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.