IR spectrum of SiH 3 OH 2 + SiH 4 : cationic OH⋯HSi dihydrogen bond versus charge-inverted SiH⋯Si hydrogen bond.

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 SiH 3 OH 2 + SiH 4 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 SiH 4 interacts with the H 2 O moiety of SiH 3 OH 2 + . The second one represents a charge-inverted SiH⋯Si ionic H-bond (CIHB), in which the SiH 4 ligand interacts with the SiH 3 moiety of SiH 3 OH 2 + . 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 SiH 3 OH 2 + SiH 4 ( D 0 ≈ 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.