Strength of the [Z-I···Hal](-) and [Z-Hal···I](-) Halogen Bonds: Electron Density Properties and Halogen Bond Length as Estimators of Interaction Energy.

Bond energy is the main characteristic of chemical bonds in general and of non-covalent interactions in particular. Simple methods of express estimates of the interaction energy, E(int), using relationships between E(int) and a property which is easily accessible from experiment is of great importance for the characterization of non-covalent interactions. In this work, practically important relationships between E(int) and electron density, its Laplacian, curvature, potential, kinetic, and total energy densities at the bond critical point as well as bond length were derived for the structures of the [Z-I···Hal](-) and [Z-Hal···I](-) types bearing halogen bonds and involving iodine as interacting atom(s) (totally 412 structures). The mean absolute deviations for the correlations found were 2.06-4.76 kcal/mol.