High-resolution solid-state MAS 73Ge NMR spectra of some organogermanes

High-resolution solid-state magic angle spinning (73)Ge NMR spectra of some organogermanium compounds were measured. Most tetrasubstituted germanes with identical substituents exhibited signals except for one case. Tetrasubstituted germanes with two kinds of different but somewhat similar substituents exhibited broad peaks. Trisubstituted germanes failed to show signals, indicating the importance of symmetry around germanium.     

29Si NMR谱对[SiW11(CH3SiOSiCH3)O39]4-结构的验证

Keggin结构杂多酸的有机衍生物[SiW_(11)(RSiOSiR)O_(39)]~(4-)(R=C_2H_5、C_6H_5、NC(CH_2)_3、C_3H_7)已有报道,根据其红外光谱中出现1040cm~(-1)(Si-O-Si的振动峰),Knoth提出了图1的结构。从中可以看出RSiOSiR基占据了Keggin结构杂多酸[SiW_(11)O_(39)]~(8-)的空缺齿顶位置。当然处于齿顶位置的硅原子和中心位置的硅原子的化学环境显然是不同的,所以可用~(29)Si NMR来鉴定这两种硅原子,并推测其结构。     

Allowed transitions in silicon isoelectronic ions

Dipole‐allowed transitions have been studied for the first few members of the Si isoelectronic sequence. Transition energies, oscillator strengths, transition probabilities and quantum defect values have been estimated for the low‐ and high‐lying excited states of s and d symmetries up to the principal quantum number n=7 for these 3p open shell ions from P⁺ to Cr¹⁰⁺. Time‐dependent coupled Hartree–Fock (TDCHF) theory has been utilized to calculate such transition properties. Most of the results for transition energies, oscillator strengths, and transition probabilities for higher excited states are new. The transition energies for low‐lying excited states agree well with experimental data wherever available. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Silicon-29 NMR Study of Alkali-Exchanged NaY Zeolites

High-resolution solid-state ²⁹Si NMR has been applied to the study of partially exchanged Li, K, and Cs NaY zeolites. The order of the ²⁹Si chemical shifts of dehydrated samples is Li, Na-Y < Na-Y < K, Na-Y. The correlation between the ²⁹Si chemical shift and the Li or K loading on Li, Na-Y or K, Na-Y was rationalized in terms of the interaction between the framework and the cations inside the small cages. Because of the restrictive migration of large Cs⁺ ions from the supercages to the small cages, the ²⁹Si chemical shift of Cs, Na-Y was found to be similar to that of Na-Y.     

Studies on Natural CXN Zeolite： Modification, Framework De-alumination and Ion-exchange

A natural CXN zeolite (stilbite, type code-STI) discovered in China was modified with NH4^ exchange by using ammonium salt and calcinations (procedure Ⅰ), or with NH4 exchange followed by treatment with acid (procedure Ⅱ). The coordination state of Si and A1 atoms in the framework, the property of ion exchange, and the adsorption of the H-STI zeolite samples prepared by different modification procedure were investigated with XRD,EDX,^29Si and ^27Al MAS NMR, Ag^ ion exchange and Ne adsorption. The results of the investigations indicate that different procedure of the modification made variety on the distribution of the framework Si atoms and A1 atoms,the content of non-framework aluminum, and the blocking channels and the shielding effect to the positions of the exchangeable cations. The H-STI zeolite prepared by the procedure Ⅱ possesses high ion exchange capacity, open and perfect pore system, and high thermal stability.     

Zur Bildung und Struktur der Phosphinophosphiniden-phosphorane tBu2P?PP(Me)tBu2 1, tBu(Me3Si)P?PP(Me)tBu2 2 und tBu2P?PP(Br)tBu2 3

Synthesis and Structure of Phosphinophosphinidene-phosphoranes tBu₂P? P?P(Me)tBu₂ 1, tBu(Me₃Si)P? P?P(Me)tBu₂ 2, and tBu₂P? P?P(Br)tBu₂ 3 A new method for the synthesis of 1 and 2 (Formulae see ?Inhaltsübersicht”?) is reported based on the reaction of 5 with substitution reagents (Me₂SO₄ or CH₃Cl). The results of the X-ray structure determination of 1 and 2 are given and compared with those of 3 . While in 3 one P? P distance corresponds to a double bond and the other P? P distance to a single bond (difference 12.5 pm) the differences of the P? P distances in 1 and 2 are much smaller: 5.28 pm in 1 , 4.68 pm in 2 . Both 1 and 2 crystallize monoclinic in the space group P2₁/n (Z = 4). 2 additionally contains two disordered molecules of the solvent pentane in the unit cell. Parameters of 1 : a = 884.32(8) pm, b = 1 924.67(25) pm, c = 1 277.07(13) pm, β = 100.816(8)°, and of 2 : a = 1 101.93(12) pm, b = 1 712.46(18) pm, c = 1 395.81(12) pm, β = 111.159(7)°, all data collected at 143 K. The skeleton of the three P atoms is bent (PPP angle 100.95° for 1 , 100.29° for 2 and 105.77° for 3 ). Ab initio SCF calculations are used to discuss the bonding situation in the molecular skeleton of the three P atoms of 1 and 3 . The results show a significant contribution of the ionic structure R₂P? P(^?)? P(⁺)(X)R₂. The structure with (partially) charged P atoms is stabilized by bulky polarizable groups R (as tBu) as compared to the fully covalent structure R₂P? P(X)? PR₂.     

镓在裸Si系和SiO2/Si系掺杂效应

Based on the diffusion action of gallium in silicon and SiO2 ,a diffusion model of gallium doping in bare silicon system and SiO_2/Si system is first presented in this paper ,the gallium doping effect in the two systems is analyzed theoretically. Experiments and applications have proved that the use of the open-tube gallium deffusion in SiO2/Si system can substantially improve diffusion quality and device characteristics .     

Field and photo-field electron emission from self-assembled Ge–Si nanostructures with quantum dots

Monolayer and multilayer Ge nanocluster structures were prepared on Si(1 0 0) using molecular beam epitaxy. The cluster size was 10 nm and cluster density was 10¹⁰ cm⁻². A stable field electron emission was obtained from these structures, showing current peaks in the current–voltage characteristics, which may be attributed to the resonant electron tunneling via the energy levels of the nanocluster potential well. For cluster multilayers, the current–voltage curves also showed current peaks with a complex shape. The cluster multilayer structures had a considerable temperature sensitivity, as well as photosensitivity, in the wavelength range from 0.4 to 10 μm.     

Synthese,Kristallstruktur und festkörper‐NMR‐spektroskopische Untersuchung neuer Oxonitridosilicate der Mischkristallreihe Ba4−xCaxSi6N10O

The new oxonitridosilicates Ba_4?xCa_xSi₆N₁₀O have been synthesized by means of high‐temperature synthesis in a radio‐frequency furnace, starting from calcium, barium, silicon diimide and amorphous silicon dioxide. The maximum reaction temperature was at about 1450 °C. The solid solution series Ba_4?xCa_xSi₆N₁₀O with a phase width 1.81 ≤ x ≤ 2.95 was obtained. The crystal structure of Ba_1.8Ca_2.2Si₆N₁₀O was determined by X‐ray single‐crystal structure determination (P2₁3, no. 198), a = 1040.2(1) pm, Z = 4, wR2 = 0.082). It can be described as a highly condensed network of corner‐sharing SiN₄ and SiON₃ tetrahedra, the voids of which are occupied by the alkaline earth ions. The structure is isotypic with that of BaEu(Ba_0.5Eu_0.5)YbSi₆N₁₁. In the ²⁹Si solid‐state MAS‐NMR spectrum two isotropic resonances at ?50.0 and ?53.6 ppm were observed.