Variable‐temperature ¹³C CP/MAS study of (Me₃Sn)₂CO₃

Abstract

Solid (Me,Sn),CO,, 1, forms polymeric zig-zag chains were bidentate M e , S n --O -C p units (containing a 0 tetrahedral Me,Sn group) connect trigonal-bipyramidal Me,SnO, units which form the polymeric backbone. Both the tetrahedral and the trigonal-bipyramidal Me,Sn moiety in solid 1 undergo 2n/3 reorientation around their respective Sn-0 bonds at ambient temperature. Although "C cross-polarization magic angle spinning (CP/MAS) spectra of 1 are strongly temperature dependent in the temperature range 160-383 K, neither lineshape analysis of these exchange-broadened 13C spectra nor 2D exchange spectroscopy allows the extraction of meaningful kinetic data for solid 1. Owing to severe overlap problems in the various "C CP/MAS spectra and because of the apparent vastly different 2n/3 jump rates for the two different Me,Sn units in solid 1, only combined information from variable-temperatureIvariable-r.f. irradiation strength 13C CP/MAS experiments in conjunction with consideration of geometric information from single-crystal x-ray difbaction yields an estimate of the respective activa-

Water in Silicate Glass: 17O NMR of Hydrous Silica, Albite, and Na2Si4O9 Glasses

“…For the dry glass, almost equal amounts of Q 3 and Q 4 species were observed as expected from the stoichiometry of this glass; that is, [NBO]/[Si] = 0.5. On the other hand, the hydrous glass shows Q 2 species in addition to the Q 3 and Q 4 species, which is consistent with the previous 29 Si NMR and CP MAS NMR investigations. , This suggests formation of silanol (Si−OH) groups in this glass. The amount of silanol groups in this glass was estimated by using the relative peak intensities of the Q n species and by assuming that additional nonbridging oxygens were generated by the introduction of water molecules, forming silanol groups.…”

“…However, for high water contents corresponding to solubilities at higher pressure, both hydroxyl and molecular H 2 O groups were found in the hydrous glasses, the ratio of molecular water to hydroxyl groups increasing rapidly with increasing water content. Recent 1 H and 2 H NMR measurements [25][26][27][28][29][30] are consistent with the IR analysis and indicate that low levels of water (2-4 wt %) are mainly present as OH groups, whereas at higher concentrations molecular H 2 O species dominate. Within binary alkali and alkaline earth silicates, there have been several IR and Raman spectroscopic studies of glasses with higher water contents, prepared by quenching hydrous liquids from high pressures and temperatures.…”

Cross-linked resins functionalized with triorganotin carboxylates: synthesis, characterization and preliminary catalytic screening in transesterification

“…the small CH 3 resonance correlates with a tin resonance at −1 ppm, and the two intense methyl resonances at −0.12 ppm and −0.17 ppm correlate with the tin resonances at −58 ppm and −69 ppm respectively. These chemical shifts are in the region of the chemical shift of (solid) polymeric trimethyltin formate 18 and trimethyltin carbonate, 19 compounds that contain trigonal-bipyramidal trans Me 3 SnO 2 units connected via bridging formate or carbonate anions respectively. This implies that the trimethyl derivative contains mostly associated tin carboxylate species, with two different chemical environments.…”

Intramolekulare Lithium‐Bewegungen im Kristall

“…In dieser Richtung werden wir weiterarbeiten. 1.670 (7), Sil-03 1.676(6), Si2-N1 1.661 (7), Si2-02 1.676(6), Si3-N2 1.679(6), Si3-0 3 1.674(5),Si4-N2 1.667(6),Si4-04 1.673(6), Lil-01 1.979 (12), Lil-N12.067 (13) Die Ursache der Phasenumwandlung von tetragonal nach kubisch ist also dynamischer Natur. Wir haben daher auch die Lageunordnung in der tetragonalen Phase als direkte Folge von Molekiilbewegungen gedeutet.…”