Disilicon Complexes with Two Hexacoordinate Si Atoms: Paddlewheel‐Shaped Isomers with (ClN4)Si?Si(S4Cl) and (ClN2S2)Si?Si(S2N2Cl) Skeletons

The reaction of 1‐methyl‐3‐trimethylsilylimidazoline‐2‐thione with hexachlorodisilane proceeds toward substitution of four of the disilane Cl atoms during the formation of disilicon complexes with two neighboring hexacoordinate Si atoms. The N,S‐bidentate methimazolide moieties adopt a buttressing role, thus forming paddlewheel‐shaped complexes of the type ClSi(μ‐mt)₄SiCl (mt=methimazolyl). Most interestingly, three isomers (i.e., with (ClN₄)Si? Si(S₄Cl), (ClN₃S)Si? Si(S₃NCl), and (ClN₂S₂)Si? Si(S₂N₂Cl) skeletons as so‐called (4,0), (3,1), and cis‐(2,2) paddlewheels) were detected in solution by using ²⁹Si NMR spectroscopic analysis. Two of these isomers could be isolated as crystalline solids, thus allowing their molecular structures to be analyzed by using X‐ray diffraction studies. In accord with time‐dependent NMR spectroscopy, computational analyses proved the cis‐(2,2) isomer with a (ClN₂S₂)Si? Si(S₂N₂Cl) skeleton to be the most stable. The compounds presented herein are the first examples of crystallographically evidenced disilicon complexes with two Si? Si‐bonded octahedrally coordinated Si atoms and representatives of the still scarcely explored class of Si coordination compounds with sulfur donor atoms.     

Overton-Region IR Registration of (≡Si–O)2Si=O and (≡Si–O)2Si〈O2〉C=O Groups on the Silica Surface

IR spectroscopy in a range of 2050–4000 cm^–1 (the range of overtones and composite frequencies) is used to study the groups (Si–O)₂Si=O and (Si–O)₂SiO₂C=O with different isotopic compositions (¹⁶O, ¹⁸O, ¹²C, and ¹³C). Analysis of the experimental data and quantum-chemical calculations of vibrational spectra for the model compounds are used to identify the IR bands. New data are obtained on the vibrational spectra of these groups. Their identification is shown to be possible in the spectral range that is convenient for the study of silica samples.     

Chlorination of charged buckyballs: reactions of C60x+ cations (x = 1–3) with Cl2, CCl4, CDCl3, CH2Cl2, and CH3Cl

The chlorination of singly and multiply charged C₆₀ cations has been investigated with the selected-ion flow tube technique. Observations are reported for the reactions of C₆₀^·+, C₆₀²⁺ and C₆₀^·3+ with Cl₂, CCl₄, CDCl₃, CH₂Cl₂ and CH₃Cl at room temperature (295 ± 2 K) in helium at a total pressure of 0.35 ± 0.02 Torr. C₆₀^·+ and C₆₀²⁺ were observed not to chlorinate, or react in any other way, with these five molecules. Chlorine also did not react with C₆₀^·3+, but bimolecular chloride transfer and electron transfer reactions, reactions that result in charge reduction/charge separation, were observed to occur with CCl₄, CDCl₃, CH₂Cl₂ and CH₃Cl. Chloride transfer was the predominant channel seen with CCl₄, CDCl₃ and CH₂Cl₂ while electron transfer dominates the reaction with CH₃Cl. These results are consistent with trends in chloride affinity and ionization energy. The reluctant chlorination of the first two charge states of C₆₀ is attributed to the energy required to distort the carbon cage upon bond formation, while the observed chloride transfer to C₆₀^·3+ is attributed to the greater electrostatic interactions with this ion.     

Peculiarities of Si and SiO2 Etching Kinetics in HBr + Cl2 + O2 Inductively Coupled Plasma

Plasma Chemistry and Plasma Processing - Peculiarities of the etching kinetics and mechanisms for Si and SiO2 in the HBr?+?Cl2?+?O2 inductively coupled plasma were...     

Synthesis and crystal structures of π complexes of copper(I) halides with diallyl disulfide 2CuX · DADS (X = Cl, Br; DADS = CH2=CH-CH2-S-S-CH2-CH=CH2)

Compounds 2CuCl · DADS (I) and 2CuBr · DADS (II) (DADS is diallyl disulfide) are prepared by the ac electrochemical synthesis, and their crystal structures are determined. The complexes are isostructural, space group P2₁/n, Z = 4; I: a = 8.995(2) Å, b = 12.541(2) Å, c = 9.644(2) Å, β = 98.74(2)°, V = 1075.3(4) ų, II: a = 9.064(2), b = 12.878(3), c = 9.832(2) Å, β = 98.61(3)°, V = 1134.7(4) ų. In complexes I and II, the tetradentate DADS ligand is chelate-bridging and is coordinated by two crystallographically independent copper atoms of two inorganic Cu₄X₄ fragments. An insignificantly distorted tetrahedral environment of each of the two copper atoms consists of the olefin group, sulfur atom, and two halogen atoms. The complexes are stabilized additionally by the formation of C-H?S hydrogen bonds involved in characteristic seven-membered rings in the structures.     

Br2+Cl2=2BrCl反应机理的理论和实验研究

用(U)MP2方法, 取6-311G*基组, 研究了反应Br2+Cl2=2BrCl的机理, 求得四中心和三中心的过渡态, 通过比较反应通道的活化能的大小, 得到如下结论: 双分子基元反应的最小活化能小于Cl2和Br2的离解能, 在没有光引发的条件下, 标题反应将以分子与分子作用形式完成; 若有光引发, Br2或Cl2先解离成原子, 再经过Br原子与Cl2反应或Cl原子与Br2反应, 能较快完成标题反应. 分别测定了光照和避光两种条件下的反应体系在412 nm处吸光度的变化, 证实了理论研究的结果.     

The unusual stability of [NpO2Cl4]2−: Synthesis and characterisation of [NpO2(DPPMO2)2Cl]2[NpO2Cl4] and [Ph3PNH2]2[NpO2Cl4]

The [NpO₂(DPPMO₂)₂Cl][NpO₂Cl₄] complex (where DPPMO₂ = bis(diphenylphosphino)methanedioxide) contains the linear neptunyl group, {NpO₂}²⁺, with two bidentate P=O donor ligands. Coordinating anion Cl^? fills the fifth equatorial coordination site yielding a complex of general formula [NpO₂(DPPMO₂)₂X]₂[Y] (1) (where X = Cl^? and Y = [NpO₂Cl₄]^2?. Reaction between our newly prepared neptunium starting material [NpO₂Cl₂(thf)]_n and phosphinimine ligand produced crystals of [Ph₃PNH₂]₂[NpO₂Cl₄] (2). Compounds 1 and 2 have been structurally characterised.     

Ab. initio calculations of Cl2SO ·nAICl3 complexes (n = 1, 2)

Fragments' of the potential energy surfaces (PES) for the SOCl₂ ·nAICl₃ (n = 1, 2) complexes were calculated by theab initio MO LCAO method using the RHF approximation for the STO-3G basis set and adding a 3d-AO for the S atom, as well as by the semiempirical MNDO method. Two local minima, assigned to the donor-acceptor complex Cl₂SO+AlCl₃ (la) and to Cl₃SOAlCl₂ (1b) were located on the PES atn = 1. Two local minima corresponding to two donor-acceptor complexes Cl₂SOAl₂Cl₆ and, were also located on the PES atn = 2. An analysis of the enthalpies of cation formation in the SOC1₂ +nAICl₃ (n = 1-3) systems calculated by theab initio method shows that the enthalpy of formation of the SOCl₊ cation atn = 2 is 17 kcal mol^–1 less than that atn = 1; the structure of the Cl₂SOAlCl₂ ⁺ cation with two strong electrophilic centers at the Al and S atoms becomes more favorable energetically atn = 3. The results of calculations for Cl₂SO ·nAICl₃ complexes by the MNDO method are in agreement with those obtained by theab initio method except for the geometry of complexes containing the Cl₃SO fragment and the charge values on the S atoms.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1116–1120, May, 1996.     

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.     

Cl2+2HI=2HCl+I2反应机理的理论研究

分别在MP2/3-21G**、CCSD(T)/3-21G**//MP2/3-21G**和B3LYP/3-21G**3种水平上, 计算研究了气相反应Cl₂+2HI=2HCl+I₂的机理, 求得一系列四中心和三中心的过渡态. 通过比较六种反应通道的活化能大小, 得到了相同的结论：双分子基元反应Cl₂+HIHCl+ICl和ICl+HII₂+HCl的最小活化能小于Cl₂、HI和ICl的解离能, 从理论上证明了反应Cl₂+2HI=2HCl+I₂将优先以分子与分子作用形式分两步完成. 用内禀反应坐标(IRC)验证了MP2/3-21G**方法计算得到的过渡态.     

Cooperative photoproduction of Xe2+Cl− in liquid Cl2/Xe solutions: Stimulated emission and gain measurements

Cooperative photogeneration of Xe₂⁺Cl⁻ can be accomplished by near UV laser excitation of Cl₂/Xe solutions with a high quantum efficiency. Gain measurements on the Xe₂⁺Cl⁻ (4²Γ) transition are reported. The liquid phase rare gas halides should be regarded as a family of ideal “dye” lasers.     

Vibrational spectra in the ν(SiH) and ν(SiD) regions of chloro and bromodisilanes and ab initio geometry studies of C2H5Cl,Si2H5Cl and 1,1-Si2H4Cl2

Infrared measurements in the gas phase are reported for the ν(SiH) and ν(SiD) regions of Si₂H₅X, Si₂D₅X, 1,1-Si₂H₄X₂ and 1,1-Si₂D₄X₂ species where X = Cl, Br. Incomplete Raman data have also been obtained. All three possible isolated SiH stretching frequencies are observed in the spectra of the Si₂D₄X₂ samples, but only two from the Si₂D₅X ones. The missing ν^is(SiH) values are obtained by use of the frequency sum rule, and by harmonic local mode force field treatments of all the available ν(SiH) and ν(SiD) data, using a procedure previously tested on disilane.Ab initio calculations of the geometries of C₂H₅Cl, Si₂H₅Cl and 1,1-Si₂H₄Cl₂ using the 6-31G* basis set are reported. Trends in r_e(CH) or r_e(SiH) values reflect trends in ν^is(CH) or ν^is(SiH) ones. The alpha, trans and gauche effects of halogen are similar in CH and SiH compounds, although smaller in the latter. In both cases, ab initio calculations predict larger effects than are observed in the spectra, especially for the α effect of halogen.A kinetic isotope effect in the halogenation of disilane may occur. Reassignment of earlier spectra of disilyl iodide species is proposed.     

为什么Si=Si重键难以形成?

硅是一种在地壳中仅次于氧的丰富元素,它的天然丰度大干它的同族元素碳约一百多倍。在我们周围的世界中,平均每四个原子就有一个是硅,所以硅单质及硅的化合物理应在化学领域中占有重要的地位。事实上单质硅及其化合物具有极其重要的工业价值,在许多现代工业中得到广泛应用。如水泥、陶瓷、玻璃、半导体材料等工业领域,尤其是近年来发展起来的硅珙产品,对现代工业更是有着巨大的贡献。如硅油可作织物、纸张处理剂、打光剂、消泡剂、脱模剂及润滑剂等。硅树脂可作为高级绝缘材料,用于电器及建筑方面,能耐高温、防潮、防水、防锈。硅橡胶具有优异的耐热、耐寒性和耐化学腐蚀的性能,作为性     

Unimolecular reactions in the CF3CH2Cl ↔ CF2ClCH2F system: isomerization by interchange of Cl and F atoms

The recombination of CF(2)Cl and CH(2)F radicals was used to prepare CF(2)ClCH(2)F* molecules with 93 ± 2 kcal mol(-1) of vibrational energy in a room temperature bath gas. The observed unimolecular reactions in order of relative importance were: (1) 1,2-ClH elimination to give CF(2)═CHF, (2) isomerization to CF(3)CH(2)Cl by the interchange of F and Cl atoms and (3) 1,2-FH elimination to give E- and Z-CFCl═CHF. Since the isomerization reaction is 12 kcal mol(-1) exothermic, the CF(3)CH(2)Cl* molecules have 105 kcal mol(-1) of internal energy and they can eliminate HF to give CF(2)═CHCl, decompose by rupture of the C-Cl bond, or isomerize back to CF(2)ClCH(2)F. These data, which provide experimental rate constants, are combined with previously published results for chemically activated CF(3)CH(2)Cl* formed by the recombination of CF(3) and CH(2)Cl radicals to provide a comprehensive view of the CF(3)CH(2)Cl* ? CF(2)ClCH(2)F* unimolecular reaction system. The experimental rate constants are matched to calculated statistical rate constants to assign threshold energies for the observed reactions. The models for the molecules and transition states needed for the rate constant calculations were obtained from electronic structures calculated from density functional theory. The previously proposed explanation for the formation of CF(2)═CHF in thermal and infrared multiphoton excitation studies of CF(3)CH(2)Cl, which was 2,2-HCl elimination from CF(3)CH(2)Cl followed by migration of the F atom in CF(3)CH, should be replaced by the Cl/F interchange reaction followed by a conventional 1,2-ClH elimination from CF(2)ClCH(2)F. The unimolecular reactions are augmented by free-radical chemistry initiated by reactions of Cl and F atoms in the thermal decomposition of CF(3)CH(2)Cl and CF(2)ClCH(2)F.     

Preparation and x-ray structure analysis of [Rh2Cl2(μ-CO)(μ-vdpp)2] [vdpp=H2C=C(PPh2)2]

Summary The complex [Rh₂Cl₂(-CO)(-vdpp)₂] (1) (vdpp=H₂C=C(PPh₂)₂) was prepared by reaction of [Rh₂(CO)₄-(-Cl)₂] with vdpp. When (1) is allowed to stand overnight under an atmosphere of CO without stirringtrans-[Rh₂Cl₂(CO)₂(-vdpp)₂] is formed as a red precipitate in low yields. On rapid addition of CO the tricarbonyl complex [Rh₂(CO)₂(-CO)(-Cl)(-vdpp)₂]-Cl is formed instead. The chemical behaviour of the vdpp-substituted complex (1) is very similar to that of the corresponding dppm-substituted complex [Rh₂(Cl₂-(-CO)(-dppm)₂] (dppm=H₂C(PPh₂)₂). this similarity also extends to the molecular structures of both compounds. Unit cell parameters of (1): space group Pben (Z=8),a=2344.7(5),b=1506.9(7),c=3021.6(9)pm. Rh-Rh 267.4(1) pm.     

The first observation of electroluminescence from di(2-naphthyl)disilene, an Si=Si double bond-containing π-conjugated compound

Air-stable, room-temperature emissive di(2-naphthyl)disilene, protected by the bulky 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (Eind) groups, can emit light in an organic light-emitting diode, thus providing the first experimental demonstration of electroluminescence from the heavy group 14 unsaturated compounds.     

On the infrared spectra of libratory modes of H2O molecules in SrX2 · 6H2 O (X = Cl,Br)

A detailed study of the libratory modes of H₂O molecules in the i.r. spectra of SrX₂ · 6H₂O (X = Cl, Br) is reported. The rocking, wagging and twisting libratory modes of (H₂O)_b (bridging type bonding) and (H₂O)_t (terminal type bonding) molecules are assigned at 705, 552, 658 and 460, 400, 438 cm⁻¹ and at 687, 532, 625 and 448, 370, 405 cm⁻¹ in the respective spectra. Using a semi-empirical relation reported by the authors in an earlier communication, the barrier height for (H₂O)_b is estimated to be 22.16 and 20.04 kcal/mole and that for (H₂O)_t to be 10.04 and 8.64 kcal/mole in the respective salts. The value of the force constants K_H and K_H′ for H₂O molecules are also reported.     

Hydrogenation of the silanone groups (≡Si-O)2Si=0. Experimental and quantum-chemical studies

The reactivity of bis(siloxy)silanone groups (Si-0)₂Si=O stabilized on a silica surface with respect to H₂ molecules was studied. The reaction was found to give the (Si-O)₂SiH(OH) groups. The rate constant for this process was determined. Its activation energy in the 300–580 K temperature range is 13.4±0.3 kcal mol^–1, and the enthalpy is 54±5 kcal mol^–1. The activation energy for the reverse reaction,viz., elimination of a hydrogen molecule, is equal to 65 kcal mol^–1. Quantum-chemical calculations of hydrogenation of F₂Si=O and (HO)₂Si=O, which are the simplest molecular models of the silanone groups, were performed. Data on the geometrical and electronic structures of transition states and on the effects of substituents at the silicon atom on the reactivity of the silanone groups in this process were obtained. The optical absorption band of the surface silanone groups was quantitatively characterized. Its maximum is located at 5.65±0.1 eV; the extinction coefficient at the maximum (220 nm) is (3±0.5) · 10^–18 cm² molec.^–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1951–1958, August, 1996.     

The structures of X2[(Mo6Cl8)Cl6]·nH2O,X=NH4, K,Rb, Cs

The title compounds were synthesized from MoCl₂ and the appropriate commercial chlorides and their structures were solved by a combination of single crystal X-ray diffraction analysis and theoretical methods. The NH₄, K and Rb compounds are essentially isostructural, and crystallize in space group Ia (No. 9) with the cell parameters (in Å) a=9.173(1), b=14.986(2), c=17.505(3), β=92.94(2)° (NH₄); a=9.140(4), b=14.852(5), c=17.445(11), β=93.48(6)° (K); a=9.215(1), b=14.941(3), c=17.532(2), β=92.70(1)° (Rb); while the Cs compound crystallizes in space group P2₁/n (No. 14) with the cell dimensions a=9.771(3), b=12.984(4), c=21.535(4), β=90.81(3)°.