Absorption spectra of SiCl4, Si2Cl6, SiF3CH3 and GeF4 in the VUV region

In the range 110–200 nm the absorption features of Si₂Cl₆ closely resemble those of SiCl₄ and the peaks observed are tentatively assigned to the Rydberg transitions of a Cl lone-pair electron. Two diffuse bands in the SiF₃CH₃ absorption are also assigned to Rydberg excitations. The spectrum of GeF₄ shows a broad band considered to be a valence excitation of the outermost orbital. The emission of the SiCl₂ (ùB₁→X̃¹A₁) transition was found in the photoexcitation of Si₂Cl₆.     

Die Bildungsenthalpien einiger Siliciumtetrahalogenid—Pyridin-Addukte

The enthalpies of formation of the addition compounds F₄Si(py)₂, Cl₄Si(py)₂, Br₄Si(py)₂ and I₄Si(py)₄ have been measured calorimetrically by two different ways (see table 1). It was not possible to confirm enthalpy data published in^{7, 8}. The sequence SiF₄4～SiBr₄>SiI₄(?) is proposed for the acceptor power of the silicon tetrahalides towards pyridine.     

Beiträge zur Chemie der Halogensilan-Addukte. VII [1]. 2,2′-Bipyridin-N-Oxid-Komplexe von Halogensilanen

Contributions to the Chemistry of Halogenosilane Adducts. VII. 2,2′-Bipyridine-mono-N-oxide Complexes of Halogenosilanes The new adducts SiF₄ · bipyO, SiCl₄ · bipyO, SiCl₄ · 2 bipyO, SiBr₄ · 2 bipyO, SiI₄ · 2 bipyO and SiI₄ · 3 bipyO have been prepared by the reaction of SiF₄, SiCl₄, SiBr₄ and SiI₄ with bipyO in the appropriate molar ratio. The 1:1 reaction of Si₂Cl₆ and bipyO yields the adduct Cl₃SiOSiCl₃ · bipy (reduction of the amineoxide), in a 1:2 molar ratio Cl₃SiOSiCl₃ · bipy and Cl₃SiOSiCl₃ · 2 bipyO are obtained. The latter compound is formed in the reaction of Cl₃SiOSiCl₃ · bipy and bipyO and also in the reaction of Cl₃SiOSiCl₃ and bipyO. The results show that bipyO is a stronger base than bipy with reference to the silanes investigated. Some properties of the compounds and structural investigations are reported. bipyO is chelating and silicon is hexacoordinated in all adducts. The following structures are suggested: SiX₄ · bipyO (molecular), [SiX₂ · 2 bipyO]X₂ (ionic), [Si · 3 bipyO]I₄ (ionic). In Cl₃SiOSiCl₃ · 2 bipyO both ligands are coordinated to one Si atom.     

UV photoelectron spectroscopy of transient species: germanium difluoride (GeF2)

The He(1) photoelectron spectrum of germanium difluoride (GeF₂) is reported. Results are analyzed on the basis of Hartree-Fock-Slater quantum-chemical calculations. A comparison is made with previous data for GeCl₂, GeBr₂, CF₂ and SiF₂.     

ChemInform Abstract: Structures,Energetics, and Vibrational Frequencies of the Silicon and Germanium Dichlorides and Dibromides and Their Dimers.

Ab initio Hartree-Fock calculations, performed to determine the geometries and energies of the ground singlet (1A1) and the first excited triplet (3B1) states of SiCl₂, SiBr₂, GeCl₂, and GeBr₂ and of the ground states of their dimers, show that the triplet state is not energetically accessible at the experimental temp. (600 °C) and therefore is not a possible model for the additional component in the electron diffraction radial distribution of GeBr₂.     

Umsetzung von gemischten Siliciumhalogeniden und von Halogendisilanen mit Pyridin und 1,10-Phenanthrolin

Zusammenfassung Die Reaktion gemischter Siliciumhalogenide mit Pyridin (=py) oder 1,10-Phenanthrolin (=phen) führte zu den Additionsverbindungen SiClBr₃(py)₂, SiClBr₃(phen), SiCl₃Br(py)₂, SiCl₃Br(phen), SiCl₂J₂(py)₄, SiCl₂J₂(phen), SiCl₃J(py)₃ und SiCl₃J(phen). Eine Dismutation der gemischten Siliciumhalogenide wurde dabei nicht beobachtet. Ihre Darstellung erfolgte durch Umsetzung von ClSi(Net ₂)₃, Cl₂Si(Net ₂)₂ und Cl₃Si(Net ₂) (et=C₂H₅) mit HBr oder HJ. Si₂Cl₆ reagierte mit 3py zu SiCl₄(py)₂ und 1/n [SiCl₂(py)] _n , Si₂Br₆ analog zu SiBr₄(py)₂ und 1/n [SiBr₂(py)] _n , Si₃Cl₈ mit 4py zu SiCl₄(py)₂ und 2/n [SiCl₂(py)] _n .

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The reactions of mixed silicon halogenides with pyridine (=py), or 1.10-phenanthroline (=phen) resulted in the addition compounds SiClBr₃(py)₂, SiClBr₃(phen), SiCl₃Br(py)₂, SiCl₃Br(phen), SiCl₂I₂(py)₄, SiCl₂I₂(phen), SiCl₃I(py)₃ and SiCl₃I(phen). Dismutation of the mixed silicon halogenides in these reactions was not observed. Their preparation was achieved by cleaving of Si–N-bonds in ClSi(Net ₂)₃, Cl₂Si(Net ₂)₂ and Cl₃Si(Net ₂) (et=C₂H₅) with HBr or HI. Si₂Cl₆ reacted with 3py forming SiCl₄(py)₂ and 1/n [SiCl₂(py)] _n . The analogous reaction of Si₂Br₆ resulted in SiBr₄(py)₂ and 1/n [SiBr₂(py)] _n . Si₃Cl₈ and 4py formed SiCl₄(py)₂ and 2/n [SiCl₂(py)] _n .

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Mit 1 Abbildung

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66. Mitt.:U. Wannagat, K. Hensen, P. Petesch undF. Vielberg, Mh. Chem.98, 1415 (1967).

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Zugleich 7. Mitt. über Verbindungen von Nichtmetallhalogeniden mit Pyridin und seinen Homologen; 6. Mitt.:U. Wannagat, K. Hensen undP. Petesch, Mh. Chem.98, 1423 (1967).

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Mit Auszügen aus den DissertationenF. Vielberg, Techn. Hochsch. Aachen 1956, undK. Hensen, T. H. Aachen 1962.     

Optical emission of GeF+4(D̃) produced by ion impact ionization of GeF4

Emission spectra produced by 1–20 keV He⁺, Ne⁺ and H⁺ impact on GeF₄ have been obtained and relative emission cross sections determined. By comparing the energy dependence of the ion impact data with that for charge-transfer ionization of SiF₄ leading to SiF⁺₄(D̃) and by reference to PE data of GeF₄, the 255, 290 and 420 nm emissions are attributed to D̃ → Ã, B̃ and C̃ transitions, respectively of GeF⁺₄. We found the D̃ → C̃ emission of SeF⁺₄ in the spectral region 510 to 730 nm.     

Infrared Laser Photochemistry of Trichlorosilane

IR multiphoton dissociation of trichlorosilane molecules in scavenger gas (O₂, CO₂, OCS, halomethanes, BCl₃, TiCl₄, etc.) media was studied. Stable, volatile dissociation products were determined. It was shown that the product formation mechanism depends on the partial pressure of SiHCl₃. At a high pressure (400–800 Pa) of SiHCl₃, its photolysis in a mixture with fluorine-, chlorine-, or bromine-containing scavengers led to the formation of products of the SiF_{4 – n} Cl _n and SiBr_{4 – n} Cl _n type, where n = 1–4. An SiHCl₃ conversion into SiCl₄ higher than 70% could be achieved. The formation mechanism was proposed for the photolysis products. At a low SiHCl₃ pressure (<70 Pa), the formation of a stable volatile product was observed only in a mixture with BCl₃, which resulted from the reaction of insertion of SiCl₂ in the B–Cl bond.     

Rate constants for silylene reactions

It is only since 1985 that the absolute rate constanss have been measured for some reactions of divalent silylene species. In this article the absolute rate constant data reported to date for the reactions of SiH₂, SiMe₂, SiMePh, SiHCl, SiCl₂, SiF₂ and SiBr₂ are reviewed and, where possible, mechanistic pathways discussed. The reactivity of silylenes is, in general, much higher than had previously been estimated on the basis of relative rate studies.     

Beiträge zur Chemie der Halogensilan-Addukte. VIII. Darstellung und Eigenschaften der kationischen Bis-2,2′-Bipyridin-Silicium-Komplexe, [SiCl2b[py2]2+ und [SiF2bipy2]2+

Contributions to the Chemistry of Halogenosilane Adducts. VIII. Preparation and Properties of the Cationic Bis-2,2′-Bipyridinesilicon Complexes, [SiCl₂bipy₂]²⁺ and [SiF₂bipy₂]²⁺ The reactions of SiCl₂bipy₂ (green isomer) and SiF₂bipy₂ with chlorine yield the new ionic complexes of Si, [SiX₂bipy₂]Cl₂ (X = Cl, F). Bromine and iodine react similarly. With these reagents, however, formation of insoluble polyhalides of the complex cations inevitably occurs rendering further investigations difficult. The compounds contain the cis-octahedral cation [SiX₂bipy₂]²⁺. They are soluble in methanol and water and are unusually stable in these solvents. [SiCl₂bipy₂]Cl₂ starts to react observably with methanol (substitution of SiCl) only after weeks. Thus reactions may be performed in this solvent. It follows from the investigation that the green isomer of SiCl₂bipy₂ is a cis-octahedral molecular complex of silicon. Two other green isomers of SiCl₂bipy₂ are shown to exist. The reactions of chlorine with these isomers yield products different from the cis-octahedral complex reported above. Ion-exchange and metathetical reactions of [SiCl₂bipy₂]Cl₂ yield the new compounds [SiCl₂bipy₂]X₂ (X = Br^?, J^?, NO₃^?, ClO₄^?, [Cr(NH₃)₂(NCS)₄]^?, PtCl₆^2?/2). All compounds contain the [SiCl₂bipy₂]²⁺-cation which is investigated in detail (¹H-, ²⁹Si-NMR, IR, UV, ESCA, conductivity, molecular weight). The use of AgF for the synthesis of ionic SiF-complexes (X = F) gives rise to more complicated reactions.     

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.     

Bildung siliciumorganischer Verbindungen. 110. Reaktionen von (Cl3Si)2CCl2, seiner Si-methylierten Derivate,von (Cl3Si)2CHCl, (Cl3Si)2C(Cl)Me und Me2CCl2 mit Silicium (Cu-Kat.)

Formation of Organosilicon Compounds. 110. Reactions of (Cl₃Si)₂CCl₂ and its Si-methylated Derivatives as well as of (Cl₃Si)₂CHCl, (Cl₃Si)₂C(Cl)Me and Me₂CCl₂ with Silicon (Cu cat.) The reactions of (Cl₃Si)₂CCl₂ 1 , its Si-methylated derivatives (Me₃Si)₂CCl₂ 8 , Me₃Si? CCl₂? SiMe₂Cl 9 , (ClMe₂Si)₂CCl₂ 10 , Me₃Si? CCl₂? SiMeCl₂ 11 , Cl₂MeSi? CCl₂? SiCl₃ 12 as well as of (Cl₃Si)₂CHCl 38 , (Cl₃Si)₂CClMe 39 and of Me₂CCl₂ with Si (Cu cat.) in a fluid bed reactor ( 38 and 39 also in a stirred solid bedreactor) arc presented. While (Cl₃Si)₂CCl₂ 1 yields C(SiCl₃)₄ 2 the 1,1,3,3-tetrachloro-2,2,4,4-tetrakis(trichlorsilyl)-1,3-disilacyclobutane Si₆C₂Cl₁₆ 3 and the related C-spiro linked disilacyclobutanes Si₈C₃Cl₂₀ 4 , Si₁₀C₄Cl₂₄ 5 , Si₁₂C₅Cl₂₈ 6 , Si₁₄C₆Cl₃₂ 7 this type of compounds is not obtained starting from the Si-methylated derivatives 8, 9, 10, 11 They Produce a number of variously Si-chlorinated and -methylated tetrasila- and trisilamethanes. However, Cl₂MeSi? CCl₂? SiCl₃ 12 forms besides of Si-chlorinated trisilamethanes also the disilacyclobutanes Si₆C₂Cl₁₅Me 34 and cis- and trans Si₆C₂Cl₁₄Me₂ 35 as well as the spiro-linked disilacyclobutanes Si₈C₃Cl₁₉Me 36 , Si₈C₃Cl₁₈Me₂ 37 . (Cl₃Si)₂CHCl 38 mainly yields HC(SiCl₃)₃ 31 and also the disilacyclobutanes cis- and trans-(Cl₃Si)HC(SiCl₂)₂CH(SiCl₃) 41 and (Cl₃Si)₂C(SiCl₂)₂CH(SiCl₃) 45 the 1,3,5-trisilacyclohexane [Cl₃Si(H)C? SiCl₂]₃ 44 as well as [(Cl₃Si)₂CH]₂SiCl₂, and (Cl₃Si)₂CClMe 39 mainly yields (Cl₃Si)₂C?CH₂and (Cl₃Si)₂besides of HC(SiCl₃)₃, MeC(SiCl₃)₃and (Cl₃Si)₃C? SiCl₂Me.,. Me₂CCl₂ 59 mainly yields Me(Cl)C?CH₂, Me₂CHCl and HCl₂Si? CMe₂? SiCl₃, besides of Me₂C(SiCl₃)₂ and Me₂C(SiCl₂H)₂ Compound 3 crystallizes triclinically in the space group P1 (Nr. 2) mit a = 900,3, b = 914,0, c = 855,3 pm, α = 116,45°, β = 101,44°, γ = 95,86° and one molecule per unit cell. Compound 4 crystallizes monoclinically in thc space group C2/c (no. 15) with a = 3158.3,b = I 103.7, c = 2037.4 pm, β = 1 16.62° and 8 molecules pcr unit cell. The disilacyclobutane ring of compound 3 is plane, showing a mean distance of d (Si-C) =19 1.8 pm and the usual deformations of endocyclic angles: α_Si = 94,2°> 85,8° = α_C.The spiro-linked disilacyclobutane rings of compound 4 are slightly folded by a mean angle of (19.0°). Their mean distances were found to be d (Si? C) = 190.4 pm relating to the central carbon atom and 192.0 pm to the outer ones, respectively. The deformations of endocyclic angles: α_Si = 93,9°> 84,4° = α_C are comparable to those of compound 3.     

Microwave Interferometry of Chemically Active Plasma of RF Discharge in Mixtures Based on Fluorides of Silicon and Germanium

The free electron concentration in hydrogen and chemically active plasmas in H₂ + SiF₄ and H₂ + GeF₄ mixtures was measured by microwave interferometry. The investigations were carried out under conditions of a RF capacitive-coupled discharge at a pressure of 1 Torr. In hydrogen plasma the concentration of free plasma electrons is 1.5 ± 0.03 × 10¹² cm^?3. When the fluoride is added to the hydrogen plasma, the electron concentration is reduced to 1.1 ± 0.05 × 10¹² cm^?3 for SiF₄ and 9.8 ± 0.05 × 10¹¹ cm^?3 for GeF₄. It is suggested that the main mechanism responsible for reducing the concentration of free electrons is the mechanism of dissociative attachment of electrons to SiF₄ and GeF₄ molecules. The difference in the electron concentration for these mixtures is due to the difference in the electron-acceptor ability of the SiF₄ and GeF₄ molecules determined by the affinity for the electron.     

Fragmentation behavior of Si2Cln+ cations (n = 1—6)

Sector-field mass spectrometry was used to probe the fragmentation patterns of the cationic silicon chlorides Si₂Cl_n ⁺ (n = 1—6). For almost all Si₂Cl_n ⁺ ions, Si—Si fragmentation predominates the Si—Cl bond cleavage both in the metastable ion and collisional activation mass spectra. Analysis of the fragmentation patterns indicates that the long-lived radical cation Si₂Cl₆ ^·+ corresponds to a complex [SiCl₂·SiCl₄]^·+ rather than the intact molecular ion of hexachlorodisilane. The behavior of Si₂Cl₅ ⁺ is consistent with the formation of the (trichlorosilyl)dichlorosilyl cation Cl₃SiSICl₂ ⁺. Structural aspects are also discussed for the other Si₂Cl_n ⁺ species. A semi-quantitative analysis of the fragmentation patterns in conjunction with the literature thermochemistry data was used to estimate some thermochemical properties of the Si₂Cl_n ⁺ cations.     

Density functional investigation of the molecular geometries,harmonic vibrational frequencies,singlet-triplet energy separations,adiabatic ionization potentials,and electron affinities of XY2 (X = Si,Ge, Sn; Y = F,Cl) systems

The geometrical and spectroscopic parameters of SiF₂, SiCl₂, GeF₂, GeCl₂, SnF₂, and SnCl₂ were determined using the linear combination of Gaussian-type orbitals-local spin density (LCGTO-LSD) method and employing both the local (LSD) and nonlocal functionals (NLSD) for the exchange-correlation energy. A general good agreement with available experimental information and with previous high-level correlated computations was found. Data on cations and anions are reported for the first time and can be used, together with those on neutral systems, to stimulate future and desirable experimental work on this significant class of molecules. © 1997 John Wiley & Sons, Inc.     

Flash photolysis of SiBr4: the UV spectrum of SiBr2

In the flash photolysis of SiBr₄ both the absorption and the emission spectra corresponding to the B̃²Σ−X̃²Π transition of SiBr have been observed. A broad, structureless absorption band has also been detected in the 340–400 nm region which could be assigned to the hitherto unreported à ¹B₁−x̃ ¹A₁ transition of SiBr₂. The decay of both absorption spectra followed first-order kinetics yielding the pseudo-first-order rate constants: k(SiBr)=2.6 × 10⁴s⁻¹ and k(SiBr₂) = 8.9 × 10³⁻¹. Assuming that the principal reactions consuming these intermediates are SiBr+SiBr₄→Si₂Br₅ and SiBr₂+SiBr₄→ Si₂Br₆, the second-order rate constants have the values k(SiBr)= 9.7×10⁹ M⁻¹s⁻¹ and k(SiBr₂)= 3.3×10⁸M⁻¹s⁻¹.     

Plasmachemistry. Formation of Chlorosilazanes,Chlorogermazanes and Related Compounds

The plasmachemically activated reaction between N₂ and SiCl₄ leads via nitrogen atoms to numerous chlorosilazanes: NSi₃Cl₉, N₂Si₄Cl₁₀, NSi₄Cl₁₁, N₂Si₄Cl₁₂, N₂Si₅Cl₁₄, N₃Si₆Cl₁₅ (3 isomers), N₂Si₆Cl₁₆ and some related compounds (NOSi₄Cl₁₁, N₂O₂Si₆Cl₁₄, N₂OSi₅Cl₁₂). GeCl₄ shows an similar behaviour. This could be shown by GC/MS‐investigations. The structures of N₂Si₅Cl₁₄, N₂Si₆Cl₁₆ and N₃Si₆Cl₁₅ have been determined by quantum chemical methods. The angle sums around the N atoms are close to 360°.     

The microwave spectrum of dichlorosilylene (SiCl2) in excited vibrational states

The microwave spectrum of dichlorosilylene in excited vibrational states has been measured in the millimetre- and submillimetre-wave regions. Rotational and centrifugal distortion constants were determined for the ν₁, ν₂, 2ν₂ and ν₃ excited states of the Si³⁵Cl₂ isotopic species and for the ν₂ and 2ν₂ states of Si³⁵Cl³⁷Cl. Analysis of the Coriolis resonance between the ν₁ and ν₃ states of Si³⁵Cl₂ yielded values of the D Coriolis interaction constant with F constrained, of two higher-order terms and also an accurate value [5.402338(95) cm⁻¹] of the energy difference between the two excited vibrational states. The rotational constants of Si³⁵Cl₂ in the first excited states of the three normal vibrations were combined with those of the ground vibrational state reported in a previous paper [M. Tanimoto et al., J. Chem. Phys. 91, 2102 (1989)] to obtain the equilibrium structure, harmonic and cubic/third-order anharmonic potential constants.     

Zum chemischen Transport der Vanadiumsilicide

Chemical Transport of Vanadium Silicides Vanadium silicides VSi₂, V₅Si₃, and V₃Si have been prepared by chemical transport with Cl₂ and SiCl₄, respectively. X-ray diffraction patterns and measurements of superconductivity were used for the characterization of the individual phases formed in the transport tubes. Siliconrich VSi₂ and nonstoichiometric V₃Si cannot be transported with Cl₂ or SiCl₄. The sequence, direction and rate of transport agree with the results of thermodynamic calculations.     

Über Ligandenumverteilungsreaktionen an ternären Siliciumtetrahalogeniden in Gegenwart von Pyridin

On Ligand-Rearrangement-Reactions at Mixed Silicon Tetrahalides in the Presence of Pyridine The exchange of substituents on mixed silicon tetrahalides completely takes place after few hours in CHCl₃ at 334 K in presence of small quantities of pyridine or pyridinium salts. The exchange equilibria does not deviate much from the values expected from ideal random sorting. Mixed silicon tetrahalides are stable for some days at 298 K in CHCl₃ in presence of pyridine or pyridinium salts respectively, so that by the reaction of binary silicon tetrahalides (SiBr₄, SiI₄) with (pyH)Cl all mixed silicon tetrahalides may be identified side by side. A separation by destillation of the mixtures is impossible because of easy dismutation reactions in presence of pyridine. The influence of pyridine takes place presumable above the formation of addition compounds.