Halogen Bonding: A Halogen-Centered Noncovalent Interaction Yet to Be Understood

摘要: In addition to the underlying basic concepts and early recognition of halogen bonding, this paper reviews conflicting views that consistently appear in area noncovalent interactions ability covalently bonded atoms molecules participate contribute packing solid-state. It may be relatively straightforward identify Type-II bonding between using conceptual framework σ-hole theory, especially when interaction is linear formed axial positive region (σ-hole) on one monomer a negative site second interacting monomer. A an electron density deficient atom X opposite R–X covalent bond, where R remainder part molecule. However, it not trivial do so secondary are involved as directionality significantly affected. We show, by providing some specific examples, bonds always follow strict topology, occurrence Type-I -III halogen-centered contacts crystals very difficult predict. many instances, simultaneously with bonds. employed Independent Gradient Model, recently proposed approach for probing strong weak molecular domains, show useful tool unraveling chemistry halogen-assisted interactions, regime. Wherever possible, we have attempted connect these results those reported previously. Though studying reasonable strength, IUPAC’s “less than sum van der Waals radii” criterion should assumed necessary sufficient feature reveal weakly bound since attractive happens occur midpoint or junction region, site.