ETS-NOCV description of σ-hole bonding.
The ETS-NOCV analysis was applied to describe the σ-hole in a systematic way in a series of halogen compounds, CF3-X (X = I, Br, Cl, F), CH3I, and C(CH3)nH3-n-I (n = 1,2,3), as well as for the example germanium-based systems. GeXH3, X = F, Cl, H. Further, the ETS-NOCV analysis was used to characterize bonding with ammonia for these systems. The results show that the dominating contribution to the deformation density, Δρ 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 CF3-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 CF3-X. In CH3-I and C(CH3)nH3-n-I, compared to CF3-I, introduction of hydrogen atoms and their subsequent replacements by methyl groups lead to the systematic decrease 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 energy indicate that the σ-hole-based bond with ammonia contains a degree of covalent contribution. In all analyzed systems, it was found that the electrostatic 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.
Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University, R. Ingardena 3, 30-060, Krakow, Poland.
Karol
K
Dyduch
Mariusz P
MP
Mitoraj
Artur
A
Michalak
D000641:Ammonia / Q000737:chemistry; D004583:Electrons; D005857:Germanium / Q000737:chemistry*; D006219:Halogens; D006859:Hydrogen / Q000737:chemistry*; D008958:Models, Molecular; D055672:Static Electricity; D013816:Thermodynamics
D006219:Halogens; D005857:Germanium; D000641:Ammonia; D006859:Hydrogen