Si Bond Length Research Articles

Insight into the TiO2 on transport behavior and heat transfer of the CaO–SiO2–FeO–MgO system at different basicities: Molecular dynamics simulation and thermodynamics

In order to promote the resource utilization of Ti-containing converter slag and reduce the loss of metallic Ti, it is necessary to clarify the relationship between the oxygen network structure and thermophysical properties of the slag. The present work uses classical molecular dynamics (CMD) simulation to study the effects of basicity (1.0–3.0) and TiO2 content (0%–10 %) on the local structural properties, viscosity, and thermal conductivity of the CaO–SiO2–FeO–MgO–TiO2 (CSFMT) system at 1873 K. The M − O (M = Ca, Si, Fe, Mg, and Ti) bond length calculated based on CMD is consistent with the experimental results, and the [SiO4] tetrahedron and [TiO6] octahedron are the basic structural units of the CSFMT system. The increase in basicity promotes the break of bridging oxygen (BO) Si–O–Si and the formation of non-bridging oxygen Si–O-M. The increase in TiO2 content promotes the formation of Ti–O–Si in the system. The basicity and TiO2 content affect the thermophysical properties of the CSFMT system by promoting and inhibiting the depolymerization of the oxygen network structure, respectively. The diffusion abilities of different atoms in the CSFMT system are in descending order of Fe > Mg > Ca > O > Si > Ti. The viscosity of the CSFMT system decreases with increasing basicity and increases with increasing TiO2 content. Increasing the proportion of BOs can weaken the anharmonicity in the polyhedral structural units and reduce phonon scattering. With increasing basicity and TiO2 content, the effective phonon mean free path decreases and increases, respectively, resulting in a decrease and an increase in the thermal conductivity of the CSFMT system. The changes in the microstructure properties of the CSFMT system can be reasonably explained by the changes in its thermodynamic properties such as enthalpy. It is worth noting that the basicity has a greater effect on the viscosity, while the TiO2 content has a more significant impact on the thermal conductivity of the CSFMT system.

Microstructure evolution and performance degradation of sol-gel silica films induced by helium ion irradiation

Helium ion implantation in the sol-gel silica films was conducted at different fluences to study the impact of ion irradiation on defects, microstructures, wettability, optical properties and laser damage performance. The damage mechanism and performance degradation of the films induced by helium ion irradiation were analyzed. The cracks are observed after ion implantation and their transverse size increases but the depth decreases with the increase of ion fluence. At the same time, many small pores appear on the film surface and further expand at larger ion fluence. The Si–O–Si bond length and bond angle are reduced by helium ion implantation, thus leading to the densification of silica films. Helium ion implantation causes Si–Si bonds and Si–O bonds to break to form the defects such as ODCs and NBOHCs, further transforming into E′ centers. After ion implantation, the film surface changes from hydrophobic to hydrophilic due to the reduction of –CH3 groups, thus degrading the anti-pollution performance of the film. The significant decreases of laser damage thresholds of silica films are resulted from the increase of E′ centers and the expansions of cracks and pores. The results provide a reference to evaluate the lifetime of silica films used in high-power laser facilities, which is very important for the research of inertial confinement fusion.

First-principle calculations to investigate electronic and optical properties of carbon-doped silicon

Silicon (Si) is a highly promising candidate for the applications of photovoltaics. However, the bandgap constraints, low conductivity, and bounded photon energy absorption make the applications restricted. Herein, we investigated the optimized structural, electronics and optical characteristics of carbon (C) doped Si by first-principle calculations. The analysis of the various doping illustrates that doping of the C atom in Si adds extra stability by reducing the Si–Si bond length from 2.3 Å to 2.002 Å Si–C bond length which leads to the shrinkage of lattice parameters. In addition, the bandgap of Si is reduced from 1.13 eV to 0.2 eV if a 14.28 % C-doping is employed. As the C-doping is reduced to 6.66 %, the bandgap increases to 0.87 eV with a transition from indirect to direct bandgap. Further reduction in C-doping varies the bandgap from 0.87 eV to 1.13 eV. The density of states calculations show that for a low C-doping, the transitions are mainly due to Si-3p and Si-3s orbitals in the valence band which leads to a higher energy level, while for higher C-doping, the C atom 2p orbital contribution causes a reduction in bandgap and addition of stability in the doped structures. The conductivity of the Si can be increased by utilizing higher C-doping which reduces hole effective mass by 46 % and electron effective mass by 24 %. Optical absorption of Si can be enhanced at a higher spectral range while adopting a higher C-doping, which shifts the absorption peak shapes from spikes to flat and extends to 7 eV photon energy.

Light‐, Middle‐ and Heavy‐Lanthanide Ate‐Complexes Bearing Ln(III)–Si bonds: Structural, Spectroscopic, and Bonding Analysis

Comprehensive SummaryRecent decades have witnessed a rapid development of the lanthanide silicon chemistry. In this research, by reacting [(THF)3LiSiPh3] with Cp3Ln(III)(THF) (Ln(III) = Sm(III), Tb(III), Dy(III), Yb(III)) or Cp2Lu(III)Cl(THF), a series of middle‐ and heavy‐lanthanocene monosilyl/disilyl ate‐complexes ([(DME)3Li][Cp3Ln(III)SiPh3] and [(DME)3Li][Cp2Lu(III)(SiPh3)2]) were synthesized. The structures of the obtained lanthanocene monosilyl/disilyl ate‐complexes were determined by single crystal X‐ray diffraction. Together with the previously reported [(DME)3Li][Cp3La(III)SiPh3] and [(DME)3Li][Cp3Ce(III)SiPh3], a complex group comprising silyl light‐, middle‐ and heavy‐lanthanocene with identical core coordination pattern are presented. The structure analysis of this group of complexes showed that their key geometric parameters, including the Ln(III)–Si bond lengths and Ln(III)–Si–Cph/Cph–Si–Cph angles, were linearly correlated with the ionic radii of Ln(III) centers. Computational studies based on density functional theory calculations suggested the strongly polarized nature of the Ln(III)–Si bonds in these ate‐complexes. The UV‐Vis spectroscopy measurements of this group of ate‐complexes showed that the characteristic absorptions were hypsochromically shifted for complexes with heavier Ln(III) centers. In addition, as revealed by the time‐dependent density functional theory analysis, the HOMOs, in which the Ln(III)–Si σ‐bonding orbitals were the dominant components, of these complexes acted as main donor orbitals in the major electron transitions.

First principle modeling of a silicene-aluminum composite anode for lithium ion batteries

The creation of new environmentally friendly and portable energy sources requires the development of technology used to produce lithium-ion batteries, especially their anodes. The aim of this study was to show the possibilities of the state-of-the-art ab initio approach for modeling battery anode materials. A quantum-mechanical study of the limiting filling of a silicene/aluminum anode with lithium has been performed. In this case, the changes in the structure, energy, and electronic properties of silicene that occur upon filling the anode have been studied. Lithium atoms are deposited both inside and on top of the channel formed by two parallel silicene sheets. The ratio of lithium to silicon varies in the range of 0.1–1.5. The gap in the silicene channel increases as the channel is filled with lithium. The filling of the silicene channel with lithium is associated with an increase in the Si–Si bond length in both silicene sheets without destruction of the channel. The infiltration of lithium into the space between the aluminum substrate and silicene sheet has been determined. Our calculation of the band structure has shown that, regardless of filling with lithium, the silicene-aluminum system exhibits metallic conductivity. The storage capacity of the combined anode (729 mAh g−1) significantly exceeds the capacity of graphite anodes. It was found that the top sheet of silicene acquires a negative electric charge upon significant lithium filling of the anode, exceeding the absolute value of the negative charge of the bottom sheet in contact with the aluminum substrate. Therefore, our model study has elucidated that the new silicene-aluminum anode is a promising material for the creation of a new generation of lithium-ion batteries.

Microscopic analysis of the valence transition in tetragonal EuPd2Si2

Under temperature or pressure tuning, tetragonal EuPd$_2$Si$_2$ is known to undergo a valence transition from nearly divalent to nearly trivalent Eu accompanied by a volume reduction. Albeit intensive work, its microscopic origin is still being discussed. Here, we investigate the mechanism of the valence transition under volume compression by $ab~initio$ density functional theory (DFT) calculations. Our analysis of the electronic and magnetic properties of EuPd$_2$Si$_2$ when approaching the valence transition shows an enhanced $c$-$f$ hybridization between localized Eu 4$f$ states and itinerant conduction states (Eu 5$d$, Pd 4$d$, and Si 3$p$) where an electronic charge redistribution takes place. We observe that the change in the electronic structure is intimately related to the volume reduction where Eu-Pd(Si) bond lengths shorten and, for the transition to happen, we trace the delicate balance between electronic bandwidth, crystal field splitting, Coulomb repulsion, Hund's coupling and spin-orbit coupling. In a next step we compare and benchmark our DFT results to surface-sensitive photoemission data in which the mixed-valent properties of EuPd$_2$Si$_2$ are reflected in a simultaneous observation of divalent and trivalent signals from the Eu $4f$ shell. The study serves as well to explore the limits of density functional theory and the choice of exchange correlation functionals to describe such a phenomenon as a valence transition.

Transportation pathway of oxygen in the cage-to-cage network of barium–strontium aluminosilicates

Oxygen transport through environmental barrier coating (EBC) to form thermally grown oxide (TGO) on the bond coat greatly affects the service life of the EBC when it is subjected to severe environments. In this work, the oxygen diffusion behaviours through barium–strontium aluminosilicates (BSAS), a typical EBC material, were investigated via ab initio molecular dynamic calculations. The results of these calculations are then verified via isotope exchange experiments. It was found that the interstitial oxygen can stably exist and diffuse through the BSAS. Three interlaced diffusion channels in the structure of BSAS were found to form a complete three-dimensional diffusion network. It was also found that the bond length of Si–Al–O can serve as a measure of the diffusion of interstitial molecular oxygen in BSAS. The oxygen permeability of BSAS can be decreased by adjusting the proportions of alkaline earth elements present in the structure, which modifies the bond lengths within the structure. The solution of alkaline earth elements increases the local migration energy barrier, leading to an increase in the overall migration energy barrier.

Interaction effects in a two-dimensional AlSi[formula omitted]P nanosheet: A first-principles study on the electronic, mechanical, thermal, and optical properties

Physical quantities such as the electronic, the mechanical, the thermal, and the optical properties of Al and P codoped silicene forming AlSi6P nanosheets are investigated by first-principle calculations within density functional theory. A particular attention of this study is paid to the interaction effect between the Al and the P atoms in the buckled silicene structure. We infer that the interaction type is attractive and it leads to an asymmetry in the density of states opening up a band gap. In contrast to BN-codoped silicene, the buckling in the Al–P codoped silicene is not much influenced by the dopants as the bond lengths of Si–P and Al–P are very similar to the Si–Si bond lengths. On the other hand, the longer bond length of Si–Al decreases the stiffness and thus induces fractures at smaller values of applied strain in AlSi6P. The elastic and the nonelastic regions of the stress–strain curve of AlSi6P depend on the placement of the Al and the P atoms. The finite band gap caused by the Al–P dopant leads to enhancement of the Seebeck coefficient and the figure of merit, and induces a redshift of peaks in the dielectric response, and the optical conductivity. Finally, properties of the real and the imaginary parts of the dielectric function, the excitation spectra, the refractive index, and the optical response of AlSi6P are reported.

Different forms of silicon nanotubes and their interactions with DNA nucleotides: A molecular dynamics study

The interaction between different forms of silicon nanotubes (SiNTs) and DNA nucleotides is investigated using molecular dynamics simulations. The optimized geometries of infinite single-walled SiNTs made of hexagonal and tetragonal lattices are assessed at the classical level based on Tersoff and Stillinger-Weber potentials. Properties such as Si–Si bond length, diameters as well as formation energy per Si atom are calculated for different SiNTs. Our results for the armchair and zigzag structures show relatively good agreements with other classical and quantum level studies. Therefore, the same method is applied to the less investigated tetragonal type nanotubes. In the next step, the interaction between different DNA nucleotides and stable SiNTs is investigated. The results indicate that the van der Waals dispersion forces are mainly responsible for the nucleotide-SiNT interaction. A unique interaction feature of each nucleotide with SiNTs provides general guidelines for the design of SiNTs-based biosensors.

The crystal chemistry of ZrSi

Reported is a revised crystal structure of β–ZrSi (TlI/CrB structure type), correcting the atomic position and bond distances. The Si–Si bond length has been modified substantially from 2.723(6) Å to 2.4411(8) Å. The β-ZrSi single crystals were grown from an arc-melted button, and were characterized using single crystal X-ray diffraction. A survey of the TlI/CrB structure type shows that changes to the nomenclature would be useful, separating it into four chemically distinct subtypes: TlI, CrB, CaSi, and ThCo. β–ZrSi is an example of the CaSi subtype. α-ZrSi crystallizes in the related FeB structure type, which is also divided here into the subtypes FeB, CeSi, and YNi. The effect of electron count on the relative phase stabilities of the CaSi and CeSi subtypes is rationalized with the aid of the Zintl concept and electronic structure calculations in the Linear Muffin-Tin Orbital (LMTO) basis.

First-principles study of effect of ideal tensile/shear strain on chemical bond length and charge density distribution of U<sub>3</sub>Si<sub>2</sub>

After the Fukushima nuclear accident in 2011, U<sub>3</sub>Si<sub>2</sub> was predicted to be an important accident tolerant fuel that can replace UO<sub>2</sub>. The results of recent studies have shown that the simulation at the micro-scale of U<sub>3</sub>Si<sub>2</sub> serving as a candidate for accident tolerant fuel is not deep enough. It is not sufficient to build fuel databases and models at a macro-scale to effectively predict some properties of U<sub>3</sub>Si<sub>2</sub>. Therefore, employing the first principles to calculate some physicochemical data of U<sub>3</sub>Si<sub>2</sub> nuclear fuel has received extensive attention. In previous work, we predicted the ideal strength of U<sub>3</sub>Si<sub>2</sub> in several low-index crystal planes/directions by the first-principles computational tensile/shear test (FPCTT/FPCST) approach. However, the fracture behavior of U<sub>3</sub>Si<sub>2</sub> has not been explained much. Therefore, in this work, the effects of ideal tensile/shear strain on the chemical bond length and charge density distribution of U<sub>3</sub>Si<sub>2</sub> are discussed to analyze the fracture behaviors of U<sub>3</sub>Si<sub>2</sub> in these low-index crystal planes/directions. The effect of strain is achieved by using the incremental simulation elements in the specified crystal plane/direction. The crystal structures of U<sub>3</sub>Si<sub>2</sub> under different strains are optimized by using the first principles based on density functional theory. The variation ranges of chemical bond length and the charge density distributions of U<sub>3</sub>Si<sub>2</sub> under different ultimate strains are summarized and calculated respectively. The results show that the elongation of the U—U bond is the main contributor to the tensile deformation of U<sub>3</sub>Si<sub>2</sub> in the [100] crystal direction under tensile load. The toughness of U<sub>3</sub>Si<sub>2</sub> in the [001] crystal direction is mainly due to the elongation of the U—Si bond and U—U bond. However, the tensile deformation produced in the [110] crystal direction of U<sub>3</sub>Si<sub>2</sub> is mainly related to the elongation of the Si—Si bond. In the (100)[010] slip system, U<sub>3</sub>Si<sub>2</sub> has great deformation and the crystal breaks when the Si—Si bond length reaches a limit of 3.038 Å. For the (001)[100], (110)[<inline-formula><tex-math id="M1">\begin{document}$ \bar 1 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20221210_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20221210_M1.png"/></alternatives></inline-formula>10] and (001)[110] slip systems of U<sub>3</sub>Si<sub>2</sub>, the crystal is broken under small shear deformation, and the change of its bond length is not obvious, reflecting that the sudden decrease of the strain energy or stress in these several slip systems may be related to the strain-induced structural phase transition of U<sub>3</sub>Si<sub>2</sub>.

First principles investigation of the structural, electronic, and optical properties of new c-Si12 silicon allotrope with a cubic structure

In this paper, some structural, electronic, and optical properties of c-Si12 silicon allotrope was investigated based on the density functional theory approach. The results were compared to some of silicon allotropes. The structural results show that both the optimal cubic lattice constant and Si–Si bond length in the c-Si12 structure are larger than the diamond-Si one, although the bulk modulus for the c-Si12 structure is smaller than the diamond-Si and other Si allotrope structures. The electronic results indicate that c-Si12 structure is a semiconductor with an indirect band gap having an energy distance about 0.187 eV between its indirect and direct band gaps. In the optical properties section, the dielectric function, energy loss function, refractive index, and reflectivity of the c-Si12 structure were investigated and compared to the experimental data for the diamond silicon allotrope. Our results indicate that in the visible range, the optical absorption of the c-Si12 structure is larger than the diamond-Si which implies the promising optical properties of the c-Si12 structure and its advantage with respect to the diamond-Si one.

Ab initio investigation of ultrasmall silicon nanocrystal doping by phosphorous

The influence of a single phosphorous impurity on structural and electronic properties of spherical, diamond-like, hydrogen-passivated, ultrasmall Si[Formula: see text]H[Formula: see text], Si[Formula: see text]H[Formula: see text], Si[Formula: see text]H[Formula: see text] and Si[Formula: see text]H[Formula: see text] nanocrystals with silicon core diameters of 0.88, 1.03, 1.26 and 1.58 nm was studied by density function theory calculations. In this ultrasmall length scale, the dependence of structural deformation and electronic properties with gradually increasing sizes has not been practically investigated. A detailed analysis of the structural deformation and charge distribution initiated by the presence of the impurity is conducted to understand how structural change occurs within this length scale, where quantum confinement effects become predominant. The Si[Formula: see text]P[Formula: see text]H[Formula: see text] nanocrystal with P[Formula: see text] located in its center is completely deformed. In a larger nanocrystal, the spherical surrounding impurity remains and the P–Si bond lengths increase. In Si[Formula: see text]P[Formula: see text]H[Formula: see text], the first sphere is expanded, energies of phosphorous formation in central and subsurface positions differ insignificantly, and the P atom can be located in both the central and subsurface positions. In all nanoparticles, the charges of central P[Formula: see text] atoms are negative. The width of the bandgap in undoped nanocrystals is much larger than in bulk silicon and depends on their sizes. The phosphorous introduces the splitting level in the bandgap located closer to the conduction band.

Computer simulation of CaSiO3 glass under compression: correlation between Si–Si pair radial distribution function and intermediate range order structure

The structural organization of CaSiO3 glass at 600 K and under pressure of 0–100 GPa is investigated by molecular dynamics simulation (MDS). Results show that the atomic structure of CaSiO3 comprises SiOn and CaOm units considered as basic structural polyhedra. At low pressure, most of the basic structural polyhedra are SiO4, CaO5, CaO6 and CaO7. At high pressure most of the basic structural polyhedra are SiO5, SiO6 and CaO9, CaO10 and CaO11. The distribution of basic structural polyhedra is not uniform resulting in formation of Ca-rich and Si-rich regions. The distribution of SiO4, SiO5 and SiO6 polyhedra is also not uniform, but it tends to form SiO4-, SiO5-, and SiO6-clusters. For the Si–O network, under compression there is a gradual transition from the tetrahedral network (SiO4) to the octahedral network (SiO6) via SiO5 polyhedra. The SiO5-clusters are the same as immediate-phase in the transformation process. The size and shape of SiO4 tetrahedra change strongly under compression. While the size of SiO5 and SiO6 has also changed significantly, but the shape is almost unchanged under compression. The SiOn polyhedra can connect to each other via one common oxygen ion (corner-sharing bond), two common oxygen ions (edge-sharing bond) or three common oxygen ions (face-sharing bond). The Si–Si bond length in corner-sharing bonds is much longer than the ones in edge-sharing and face-sharing bonds. The change of intermediate range order (IRO) structure under compression relating to edge- and face-sharing bonds amongst SiOn at high pressure is the origin of the first peak splitting of the radial distribution functions of Si–Si pair. Under compression, the number of non-bridging oxygen (NBO) decreases. This makes the Si–O network more polymerized. At low pressure, most of the Ca2+ ions incorporate into the Si–O network via NBOs. At high pressure, the amount of NBO decreases, Ca2+ ions mainly incorporate into the Si–O network via bridging oxygen (BO) that belongs to SiO5 and SiO6 with a negative charge. And this is the principle for immobilization of heavy metal as well as fissile materials in hazardous waste (nuclear waste).

Dopant activation mechanism of Bi wire-δ-doping into Si crystal, investigated with wavelength dispersive fluorescence x-ray absorption fine structure and density functional theory

We successfully characterized the local structures of Bi atoms in a wire-δ-doped layer (1/8 ML) in a Si crystal, using wavelength dispersive fluorescence x-ray absorption fine structure at the beamline BL37XU, in SPring-8, with the help of density functional theory calculations. It was found that the burial of Bi nanolines on the Si(0 0 1) surface, via growth of Si capping layer at 400 °C by molecular beam epitaxy, reduced the Bi–Si bond length from to Å. We infer that following epitaxial growth the Bi–Bi dimers of the nanoline are broken, and the Bi atoms are located at substitutional sites within the Si crystal, leading to the shorter Bi–Si bond lengths.

Crystal structures of three sterically congested disilanes.

In the three sterically congested silanes, C24H38Si2 (1) (1,1,2,2-tetra-isopropyl-1,2-di-phenyl-disilane), C24H34Br4Si2 (2) [1,1,2,2-tetra-kis-(2-bromo-propan-2-yl)-1,2-di-phenyl-disilane] and C32H38Si2 (3) (1,2-di-tert-butyl-1,1,2,2-tetra-phenyl-disilane), the Si-Si bond length is shortest in (1) and longest in (2), with (3) having an inter-mediate value, which parallels the increasing steric congestion. A comparison of the two isopropyl derivatives, (1 and 2), shows a significant increase in the Si-C(ipso) distance with the introduction of bromine. Also, in the brominated compound 2, attractive inter-molecular Br⋯Br inter-actions exist with Br⋯Br separations ca 0.52 Å shorter than the sum of the van der Waals radii. In compound 2, one of the bromo-isopropyl groups is rotationally disordered in an 0.8812 (9):0.1188 (9) ratio. Compound 3 exhibits 'whole mol-ecule' disorder in a 0.9645 (7):0.0355 (7) ratio with the Si-Si bonds in the two components making an angle of ca 66°.

Ab initio computational study of 1-methyl-4-silatranone and attempts at its conventional synthesis

1-Methyl-4-silatranone could exhibit the structural aspects of a typical silatrane including a short N–Si bond distance reflecting a dative bond. But given the significant amide resonance in a [3.3.3] bridgehead bicyclic lactam, the lone pair could be shared with the carbonyl group leading to a very long N–Si bond, essentially a “non-silatrane.” Ab initio calculations (MP2/6-311 + G*) predict that ground state conformations of this molecule are best regarded as lactams rather than silatranes, the most stable having a calculated N–Si bond length of 2.902 A and an N–CO bond length of 1.387 A. The calculated transition state for inversion of the amide ring retains very little amide resonance (N–CO, 1.440 A). Some of this loss is compensated through tightening of the N–Si bond (2.422 A), leading to a net energy of activation of ca 8 kcal/mol. Attempts to synthesize 1-methyl-4-silatranone using conventional pathways successful for 1-methylsilatrane [condensations employing N,N-bis(2-hydroxyethyl)glycolamide in place of tris(2-hydroxyethyl)amine] were unsuccessful. This is due to the net loss in resonance energy of the amide reactant relative to that in the [3.3.3] system, the essential absence of the N–Si dative bond, and the rigidity introduced by the planar amide linkage in the starting material. A more likely pathway to successful synthesis should be formation of the amide linkage in the final step.

Molecular dynamics simulations of microstructural properties of CaO–SiO2–TiO2 fluorine-free slag systems

The microstructural properties of F-free slag, the CaO–SiO2–TiO2 (CST) systems, are investigated by molecular dynamics (MD) simulations. The results show that in the CST system, the average bond length of Si–O remains in 1.61 Å. The addition of TiO2 contributes to the increase in the concentrations of 4-coordinated Si and 4-coordinated Ti. Increasing the amount of CaO decreases the proportion of bridging oxygen (BO) atoms and the degree of network connectivity (Q3 and Q4), suggesting the simplification of melt polymerisation. Substituting CaO with SiO2 and maintaining a constant TiO2 level causes the microstructure of the slag to become more complex. Both SiO2 and TiO2 contribute to the more complex structures of the melts. Simultaneously, Si–O–Ti linkages are more favourable than Si–O–Si or Ti–O–Ti linkages. Thus, TiO2 is regarded as network former in terms of its structure within CST system when the content of TiO2 excessed 28 mass%.

DFT study of the 1-aryl-1-fluoro-5-methylquasisilatrane stereoisomers. NBO and QTAIM analysis

DFT quantum chemical calculations were carried out for conformational isomers of 1-aryl-1-fluoro-5-methylquasisilatranes Ar(F)Si(OCH2CH2)2NMe (Ar=Ph (1), 4-MeC6H4 (2), 4-MeOC6H4 (3), 4-ClC6H4 (4), 3-BrC6H4 (5), 3-NO2C6H4 (6)) with a fluorine atom in the axial (isomers a) or equatorial (isomers b) position relative to nitrogen atom of the N→ Si intramolecular coordination bond. The electronic effect of the axial aromatic substituent results in strengthening of this bond to a greater extent compared to its equatorial position. Relations between the N→ Si bond lengths and the energies of nitrogen lone pair with σ∗SiX(ax) orbital interaction (NBO) as well as the N→ Si bond energies (QTAIM) are observed in compounds 1–6.

A Triatomic Silicon(0) Cluster Stabilized by a Cyclic Alkyl(amino) Carbene

AbstractReduction of the neutral carbene tetrachlorosilane adduct (cAAC)SiCl4 (cAAC=cyclic alkyl(amino) carbene :C(CMe2)2(CH2)N(2,6‐iPr2C6H3) with potassium graphite produces stable (cAAC)3Si3, a carbene‐stabilized triatomic silicon(0) molecule. The Si−Si bond lengths in (cAAC)3Si3 are 2.399(8), 2.369(8) and 2.398(8) Å, which are in the range of Si−Si single bonds. Each trigonal pyramidal silicon atom of the triangular molecule (cAAC)3Si3 possesses a lone pair of electrons. Its bonding, stability, and electron density distributions were studied by quantum chemical calculations.