Blue-Shifting Hydridic Hydrogen Bonds in Complexes of (Me3Si)3SiH.

Hydridic hydrogen bonds, formed by X-H···Y interactions with negatively charged hydrogen, expand the conventional view of H-bonding beyond elements that are more electronegative than hydrogen. Using a highly polarizable silane donor (Me₃Si)₃SiH, we systematically examined various electron acceptors (σ- and π-hole) and observed both red and blue shifts in the X-H stretching frequency. We provide the first experimental evidence of a blue-shifting hydridic bond and report the largest experimental blue shift for any hydrogen-bonded system. Thermodynamic, spectroscopic, and theoretical analyses show that the dispersion energy is crucial for stabilizing these complexes and reproducing their spectral signatures. Notably, the IR band intensity increases for red-shifting bonds and increases or decreases for blue-shifting hydridic bonds, offering a distinct spectroscopic fingerprint. Adiabatic ALMO-EDA calculations indicate that red shifts in hydridic bonds primarily arise from electrostatics and dispersion rather than charge transfer. It can be thus concluded that protonic as well as hydridic hydrogen bonds exhibit similar spectral manifestations, namely, the red or blue shift of the X-H stretching frequency connected with the intensity increase or decrease. These findings broaden hydrogen-bonding paradigms for diverse chemical applications.