Electron Density and Electrostatic Potential of Coesite

Downs, James W.

doi:10.1021/j100018a016

Cited by 37 publications

(27 citation statements)

References 4 publications

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“…Table 2 compares the results obtained for the coesite structure with the two experimental electron density maps available. [32,33] Here, both experimental data and PACHA results suggest that atom Si1 should be more positively charged than atom Si2. Values reported by Gibbs et al [32] and PACHA results also suggest a clear separation between atoms O1 and O2, which belong to sixor eight-rings, and atoms O3, O4, and O5, which belong to fourrings.…”

Section: Electron Density Maps and Solid-state Nmrmentioning

confidence: 68%

Nonempirical Quantification of Molecular Interactions in Supramolecular Assemblies

Henry¹

2002

ChemPhysChem

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Section: Electron Density Maps and Solid-state Nmrmentioning

confidence: 68%

Nonempirical Quantification of Molecular Interactions in Supramolecular Assemblies

Henry¹

2002

ChemPhysChem

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“…Coesite has eight unique Si-O bonds and five unique Si-O-Si groups in the unit cell [15], and it is an ideal material for studying the properties of the SiO bonds [15,16]. Coesite is a framework silicate in which each silicon atom is bonded to four oxygen atoms forming a silicate tetrahedron, and each oxygen atom is bonded to two silicon atoms forming a SiOSi disiloxy group.…”

Section: Introductionmentioning

confidence: 99%

Coesite Formation at Ambient Pressure and Low Temperatures

Martı́nez

Vázquez-Durán

Martínez-Castañón

et al. 2008

Advances in Materials Science and Engineering

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Partial crystallization of silica xerogel in the form of coesite has been obtained at low-pressure conditions and temperatures of ∼565• C, in samples containing chlorophyll aggregates dispersed in amorphous silica. Silica xerogel samples were prepared by the sol-gel method using an ethanol:H 2 O:TEOS molar ratio of 4:11.6:1 and loaded with extracts from frozen spinach leaves. The silica xerogel microstructure of the powders was studied as a function of annealing temperature. It was found that partial crystallization of the glass matrix in the form of coestite was obtained at lower pressure than those specified by the phase diagram. Chlorophyll aggregates were added to the starting solutions which, upon thermal treatments, form small colloidal particles in the glass matrix. The presence of coesite is corroborated by the Rietveld refinement method.

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“…Right: chains of edge-sharing`octahedra' running along [001]. (Downs, 1995), danburite (Downs & Swope, 1992), topaz (Ivanov et al, 1998), spodumene (Kuntzinger & Ghermani, 1999 and ®brous zeolites (Kuntzinger et al, 1998;Kirfel & Gibbs, 2000). In the latter reference, the topological results for 32 SiÐO, 24 AlÐO, 14 CaÐO and 12 NaÐO unique bonds were compiled and analysed in terms of both mean values and correlations between bond lengths, oxygen-bonded radii, b.c.p.…”

Section: Introductionmentioning

confidence: 99%

Electron-density distribution in stishovite, SiO₂: a new high-energy synchrotron-radiation study

et al. 2001

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The electron-density distribution of the high-pressure polymorph of SiO 2 , stishovite [a = 4.177 (1) , c = 2.6655 (5) A Ê , space group P4 2 amnm, Z = 2], has been redetermined by single-crystal diffractometry using synchrotron radiation of 100.42 and 30.99 keV, respectively, in order to obtain essentially absorptionand extinction-free data. Room-temperature diffraction experiments on two samples of irregular shape were carried out on two different diffractometers installed at HASYLAB/DESY, Hamburg, Germany. The structure re®nement on the high-energy data converged at R(F ) = 0.0047, wR(F ) = 0.0038, GoF = 0.78, for a multipole model with neutral atoms and multipole expansions up to seventh order. For each atom, the radial expansion coef®cients of the multipole orders (l > 0) were constrained to a common value. The absence of extinction was indicated by a re®ned correction parameter equalling zero within error limit. The excellent quality of the data is also illustrated by a high-order (HO) re®nement (s > 0.7 A Ê À1 ) yielding R(F ) = 0.0060, wR(F) = 0.0048, GoF = 0.85. Both static deformation electron-density distribution and structure amplitudes compare well with corresponding results obtained from band-structure calculations using the linearized-augmented-plane-wave (LAPW) method. Ensuing topological analysis of the total model electron density distribution revealed bond critical point properties for the two unique SiÐO bonds, indicating a predominantly closed-shell interaction mixed with a signi®cant shared interaction contribution that decreases with increasing interatomic distance. Calculation of atomic basins yielded charges of +3.39 e and À1.69 e for Si and O, respectively, in good agreement with the theoretically calculated values of +3.30 e and À1.65 e. The volumina of the Si and O basins are 2.32 and 10.48 A Ê 3 , corresponding to spheres with radii of 0.82 and 1.36 A Ê , respectively. The results also conform well with correlations between bond length and bond critical point properties reported in the literature for geometry-optimized hydroxyacid molecules. Estimates of the Si cation electronegativity indicate that the change of Si coordination by oxygen from 4 to 6 is accompanied by an increase of the ionicity of the SiÐO bond of about 7%.

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Electron Density and Electrostatic Potential of Coesite

Cited by 37 publications

References 4 publications

Nonempirical Quantification of Molecular Interactions in Supramolecular Assemblies

Nonempirical Quantification of Molecular Interactions in Supramolecular Assemblies

Coesite Formation at Ambient Pressure and Low Temperatures

Electron-density distribution in stishovite, SiO₂: a new high-energy synchrotron-radiation study

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Electron Density and Electrostatic Potential of Coesite

Cited by 37 publications

References 4 publications

Nonempirical Quantification of Molecular Interactions in Supramolecular Assemblies

Nonempirical Quantification of Molecular Interactions in Supramolecular Assemblies

Coesite Formation at Ambient Pressure and Low Temperatures

Electron-density distribution in stishovite, SiO2: a new high-energy synchrotron-radiation study

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Electron-density distribution in stishovite, SiO₂: a new high-energy synchrotron-radiation study