THE HYDROGEN BOND STRENGTH IN TERMS OF THE TOPOLOGICAL PROPERTIES OF THE ELECTRON DENSITY DISTRIBUTION.
Enrique Espinosa1,2, Elies Molins1, Claude Lecomte2 and Carlos Miravitlles1.
1Institut de Ciencia de Materials de
Barcelona (CSIC), Campus de la Universitat Autonoma de Barcelona,
08193 Bellaterra (Cerdanyola), Spain.
2Laboratoire de Cristallographie et
Modélisation des Matériaux Minéreaux et Biologiques, URA CNRS
809, Université 'Henri Poincaré', Nancy 1, BP 239, 54506
Vandoeuvre-les-Nancy Cédex, France.
E-mail: elies.molins@icmab.es
Keywords: Charge
density, hydrogen bond, bond energy.
Interatomic interactions such as hydrogen bonds (HB's) can be adequately described and classified by the topological properties of the electron density r(r) at the (3,-1) critical points rCP, where the gradients of r(r) vanish [1]. We have analysed [2] the topological properties of r(r) at the intermolecular critical points of 83 experimentally observed HB's [X-H...O (X=C,N,O)] on a large set of compounds, obtained from accurate X-ray diffraction experiments. In spite of different models, methods and experimental conditions employed to obtain the topological properties of r(r), we show that, for closed-shell interactions, the kinetic energy density G(rCP) and the potential energy density V(rCP) at the critical point, depend exponentially on the H...O distance. We point out the positive correlation found between the V(rCP) and the HB energy when their functionalities against the H...O distance are compared. Recently [3], we have also observed that the positive and the negative curvatures of r(r) at the H...O critical point exhibit linear relationships against, respectively, G(rCP) and V(rCP). The proportional behaviors found between those quantities show that the strength of the hydrogen bond interaction can be indistinctly interpreted in terms of any of them.