jp9b11762_si_001.pdf (3.06 MB)
Attenuated Deuterium Stabilization of Hydrogen-Bound Complexes at Room Temperature
journal contribution
posted on 2020-02-24, 20:16 authored by Alexander Kjaersgaard, Emil Vogt, Nanna Falk Christensen, Henrik G. KjaergaardWe
have observed nine bimolecular hydrogen- or deuterium-bound
complexes at room temperature using Fourier transform infrared (FTIR)
spectroscopy. The complexes were formed using methanol or ethanol
as hydrogen bond donors, as well as deuterated isotopologues of these,
in order to study isotopic effects on hydrogen bonds. The complexes
were formed using either a dimethylether- (O) or trimethylamine (N)
acceptor, to facilitate comparison of two different types of hydrogen
or deuterium bonds, OH(D)·O and OH(D)·N. For each complex,
the characteristic OH- or OD-stretching fundamental band in the bimolecular
complex was observed. The Gibbs energy of complex formation was determined
at room temperature for each complex to compare the relative stability
of hydrogen- and deuterium-bound bimolecular complexes. It is well
known that deuterium-bound complexes are more stable at low temperatures
because of the lower frequency of its intermolecular modes and thus
a lower zero point vibrational energy. However, at room temperature,
entropic contributions to the stability should also be considered.
At room temperature, we find the Gibbs energy of complex formation
for each pair of corresponding hydrogen- and deuterium-bound complex
to be similar. The similar values of the Gibbs energies at room temperature
is explained from a difference in the entropy, upon complexation,
which favors the formation of the hydrogen-bound complex more than
the deuterium-bound complex at higher temperatures.