Germanium oxide structure

Ni [182], V [183], and A1 [184]. SU-M [185] is a mesoporous germanium oxide with crystalline pore walls, possessing one of the largest primitive cells and the lowest framework density of any inorganic material. The channels are defined by 30-rings. Structural and thermal information show that there exists a mismatch between framework stability and template decomposition. The latter requires temperatures higher than 450 °C, while the structure is preserved only until 300 °C. 

The heat effect is one of the main characteristics of every chemical process. The heat effects of the reactions occurring at the solid surface and involving gas-phase molecules can be directly measured. To do this, one must know the amount of heat release during the reaction (microcalorimetry) and the number of absorbed gaseous molecules (volumo-metry). The heat effects of some reactions proceeding at the surfaces of activated silicon and germanium oxides and accompanied by the modification of the chemical structure of active sites are given in Table 7.4. 

This unusual reaction has been proposed to occur via a four-center mechanism131. While no structural information was derived from the original experiments, calculations at the HF level predict that a linear structure corresponding to protonated germanium oxide, GeOH+, is considerably more stable than the alternative linear HGeO+ structure151. 

Germanium oxide, GeOg differs from Si02 in that in addition to a quartz type structure in which the coordination numbers of germanium and oxygen are respectively 4 and 2, there exists a second modification with a rutile structure (coordination numbers respectively 6 and 3). The reason for the formation of the second structure is not clear, but it may be due to an increased contribution from the ionic form of the GeO bond. 

The polycondensation of BHET to PET proceeds in the melt at temperatures of 270-305 °C, under vacuum (< 1 mbar absolute pressure) and in the presence of Lewis acid metal compounds, such as titanium alkoxides, dialkyltin oxide, gallium oxide, germanium oxide, thallium oxide, lanthanide salts, and most commonly, antimony oxide [1,2, 22-26]. Under polymerization reaction conditions, these catalysts are generally converted to their alkoxides with ethylene glycol. Typical of such alkoxides is antimony(III) glycolate, the active catalyst for the majority of the world s PET production [27] (cf. Structure 1). 

For the first time, a zeolite having three interconnected channel systems of different pore entrances (ITQ-22) was synthesized possessing 8-, 10 and 12-membered ring channels [39J. l,5-bis-(methylpyrrolidinium)-pentane was used as a structure-directing agent. It was found that germanium oxide controls and probably also stabilizes the formation of D4R units of this zeolite structure. 

Sayers DE, Hesterberg D, Zhou W, Robarge WP, Plummer GM (1997) XAFS characterization of copper contamination in the unsaturated and saturated zones of a soil profile. J de Physique IV 7 (Colloque C2, X-Ray Absorption Fine Structure, Vol. 2) 831-832 Sayers DE, Lytle FW, Stem EA (1972) Structure determination of amorphous germanium, germanium oxide, and germanium selenide by Fourier analysis of extended X-ray absorption fine structure (EXAFS). J Non-Crystal Solids 8-10 401-407... 

A bis(chelate) structure was found for the closely related germylene [MeC(NPr )2]2Ge, which was also made from GeCl2(dioxane) and 2 equivalents of the lithium amidinate (colorless crystals, 81%). The same synthetic approach was used to make bis(amidinato) metal dichlorides of silicon and germanium in high yields (83-95%). Rapid oxidative addition of chalcogen atom sources (styrene sulfide and elemental Se) to the germylene derivatives resulted in a series... 

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