Karol Dyduch - Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University

The ETS-NOCVanalysis was applied to describe the σ -hole in a systematic way in a series of halogen com- pounds, CF 3 -X ( X 0 I, Br, Cl, F), CH 3 I, and C(CH3) n H 3-n -I ( n 0 1,2,3), as well as for the example germanium-based systems. GeXH 3 , X 0 F,Cl,H.Further,theETS-NOCV analysis was used to characterize bonding with ammonia for these systems. The results show that the dominating contribution to the deformation density, Δ ρ 1 , exhibits the negative-value area with a minimum, corresponding to σ

hole. The “ size ” (spatial extension of negative value) and “ depth ” (minium value) of the σ -hole varies for different X in CF 3 -X, and is influenced by the carbon substituents (fluorine atoms, hydrogen atoms, methyl groups). The size and depth of σ -hole decreases in the order: I, Br, Cl, F in CF 3 -X. In CH 3 -I and C(CH3) n H 3-n -I, compared to CF 3 -I, introduction of hydrogen atoms and their subsequent replacements by methyl groups lead to the systematic de- crease in the σ -hole size and depth. The ETS-NOCV σ -hole picture is consistent with the existence the positive MEP area at the extension of σ -hole generating bond. Finally, the NOCV deformation density contours as well as by the ETS orbital-interaction e nergy indicate that the σ -hole-based bond with ammonia contains a degree of covalent contribu- tion. In all analyzed systems, it was found that the electro- static energy is approximately two times larger than the orbital-interaction term, confirming the indisputable role of the electrostatic stabilization in halogen bonding and σ -hole bonding.