Spectroscopic and Computational Evidence of Intramolecular Au(I)⋅⋅⋅H(+)−N Hydrogen Bonding

Despite substantial evidence of short Au⋅⋅⋅H−X contacts derived from a number of X‐ray structures of Au(I) compounds, the nature of Au(I)⋅⋅⋅H bonding in these systems has not been clearly understood. Herein, we present the first spectroscopic evidence for an intramolecular Au(I)⋅⋅⋅H(+)−N hydrogen bond in a [Cl−Au−L](+) complex, where L is a protonated N‐heterocyclic carbene. The complex was isolated in the gas phase and characterized with helium‐tagging infrared photodissociation (IRPD) spectra, in which H(+)−N‐mode‐derived bands evidence the intramolecular Au(I)⋅⋅⋅H(+)−N bond. Quantum chemical calculations reproduce the experimental IRPD spectra and allow to characterize the intramolecular Au⋅⋅⋅H(+)−N bonding with a short r (Au⋅⋅⋅H) distance of 2.17 Å and an interaction energy of approximately −10 kcal mol(−1). Various theoretical descriptors of chemical bonding calculated for the Au⋅⋅⋅H(+)−N interaction provide strong evidence for a hydrogen bond of moderate strength.