Does electron density in bond critical point reflect the formal charge distribution in H-bridges? The case of charge-assisted hydrogen bonds (CAHBs)

The charge-assisted hydrogen bond (CAHB) was investigated for a set of H-bridges of N–H⋯Cl type. The properties of these bonds, i.e. interaction energy and electron density measured in a specific point of the bond, were represented as functions of H⋯Cl distance. It appears that the energy of interaction is very strongly affected by formal charges, which may be explained by the presence of efficient interaction between formal ions. Surprisingly, the electron density measured in the H-bond critical point is totally independent of the formal charges. For the given H⋯Cl distance the ρBCP value is the same, no matter whether neutral molecules or oppositely charged ions interact with each other.