IR spectrum of SiH3OH2+SiH4: cationic OH⋯HSi dihydrogen bond versus charge-inverted SiH⋯Si hydrogen bond

Abstract

The low electronegativity of Si gives rise to a variety of nonconventional intermolecular interactions in clusters of silanes and their derivatives, which have not been well characterized yet. Herein, we characterize the structures of various isomers of bare and Ar-tagged SiH₃OH₂⁺SiH₄ dimers composed of protonated silanol and silane by infrared photodissociation (IRPD) of mass-selected ions and dispersion-corrected density functional calculations (B3LYP-D3/aug-cc-pVTZ). The analysis of the IRPD spectra recorded in the OH stretch range reveals the competition between two types of nonconventional hydrogen bonds (H-bonds). The first one represents a OH⋯HSi ionic dihydrogen bond (DHB), in which SiH₄ interacts with the H₂O moiety of SiH₃OH₂⁺. The second one represents a charge-inverted SiH⋯Si ionic H-bond (CIHB), in which the SiH₄ ligand interacts with the SiH₃ moiety of SiH₃OH₂⁺. The latter may also be considered as a weak three-centre two-electron (3c–2e) bond. Although both types of H-bonds are computed to have comparable interaction strengths for SiH₃OH₂⁺SiH₄ (D₀ ≈ 35–40 kJ mol⁻¹), DHB isomers dominate the population in the supersonic plasma expansion, while the abundance of CIHB isomers is roughly one order of magnitude lower, probably as a result of entropic factors.