Probing "hydridic hydrogen bonds" using energy decomposition analysis based on absolutely localized molecular...

The concept of "hydridic hydrogen bonds (HBs)" was recently proposed by Hobza and co-workers [Civiš et al., J. Am. Chem. Soc., 2023, 145, 8550] to describe X-H⋯Y interactions where the X atom is more electropositive than hydrogen. Here, we investigate prototypical "hydridic HBs" formed between trimethylsilane (Me₃SiH) and various electrophilic acceptors using energy decomposition analysis methods based on absolutely localized molecular orbitals (ALMO-EDA). New insights into the physical origin of these interactions and the associated vibrational frequency shifts are obtained. Compared to conventional, protonic HBs, "hydridic HB" complexes feature a more pronounced contribution from dispersion interactions to binding, and the key polarization and charge-transfer effects originate from the electron-rich Si-H bond rather than from the H-acceptor. Using the adiabatic ALMO-EDA approach, we further reveal the dominant role of permanent electrostatics (along with charge transfer in some cases) in driving the redshifts in the Si-H stretching frequency, differing from the factors leading to red- or blueshifts in conventional HBs. These findings clearly demonstrate that the apparent similarities between "hydridic HBs" and conventional, protonic HBs arise from fundamentally different physical origins, suggesting that alternative terminology, such as halogen, pnictogen, and tetrel bonds (based on the character of the H-acceptor), or hydride bonds (to retain an H-centered perspective), should be considered for complexes involving hydridic H-donors.