Infrared spectroscopy of phenol-triethylsilane dihydrogen-bonded cluster and its cationic analogues: intrinsic strength of the Si-H···H-O dihydrogen bond.

Spectroscopic and theoretical investigations have been carried out for neutral phenol-triethylsilane clusters to reveal an intrinsic nature of the Si-H···H-O type dihydrogen bond. On the basis of the laser-induced fluorescence and infrared spectra, four isomers are identified. Three of them have a structure in which the dihydrogen bond and the dispersion interaction are competing in the stabilization of the cluster. However, the other isomer is found to have a distinct structure in which the dihydrogen bond is much stronger than the other isomers. In addition to the neutral clusters, cationic phenol(+)-diethylmethylsilane and phenol(+)-triethylsilane clusters are investigated by infrared photodissociation spectroscopy. It is found that the dihydrogen bond is the dominant intermolecular interaction in these clusters. On the basis of the red shifts of the OH stretching bands, it is revealed that the strength of the Si-H···H-O dihydrogen bond is stronger than that of the π-type hydrogen bond. The proton affinities of triethylsilane and diethylmethylsilane estimated by the theoretical calculation are larger than those of benzene and ethylene. These results are consistent with our experimental observations.