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.