A mapping of the electron localization function for the silica polymorphs: evidence for domains of electron pairs and sites of potential electrophilic attack

Gibbs, G. V.; Cox, David F.; Crawford, T. Daniel; Boisen, M. B.; Lim, Mina

doi:10.1007/s00269-001-0237-z

Cited by 19 publications

(16 citation statements)

References 29 publications

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“…The proposed incorporation of H in coesite is in accordance with another type of hydrogarnet substitution, with Si T2 being replaced by (OH) 4 . Only the O atoms O2, O3, O4, and O5 are the proton acceptors, and O1 is not involved, which is in agreement with the findings of Gibbs et al (2002). This is the only model that can explain the pleochroic and high-pressure behavior of bands n 7 -n 10 .…”

Section: Figuresupporting

confidence: 88%

“…According to Koch-Müller et al (2001) O2, O3, O4, and O5 are the proton accepting O atoms. This is in excellent agreement with the results of Gibbs et al (2002) based on mapping of the electron localization function for coesite. Although the mechanism of hydrogen incorporation in coesite can be explained by the hydrogarnet substitution, the arrangement of the four OH-groups in the coesite structure is quite different from the arrangement of the OH-groups in garnet.…”

Section: Introductionsupporting

confidence: 90%

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OH⁻in synthetic and natural coesite

Koch‐Müller

Dera

Fei

et al. 2003

American Mineralogist

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The incorporation of hydrogen into the coesite structure was investigated at pressures ranging from 4.0-9.0 GPa and temperatures from 750-1300 ∞C using Al and B doped SiO 2 starting materials. The spectra show four sharp bands (n 1 , n 2a , n 2b , and n 3 ) in the energy range of 3450-3580 cm -1 , consistent with the hydrogarnet substitution [Si 4+(T2) + 4O 2-= va T2 + 4OH -], two weak sharp bands at 3537 and 3500 cm -1 (n 6a and n 6b ) attributed to B-based point defects, and two weaker and broad bands at 3300 and 3210 cm -1 (n 4 and n 5 ) attributed to substitution of Si 4+ by Al 3+ + H. More than 80% of the dissolved water is incorporated via the hydrogarnet substitution mechanism. The hydrogen solubility in coesite increases with pressure and temperature. At 7.5 GPa and 1100 ∞C, 1335 H/10 6 Si is incorporated into the coesite structure. At 8.5 GPa and 1200 ∞C, the incorporation mechanism changes: in the IR spectra four new sharp bands appear in the energy range of 3380-3460 cm -1 (n 7 -n 10 ) and the n 1 -n 3 bands disappear. Single crystal X-ray diffraction, Raman spectroscopy, polarized single-crystal and in situ high-pressure FTIR spectroscopy confirm that the new bands are due to OH -in coesite. The polarization and high-pressure behavior of the n 7 -n 10 OH bands is quite different from that of the n 1 -n 3 bands, indicating that the H incorporation in coesite changes dramatically at these P and T conditions. Quantitative determination of hydrogen solubility in synthetic coesite as a function of pressure, temperature, and chemical impurity allow us to interpret observations in natural coesite. Hydrogen has not previously been detected in natural coesite samples from ultra high-pressure metamorphic rocks. In this study, we report the first FTIR spectrum of a natural OH-bearing coesite. The dominant substitution mechanism in this sample is the hydrogarnet substitution and the calculated hydrogen content is about 900 z ± 300 H/10 6 Si. The coesite occurs as an inclusion in diamond together with an OH-bearing omphacite. The shift of the OH-bands of coesite and omphacite to lower energies indicates that the minerals are still under confining pressure.

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Section: Figuresupporting

confidence: 88%

Section: Introductionsupporting

confidence: 90%

OH⁻in synthetic and natural coesite

Koch‐Müller

Dera

Fei

et al. 2003

American Mineralogist

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“…8a clearly shows that the surface of the S-TiO 2 was composed of Ti, O, S and C elements. Carbon was ascribed to the residual carbon from the precursor solution and the adventitious hydrocarbon from XPS instrument itself [30,54]. Fig.…”

Section: Resultsmentioning

confidence: 99%

“…The ELF slice in Fig. 3 exhibited different character with less localization around O (or S) and the blue areas of zero localization were reduced to the immediate neighborhood of Ti with the remaining interstice areas characterized by free electron gas like behavior [53][54][55]. Additionally, the non-localization area increased with the increase of the dopant concentration till 2.78 at.% of the S doping concentration.…”

Section: Bader Charge Distribution and Elf Analysismentioning

confidence: 89%

Combination study of DFT calculation and experiment for photocatalytic properties of S-doped anatase TiO2

Liu

Zhou

Yang

et al. 2014

Applied Surface Science

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“…The calculations show that the bond lengths decrease linearly as the theoretical value of the electron density at the bond critical point, ρ( r c ), increases together with a concomitant increase in the curvatures of the electron density at the point both perpendicular and parallel to the bond path. A mapping of the theoretical Δρ deformation density, the electron localization function, ELF, and the Laplacian −∇ 2 ρ distributions for the silica polymorphs quartz, coesite, and stishovite, have also served to highlight sites of potential chemical reactivity and favorable docking sites for hydrogen − in the lone-pair regions of the oxide anions.…”

Section: Introductionmentioning

confidence: 99%

An Exploration of Theoretical and Experimental Electron Density Distributions and SiO Bonded Interactions for the Silica Polymorph Coesite

Gibbs

Whitten²,

Spackman³

et al. 2003

J. Phys. Chem. B

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A multipole representation of the experimental electron density distribution for the high-pressure silica polymorph coesite, using Hirshfeld-type radial functions, has been generated with single-crystal X-ray diffraction data recorded to a sin θmax/λ value of 1.21 Å-1 at 100 K. Unlike an earlier modeling of the distribution, where a more limited data set was analyzed, deformation electron density maps display banana-shaped isosurfaces in the lone-pair regions of each of the oxide anions involved in the bent SiOSi angles as well as teardrop-shaped ones along each of the SiO bond vectors. They also display a ring torus isosurface about O1, the oxide anion involved in the straight angle. Laplacian −∇2ρ maps display belt-shaped isosurfaces, centered near the apexes of the bent angles, that wrap about halfway around the oxide anions, with a ring torus-shaped isosurface surrounding O1. An analysis of −∇2ρ revealed that the (3,−3) critical point associated with the anions involved in the bent angles are associated in general with larger maxima than that associated with the straight angle, evidence that the electron density is more locally concentrated on the oxide anions involved in the bent angles. As such, these anions are asserted to be more susceptible to electrophilic attack by hydrogen, a feature that provides an experimental basis for why hydrogen in H- and Al-bearing coesite avoids O1 and is observed to dock in the vicinity of the oxide anions involved in the bent angles. The bond critical point properties of the experimental multipole representation of the electron density distribution for coesite together with those for the very high-pressure silica polymorph, stishovite, conform with those calculated for the SiO bonded interactions for a relatively large number of silicate crystals. Not only are they similar in value with the theoretical properties, but together they correlate with the observed SiO bond lengths as predicted by the calculations. The observed SiO bonds display a relatively wide range of ∇2ρ(r c) values between ∼10 e Å-5 for stishovite and ∼20 e Å-5 for coesite. The larger ∇2ρ(r c) values recorded for coesite, considered typical of first row closed-shell ionically bonded atoms, may not be typical for a closed-shell bonded interaction involving second row atoms such as the four-coordinate Si in coesite. The maxima along the bond vectors and in the lone-pair regions displayed by the experimental Δρ and −∇2ρ maps are indicative of shared covalent bonded interactions. The evidence suggests that the value of the electron density at the bond critical point for a given bonded interaction is a reliable measure of bond type: the larger the value ρ(r c), the greater the shared covalent interaction.

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A mapping of the electron localization function for the silica polymorphs: evidence for domains of electron pairs and sites of potential electrophilic attack

Cited by 19 publications

References 29 publications

OH⁻in synthetic and natural coesite

OH⁻in synthetic and natural coesite

Combination study of DFT calculation and experiment for photocatalytic properties of S-doped anatase TiO2

An Exploration of Theoretical and Experimental Electron Density Distributions and SiO Bonded Interactions for the Silica Polymorph Coesite

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A mapping of the electron localization function for the silica polymorphs: evidence for domains of electron pairs and sites of potential electrophilic attack

Cited by 19 publications

References 29 publications

OH−in synthetic and natural coesite

OH−in synthetic and natural coesite

Combination study of DFT calculation and experiment for photocatalytic properties of S-doped anatase TiO2

An Exploration of Theoretical and Experimental Electron Density Distributions and SiO Bonded Interactions for the Silica Polymorph Coesite

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OH⁻in synthetic and natural coesite

OH⁻in synthetic and natural coesite