Synthesis, Structure and Electrochemical Properties of Acetamide- and Caprolactam-Containing Silicon Catecholates

Hexacoordinated heteroligand silicon catecholates, although being prospective as easily soluble compounds with high hydrolytic stability and diverse redox properties, have been insufficiently studied. The transesterification of 1-(trimethoxysilylmethyl)-2-oxohexahydroaze or N-methyl-N-(trimethoxysilylmethyl)acetamide by two equivalents of catechol derivatives in the presence of dicyclohexylamine afforded a series of target compounds in good yield. The complexes were characterized using elemental analysis, FTIR, 1H, 13C and 29Si NMR spectra, X-ray crystallography and cyclic voltammetry. X-ray diffraction confirmed that the silicon atom possesses the octahedral geometry of the SiCO5 polyhedron that remains unchanged in solution as it follows from 29Si NMR data. The compounds demonstrated up to three oxidation waves; and the reduction profile strongly depended on the nature of the substituents on a catecholate anion.

The study of the modification methylphenylsiloxane resin with dimethylene links metal compounds and boric acid

In this paper we study the effect of modified metal compounds and boric асid (E), where Element = B, Ti, Zr, Al on the thermal stability of methylphenylsiloxane resins derived from alkoxysilanes. Currently interested in the reaction for producing oligosilsesquioxanes based on acidolysis alkoxysilanes. In this regard, the author was tasked with obtaining new methylphenylsiloxane resins with different properties. In this paper, we study the properties of new methylphenylsiloxane resins (MFSS), modified metal compounds and boric acid. New MFSS obtained by a new universal technology-acidolysis mixture of methyltriethoxysilane (MTEOS) and phenyltriethoxysilane (PHTEOS) with various radicals, which are environmentally friendly raw materials. The obtained MFSS were characterized by NMR spectroscopy on 1H and 29Si nuclei. The spectra were recorded at room temperature in deuteroacetone using a Bruker AM-360 Fourier spectrometer. 29Si NMR spectra were measured using the pulse program "Inverse Gated Heteronuclear Decoupling". Thermogravimetric analysis was performed on the device Derivatograph-H (firm Mom). TGA studies were carried out in the argon atmosphere and in air at a heating rate of 10 ºC/min. The acidolysis reaction of methyltriethoxysilane and phenyltriethoxysilane is a convenient and versatile method for the synthesis of new heat-resistant methylphenylsiloxane resins. In the course of the study, it was found that the resins obtained on the basis of organoalkoxysilanes are characterized by higher thermal and thermo-oxidative stability. It is shown that the modification methylphenylsiloxane resin dimethylsiloxane links in the main chain elementlocalname fragments of ≡Si-O-Element-O-Si≡, where element = B, Ti, Zr, Al increases its resistance to the level methylphenylsiloxane resin without dimethylsiloxane links.

New methylphenylsiloxane resin based on alkoxysilanes

Currently interested in the reaction for producing oligosilsesquioxanes based on acidolysis alkoxysilanes. In this regard, the author was given the following tasks: development of optimal synthesis conditions; preparation of new methylphenylsiloxane resins with different properties. In this paper, the properties of new methylphenylsiloxane resins (MPR) with various radicals in silicon were studied. New IFSS were obtained by a new universal technology-acidolysis of a mixture of methyltriethoxysilane (MTEOS) and phenyltriethoxysilane (PTEOS) with various radicals, which are environmentally friendly raw materials. The obtained MPR were characterized by NMR spectroscopy on 1H and 29Si nuclei. Spectra were recorded at room temperature in deuteroacetone using Bruker AM-360 Fourier spectrometer. 29Si NMR spectra were measured using the pulse program "Inverse Gated Heteronuclear Decoupling". The content of residual functional groups (Si-OH, Si-OEt) in IFSS was determined by functional analysis methods. Determination of ethoxy groups and hydroxy groups was carried out by iodometric and aluminohydride method, respectively. Thermogravimetric analysis was performed on the device Derivatograph-H (firm Mom). TGA studies were carried out in the argon atmosphere and in the air at a heating rate of 10 ºC/min. Measurements of kinematic viscosity of 20 % and 50% by weight. toluene solutions of MPR were carried out at 20 °C on the viscometer HPV-2. The reaction acidolysis of methyltriethoxysilane and oligophenylenes is a convenient and versatile method for the synthesis of new heat-resistant resins methylphenylsiloxanes. In the course of the study, it was found that the resins obtained on the basis of organoalkoxysilanes are characterized by higher thermal and thermo-oxidative stability.

29Si NMR Chemical Shifts in Crystalline and Amorphous Silicon Nitrides

We investigate 29Si nuclear magnetic resonance (NMR) chemical shifts, δiso, of silicon nitride. Our goal is to relate the local structure to the NMR signal and, thus, provide the means to extract more information from the experimental 29Si NMR spectra in this family of compounds. We apply structural modeling and the gauge-included projector augmented wave (GIPAW) method within density functional theory (DFT) calculations. Our models comprise known and hypothetical crystalline Si3N4, as well as amorphous Si3N4 structures. We find good agreement with available experimental 29Si NMR data for tetrahedral Si[4] and octahedral Si[6] in crystalline Si3N4, predict the chemical shift of a trigonal-bipyramidal Si[5] to be about −120 ppm, and quantify the impact of Si-N bond lengths on 29Si δiso. We show through computations that experimental 29Si NMR data indicates that silicon dicarbodiimide, Si(NCN)2 exhibits bent Si-N-C units with angles of about 143° in its structure. A detailed investigation of amorphous silicon nitride shows that an observed peak asymmetry relates to the proximity of a fifth N neighbor in non-bonding distance between 2.5 and 2.8 Å to Si. We reveal the impact of both Si-N(H)-Si bond angle and Si-N bond length on 29Si δiso in hydrogenated silicon nitride structure, silicon diimide Si(NH)2.

Diatoms response to salinity changes: investigations using single pulse and cross polarisation magic angle spinning 29Si NMR spectra

Diatoms Thalassiosira pseudonana and Chaetoceros muelleri (Bacillariophyceae) were cultured at three different salinities and examined using 29Si MAS-NMR spectroscopy.