Spektroskopische Untersuchungen an Siliciumverbindungen XVII. Spektroskopische Untersuchungen an Silanolen

Abstract

Dargestellt sowie infrarot‐ und ramanspektroskopisch untersucht wurden die Silanole (CH3)3SiOH, (C2H5)3SiOH, (n‐C3H7)3SiOH, (n‐C4H9)3SiOH, (C6H5)3SiOH, (C6H5)2CH3SiOH, C6H5(CH3)2SiOH, (CH3)3SiOD und (C2H5)3SiOD. In den IR‐Spektren der Silanole treten bei Konzentrationsänderungen in Lösung in zwei Gebieten bei einigen Banden Frequenz‐ und Intensitätsänderungen auf. Es wurde versucht die Banden so weit als möglich zuzuordnen.

Effect of the Silyl Substitution on Structure and Vibrational Spectra of Hydrogen-Bonded Networks in Dimers, Cyclic Trimers, and Tetramers

“…Despite the pronounced dependence of the δ SiOH mode on the cluster size, this feature hardly may be used for the identification of oligomers of the more complex silanols because of contamination of the 1100−1300 cm -1 spectral range by the deformation modes of substituents. , The more common range for these purposes is that of OH stretching vibrations. There are no experimental data on silanol, but certain bands of methanol clusters in this region were ascribed to dimers, trimers, and tetramers. , The general agreement of our predicted (with fixed scaling factors) vibrational frequencies of methanol clusters with the experiment is fair (Table ), although in the methanol trimer the predicted separation between the two high-frequency bands (13 cm -1 ) is considerably smaller than the experimental one (31 cm -1 ).…”

“…Despite the pronounced dependence of the δ SiOH mode on the cluster size, this feature hardly may be used for the identification of oligomers of the more complex silanols because of contamination of the 1100-1300 cm -1 spectral range by the deformation modes of substituents. 20,21 The more common range for these purposes is that of OH stretching vibrations. There are no experimental data on silanol, but certain bands of methanol clusters in this region were ascribed to dimers, 91 trimers, 92 and tetramers.…”

“…However, there exist spectral data on trimethylsilanol in different phases. [19][20][21][22] Although the structure of the trimethylsilanol liquid phase is unknown, we may consider that the OH stretching frequency of the tetramer is close to the hydrogen bond network limit. This assumption is based on the fact that the experimental frequency of the water tetramer 3416 cm -1 68 is close to 3415 cm -1 for liquid water.…”

“…However, to the best of our knowledge, experimental vibrational spectra are known only for a few silanols; the most complete experimental spectral data exist for trimethylsilanol. [19][20][21][22] In contrast to the absence of both experimental and theoretical data on silanol oligomers, there exist numerous studies of water dimers, trimers, and tetramers. Studies of the methanol clusters are less abundant, but these species received considerable attention in recent years.…”

“…However, sterical hindrance of substituents in the more crowded silanols prevents formation of tetramers, and, as a result, the dimers are formed. − Because vibrational spectroscopy is a regular tool for the monitoring of sol−gel processes, the knowledge of vibrational spectra of individual silanols and the frequency changes in the process of their condensation may be very helpful for the experimental research. However, to the best of our knowledge, experimental vibrational spectra are known only for a few silanols; the most complete experimental spectral data exist for trimethylsilanol. − …”