2E12
Properties of molecular structures by quantum energy density analysis(Kyoto University, Dep. Of Microengineering*, Wroclaw University of Technology,Chemistry Dep.**) ○ Pawel Szarek*,**, Akitomo Tachibana*, Andrzej W. Sokalski**

The chemical system is characterized by electronic distribution (determined by wavefunction) that links and unites the net of atomic nuclei. Such molecular connectivity
possessing electronic origin may exhibit different (covalent or non-covalent) nature.
It is needed to evaluate interaction properties in order to better understanding ofmechanisms that rule our experiments. This knowledge helps to interpret experimental results
and planning new experiments. For example, does the hydrogen bond (h-bond, for short) is
not covalent but rather physical interaction (like vdW)? There have been distinguished several
types of h-bond like interactions: usual h-bonds involving lone pairs of O and N atoms, other
involving halogen ions, or noble gases[1], or as extraordinary as interaction with π-electrons(or similar interactions although without proton bridge [2]) and dihydrogen bonds. They allseem to have slightly different origin. How to generalize the model for such interactions tomake clear and unify definition as in case of covalent, ionic or metallic bonds? Somephenomena related with h-bond (covalency in ice [3], existence of cooperative effects due tocharge flow between h-bonds [4], electron transfer, dipole models) cause difficult questions
for modeling. There are opponents of electrostatic character as well as partial covalency ofhydrogen bond. Although many concepts have been applied to explain the mechanism offormation of this particular interaction (i.e. Coulson “ionic resonance”, Lewis donor-acceptor
concept, Pauling’s model or Bader atoms in molecules theory) many doubts remain. As
benzene molecule has its own structure and can not be composed of structural elements fromother molecules in exact way, in the same fashion hydrogen bond needs its own idealized,working model. Many correlations between h-bond energy and other parameters are known[5]. However, before the generalized model might be obtained, the common points have to beextracted for all interaction patterns, from leading terms in interaction energy to electronic
properties and quantum effects.
The electronic interactions expressed in terms of the new quantum energy density
analysis provide reliable evaluation of inter-atomic and inter-molecular bonding. Rational
utilization of properties of “hard” and “soft” molecular structures leads to cheaper and more
efficient chemistry and opens way to new materials and technologies.

H

H
O

HO

O
H

H

O
H

Donor
H2O
Acceptor
H2O

Figure 1. Hydrogen bond in water dimmer: a) electron density change in system as a difference of dimmer electron density and densities ofmonomers; blue corresponds to regions of decreased electron density (hydrogen atoms of acceptor water molecule and bridging proton),while red indicates increase of electron density (lone pairs of oxygen atoms and O-H bond between donating O atom and bridging H atom);b) Stabilization Energy Density; blue areas denote local stabilization and red – local destabilization of bonding interaction; destabilization ismainly caused by withdraw of electrons from the local area.

Acknowledgements:
This work was supported by the Japanese Government (Monbukagakusho)
Scholarship through Kyoto University.
References:[1] Vincenzo Aquilanti et al., Angew. Chem. Int. Ed. 2005, 44, 2356 –2360[2] Marcin Hoffmann et al., J. Phys. Chem. A 2005, 109, 4568-4574[3] E. D. Isaacs et al., Phys. Rev. Lett., 82 (3) 600-603, 1999
[4] Hongwei Tan et al., J. Phys. Chem. A 2005, 109, 6303-6308[5] S. J. Grabowski, Chem. Phys. Lett., 338 (2001) 361-366