Monomeric silicon chemicals

Monomeric silicon chemicals are known as silanes. A silane that contains at least one silicon-carbon bond (e.g. Si-C2H5) is an organosilane. The carbon-silicon bond is very stable and non-polar. In the presence of an alkyl group it... 

Monomeric silicon chemicals are known as silanes. A silane has the chemical formula 1 in... 

Monomeric silicon chemicals are known as silanes. A silane has the chemical formula 1 in which Ri, R2, R3, and R4 can be the same substituent or four different substituents. The... 

The study of silicon halides began in the eady 1800s (1). Since then, essentially all of the monomeric silicon halides have been extensively studied and reported in the literature. These include mixed silicon halides and halohydrides. A large number of halogenated polysilanes have also been reported (1). Despite the extensive research in silicon halides, only two of these chemicals are produced on alaige industrial scale (excluding oiganohalosilanes). These are tetrachlorosilane [10026-04-7], SiCl and trichlorosilane [1025-78-2], HSiCl. ... 

Two major classes of hydrophobic chemical substances can be applied to glass in ultrathin layers to inhibit surface wetting. Siloxanes or polysiloxanes or silicones are polymers with a backbone of alternating silicon and oxygen atoms. These macromolecules are quite chemically inert, show resistance to water, and exhibit stability at high and low temperatures. The most common siloxane polymer, polydimethylsiloxane, is composed of the monomeric (i.e., repeating) unit illustrated in Fig. 7.5.1. 

These new silyl complexes are monomeric in benzene solution, but are dimeric in the solid state. The crystal structure of the samarium analogue (Figure 1) shows that dimers form via intermolecular Sm-CH3-Si interactions. The Sm-Si distance, 3.052 (8) A, is to our knowledge the longest metal-silicon distance known. As with other complexes that display Ln-CH3-Si interactions in the solid state, evidence for these interactions in solution is not observed in NMR spectra. The [H NMR chemical shifts for the neodymium... 

A powerful technique for investigating these different species is 29Si-NMR (see Fig. 8.1). Different lines can be observed in the 29Si-NMR spectrum of a silicate solution corresponding to the differently positioned 29Si nuclei in the (poly)sili-cate ions. The highest values for the chemical shift (8 = -71.5 ppm with respect to tetra methyl silane) are found for the monomeric silicate units while the resonances of fully condensed silicon atoms (i.e. Si-(0-Si)4 tetrasiloxy silane) are to be found at the lowest values for the chemical shift (8 = -110 ppm). 

Silicon oxide nanostruaures are prepared by local anodic oxidation on dodecyl-terminated silicon. Cationic dye molecules (Rhodamin 6G) bound electrostatically to the generated nanostructures are investigated by optical methods. Quenching of luminescence due to the interaction of the excited states with silicon can be found. The luminescence signal is attributed to monomeric Rh6G molecules with a slight blue shift of the emission due to the changed chemical environment... 

Silicone nanospheres with different particle diameters, crosslinking density, and chemical functionalization are accessible by aqueous hydrolysis-condensation sequences of silane and siloxane precursors [1-3] and subsequent isolation. Grafting of functionalized particles with organopolymers [1] or surface modification [2] results in nanosized silicone domains which are readily dispersible in monomeric and polymeric systems. A variety of these versatile, tailor-made products will soon be launched by Wacker on a commercial scale. 

Attempts to isolate 204 and 205 provide only the silanols 200 or 32. The sign and magnitude of the Si-NMR chemical shift is indicative of tetracoordinate silicon species [77], yet it does not match any of the previously synthesized tetracoordinate silanes. The possibility that 204 and 205 are oligomers was eliminated by a Si-NMR crossover experiment [30]. Structural possibilities that remained for 204 and 205 required that they be monomeric and tetracoordinate. The tetrabutylam-monium silyloxide salt ( )-206 and a TBAF hydrogen bond complex ( )-205 were proposed (Figure 7.2). The silyloxide salt is ruled out by independent synthesis of the corresponding tetramethylammonium salt, the Si-NMR chemical shift (—26.23 ppm) of which does not correspond to that for 206. Because compound... 

Most ceramics and glasses are based on silica. The problem then is to form Si-O-M bonds in the molecular precursor and to keep them during the whole hydrolysis and condensation processes. However, silicon has a rather high electronegativity (XSi=L74) and does not show any tendency toward coordination expansion. Its chemical reactivity toward hydrolysis and condensation is therefore quite low. Silicon alkoxides Si(OR)4 always exhibit a monomeric tetrahedral molecular structure and very few heterometallic alkoxides or oxo-alkoxides are formed with silicon (4). It is therefore difficult to prepare homogeneous multicomponent gels in silicate systems... 

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