Reactive Noble-Gas Compounds Explored by 3D Electron Diffraction: XeF-MnF Adducts and a Facile Sample Handling Procedure.

Recent advances in 3D electron diffraction (3D ED) have succeeded in matching the capabilities of single-crystal X-ray diffraction (SCXRD), while requiring only submicron crystals for successful structural investigations. One of the many diverse areas to benefit from the 3D ED structural analysis is main-group chemistry, where compounds are often poorly crystalline or single-crystal growth is challenging. A facile method for loading and transferring highly air-sensitive and strongly oxidizing samples at low temperatures to a transmission electron microscope (TEM) for 3D ED analysis was successfully developed and tested on xenon(II) compounds from the XeF-MnF system.

Iridium Stabilizes Ceramic Titanium Oxynitride Support for Oxygen Evolution Reaction.

Decreasing iridium loading in the electrocatalyst presents a crucial challenge in the implementation of proton exchange membrane (PEM) electrolyzers. In this respect, fine dispersion of Ir on electrically conductive ceramic supports is a promising strategy. However, the supporting material needs to meet the demanding requirements such as structural stability and electrical conductivity under harsh oxygen evolution reaction (OER) conditions.

Improving the HER Activity and Stability of Pt Nanoparticles by Titanium Oxynitride Support.

Water electrolysis powered by renewables is regarded as the feasible route for the production of hydrogen, obtained at the cathode side through electrochemical hydrogen evolution reaction (HER). Herein, we present a rational strategy to improve the overall HER catalytic performance of Pt, which is known as the best monometallic catalyst for this reaction, by supporting it on a conductive titanium oxynitride (TiON ) dispersed over reduced graphene oxide nanoribbons. Characterization of the Pt/TiON composite revealed the presence of small Pt particles with diameters between 2 and 3 nm, which are well dispersed over the TiON support.

Coordination of a Neutral Ligand to a Metal Center of Oxohalido Anions: Fact or Fiction?

Can a neutral ligand bond to a metal center of a square pyramidal oxohalido anion at the available sixth octahedral position? Crystal structures of some compounds indeed suggest that ligands, such as THF, pyridine, HO, NH, and CHCN, can interact with the central metal atom, because they are oriented with their heteroatom toward the metal center with distances being within the bonding range. However, this assumption that is based on chemical intuition is wrong. In-depth analysis of interactions between ligands and oxohalido anions (e.

Two-dimensional oxide quasicrystal approximants with tunable electronic and magnetic properties.

Recently, the discovery of the quasiperiodic order in ultra-thin perovskite films reinvigorated the field of 2-dimensional oxides on metals, and raised the question of the reasons behind the emergence of the quasiperiodic order in these systems. The effect of size-mismatch between the two separate systems has been widely reported as a key factor governing the formation of new oxide structures on metals. Herein, we show that electronic effects can play an important role as well.

Surprising Lateral Interactions between Negatively Charged Adatoms on Metal Surfaces.

Even something as conceptually simple as adsorption of electronegative adatoms on metal surfaces, where repulsive lateral interactions are expected for obvious reasons, can lead to unanticipated behavior. In this context, we explain the origin of surprising lateral interactions between electronegative adatoms observed on some metal surfaces by means of density functional theory calculations of four electronegative atoms (N, O, F, Cl) on 70 surfaces of 44 pristine metals. Four different scenarios for lateral interactions are identified, some of them being unexpected: (i) They are repulsive, which is the typical case and occurs on almost all transition metals.

Reactivity of VOF with N-Heterocyclic Carbene and Imidazolium Fluoride: Analysis of Ligand-VOF Bonding with Evidence of a Minute π Back-Donation of Fluoride.

Reaction of vanadium(V) oxide trifluoride (VOF) and the new "naked" fluoride reagent [(L)H][F] (L = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2 H-imidazol-2-ylidene) leads to the isolation of [(L)H][VOF] (1) where the long sought discrete [VOF] anion was finally obtained. The neutral [(L)VOF] (2) complex was synthesized by a similar reaction between VOF and bulky N-heterocyclic carbene (NHC) ligand L. In this context, we analyzed, by means of DFT calculations, intermolecular interactions between [(L)VOF] (2) complexes in the crystal structure and realized that these interactions have a significant effect on the V-F bond length.

Decisive Role of Perimeter Sites in Silica-Supported Ag Nanoparticles in Selective Hydrogenation of CO to Methyl Formate in the Presence of Methanol.

Methyl formate synthesis by hydrogenation of carbon dioxide in the presence of methanol offers a promising path to valorize carbon dioxide. In this work, silica-supported silver nanoparticles are shown to be a significantly more active catalyst for the continuous methyl formate synthesis than the known gold and copper counterparts, and the origin of the unique reactivity of Ag is clarified. Transient in situ and operando vibrational spectroscopy and DFT calculations shed light on the reactive intermediates and reaction mechanisms: a key feature is the rapid formation of surface chemical species in equilibrium with adsorbed carbon dioxide.

Discrete GeF Anion Structurally Characterized with a Readily Synthesized Imidazolium Based Naked Fluoride Reagent.

The recently prepared novel naked fluoride reagent 1,3-bis(2,6-diisopropylphenyl)imidazolium fluoride ([(L)H][F]), treated with an excess of MF (M = Si, Ge), results in isolation of [(L)H][MF] products with the elusive trigonal bipyramidal MF anions. Specific steric characteristics of the [(L)H] cation readily support isolation of monomeric and discrete trigonal bipyramidal fluorido anions of silicon and germanium. Based on combination of experimental results and DFT calculations, we demonstrate that the role of bulky cation is not solely due to steric hindering but also due to electrostatic effects, which are important in the design of such uncommon species.

DFT and TPD study of the role of steps in the adsorption of CO on copper: Cu(4 1 0) versus Cu(1 0 0).

Adsorption of carbon monoxide (CO) was studied on stepped Cu(4 1 0) by temperature programmed desorption (TPD) and density-functional-theory (DFT) calculations. For comparison, the adsorption of CO was characterized also on Cu(1 0 0) by DFT calculations. On Cu(4 1 0) TPD reveals two desorption peaks: a high temperature peak (∼210 K) is attributed to the desorption of CO from step-edge sites and low temperature peak (∼170 K) to desorption from terrace sites.

Effect of Mercapto and Methyl Groups on the Efficiency of Imidazole and Benzimidazole-based Inhibitors of Iron Corrosion.

We report on the combined experimental and computational study of imidazole- and benzimidazole-based corrosion inhibitors containing methyl and/or mercapto groups. Electrochemical measurements and long-term immersion tests were performed on iron in NaCl solution, whilst computational study explicitly addresses the molecular level details of the bonding on iron surface by means of density functional theory calculations (DFT). Experimental data were the basis for the determination of inhibition efficiency and mechanism.

A DFT study of adsorption of imidazole, triazole, and tetrazole on oxidized copper surfaces: Cu₂O(111) and Cu₂O(111)-w/o-CuCUS.

Azoles and their derivatives are known for their corrosion inhibition ability for copper. For this reason the bonding of imidazole, triazole, and tetrazole-used as archetypal models of azole corrosion inhibitors-to Cu2O(111) and Cu2O(111)-w/o-Cu(CUS) was characterized using density functional theory (DFT) calculations. The former surface contains coordinatively-saturated (CSA) and coordinatively-unsaturated (CUS) Cu sites, whereas the latter lacks the CUS sites.

Ab initio modeling of the bonding of benzotriazole corrosion inhibitor to reduced and oxidized copper surfaces.

The bonding of benzotriazole-an outstanding corrosion inhibitor for copper-on reduced and oxidized copper surfaces is discussed on the basis of density functional theory (DFT) calculations. Calculations reveal that benzotriazole is able to bond with oxide-free and oxidized copper surfaces and on both of them it bonds significantly stronger to coordinatively unsaturated Cu sites. This suggests that benzotriazole is able to passivate the reactive under-coordinated surface sites that are plausible microscopic sites for corrosion attack.

Molecular modeling of organic corrosion inhibitors: why bare metal cations are not appropriate models of oxidized metal surfaces and solvated metal cations.

The applicability of various models of oxidized metal surfaces - bare metal cations, clusters of various size, and extended (periodic) slabs - that are used in the field of quantum-chemical modeling of corrosion inhibitors is examined and discussed. As representative model systems imidazole inhibitor, MgO surface, and solvated Mg(2+) ion are considered by means of density-functional-theory calculations. Although the results of cluster models are prone to cluster size and shape effects, the clusters of moderate size seem useful at least for qualitative purposes.

Triazole, benzotriazole, and naphthotriazole as copper corrosion inhibitors: I. Molecular electronic and adsorption properties.

The gas-phase adsorption of 1,2,3-triazole, benzotriazole, and naphthotriazole-considered as corrosion inhibitors-on copper surfaces was studied and characterized using density functional theory (DFT) calculations. We find that the molecule-surface bond strength increases with increasing molecular size, thus following the sequence: triazole View Article and Find Full Text PDF

DFT study of gas-phase adsorption of benzotriazole on Cu(111), Cu(100), Cu(110), and low coordinated defects thereon.

The adsorption of benzotriazole--an outstanding corrosion inhibitor for copper--on Cu(111), Cu(100), Cu(110), and low coordinated defects thereon has been studied and characterized using density functional theory (DFT) calculations. We find that benzotriazole can either chemisorb in an upright geometry or physisorb with the molecular plane being nearly parallel to the surface. While the magnitude of chemisorption energy increases as passing from densely packed Cu(111) to more open surfaces and low coordinated defects, the physisorption energy is instead rather similar on all three low Miller index surfaces.

What determines the inhibition effectiveness of ATA, BTAH, and BTAOH corrosion inhibitors on copper?

Three corrosion inhibitors for copper-3-amino-1,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotriazole (BTAOH)-were investigated by corrosion experiments and atomistic computer simulations. The trend of corrosion inhibition effectiveness of the three inhibitors on copper in near-neutral chloride solution is determined experimentally as BTAH ≳ ATA ≫ BTAOH. A careful analysis of the results of computer simulations based on density functional theory allowed to pinpoint the superior inhibiting action of BTAH and ATA as a result of their ability to form strong N-Cu chemical bonds in deprotonated form.

Density functional theory study of ATA, BTAH, and BTAOH as copper corrosion inhibitors: adsorption onto Cu(111) from gas phase.

A low-coverage gas-phase adsorption of three corrosion inhibitors-3-amino-1,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotriazole (BTAOH)-on perfect Cu(111) surface has been studied and characterized using density functional theory calculations. We find that the molecules in neutral form chemisorb weakly to the perfect surface in an upright geometry. The strength of the chemisorption increases in the order BTAH < BTAOH < ATA with adsorption energies of -0.

QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials.

QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License.

Ethene stabilization on Cu(111) by surface roughness.

The molecular vibrations of ethene adsorbed on roughened Cu(111) surfaces have been investigated with high resolution electron energy loss spectroscopy and density-functional-theory calculations. The roughness was introduced by sputtering or evaporation of copper, respectively, on the cooled surface. We found stabilization of the ethene layer compared to ethene adsorbed on pristine Cu(111).

The collimation angle shift of desorbing product N2 in a steady-state N2O+CO reaction on Rh(110).

The angular distribution of desorbing product N2 was studied in N2O decompositions on Rh(110) in the temperature range of 60-700 K. The N2 desorption collimates along 62 degrees -68 degrees off normal toward either the [001] or [001] direction in a transient N2O decomposition below ca. 470 K or in the steady-state N2O+CO reaction above 540 K.

Methane dehydrogenation on Rh@Cu(111): a first-principles study of a model catalyst.

The issue of tuning the relative height of the first two dehydrogenation barriers of methane (CH(4) --> CH(3) + H and CH(3) --> CH(2) + H) is addressed using density-functional theory. It is shown that the combination of a very active reaction center-such as Rh-with a more inert substrate-such as Cu(111)-may hinder the second dehydrogenation step with respect to the first, thus resulting in the reverse of the natural order of the two barriers' heights.

Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110).

The angular and velocity distributions of desorbing product N(2) were examined over the crystal azimuth in steady-state NO+CO and N(2)O+CO reactions on Pd(110) by cross-correlation time-of-flight techniques. At surface temperatures below 600 K, N(2) desorption in both reactions splits into two directional lobes collimated along 41 degrees -45 degrees from the surface normal toward the [001] and [001] directions. Above 600 K, the normally directed N(2) desorption is enhanced in the NO reduction.