Silicon germanium compounds determination

Multinuclear ( H, 13C, nB) NMR spectroscopy is undoubtly the most useful and powerful method for the investigation of the organoboration of 1-alkynyltin, -germanium, and -silicon compounds allowing not only the structure of the final products to be determined but also the product ratio to be ascertained (Tables 6-8). 

It is generally accepted that multinuclear NMR spectroscopy is a very useful means to prove whether a hypercoordinated state is involved or not. Thus, hypercoordination is often associated with a low frequency shift of the Si signal in the case of silicon compounds. A large line broadening was also reported for germanium hypercoordination. Takeuchi et al. determined the Ge chemical shifts and linewidths for aU of the compounds they prepared.In addition, they prepared and determined the Ge NMR spectra of 66, 93, 96 and other compounds for reference. The results are summarized in Table 10. 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

Electron diffraction determinations " Intermolecular contacts in Table 11 Silicon-transition-metal compounds in Table 10 Averaged two-bond contacts between oxygen and silicon or germanium Mes = 2,4,6-trimethylphenyl See the text... 

The most commonly measured property for these types of molecules is their dissociation energy or atomization energy. According to a recent review ( ) these have been experimentally determined for approximately 50 homonuclear diatomic metal molecules, 15 polyatomic metal molecules (including germanium but excluding silicon and antimony), 110 diatomic intermetallic compounds and more than 20 polyatomic intermetallic molecules. 

The Gutzeit method was applied in determinations of arsenic i.a. in germanium and its compounds [49], silicon [49,50], and petroleum products [48]. 

In the analysis of a number of materials (e.g., silicon- and germanium compounds and volatile reagents) traces of boron are pre-concentrated and boron is then separated by volatilization of the matrix. Mannitol, which forms a non-volatile complex with boric acid, is added to retain all the boron present in the residue [20]. Boron is fairly volatile in acidic media. While boron traces are determined in chlorosilanes, it is advisable to add some chlorotriphenylmethane [21], which forms a non-volatile compound with boron thus preventing its volatilization, when the matrix is evaporated. Ref. 21 is not cited. 

The most famous of Mendeleev s predictions involved eka-boron (scandium), eka-aluminium (gallium), and eka-silicon (germanium). For example, for eka-silicon he predicted its atomic weight, its density, the compounds it would form, and details about their physical properties. When thirteen years later germanium was discovered and it was determined that Mendeleev s predictions had been correct, scientists began to recognize the importance of the Periodic Table, and its discovery was quite naturally associated with Mendeleev, who encouraged this association. 

Miscellaneous Physical Measurements.— In this section are included physical data not previously mentioned. Binding energies of silicon, germanium, tin, and lead compounds have been determined by X-ray photoelectron spectros-copy. The enthalpies of formation of several trimethyl-silyl, -germyl. 

Three of these elements were soon discovered (they were named scandium, gallium, and germanium by their discoverers), and it was found that their properties and the properties of their compounds are very close to those predicted by Mendelyeev for eka-boron, eka-aluminum, and eka-silicon, respectively. Since then the elements technetium, rhenium, and protactinium have been discovered or made artificially, and have been found to have properties similar to those predicted for eka-manganese, dvi-manganese, and eka-tantalum. A comparison of the properties predicted by Mendelyeev for eka-silicon and those determined experimentally for germanium is given below. 

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