Determination Of Coordination Number Research Articles

Corrigendum: On the Determination of Coordination Numbers of Coupled DEM-DFN Model for Modeling Fractured Rocks

Corrigendum: On the Determination of Coordination Numbers of Coupled DEM-DFN Model for Modeling Fractured Rocks

Corrigendum: On the Determination of Coordination Numbers of Coupled DEM-DFN Model for Modeling Fractured Rocks

Corrigendum: On the Determination of Coordination Numbers of Coupled DEM-DFN Model for Modeling Fractured Rocks

On the Determination of Coordination Numbers of Coupled DEM-DFN Model for Modeling Fractured Rocks

Natural fractured rocks usually contain background granular media and multi-scale fractures. The coordination number is a crucial factor to characterize the connection of microstructural elements. The determination of coordination numbers for modeling fractured rocks is essential to interpret the distribution of cracks related to micromechanical properties. We have built a consistent workflow of discrete element models (DEMs) coupled with discrete fracture networks (DFNs). This DEM-DFN model could provide a simple formulation for high calculation efficiency to model a more realistic and detailed description of fracture system. A series of numerical experiments are set up, aiming to correlate window radius, particle size, and crack length, which will benefit the window selection for measuring coordination numbers based on the crack characteristics. The coordination number determined in the DEM-DFN modeling can be used to identify crack patterns in the spatial distribution.

Absorption of Hydrocarbons on Palladium Catalysts: From Simple Models Towards Machine Learning Analysis of X-ray Absorption Spectroscopy Data

Element selectivity and possibilities for in situ and operando applications make X-ray absorption spectroscopy a powerful tool for structural characterization of catalysts. While determination of coordination numbers and interatomic distances from extended spectral region is rather straightforward, analysis of X-ray absorption near-edge structure (XANES) spectra remains a highly debated and topical problem. The latter region of spectra is shaped depending on the local 3D geometry and electronic structure. However, there is no straightforward procedure for the unambiguous extraction of these parameters. This work gives a critical vision on the amount of information that can be practically extracted from Pd K-edge XANES spectra measured under in situ and operando conditions, in which adsorption of reactive molecules at the surface of palladium with further formation of subsurface and bulk palladium carbides are expected. We investigate how particle size, concentration of carbon impurities, and their distribution in the bulk and at the surface of palladium particles affect Pd K-edge XANES features and to which extend they should be implemented in the theoretical model to adequately reproduce experimental data. Then, we show how the step-by-step increasing the complexity of the theoretical model improves the agreement with experiment. Finally, we suggest a set of formal descriptors relevant to possible structural diversity and construct a library of theoretical spectra for machine-learning-based analysis of the experimental data.

Ligand Exchange Processes on Solvated Lithium Cations. VI. Determination of Coordination Numbers by Ligand Substitution and 7Li NMR

Graphical Abstract Ligand Exchange Processes on Solvated Lithium Cations. VI. Determination of Coordination Numbers by Ligand Substitution and 7 Li NMR On the basis of 7 Li NMR studies the coordination mode of phenantroline (phen) and bipyridine (bipy) to Li + ions was found to be [Li(phen) 2 ] + and [Li(bipy) 2 ] + in the weakly coordinating solvent nitromethane. A large chemical shift of the 7 Li signal indicated a strong interaction between the ligand and the metal center. The related sp 2 -hybridized N-donor ligand 2,2´-bis[(4S)-4-benzyl-2- oxazoline] (biox) showed a negligible effect on the 7 Li shift, suggesting that almost no interaction occurs between the Li + center and biox as compared to Li + and the solvent γ -butyrolactone. Corresponding DFT (RB3LYP/LANL2DZp) calculations have clearly indicated that the poor coordination of biox is not caused by steric effects but rather by the electronic nature of the heterocyclic biox system.

Spectroscopic Study and Local Coordination of Polyphosphate Colloidal Systems

The interaction between metaphosphate chains and the metal ions Ca2+ and Eu3+ has been studied in water by Eu3+ luminescence, infrared absorption, and 31P NMR spectroscopy. Two main families of sites could be identified for the metal ions in the aqueous polyphosphate colloidal systems: (1) cagelike sites provided by the polyphosphate chain and (2) a family which arises following saturation of cagelike sites. Occupation of this second family leads to supramolecular interactions between polyphosphate chains and the consequent destabilization of the colloidal system. In the polyphosphate-Ca2+ system, this destabilization appears as a coacervation process. Equilibrium existing between colloidal species as a function of the compositions could be reasoned based on the spectroscopic measurements. The determination of coordination numbers and the correlation of the results with the observation of coacervates show that Eu3+ luminescence properties can be used to probe in a unique way the coacervation process.

Structural properties of amorphous carbon films by molecular dynamics simulation

Structure and properties of amorphous carbon film was investigated by molecular dynamics simulation using a Tersoff potential for carbon–carbon interaction. Quantitative determination of coordination numbers, atomic density, and pair correlation function was adapted to investigate the relationship between incident energies and structural properties. The structural properties of the amorphous carbon film made by the simulations were compared with those of the films deposited by filtered vacuum arc (FVA) process. As in the experimental result, the structural properties of the modeled film have their maximum values when the incident energy of deposited atoms is between 50 and 75 eV. At the optimum kinetic energy condition, we could observe in pair correlation functions that significant amount of carbon atoms were placed at a meta-stable site of atomic distance of 2.1 Å. By melting and quenching simulation of diamond lattice, it could be shown that the population of the meta-stable site is proportional to the quenching rate. These results suggest that the hard and dense diamond-like film could be obtained when the localized thermal spike due to the collision of the high-energy carbon ion can be effectively dissipated to the lattice.

Structural properties of amorphous carbon films by molecular dynamics simulation

Structure and properties of amorphous carbon film was investigated by molecular dynamics simulation using a Tersoff potential for carbon–carbon interaction. Quantitative determination of coordination numbers, atomic density, and pair correlation function was adapted to investigate the relationship between incident energies and structural properties. The structural properties of the amorphous carbon film made by the simulations were compared with those of the films deposited by filtered vacuum arc (FVA) process. As in the experimental result, the structural properties of the modeled film have their maximum values when the incident energy of deposited atoms is between 50 and 75 eV. At the optimum kinetic energy condition, we could observe in pair correlation functions that significant amount of carbon atoms were placed at a meta-stable site of atomic distance of 2.1 Å. By melting and quenching simulation of diamond lattice, it could be shown that the population of the meta-stable site is proportional to the quenching rate. These results suggest that the hard and dense diamond-like film could be obtained when the localized thermal spike due to the collision of the high-energy carbon ion can be effectively dissipated to the lattice.

Topology of the structure of metal sublattices in inorganic compounds

The Voronoi-Dirichlet polyhedron (VDP) method is used to study the topology of atomic metal sublattices in the structures of 350 inorganic compounds. For the sample under consideration, it is confirmed that the rule of twelve and fourteen neighbors is valid. It is found for 26 compounds that the environment of metal atoms in the cationic framework possesses noncrystallographic features. The advantages of using the VDP method for determination of coordination numbers of atoms are shown on several examples. The local and global homogeneity of the structures of the compounds is discussed.

The determination of coordination numbers for binary alloys using energy selected electron diffraction

In determining the reduced density function, G( r), from electron diffraction patterns of an amorphous or polycrystalline alloy AB using the technique of RDF analysis (Cockayne and McKenzie, 1988), it is necessary to make the approximation that the ratio of the scattering factors K = ⨍ B( s)/⨍ A ( s) is independent of s, the scattering angle parameter. This paper reports an investigation of the effects of this approximation upon the values of coordination numbers determined.

Determination of co-ordination numbers and oxidation states in chromium oxides by extended X-ray absorption fine structure spectroscopy

Chromium and iron K-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) measurements for several phases in the Sr2CrxFe2 –xO5 +y system have established that there are substantial numbers of chromium atoms with either short (ca. 1.65 A) or long (ca. 1.91 A) distances to oxygen. These can be attributed to high oxidation states of chromium in tetrahedral co-ordination and Cr3+ ions in octahedral co-ordination, respectively. There is also some evidence for chromium in edge-sharing polyhedra, but not in face-sharing polyhedra, while the iron is in corner-sharing polyhedra. Possible model structures for the 15R phase are discussed.

Carbon-carbon and carbon-hydrogen bond activation at ditungsten centers supported by alkoxide ligands

Abstract

Determination of coordination number by magnetic resonance in reentrant ferromagnets

In ferromagnets near the percolation concentration, reentrant ferromagnets, the observed low temperature increase in magnetic resonance linewidth is shown, at high fields, to result from relaxation via isolated spins. The correlation leads to a novel and simple method for determination of the coordination number.

A Less Arbitrary Determination of Coordination Numbers in Disordered Systems

Abstract The radial distribution functions, 4πr2gij(r), of molten alkali halides, obtained by Monte Carlo simulations, have been deconvoluted into contributions from the first, second, third, etc. neighbours. These individual distribution functions indicate that in alkali halide melts the first coordination sphere of the ions contains an integral or half integral number of unlike charged ions. The shapes of the individual distribution functions show characteristic changes from first coordination shell neighbours to second shell ones and this can be utilised to make the selection of the boundary of the coordination sphere less arbitrary. Such a deconvolution reveals more of the structure in the case of the like charged ion distributions as well.

Short‐range structure determination by EXAFS spectroscopy: Theory, experimental technique and spectral analysis

AbstractA physico‐chemical description of the extended X‐ray absorption fine structure (EXAFS) phenomenon is given and experimental methods for its measurement in transmission mode are indicated. Pros and cons of various procedures for careful evaluation of the experimental absorption data are described, which comprise background removal according to Victoreen's relation or by polynomial fitting and criteria for Fourier filtering methods are given. Three different approaches for EXAFS signal analysis are discussed namely fitting with parametrized amplitude and phase functions, comparison of experimental data with theoretical EXAFS spectra and Fourier transform techniques; the limits of applicability of these procedures are indicated. A critical evaluation is given for the various methods for correction of the resulting radial distribution function in order to comply with crystallographic distances. The determination of coordination numbers is discussed and the procedures are illustrated with results for metallic titanium, rutile and anatase.

Characterisation of two-, three-, and four-co-ordinate gold(I) complexes by197Au Mössbauer and31P-{1H} nuclear magnetic resonance spectroscopy

The isolation of some new three- and four-co-ordinate gold(I) complexes is reported. 197Au Mossbauer data are given for two-, three-, and four-co-ordinate complexes, and the technique is shown to be well suited to the determination of co-ordination numbers. For the two- and three-co-ordinate systems the point-charge (partial quadrupole splitting) approach works well, provided that the structures are regular. 31P-{1H} n.m.r. data for the Au+–P(C6H11)Ph2 system show that a maximum of three ligands can be bound to the cation. Data for this and other ligands are correlated with the ligand cone angles. Inconsistencies between the species present in solution and those obtained by crystallisation are discussed.

Spin density distribution and 13C relaxation in pyridine-N-oxide—nickel acetylacetonate complexes

The spin density distribution on the aromatic carbons of several pyridine-N-oxide-Ni[AA] 2 complexes in chloroform solution have been determined by 1H and 13C contact shift measurements. The 13C longitudinal relaxation results mainly from the hyperfine dipolar interaction induced by the spin density localized on Ni II and on the 13C centered 2 pz orbital whereas the transverse relaxation is strongly dependent on the scalar hyperfine interaction. The temperature dependence of T 1e as well as the ligand to metal distance and the ▪ angle are deduced from the 13C relaxation times. It is shown that the relaxation experiments may be applied to the determination of coordination numbers.

Determination of co-ordination number in some compounds of magnesium and aluminium: a comparison of X-ray photoelectron (ESCA) and X-ray emission spectroscopies

The effect of changes in co-ordination number (four to six, oxygen ligands) upon 2p and 2s ionisation energies of magnesium and aluminium is shown to be about ten times greater (i.e. ca. 2 eV) than the effect upon the Kα emission energy, X-ray photoelectron spectroscopy (ESCA) is therefore to be preferred to X-ray emission spectroscopy for the determination of co-ordination number; at constant co-ordination number orbital energies are also affected by the nature of the ligands.

Coordination compounds with thioxane oxide and thiacyclohexane oxide as ligands. Their use in determination of coordination numbers to oxygen ligands for non-transition metal cations

Thioxane oxide (TSO) and thiacyclohexane oxide (TCHO) were found to be good ligands for coordination to metal ions, both transition and non-transition. Many new compounds have been prepared. The results with the non-transition metal perchlorates are of particular interest because the ratio of bound sulfoxide molecules to metal cations gives information on the coordination number to oxygen of the metal ions.