Dimethylsilanediol: Structure and vibrational spectra by IR and Raman spectroscopies and quantum chemical calculations

Despite the predictable relation between the structure of the silanediol group and its biological activity (some peptidomimetics containing the R′R″Si(OH)2 group have proven efficiency as inhibitors of aspartyl and metalloproteases), few theoretical or experimental works deal with the study of the structural and/or vibrational properties of this functional group. Thus, intending to overcome this lack of information, the present paper is focused on one of the simplest possible alkylsilanediols, namely, dimethylsilanediol (DMSD). In this way, a thorough quantum chemical analysis allowed us identifying two different conformations that represent minima in the potential energy surface (PES) of the molecule, depending on the relative orientation that the OH groups would adopt respect each other. Natural bond orbital calculations confirm that the anomeric effect would be responsible of the higher stability of the so-called conformer II (C2 symmetry, structure classically assumed as the unique possible conformation of the silanediol group) compared with conformer I (C1 symmetry), although the energy difference between both structures steadily decreases with the increase of the size of the basis set chosen (ΔE0 = 0.84 kcal/mol; B3LYP/aug-cc-pVQZ). In addition to the theoretical work, DMSD was synthesized and its IR spectra (in solid phase and dimethylsulfoxide solution) and Raman spectrum (in solid phase) were, for the first time, completely assigned with the support of DFT calculations. Besides the above mentioned conformers, and in order to achieve a better description of the vibrational bands that are shifted in the experimental spectra due to intermolecular interactions, two hydrogen bonded dimers of DMSD were modeled and their vibrational spectra were calculated. The results of this work point to the plausible presence of stable moderate-size hydrogen bonded oligomers of DMSD even in solution.