Si-O Bond Length Research Articles

Toward a comprehensive understanding of solid-state core-level XPS linewidths: Experimental and theoretical studies on theSi 2pandO 1slinewidths in silicates

High resolution X-ray Photoelectron Spectroscopy (XPS) core-level $\text{Si}\text{ }2p$ and $\text{O}\text{ }1s$ spectra of the nonconductors $\ensuremath{\alpha}{\text{-SiO}}_{2}$ (quartz) at 120 and 300 K and vitreous ${\text{SiO}}_{2}$ at 300 K were obtained with a Kratos Axis Ultra XPS instrument (instrumental resolution of $l0.4\text{ }\text{eV}$) which incorporates a unique charge compensation system that minimizes differential charge broadening on nonconductors. The $\text{Si}\text{ }2p$ and $\text{O}\text{ }1s$ linewidths at 300 K ($\ensuremath{\sim}1.1$ and $\ensuremath{\sim}1.2\text{ }\text{eV}$, respectively) are similar for all silicates (and similar to previous thin film ${\text{SiO}}_{2}$ spectra obtained previously), showing that differential charging does not contribute significantly to our spectra. At 120 K, there is a small decrease (0.04 eV) in the $\text{Si}\text{ }2p$ linewidth of $\ensuremath{\alpha}{\text{-SiO}}_{2}$, but no measurable decrease in $\text{O}\text{ }1s$ linewidth. The $\text{O}\text{ }1s$ lines are generally and distinctly asymmetric. We consider all possible sources of line broadening and show that final state vibrational broadening (FSVB) and phonon broadening are the major causes of the broad and asymmetric lines. Previous high resolution gas phase XPS studies have identified large FSVB contributions to the $\text{Si}\text{ }2p$ spectra of ${\text{SiCl}}_{4}$, ${\text{SiF}}_{4}$, and $\text{Si}{({\text{OCH}}_{3})}_{4}$ molecules, and this vibrational structure leads total $\text{Si}\text{ }2{p}_{3/2}$ linewidths of up to $\ensuremath{\sim}0.5\text{ }\text{eV}$, even with individual peak linewidths of $l0.1\text{ }\text{eV}$. The Si atom of $\text{Si}{({\text{OCH}}_{3})}_{4}$ is an excellent analog for Si in crystalline ${\text{SiO}}_{2}$ because the Si-O bond lengths and symmetric stretch frequencies are similar in both compounds. Similar vibrational contributions to the $\text{Si}\text{ }2p$ and $\text{O}\text{ }1s$ spectra of solid silicates are anticipated if the $\text{Si}\text{ }2p$ and $\text{O}\text{ }1s$ core-hole states produce similar changes to the Si-O bond length in both phases. To investigate the possibility, Car-Parrinello molecular dynamics calculations were performed and show that changes to Si-O bond lengths between ion and ground states $(\ensuremath{\Delta}r)$ for both $\text{Si}\text{ }2p$ and $\text{O}\text{ }1s$ hole states are similar for both crystalline ${\text{SiO}}_{2}$ and gaseous $\text{Si}{({\text{OCH}}_{3})}_{4}$. $\ensuremath{\Delta}r$ are $\ensuremath{-}0.04\text{ }\text{\AA{}}$ for $\text{Si}\text{ }2p$ and $\ensuremath{\sim}+0.05\text{ }\text{\AA{}}$ for $\text{O}\text{ }1s$ in both compounds. Indeed, the vibrational envelope from the $\text{Si}\text{ }2p$ spectrum of $\text{Si}{({\text{OCH}}_{3})}_{4}$, broadened to our instrumental linewidth of 0.4 eV, accounts for the majority $(\ensuremath{\sim}0.8\text{ }\text{eV})$ of the $\text{Si}\text{ }2{p}_{3/2}$ linewidth for crystalline ${\text{SiO}}_{2}$ $(\ensuremath{\sim}1.1\text{ }\text{eV})$ with phonon broadening accounting for the remainder. The results provide excellent support for the tenet that final state vibrational splitting, as seen in the gas phase molecules, similarly affects the solid-state spectra. The calculations also indicate that the $\text{O}\text{ }1s$ linewidths should be larger than the $\text{Si}\text{ }2p$ linewidths, as observed in our spectra. FSVB should also lead to small peak asymmetries, as seen in the $\text{O}\text{ }1s$ spectra. The contribution of phonon broadening to the linewidth is also evaluated and shown to be comparable to the FSVB contribution at 120 and 300 K but considerably smaller at very low temperatures.

Bonded interactions in silica polymorphs, silicates, and siloxane molecules

Experimental model electron density distributions obtained for the silica polymorphs coesite and stishovite are comparable with electron density distributions calculated for various silicates and siloxane molecules. The Si-O bond lengths and Si-O-Si angles calculated with first-principles density functional theory methods as a function of pressure are also comparable with the bond lengths and angles observed for coesite and quartz within the experimental error. The similarity of the topological properties of the Si-O bonded interactions and the experimental and the geometry-optimized structures for the silica polymorphs provide a basis for understanding the properties and crystal chemistry of silica. The agreement supports the argument that the bulk of the structural and physical properties of the silica polymorphs are intrinsic properties of molecular-like coordination polyhedra such that the silica polymorphs can be pictured as “supermolecules” of silica bound by virtually the same forces that bind the Si and O atoms in simple siloxane molecules. The topology of the electron density distribution is consistent with the assertion that the Si-O bonded interaction arises from the net electrostatic attraction exerted on the nuclei by the electron density accumulated between the Si and O atoms. The correlation between the Si-O bond length and Si-O-Si angle is ascribed to the progressive local concentration of the electron density in the nonbonded lone pair region of the O atom rather than to a bonded interaction that involves the d-orbitals on Si.

Computational simulations of the structure of Japan twin boundaries in quartz

The structures of Japan twin boundaries in quartz are studied through molecular dynamics simulations and energy minimization calculations. Four types of twinning are grouped under the Japan twin law, comprising 10 subtypes of geometrical configurations based on the structural handedness and composition plane. For each subtype, the twin displacement vector is determined and the structures of the twin boundaries with {11 22} or {TT22} composition plane are simulated. It is shown that six subtypes composed of two crystals with same-handed structure have the same type of SiO 4 tetrahedral linkage at twin boundaries. The twin boundary structures of these six subtypes can be further divided into two enantiomorphic structures composed of right- or left-handed quartz. The other four subtypes are composed of combinations of right- and left-handed quartz, and are structurally distinct from the same-handed group. The twin boundary energies of the same-handed group are lower than for the opposite-handed group. The Si-O bond lengths in the region of the twin boundary differ by no more than 0.05 A from those in the bulk quartz for all subtypes. The differences between the Si-O-Si angles at the twin boundaries and in the bulk exceed 20°, whereas the differences in O-Si-O angles are less than 10°. The present calculations demonstrate that SiO 4 tetrahedra at Japan twin boundaries are very stiff in comparison with inter-tetrahedral forces, consistent with previous reports for silica polymorphs, and that structural matching of twin individuals is primarily achieved through the rotation of SiO 4 tetrahedra.

The gas-phase structure of the decasilsesquioxane Si10O15H10

The equilibrium molecular structure of the decasilsesquioxane, Si(10)O(15)H(10), in the gas phase has been determined by gas electron diffraction. Molecular dynamics calculations were used to give amplitudes of vibration and differences between interatomic distances in the equilibrium structure and the vibrationally averaged distances that are given directly by the diffraction data. The molecules have D(5h) symmetry, and do not show the distortions that are apparent in the crystalline phase. The ten-membered silicon-oxygen rings are found to be particularly flexible in the gas phase, a phenomenon that was also seen in crystal structures. The Si-O bond lengths in the ten-membered rings are 161.6(2) pm long and in the eight-membered rings they are 162.2(3) pm, with Si-O-Si angles of 155.0(5) and 153.9(7) degrees , respectively.

Sixfold-Coordinated Amorphous Polymorph ofSiO2under High Pressure

We have developed synchrotron x-ray absorption and diffraction techniques for measuring the density and structure of noncrystalline materials at high pressures and have applied them to studying the behavior of SiO2 glass. The density, coordination number, and Si-O bond length at a pressure of 50 GPa were measured to be 4.63 g/cm;{3}, 6.3, and 1.71 A, respectively. Based on the density data measured in this study and the sound velocity data available in the literature, the bulk modulus at 50 GPa was estimated to be 390 GPa, which is consistent with the pressure dependence of the density in the vicinity of 50 GPa. These results, together with the knowledge from our exploratory study, suggest that SiO2 glass behaves as a single amorphous polymorph having a sixfold-coordinated structure at pressures above 40-45 GPa up to at least 100 GPa.

29Si, 27Al, 1H and 23Na MAS NMR Study of the Bonding Character in Aluminosilicate Inorganic Polymers

Si-29, Al-27, H-1 and Na-23 solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) has been used to relate nominal composition, bonding character and compressive strength properties in aluminosilicate inorganic polymers (AIPs). The Si-29 chemical shift varies systematically with Si-to-Al ratio, indicating that the immediate structural environment of Si is altering with nominal composition. Fast H-1 MAS and Si-29 T (SiH)/T-1 rho relaxation measurements demonstrated that occluded pore H2O mobility within the disordered cavities is slow in comparison with H2O mobility characteristics observed within the ordered channel structures of zeolites. The Al-27 MAS NMR data show that the Al coordination remains predominantly 4-coordinate. In comparison with the Si-29 MAS data, the corresponding Al-27 MAS line shapes are relatively narrow, suggesting that the AlO4 tetrahedral geometry is largely unperturbed and the dominant source of structural disorder is propagated by large distributions of Si-O bond angles and bond lengths. Corresponding Na-23 MAS and multiple-quantum MAS NMR data indicate that Na speciation is dominated by distributions of hydration states; however, more highly resolved Na-23 resonances observed in some preparations supported the existence of short-range order. New structural elements are proposed to account for the existence of these Na resonances and an improved model for the structure of AIPs has also been proposed.

17O and29Si NMR Parameters of MgSiO3Phases from High-Resolution Solid-State NMR Spectroscopy and First-Principles Calculations

The 29Si and 17O NMR parameters of six polymorphs of MgSiO3 were determined through a combination of high-resolution solid-state NMR and first-principles gauge including projector augmented wave (GIPAW) formalism calculations using periodic boundary conditions. MgSiO3 is an important component of the Earth's mantle that undergoes structural changes as a function of pressure and temperature. For the lower pressure polymorphs (ortho-, clino-, and protoenstatite), all oxygen species in the 17O high-resolution triple-quantum magic angle spinning (MAS) NMR spectra were resolved and assigned. These assignments differ from those tentatively suggested in previous work on the basis of empirical experimental correlations. The higher pressure polymorphs of MgSiO3 (majorite, akimotoite, and perovskite) are stabilized at pressures corresponding to the Earth's transition zone and lower mantle, with perovskite being the major constituent at depths >660 km. We present the first 17O NMR data for these materials and confirm previous 29Si work in the literature. The use of high-resolution multiple-quantum MAS (MQMAS) and satellite-transition MAS (STMAS) experiments allows us to resolve distinct oxygen species, and full assignments are suggested. The six polymorphs exhibit a wide variety of structure types, providing an ideal opportunity to consider the variation of NMR parameters (both shielding and quadrupolar) with local structure, including changes in coordination number, local geometry (bond distances and angles), and bonding. For example, we find that, although there is a general correlation of increasing 17O chemical shift with increasing Si-O bond length, the shift observed also depends upon the exact coordination environment.

Molecular Dynamics Study of the Structure in Vitreous Silica with COMPASS Force Field at Elevated Temperatures

Vitreous silica, as high temperature resistant material, has not been completely studied with the influence of extreme working conditions due to experimental limitations. In this work, the structure correlations of vitreous silica were investigated by molecular dynamics method at elevated temperatures from 0 K to 4000 K. COMPASS force field was firstly used in simulating vitreous silica. The temperature dependence of volume for vitreous silica was studied and a maximum of volume was found. The calculated density and the thermal expansion coefficient are close to experimental results. The evolutions of structure in thermal history were discussed in detail. The correlations between the average Si-O bond length and the Si-O-Si bond angle is shown in agreement with the studies used other potentials in literatures. It is proved that the COMPASS force field is appropriate for simulating vitreous silica in some extent, especially in depicting the Si-O interaction and the [SiO4] tetrahedron. Finally, the origin of the volume maxima was discussed based on the analysis of the structure.

X-ray diffraction investigation of siloxanes. III. Structure and configuration of cyclic tetra-and pentasiloxanes bearing different organic substituents at silicon atoms

Single crystal X-ray diffraction is applied to elucidate the structures of six tetra-and one penta-siloxane compounds differing in the nature and position of silicon-sitting organic substituents (Me — methyl, Ph — phenyl, mPh — methoxyphenyl, 2mPh — dimethoxyphenyl, 3mPh — trimethoxypehnyl, and C4H6N — butironitrile). Charge states of atoms in the siloxane molecules are calculated, and the effect of oxygen-containing radicals on the Si-O bond lengths and Si-O-Si bond angles affecting the configurations of the tetra-and pentasiloxane cycles is shown.

X-ray diffraction investigation of siloxanes. II. Dependence of the structure of cyclic trisiloxanes on the nature of organic substituents at the silicon atom

The structure of six cyclic trisiloxane compounds with various combinations of carbon and oxygen-containing organic radicals Me, Ph, 2mPh, and 3mPh attached to the silicon atoms and lying in different positions of the trisiloxane cycle has been studied. The Si-O bond lengths vary within wide limits (1.607(5)–1.643(2) A). Introduction of one or two 2mPh or 3mPh oxygen-containing radicals in the 1,1-position of the trisiloxane ring results in Si-O interatomic distances shortened to 1.624(3) A. When two 3mPh radicals are in the 1,3-positions, the Si-O bond length decreases to 1.607(5) A. The calculated charges on the silicon and oxygen atoms of the siloxane ring indicated that there is poor correlation between the charged state of the silicon atom and the Si-O bond length.

Si−O Bonded Interactions in Silicate Crystals and Molecules: A Comparison

Bond critical point, local kinetic energy density, G(rc), and local potential energy density, V(rc), properties of the electron density distributions, rho(r), calculated for silicates such as quartz and gas-phase molecules such as disiloxane are similar, indicating that the forces that govern the Si-O bonded interactions in silica are short-ranged and molecular-like. Using the G(rc)/rho(rc) ratio as a measure of bond character, the ratio increases as the Si-O bond length, the local electronic energy density, H(rc)= G(rc) + V(rc), and the coordination number of the Si atom decrease and as the accumulation of the electron density at the bond critical point, rho(rc), and the Laplacian, inverted Delta2 rho(rc), increase. The G(rc)/rho(rc) and H(rc)/rho(rc) ratios categorize the bonded interaction as observed for other second row atom M-O bonds into discrete categories with the covalent character of each of the M-O bonds increasing with the H(rc)/rho(rc) ratio. The character of the bond is examined in terms of the large net atomic charges conferred on the Si atoms comprising disiloxane, stishovite, quartz, and forsterite and the domains of localized electron density along the Si-O bond vectors and on the reflex side of the Si-O-Si angle together with the close similarity of the Si-O bonded interactions observed for a variety of hydroxyacid silicate molecules and a large number of silicate crystals. The bond critical point and local energy density properties of the electron density distribution indicate that the bond is an intermediate interaction between Al-O and P-O bonded interactions rather than being a closed-shell or a shared interaction.

2,2,4,4‐Tetra‐tert‐butyl‐1,3,5,2,4‐benzotrioxadisilepine‐7‐carbaldehyde

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2,2,4,4-Tetra-tert-butyl-1,3,5,2,4-benzotrioxadisilepine-7-carbaldehyde

The molecule of the title compound, C23H40O4Si2, features an approximate non-crystallographic C2 symmetry axis. The aldehyde group is disordered over two positions with similar occupancies. The geometry of the isolated molecule was studied by ab initio quantum mechanical calculations employing a molecular orbital Hartree-Fock method. The calculations reproduce well the equilibrium geometry but slightly overestimate the value of the Si-O bond lengths of the trioxadisilepine ring.

A Raman spectroscopic study of high-uranium zircon from the Chernobyl "lava"

We have studied technogenic, high-uranium zircon, which crystallised from melt formed during the accident at the Chernobyl Nuclear Power Plant in 1986, by confocal Raman spectroscopy, electron microprobe, and backscattered electron imaging. The correlation between Raman and electron microprobe measurements allowed studying mode behaviour as a function of U content of the strongly zoned zircon crystals. The USiO 4 content in the crystals ranges between 0.6 and 11.6 mol. %, corresponding to 0.8 and 15.8 wt. % UO 2 , respectively. The frequency of the v 1 (SiO 4 ) symmetrical and v 3 (SiO 4 ) anti-symmetrical stretching mode decreases by 0.67(3) and 0.75(3) cm -1 per mol. % USiO 4 , respectively, which is a result of an increasing Si-O bond length with increasing U content. The lattice modes show a comparable shift to lower frequencies, whereas the internal v 2 (SiO 4 ) and v 4 (SiO 4 ) bending modes exhibit no or only a small shift to lower frequencies ( -1 per mol. % U). Only the frequency of the lowest energy band (E g ) near 202 cm -1 increases slightly with increasing U content, which is unexpected and indicates that the cation-(SiO 4 ) 4- potentials, the electron orbitals, and/or the cation radius have a strong effect on this mode. The line broadening, reflecting the range of local distortions ( i.e. , microscopic strain), is most pronounced for the lattice modes, in agreement with the large size difference of both cations. We found that the E g lattice modes, involving the movement of the SiO 4 tetrahedron and the cation within the a(b) plane, show significantly larger line broadening with increasing U concentration than the B 1g modes, involving lattice vibrations along the c axis. This suggests that the microscopic strain is significant larger in the a(b) plane than along the c axis, which can be explained by the structural properties of zircon.

Point-charge calculation of quadrupolar parameters for bridging oxygen sites in vitreous silica: Structural implications

The quadrupolar coupling constant Cq and the asymmetry parameter $\ensuremath{\eta}$ for the bridging oxygen sites in vitreous silica structures derived via classical molecular dynamics simulation have been calculated using the point-charge lattice summation method. The results of these calculations indicate that while Cq is a function of both the Si-O-Si angle and the associated Si-O distances, $\ensuremath{\eta}$ depends only on the Si-O-Si angle. The analytical forms of these functional dependences are found to be similar to those reported in previous studies based on ab initio calculations on small clusters. However, the magnitude of Cq is found to decrease with increasing Si-O distance in contrast with a reverse trend obtained in previous ab initio calculations on small clusters. The present results, when combined with the previously reported $^{17}\mathrm{O}$ nuclear magnetic resonance spectroscopic results for bridging oxygen sites in vitreous silica, imply a strong negative correlation between Si-O bond lengths and Si-O-Si bond angles in the glass structure. Such a negative correlation is consistent with the anomalous density variation in silica as well as with energetic considerations.

High-resolution 17O MAS NMR spectroscopy of forsterite ( -Mg2SiO4), wadsleyite ( -Mg2SiO4), and ringwoodite ( -Mg2SiO4)

The high sensitivity of the satellite-transition (ST) MAS NMR technique was exploited to obtain high-resolution 17 O MAS NMR spectra of the three polymorphs of Mg 2 SiO 4 : forsterite (α-Mg 2 SiO 4 ), wadsleyite (β-Mg 2 SiO 4 ), and ringwoodite (γ-Mg 2 SiO 4 ). High NMR sensitivity was important in this application because 17 O-enriched, Fe-free materials are required for 17 O NMR and high-pressure syntheses of the dense β and γ polymorphs result in a only a few milligrams of these solids. In all, eight distinct O species were identified and assigned: three in forsterite, four in wadsleyite, and one in ringwoodite, in agreement with the number of O sites in their crystal structures. The isotropic chemical shifts extracted are in excellent agreement with a previously published correlation with Si-O bond length. However, unexpectedly large quadrupolar coupling constants were found for the non-bridging O species in the dense polymorphs wadsleyite and ringwoodite.

The 10 A phase: Crystal structure from single-crystal X-ray data

Here we report the results of the first three-dimensional refinement of the 10 Å phase performed with single-crystal X-ray data. The 10 Å phase, Mg 3 Si 4 O 10 (OH) 2 H 2 O, is monoclinic, space group C2/m, a = 5.323(1)Å, b = 9.203(1)Å, c = 10.216(1)Å, β = 99.98(1)°, V = 492.9(2) Å 3 ; the calculated density, assuming Z = 2, is 2.676 g.cm -3 . The structure has been solved by direct methods and refined by least-squares method with anisotropic displacement parameters. The final agreement index (R 1 ) was 0.088 for 54 refined parameters and 499 unique observed reflections collected with a diffractometer with a CCD detector. The structure of the 10 Å phase is very similar to that of a homo-octahedral, 1 M trioctahedral mica: it is a silicate consisting of 2:1 tetrahedral-octahedral layers parallel to (001). The mean Si-O, Mg1-O, and Mg2-O bond lengths are 1.626, 2.082, and 2.081 Å, respectively. The ditrigonal rotation angle α is 0.53°. The interlayer of the 10 Å phase is occupied by water molecules. According to the oxygen occupancy, 1 H 2 O p.f.u. is assumed in the investigated sample. Although the average water oxygen position is in the mid-plane, structural refinement suggests disorder along c*. Twelve hydrogen bonds are located between the water molecule and the 6 + 6 oxygen atoms of the basal rings of adjacent tetrahedral sheets (water-oxygen distances averaging 3.19 Å). Therefore there are six possible orientations for the water molecule, with six hydrogen bonds pointing toward the upper basal ring and six pointing toward the lower ring of tetrahedral sheets. The orientational disorder of water, in agreement with previous Raman spectroscopy data, is a feature relevant to the evaluation of thermodynamic functions and thermal stability of the 10 Å phase, which is a possible water carrier (9.1 wt%) in subducting slabs at high pressure.

Local structural heterogeneity, mixing behaviour and saturation effects in the grossular?spessartine solid solution

Local structural heterogeneities in crystals of the binary grossular-spessartine solid solution have been analyzed using powder IR absorption spectroscopy. Wavenurnber shifts of the highest energy Si-O stretching mode in spectra collected at room temperature are consistent with variations in Si-O bond length from structural data. They show a smaller positive deviation from linearity across the Join than is seen for the grossular-pyrope and grossular-almandine binaries. The effective line widths, Deltacorr, of three selected wavenumber regions all deviate positively from linear behaviour. An empirical calibration of this excess spectroscopic property, obtained by comparison with calorimetric enthalpy of mixing data, gives an estimate for the symmetric Margules parameter of W-spec(H) = 14.4(7) kJ mol(-1) in DeltaH(mix) = W-spec(H) XGrXSp. W-spec(H) values derived on the same basis four aluminosilicate garnet solid solutions analyzed by IR spectroscopy vary with DeltaV(2), where DeltaV represents the difference in molar volume between the end members of each binary system. Measurements of lattice parameters and IR spectra were made over a range of temperatures for seven samples with different compositions. Positive excess molar volumes of mixing at low temperature (30 K) may be larger than the excess molar volumes at room temperature. The saturation temperatures of the molar volumes show no correlation with composition, however, in contrast with what had been expected on the basis of data for the grossular-pyrope binary. Saturation temperatures for spectroscopic parameters and lattice parameters of samples with compositions Gr15Sp85 and Gr60Sp40 seem to be outliers in all experiments. It is concluded that the data hint at systematic changes in saturation temperatures across the solid solution, with implications for both the excess entropy of mixing and the excess volume of mixing, but more precise data or further sample characterization are needed to prove that this composition dependence is real in garnet solid solutions.

Molecular dynamics simulation of disordered zircon

The melting of zircon and the amorphous state produced by quenching from the melt were simulated by molecular dynamics using a new partial charge model combined with the Ziegler-Biersack-Littmark potential. The model has been established for the description of the crystalline and aperiodic structures of zircon in order to be used for the simulation of displacement cascades. It provides an excellent fit to the structure, and accounts with convenient precision the mechanical and thermodynamic properties of zircon. The calculated melting temperature is about 2100 K. The activation energy for self-diffusion of ions in the liquid state was determined to be 190-200 kJ/mole. Melt quenching was employed to produce two different disordered states with distinct densities and structures. In the high density disordered state, the zircon structure is intact but the bond angle distributions are broader, 4% of the Si units are polymerized, and the volume swelling is about 8%. In the low density amorphous state, the Zr and Si coordination numbers are lower, and the Zr-O and Si-O bond lengths are shorter than corresponding values for the crystal. In addition, a highly polymerized Si network, with average connectivity of two, is observed in the low density amorphous state. These featuresmore » have all been experimentally observed in natural metamict zircon. The present findings, when considered in light of experimental radiation effects studies, suggest that the swelling in zircon arises initially from disorder in the zircon crystal, and at high doses the disordered crystal is unable to accommodate the volume expansion and transforms to the amorphous state.« less

Three-dimensional configurations of organic/inorganic hy-brid nanostructural blocks (I). A quantum mechanical in-vestigation for ladder-like structure of vinylsilsesquioxane

The organic/inorganic hybrid nanostructural vinylsilsesquioxanes (VSSO) were prepared from the hydrolytic condensation of vinyltrimethoxysilane (VMS). The proposed formulas of VSSO were assigned with standard spectroscopic techniques, FTIR, NMR ( 1 H, 13 C and 29 Si) and MALDI-TOF MS, and a generic formula of the SSO, T n (OH) x (OR′) y ( x , y = 0, 1, 2…; n = 1, 2…; T = RSiO 1.5 −( x + y )/2 n ). Geometric parameters (Si-O and Si-C bond lengths, Si-O-Si and O-Si-O bond angles) and total energies of the multi-structures of VSSO were calculated by a quantum mechanical investigation and molecular symmetries. According to the results of the calculation, most molecules had stabler ladder structures than the cage isomers, therefore, the most probably reasonable and optimum structure of the VSSO system was the ladder type.