Ether-like Si-Ge hydrides for applications in synthesis of nanostructured semiconductors and dielectrics.
Hydrolysis reactions of silyl-germyl triflates are used to produce ether-like Si-Ge hydride compounds including H(3)SiOSiH(3) and the previously unknown O(SiH(2)GeH(3))(2). The structural, energetic and vibrational properties of the latter were investigated by experimental and quantum chemical simulation methods. A combined Raman, infrared and theoretical analysis indicated that the compound consists of an equal mixture of linear and gauche isomers in analogy to the butane-like H(3)GeSiH(2)SiH(2)GeH(3) with an exceedingly small torsional barrier of approximately 0.2 kcal mol(-1). This is also corroborated by thermochemistry simulations which indicate that the energy difference between the isomers is less than 1 kcal mol(-1). Proof-of-principle depositions of O(SiH(2)GeH(3))(2) at 500 degrees C on Si(100) yielded nearly stoichiometric Si(2)Ge(2)O materials, closely reflecting the composition of the molecular core. A complete characterization of the film by RBS, XTEM, Raman and IR ellipsometry revealed the presence of Si(0.30)Ge(0.70) quantum dots embedded within an amorphous matrix of Si-Ge-O suboxide, as required for the fabrication of high performance nonvolatile memory devices. The use of readily available starting materials coupled with facile purification and high yields also makes the above molecular approach an attractive synthesis route to H(3)SiOSiH(3) with industrial applications in the formation of Si-O-N high-k gate materials in high-mobility SiGe based transistors.
Molecular structures of digermyl ether and digermyl sulphide in the gas phase, studied by electron diffraction
The structures of digermyl ether and digermyl sulphide have been determined in the gas phase by the sector microphotometer method of electron diffraction. The principal parameters for digermyl ether are: r(Ge–O)= 1·766 ± 0·004 A, r(Ge–H)= 1·531 ± 0·011 A, ∠(Ge–O–Ge)= 126·5 ± 0·4°: for digermyl sulphide, r(Ge–S)= 2·209 ± 0·004 A, r(Ge–H)= 1·512 ± 0·016 A, ∠(Ge–S–Ge)= 98·9 ± 0·3°.
New Sweet-Tasting C21-Pregnane Glycosides from Pericarps of Myriopteron extensum.
Ten novel C21 pregnane glycosides, extensumside C-L (1-10), were isolated as highly sweet-tasting substances from the edible pericarps of Myriopteron extensum (Wight) K. Schum by sensory-guided fractionation and purification. Their structures were determined through 1D and 2D NMR, such as HSQC, HMBC, 1H-1H COSY, HSQC-TOCSY, and ROESY, as well as other spectroscopic analysis combined with chemical evidence. These compounds shared the same aglycone, 3β,16α-dihydroxy-pregn-5-en-20-one, and contained the deoxysugar chain and the glucose chain which were linked to C-3 and C-16 of the aglycone, respectively. The sweetness potency was evaluated by a human sensory panel test and preliminary structure-taste relationship was discussed. The sweetness intensities of these compounds are between 50 and 400 times greater than that of sucrose. Furthermore, quantitation analyses of compounds 1, 3, 4, and 6 in different parts of M. extensum indicated that the concentrations of these sweet components in the pericarps are obviously higher than those in stems and roots.