The crystal structures of potassium and cesium bistrifluoroacetates were
determined at room temperature and at 20 K and 14 K, respectively, with the
single crystal neutron diffraction technique. The crystals belong to the I2/a
and A2/a monoclinic space groups, respectively, and there is no visible phase
transition. For both crystals, the trifluoroacetate entities form dimers linked
by very short hydrogen bonds lying across a centre of inversion. Any proton
disorder or double minimum potential can be rejected. The inelastic neutron
scattering spectral profiles in the OH stretching region between 500 and 1000
cm^{-1} previously published [Fillaux and Tomkinson, Chem. Phys. 158 (1991)
113] are reanalyzed. The best fitting potential has the major characteristics
already reported for potassium hydrogen maleate [Fillaux et al. Chem. Phys. 244
(1999) 387]. It is composed of a narrow well containing the ground state and a
shallow upper part corresponding to dissociation of the hydrogen bond.Comment: 31 pages, 7 figure

Alain Cousson

Baker A. N.

François Fillaux

John Tomkinson

Juan F. R. Archilla

Klug C. A.

Lovesey S. W.

Novak A.

Pimentel G.

Scheiner S.

Schuster P.

Vinogradov S. N.

English

arXiv

The crystal structures of potassium and cesium bistrifluoroacetates, KH CF3COO2 and
CsH CF3COO2, respectively, were determined at room and cryogenic temperatures with the single
crystal neutron diffraction technique. The crystals belong to the monoclinic space groups, I2/a and
A2/a, respectively, and there is no evidence of any structural phase transition. In both crystals,
trifluoroacetate entities in centrosymmetric dimers are linked by very short hydrogen bonds lying
across a center of inversion. The thermal parameters provide no evidence of any double minimum
potential for hydrogen bond protons. Single-minimum potentials were determined via best fitting to
the inelastic neutron scattering spectral profiles of the stretching vibrations. They comprise a narrow
well for the ground state and a very broad quasiharmonic well for excited states. The spread out of
the wave functions of these states shows that protons are no longer confined between the oxygens.
Presumably, they are attracted by the lone pairs of oxygen atoms. These potentials emphasize the
covalent nature of the OO bond and the ionic character of the hydrogen bond proton

Fillaux, François

Cousson, Alain

Archilla, Juan F. R.

Tomkinson, John

idUS. Depósito de Investigación Universidad de Sevilla

The Journal of Chemical Physics

A neutron scattering study of strong-symmetric hydrogen bonds in potassium and cesium hydrogen bistrifluoroacetates: Determination of the crystal structures and of the single-well potentials for protons

International audienceThe crystal structures of potassium and cesium bistrifluoroacetates, KH(CF$_3$COO)$_2$ and CsH(CF$_3$COO)$_2$, respectively, were determined at room and cryogenic temperatures with the single crystal neutron diffraction technique. The crystals belong to the monoclinic space groups, $I2/a$ and $A2/a$, respectively, and there is no evidence of any structural phase transition. In both crystals, trifluoroacetate entities in centrosymmetric dimers are linked by very short hydrogen bonds lying across a center of inversion. The thermal parameters provide no evidence of any double minimum potential for hydrogen bond protons. Single-minimum potentials were determined via best fitting to the inelastic neutron scattering spectral profiles of the stretching vibrations. They comprise a narrow well for the ground state and a very broad quasi-harmonic well for excited states. The spread out of the wave functions of these states shows that protons are no longer confined between the oxygens. Presumably, they are attracted by the lone-pairs of oxygen atoms. These potential emphasize the covalent nature of the OO bond and the ionic character of the hydrogen bond proton

Archilla, Juan, F. R.

HAL: Hyper Article en Ligne

A neutron scattering study of strong symmetric hydrogen bonds in potassium and cesium hydrogen bistrifluoroacetates: Determination of the crystal structures and of the single-well potentials for protons

HAL-CEA

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