SCF Xα SW calculations of chemical shifts of X-ray and electron emission lines and relaxation properties of SiX4 molecules

SCF Xα SW calculations of the 1s and 2p binding energies, KLL Auger energies and Kα transition energies for the molecules SiH₄, SiCl₄ and SiF₄ and the corresponding atomic Xα calculations for charged free silicon ions have been carried out. The results provide information about relaxation properties and anomalous chemical Kα shifts in hydrides.     

Bildung siliciumorganischer Verbindungen. LXII. Teilbromierte Carbosilane

Formation of Organosilicon Compounds. LXII. Partial Brominated Carbosilanes The photobromination of 1 leads to compound 2 as well as to C-chlorinated derivatives if the time of reaction is prolonged. Compound 2 is also formed from (Br₂Si–CH₂)₃; Gl. (1) see ?Inhaltsübersicht”?. In a corresponding reaction (Cl₃Si–CH₂)₂SiCl₂ gives successively Cl₃Si–CHBr–SiCl₂–CH₂–SiCl₃, Cl₃Si–CBr₂–SiCl₂–CH₂–SiCl₃ and Cl₃Si–CCl₂–SiCl₂–CH₂–SiCl₃. (Cl₃Si)₂CBr₂ is accessible through the photobromination of (Cl₃Si)₂CH₂. The reactivity of the CBr₂-group is quite obvious in the reaction of Cl₂Si–CBr₂–SiCl₂–CH₂–SiCl₃ with LiAlH₄ yielding (H₃Si–CH₂)₂SiCl₂ as well as in the reaction of compound 2 with CH₃MgCl yielding [(CH₃)₂Si–CH₂]₃. By treatment of the SiH groups with bromine the preparation of compounds with the general formulas CH₃SiH_nBr_3?n; (H_3?nSiBr_n)₂CH₂; (H_3?nSiBr_n? CH₂)₂SiH_2?nBr_n; (H_2?nBr_nSi? CH₂)₃ and (H_3?nSiBr_n)₂CCl₂ is possible. Analysis of the nmr spectra shows that 1,3-Dibromo-1,3,5-trisilacyclohexane is formed to 67% in the trans and to 33% in the cis configuration; 1,3,5-Tribromo-1,3,5-trisilacyclohexane is formed to 80–90% in teh cis-trans configuration. The results of ¹H and ²⁹Si NMR investigations are reported.     

An MS Xα and ETS study of the influence of “d” orbitals on the electron affinities of thio-substituted benzenes

The electron transmission spectra of the o,o′-dimethyl substituted benzenes 2,6-(CH₃)₂C₆H₃-XR (X = O,S, NR: R = H, CH₃) show that the substituents adopt a planar (R = H) or rotated (R = CH₃) conformation depending upon their size and they suggest that in the sulphur derivatives the ²B₁ H anion states are stabilized by S3d orbital participation. MS Xα calculations performed on both the planar and orthogonal forms of the model systems p-(XH)₂-C₆H₄ (X = O, S) support this hypothesis and assign the extra resonance present in the ET spectra of the thio derivatives to electron capture into [ σ_S-R* MOS. strongly mixed with sulphur 3d orbitals ( = 33% d character).     

A theoretical study of the SiCl3 and GeCl3 radicals

Ab initio UHF and SW xα calculations have been performed on the SiCl₃ and GeCl₃ radicals. Geometrical structures and inversion barriers were predicted from ab initio calculations, and ionization potentials, electron affinities and electronegativities were obtained via the SW Xα method. Changes in geometrical and electronic properties along the series (XCl₃; X = C, Si, Ge) are discussed.     

Analysis of XPS and XES of diamond and graphite by DFT calculations using model molecules

X‐ray photoelectron and emission spectra (XPS and XES) of diamond and graphite have been analyzed by deMon density‐functional theory (DFT) calculations using the model adamantane derivative (C₁₀H₁₂(CH₃)₄) and pyrene (C₁₆H₁₀) molecules, respectively. The theoretical valence photoelectron and C Kα X‐ray emission spectra for the allotrope are in good accordance with the experimental ones. The combined analysis of the valence XPS and C Kα XES enables us to divide the valence electronic distribution into the individual contributions for pσ‐, and pπ‐bonding MOs of the diamond and graphite, respectively. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 102–108, 2001     

Bildung siliciumorganischer Verbindungen. XXXIX. Teilchlorierte Carbosilane

1. Photochlorination in CCl₄ of the Si-chlorinated carbosilanes (Cl₃Si? CH₂)₂SiCl₂ and (Cl₂Si? CH₂)₃ leads to totally chlorinated compounds, e. g. (Cl₃Si? CCl₂)₂SiCl₂. After chlorination has started at one CH₂ group, formation of a CCl₂ group is preferred before another CH₂ group is involved into the reaction. Thus preparation of compounds a, b, c is possible. Cl₃Si? CCl₂? SiCl₂? CH₂? SiCl₃ (a) for (b) and (c) (see “Inhaltsübersicht”). SO₂Cl₂ (benzoyl peroxide) as chlorinating agent reacts more slowly, and opens an access to carbosilanes containing CHCl groups such as (d), Cl₃Si-CHCl? SiCl₂? CH₂? SiCl₃ (e). Reactions of compounds (a) to (d) with LiAlH₄ yields carbosilanes with SiH groups, and partially chlorinated C atoms. 2. By the high reactivity of Si? CCl₂? Si groups an exchange of Cl atoms of CCl groups in perchlorinated carbosilanes is possible for H atoms of Si? H groups in perhydrogenated carbosilanes, thus allowing the preparation of compounds containing CHCl and SiHCl groups, e. g. according to Gl.(1) (Inhaltsübersicht). Further reactions, formulated as the last equations in Inhaltsübersicht, are reported as well as the rearrangement of H₃Si? CHCl? SiH₃.     

Ab initio calculations of complexes of tetrachlorides of Group IVA elements: VIII. Structure of SiCl<Subscript>4</Subscript> complexes with hexamethylphosphoric triamide and dynamics of their formation

Quantum-chemical calculations of the systems SiCl₄←OP[N(CH₃)₂]₃ and SiCl₄←2OP[N(CH₃)₂]₃ with complete optimization of their geometry at various Si←O distances were performed by the RHF/6-31G(d) method. The first system was also calculated by the MP2/6-31G(d) method. The calculations of the systems with the complete geometry optimization resulted in trigonal-bipyramidal and trans-octahedral structures, respectively, having energy minima. When the components of the latter system approach each other, first their mutual polarization occurs, and then it is accompanied by electron density transfer from the H and P atoms of the electron-donor molecules to the Cl atoms of the acceptor. The results of the calculation of the trans-octahedral complex agree with the experimental ³⁵Cl NQR data. The electron density of Cl atoms increases upon complex formation, mainly due to an increase in their p _σ electron density.     

Bildung siliciumorganischer Verbindungen. XXXVIII. Umsetzung perchlorierter Carbosilane mit LiAlH4

By LiAlH₄ (Cl₃Si)₂CH₂, (Cl₂Si? CH₂)₂SiCl₂ are reduced to (H₃Si)₂CH₂ (a), (H₃Si? CH₂)₂SiH₂ (b) and (H₂Si? CH₂)₃(c). However with the compounds (Cl₃Si)₂CCl₂, (Cl₃Si? CCl₂0₂SiCl₂ and (Cl₂Si? CCl₂)₃ cleavages of the Si? C-bond and reduction of the CCl-groups occur apart from the normal reduction of the Si-Cl-groups to (H₃Si)₂CCl₂ (d), (H₃SiCCl₂)₂SiH₂ (e) and (H₂Si? CCl₂)₃. Excess LiAlH₄ favours this cleavage, the exact amount of a quarter of a mole LiAlH₄ per SiCl-group allows the formation of (d), (e), (f). The cleavage of (e) is in accordance with: (1), (2),(3). Therefore SiH₃₄ and (H₃Si)₂CCl₂ are the main-reaction-products and CH₃SiH₃ is formed acc. to equ. (3). Because of the cleavage of (H₂Si? CCl₂)₃ with LiAlH₄ H₃Si? CCl₂? SiH₂? CH₃and H₃Si? CH₂? SiH₂? CH₂? SiH₂? CH₃ are preferentially formed after the hydrolysis. The CH₂-containing compounds (a), (b), (c) cannot be cleaved in an analogous reaction.     

Reactions of silylphosphines and silylarsines with covalent halides

The reactions of (CH₃)₃SiP(CH₃)₂ and (CH₃)₃SiAs(CH₃)₂ with SiCl₄, SiF₄, SO₂Cl₂, and SO₂F₂ have been studied. The cleavage of the SiP bond occurs more readily than the cleavage of the SiAs bond. The covalent halides containing oxygen give products that are harder to predict than do the nonoxygenated halides.     

Reactions of organylhalosilanes with 1,1,3,3-tetra- and hexamethyldisilazane

Organylchlorosilanes, and also SiCl₄, decompose 1,1,3,3-tetra- and hexamethyl-disilazanes with formation of hitherto unknown organylchlorosilazanes of general formulas R_4–nSiCl_n–1NHSiH(CH₃)₂ and R_4–nSiCl_n–1NHSi(CH₃)₃ (n=2–4) in yields of 54–98%. The IR and mass spectra of the prepared compounds were studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1159–1162, May, 1991.     

Das Hexamethyl-trisila-tetraphospha-nortricyclen,P4(Sime2)3

Hexamethyl-trisila-tetraphospha-nortricyclene, P₄ Sime₂₃ Reaction of white phosphorus with Na/K alloy and subsequent treatment with me₂SiCl₂ (me = CH₃) yields crystalline P₄(Sime₂)₃ (m. p. 159–160°C) along with polymeric silylphosphanes. The structure is derived from ³¹P-n.m.r.and mass spectra and turns out to be analogous to P₄S₃.     

DFT(B3LYP) calculations of silatranes and their radical cations. First ionization potentials

DFT(B3LYP) and 2 quantum chemical calculations have been performed for 1-substituted silatranes XSi(OCH₂CH₂)N (X = H, CH₃, CH₂Cl, F), their radical cations, and first ionization potentials (IP₁) of these silatranes. The calculated values of IP₁ agree well with the experiment and make it possible to assign the first band to IP₁ in the photoelectron spectra. Analysis of spin density distribution and electronic charges in the radical cations suggests that ionization occurs mainly due to the lone electron pair of nitrogen, participating in intramolecular coordination. The N → Si interaction is broken, and the N...Si distance increases to 335–340 pm.     

Silylene additions to cyclopentadiene and 1,3-cyclohexadiene. Evidence for the addition mechanism

Additions of SiH₂, SiCl₂ and Si(CH₃)₂ to cyclopentadiene and of Si(CH₃)₂ to 1,3-cyclohexadiene were carried out by copyrolysis of an appropriate disilane and the diene. All observed products are believed due to 1,2-addition of silylenes forming bicyclic vinylsilacyclopropane derivatives which undergo non-concerted rearrangements.     

Metal-containing initiator systems. V. Radical and cationic polymerizations with initiator systems of reduced nickel and chlorosilanes

The polymerizations of methyl methacrylate, styrene, and isobutyl vinyl ether with the binary systems of reduced nickel and chlorosilanes [(CH₃)_nSiCl_4?n, n = 0–3] have been investigated. It was found that these systems could act as both radical and cationic initiators, depending on the nature of vinyl monomers used. The kinetic investigations indicated that methyl methacrylate polymerized via a radical mechanism, and the initiating activity of chlorosilanes decreased in the following order: SiCl₄ > CH₃SiCl₃ > (CH₃)₂SiCl₂ > (CH₃)₃SiCl ? 0. Cationic initiations were observed in the polymerizations of styrene and isobutyl vinyl ether. In the latter case, the activity of chlorosilanes was in the following order: (CH₃)₃SiCl > (CH₃)₂SiCl₂ > CH₃SiCl₃ ? SiCl₄. From the results obtained, a possible mechanism of selective initiation with these systems is proposed and discussed.     

Shape resonance energies in the Xα scattered-wave cluster model. A study of CO and N2 adsorbed on Ni surfaces

Xα scattered-wave calculations have been performed to compare the photon energy dependence of the valence level photoionization cross sections of molecular CO and N₂ and of Ni clusters simulating the adsorption of these molecules in the range of the shape resonances. Care has to be taken to avoid muffin-tin artifacts, and a suitable means is comparison of the chemosorption cluster with a model cluster whose outer sphere is enlarged to match that of the former. By this scheme, the observed chemisorption-induced shifts of the shape resonance energies to higher values can be accounted for quantitatively for N₂ and qualitatively for CO. Changes of resonance widths and of $\text{4}\text{σ}\text{/5}\text{σ}$ peak height ratios are reproduced semi-quantitatively.     

Synthesis,Crystal Structure,and Spectroscopic Characterization of the Borazine Derivatives [B{CH2(SiCl3)}NH]3 and [B{CH2(SiCl2CH3)}NH]3

The borazine derivatives B, B′, B″‐tris[(trichlorosilyl)methyl]borazine [B{CH₂(SiCl₃)}NH]₃ ( 1 ), and B, B′, B″‐tris[{dichloro(methyl)silyl}methyl]borazine [B{CH₂(SiCl₂CH₃)}NH]₃ ( 2 ) were prepared by reacting (Cl₃Si)CH₂(BCl₂) ( 3 ) and [Cl₂(CH₃)Si]CH₂(BCl₂) ( 4 ) with hexamethyldisilazane (hmds), respectively. Both compounds, 1 and 2 crystallize in space group R3c with a = 1712.53(4), c = 1230.33(4) pm, Z = 6, R₁ = 0.030, and a = 1713.8(2), c = 1258.7(2) pm, Z = 6, R₁ = 0.034, respectively. According to the single crystal X‐ray diffraction analyses, the title compounds show a planar B₃N₃ six‐membered ring with B—N distances of 142.3(3) pm (point symmetry C₃) and synfacial oriented substituents. The borazine derivatives have also been characterized by NMR and IR spectroscopy as well as by MS spectrometry.     

Photopolymerization of vinyl monomers in the presence of chlorosilane compounds

The photopolymerization of vinyl monomers (methyl methacrylate and styrene) was investigated in the presence of chlorosilane compounds. It was found that these additives acted as photosensitizers. In the case of the photopolymerization of methyl methacrylate, the rate of polymerization was found to be proportional to the concentration of methyl methacrylate and to the square root of the chlorosilane concentration. The chain-transfer constants of these photosensitizers, SiCl₄, CH₃SiCl₃, (CH₃)₂SiCl₂, (CH₃)₃-SiCl, and (CH₃)₄Si, with ultraviolet irradiation were 25.6 × 10^?3, 18.4 × 10^?3, 17.5 × 10^?3, 14.4 × 10^?3 and 0.5 × 10^?3, respectively, for methyl methacrylate.     

Darstellung und Eigenschaften einiger Hochchlorierter Oligosilane

Preparation and Properties of Some Highly Chlorinated Oligosilanes Tetrakis(trichlorosilyl)silane (neo-Si₅Cl₁₂) is cleaved by HCl in SiCl₄ solution to tris(trichlorosilyl)silane, HSi(SiCl₃)₃, and SiCl₄. HSi(SiCl₃)₃ and bis(trichlorosilyl)silane, H₂Si(SiCl₃)₂, can also be prepared in good yield by reaction of the methoxy compounds HSi[Si(OCH₃)₃]₃ and H₂Si[Si(OCH₃)₃]₂ with BCl₃. The mass, ¹H-n.m.r., and vibrational spectra of HSi(SiCl₃)₃ and H₂Si(SiCl₃) as well as some ¹H-n.m.r. data of HClSi(SiCl₃)₂, HCl₂SiSiCl₃ and H₂ClSiSiCl₃ are reported and discussed. An improved synthesis for neo-Si₅Cl₁₂ is given.     

Angle-resolved photoelectron measurements on the 2p orbitals of Si in SiF4 and Si(CH3)4 in the gas phase

Angle-resolved photoelectron measurements have been carried out on the 2p orbital of Si in the gas-phase molecules SiF₄ and Si(CH₃)₄ as a function of energy from 3 to 45 eV above the ionization threshold. From these data the angular distribution parameter, β, has been obtained. Below a photoelectron energy of 15 eV the angular distribution parameter for these two molecules differ by as much as 0.4 units. The differences in the behavior of β near threshold for the two molecules is attributed to the different molecular environment of the silicon atom. To test this idea, calculations have been made on β for neutral and charged atomic silicon.