previous estimates. The perpendicular conductivity can be related to the small, but non-negligible, disproportionation energy. An analysis of the charge distributions reveal that both models of conductivity have a common electron-phonon mechanism, suggesting that the remarkable superconductivity in (SN) X is best explained as a combination of the effective exchange and mixed-valence modes of conductivity. [Copyright &y& Elsevier]

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Silicon (Si) has long been known to play a major physiological and structural role in certain organisms, including diatoms, sponges, and many higher plants, leading to the recent identification of multiple proteins responsible for Si transport in a range of algal and plant species. In mammals, despite several convincing studies suggesting that silicon is an important factor in bone development and connective tissue health, there is a critical lack of understanding about the biochemical pathways that enable Si homeostasis. Here we report the identification of a mammalian efflux Si transporter, namely Slc34a2 (also termed NaPiIIb), a known sodium-phosphate cotransporter, which was upregulated in rat kidney following chronic dietary Si deprivation. Normal rat renal epithelium demonstrated punctate expression of Slc34a2, and when the protein was heterologously expressed in Xenopus laevis oocytes, Si efflux activity (i.e., movement of Si out of cells) was induced and was quantitatively similar to that induced by the known plant Si transporter Os Lsi2 in the same expression system. Interestingly, Si efflux appeared saturable over time, but it did not vary as a function of extracellular [Formula: see text] or Na + concentration, suggesting that Slc34a2 harbors a functionally independent transport site for Si operating in the reverse direction to the site for phosphate. Indeed, in rats with dietary Si depletion-induced upregulation of transporter expression, there was increased urinary phosphate excretion. This is the first evidence of an active Si transport protein in mammals and points towards an important role for Si in vertebrates and explains interactions between dietary phosphate and silicon., (Copyright © 2017 the American Physiological Society.)