Non-tetrahedral Structures Research Articles

NaCl salt effect on water structure: a Monte Carlo simulation study

ABSTRACT Monte Carlo simulations and the nearest neighbour approach have been employed in the present study to investigate the effect of NaCl salt on the local structure of water at ambient conditions. The calculations are performed at increasing concentration of NaCl starting from C = 0.5 m up to 6 m. We investigate the influence of ions on the tetrahedral structure and the hydrogen-bonded network of water. The analysis shows that increasing salt concentration results in a reduction of the tetrahedral arrangement of water in favour of a non-tetrahedral arrangement. The use of the nearest neighbour approach allows us to determinate the origin and angular characteristics of this non-tetrahedral structure. Moreover it is demonstrated that compared to Na+, Cl− ion has a larger effect on the tetrahedral structure of water.

Design of I2–II–IV–VI4 Semiconductors through Element Substitution: The Thermodynamic Stability Limit and Chemical Trend

Through element substitution in Cu2ZnSnS4, a class of kesterite-structured I2–II–IV–VI4 semiconductors can be designed as novel functional materials. Using the first-principles calculations, we show that this element-substitution design is thermodynamically limited, that is, although I2–II–IV–VI4 with I = Cu, Ag, II = Zn, Cd, Hg, IV = Si, Ge, Sn, and VI = S, Se, Te are stable quaternary compounds, those with II = Mg, Ca, Sr, Ba, IV =Ti, Zr, Hf, and VI = O are unstable against the phase-separation into the competing binary and ternary compounds. Three main phase-separation pathways are revealed. In general, we show that if the secondary II–VI or I2–IV–VI3 phases prefer to have nontetrahedral structures, then the I2–II–IV–VI4 semiconductors tend to phase separate. This finding can be used as a guideline for future design of new quaternary semiconductors.

Structures of d4 MH3X: a Computational Study of the Influence of the Metal and the Ligands

Density functional theory (DFT, PBE0, and range separated DFT, RSH + MP2) and coupled-cluster with single and double and perturbative triple excitations (CCSD(T)) calculations have been used to probe the structural preference of d(4) MH(3)X(q) (M = Ru, Os, Rh(+), Ir(+), and Re(-); X = H, F, CH(3), CF(3), SiH(3), and SiF(3)) and of MX(4) (M = Ru; X = H, F, CH(3), CF(3), SiH(3), and SiF(3)). Landis et al. have shown that complexes in which the metal is sd(3) hybridized have tetrahedral and non-tetrahedral structures with shapes of an umbrella or a 4-legged piano stool. In this article, the influence of the metal and ligands on the energies of the three isomeric structures of d(4) MH(3)X and MX(4) is established and rationalized. Fluoride and alkyl ligands stabilize the tetrahedral relative to non-tetrahedral structures while hydride and silyl ligands stabilize the non-tetrahedral structures. For given ligands and charge, 4d metal favors more the non-tetrahedral structures than 5d metals. A positive charge increases the preference for the non-tetrahedral structures while a negative charge increases the preference for the tetrahedral structure. The factors that determine these energy patterns are discussed by means of a molecular orbital analysis, based on Extended Hückel (EHT) calculations, and by means of Natural Bond Orbital (NBO) analyses of charges and resonance structures (NRT analysis). These analyses show the presence of through-space interactions in the non-tetrahedral structures that can be sufficiently stabilizing, for specific metals and ligands, to stabilize the non-tetrahedral structures relative to the tetrahedral isomer.

MOLECULAR DYNAMICS STUDY ON LOCAL STRUCTURE OF MOLTEN SILICON

A modified Tersoff potential developed by extending atomic interaction distancehas been applied to simulating the properties of liquid silicon with molecular dynamics. The radical distribution functions with coordination number 6.9 and bond length 0.254nm from the simulation are in good agreement with the experimental results from X-ray diffraction and neutron scattering. The configurations simulated indicate that a chain-network structure is formed among silicon atoms in liquid silicon,and a majority of atoms remain tetrahedral local structure with near-neighbour atoms. The presence of two peaks,~57° and ~102°,in bond angle probability distribution indicates a very complicated structure in liquid silicon. Based on the instantaneous configurations given by the simulation,the local structures in liquid states have been studied with bond-order parameter method. The results show there are ~82% tetrahedron structures in the near-neighbour structures in liquid state and the square deviation of bond-orientational luctuation is about 5.2°. The results also show that except thericosahedron structure,the non-tetrahedral structures may include some other near-neighbour structures.

Algebraic Description of Coordination Sequences and Exact TopologicalDensities for Zeolites

Coordination sequences (CS) have been calculated for all approved zeolite topologies, all dense SiO2 polymorphs and 16 selected non-tetrahedral structures and the algebraic structure of these CS's has been analyzed. Two algebraic descriptions of coordination sequences are presented. One description uses periodic sets of quadratic equations and is already established in the literature. The second description employs generating functions, which are well known in combinatorics but are used here for the first time in connection with coordination sequences. The algebraic analysis based on generating functions turns out to be more powerful than the other approach. Based on the algebraic analyses, exact topological densities are derived and tabulated for all the structures investigated. In addition, `n-dimensional sodalite' is observed to have an especially simple n-dimensional graph.

ChemInform Abstract: The Nontetrahedral Structure and Fluxional Character of SiLi4. A Violation of Both van′t Hoff and Electrostatic Bonding Principles.

ChemInform Abstract: The Nontetrahedral Structure and Fluxional Character of SiLi4. A Violation of Both van′t Hoff and Electrostatic Bonding Principles.

The nontetrahedral structure and fluxional character of SiLi4. A violation of both van't Hoff and electrostatic bonding principles

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe nontetrahedral structure and fluxional character of SiLi4. A violation of both van't Hoff and electrostatic bonding principlesPaul v. R. Schleyer and Alan E. ReedCite this: J. Am. Chem. Soc. 1988, 110, 13, 4453–4454Publication Date (Print):June 1, 1988Publication History Published online1 May 2002Published inissue 1 June 1988https://doi.org/10.1021/ja00221a078RIGHTS & PERMISSIONSArticle Views142Altmetric-Citations27LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (298 KB) Get e-Alerts Get e-Alerts

Preparation of colloidal silicon and preliminary photochemical experiments

A photochemically active powder of silicon is obtained by the slow combustion of silane. The powder contains 33% oxygen and is soluble, to a large extent, in water and alcohols. Its X-ray diffraction pattern indicates the presence of 1.5 nm aggregates of nontetrahedral structure. Illumination of the Si particles in the presence of air leads to photo-anodic corrosion. In deaerated solutions, Ag + and methylviologen ions are reduced, the respective quantum yields in 3 × 10 −3 M solution being 0.1 and 0.02%.

Theoretical study of the carbenoid CH 2FLi: Structures and energies of the stable configurations and transition states

The potential energy surface of the singlet carbenoid CH 2FLi has been examined using ab initio methods including electron correlation and zero-point energy corrections. The three non-tetrahedral structures found earlier are confirmed to be minima, but only the lowest energy structure 1 should be experimentally observable. Two other local minima, 2 and 3, should rearrange to 1 with minimal activation. On the other hand, 1 should be quite rigid configurationally. This structure is predicted to be stable with respect to separated singlet methylene and lithium fluoride monomer by 49.3 kcal/mol, though the reaction of two molecules of 1 to form ethylene and two lithium fluoride monomers is exothermic by 98 kcal/mol.