ATOMIC QUADRUPOLAR MOMENT AND LAPLACIAN DISTRIBUTION OF THE CHARGE DENSITY IN HALOGEN BONDING COMPLEXES

DUARTE, D. J. R.; SOSA, G. L.; PERUCHENA, N. M.

Santiago de Compostela

Congreso; Ninth Triennal Congress of the World Association of Theoretical and Computational Chemists, WATOC2011; 2011

WORLD ASSOCIATION THEORETICAL COMPUTATIONAL CHEMISTS

The analysis of the atomic quadrupolar moment and the Laplacian distribution of the charge density were employed in the description of halogen bonds between the ammonia as Lewis base and Lewis acids, D–X (with X= F, Cl, Br and I; and with D= –H, –CN, and –F as halogen donor group). The geometries of all the complexes were fully optimized using the Moller–Plesset second-order perturbation theory with the 6-311++G(2d,2p) basis set. For iodine atoms, an effective core potential (ECP) was used. Criteria based on a topological analysis of the electron density were used in order to characterize the nature of these interactions. The results have allowed us to understand the origin of the halogen bond. The halogen-bonded complexes result from the interaction between the charge density provided by the lone pair of donor atom of Lewis base (N) and the charge density depletion localized on the outermost portion of the X halogen atom centered on the D–X axis bonds (ó-hole). Such charge depletion, on the X atom, results from the electron density withdrawing of the D group, covalently bonded to X atom, that produce an unsymmetrical electron charge density distribution. Consequently, a decrease of the charge density is observed in the front part of the X atom, which makes this atom more prone to uptake of the charge density provided by the lone pair of Lewis base. We found that the Laplacian distribution and the atomic quadrupole moment on the halogen atom show that the electron density is not increased along of the direction of the X···N bond, but this one increases in the orthogonal direction to the bond forming (X···N). Finally, this work shows the important answers that the AIM analysis provides on the characteristics of the halogen bonds.