Solid State Dynamic Properties of Tetrakis(trimethylsilyl)methane: High-Resolution Solid State 13C and 29Si NMR Investigations

✍ Scribed by Abil E. Aliev; Kenneth D.M. Harris; David C. Apperley; Robin K. Harris

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 298 KB
• Volume: 110
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1994.1174

✦ Synopsis

The dynamic properties of solid tetrakis(trimethylsily))methane (\left(\mathrm{C}\left(\mathrm{Si}\left(\mathrm{CH}{3}\right){3}\right){4} ;\right.) TTMSM) have been determined using high-resolution solid state ({ }^{13} \mathrm{C}) and ({ }^{29} \mathrm{Si}) NMR spectroscopy. TTMSM is known to undergo a phase transition from a high-temperature "rotator" phase, in which there is isotropic reorientational motion of the molecule within the solid, to a low-temperature phase in which the molecular motion becomes anisotropic. In this low-temperature phase, one (\mathrm{SiMe}{3}) group of the TTMSM molecule becomes inequivalent from the other three (\mathrm{SiMe}{3}) groups and the molecules undergo two different types of dynamic process. These are classified as (1) exchange between the crystallographically unique (\mathrm{SiMe}{3}) group and an (\mathrm{SiMe} e_{3}) group within the set of three equivalent (\mathrm{SiM} e_{3}) groups, and (2) hindered rotation of each (\mathrm{SiMe} e_{3}) group about the relevant C|central]-Si bond. The energy barriers for these dynamic processes are discussed, and the dynamic behavior of TTMSM is compared with that reported previously for solid tetrakis(trimethylsily))silane. The ({ }^{13}) C NMR results strongly suggest that the molecular symmetry of the TTMSM molecule in the low-temperature phase is (C_{3} .1994) Academic Press, Inc.