Comparison of Conventional and Nonconventional Hydrogen Bond Donors in Au- Complexes.

Abstract

Although gold has become a well-known nonconventional hydrogen bond acceptor, interactions with nonconventional hydrogen bond donors have been largely overlooked. In order to provide a better understanding of these interactions, two conventional hydrogen bonding molecules (3-hydroxytetrahydrofuran and alaninol) and two nonconventional hydrogen bonding molecules (fenchone and menthone) were selected to form gas-phase complexes with Au–. The Au–[M] complexes were investigated using anion photoelectron spectroscopy and density functional theory. Au–[fenchone], Au–[menthone], Au–[3-hydroxyTHF], and Au–[alaninol] were found to have vertical detachment energies of 2.71 ± 0.05, 2.76 ± 0.05, 3.01 ± 0.03, and 3.02 ± 0.03 eV, respectively, which agree well with theory. The photoelectron spectra of the complexes resemble the spectrum of Au– but are blueshifted due to the electron transfer from Au– to M. With density functional theory, natural bond orbital analysis, and atoms-in-molecules analysis, we were able to extend our comparison of conventional and nonconventional hydrogen bonding to include geometric and electronic similarities. In Au–[3-hydroxyTHF] and Au–[alaninol], the hydrogen bonding comprised of Au–···HO as a strong, primary hydrogen bond, with secondary stabilization by weaker Au–···HN or Au–···HC hydrogen bonds. Interestingly, the Au–···HC bonds in Au–[fenchone] and Au–[menthone] can be characterized as hydrogen bonds, despite their classification as nonconventional hydrogen bond donors.