Hexahalogenated and their mixed benzene derivatives as prototypes for the understanding of halogen···halogen intramolecular interactions: New insights from combined DFT, QTAIM‐, and RDG‐based NCI analyses

Abstract

A large number of fully halogenated benzene derivatives containing the fluorine, chlorine, bromine, and iodine atoms have been experimentally synthesized both as single- and co-crystals (e.g., Desiraju et al., Chem. Eur. J. 2006, 12, 2222), yet the natures of the halogen ··· halogen interactions between the vicinal halogens in these compounds within the intramolecular domain are undisclosed. Given a fundamental understanding of these interactions is incredibly important in many areas of chemical, biological, supramolecular, and material sciences, we present here our newly discovered theoretical results that delineate whilst the nature of an F···F interaction in a pair of two adjacent fluorine atoms in either of the hexafluorobenzene and 1,4-dibromotetrafluorobenzene compounds examined is almost unclear, each of the latter three hexahalogenated benzene derivatives (viz., C6 Cl6 , C6 Br6 , and C6 I6 ), and each of the seven of their fully mixed hexahalogenated benzene analogues, are found to be stabilized by means of a number of halogen···halogen interactions, each a form of long-range attraction within the intramolecular domain. The Molecular Electrostatic Surface Potential model was found to be unsurprisingly unsuitable in unraveling any of the aforesaid attractions between the halogen atoms. However, such interactions successfully enunciated by a set of noncovalent interaction descriptors of geometrical, topological, and electrostatic origins. These latter properties were extracted combining the results of the Density Functional Theory electronic structure calculations with those revealed from Atoms in Molecules, and Reduced Density Gradient charge density-based topological calculations, and are expounded in detail to formalize the conclusions. © 2015 Wiley Periodicals, Inc.

Revealing Factors Influencing the Fluorine‐Centered Non‐Covalent Interactions in Some Fluorine‐Substituted Molecular Complexes: Insights from First‐Principles Studies

“…As illustrated in Figures 4 and 5, the interactions between the negative sites on the fluorine atoms are highly directional in some complexes, forming a type‐II halogen bond pattern (to avoid confusion, we note that a halogen bond pattern does not imply type‐II halogen bond by itself) ,. For instance, the ∠C−F⋅⋅⋅F are 171.6 and 175.7° for the geometries illustrated in b) and c) of Figure , respectively.…”

Do surfaces of positive electrostatic potential on different halogen derivatives in molecules attract? like attracting like!

“…Note that the F•••X contacts in the studied complexes might not be called as either type‐I or type‐II halogen bonding, as each of these is formed between two positive sites through their head‐on approaches. This claim is in accord with the IUPAC 2013 feature, “In a typical halogen‐bonded complex RX•••Y: the angle RX•••Y tends to be close to 180°, i.e., the halogen bond acceptor Y approaches X along the extension of the RX bond.” And that a type‐II halogen bond is formed when there is an evidence of attraction between the positive site on the halogen and the negative site on the interacting monomer …”

Nature of halogen‐centered intermolecular interactions in crystal growth and design: Fluorine‐centered interactions in dimers in crystalline hexafluoropropylene as a prototype

“…This does not, however, require that an electron density deficient region is/would be always positive. In fact, it could be negative as well …”

“…Covalently bound halogen derivatives in molecules display two types of bonding modes to form molecular complexes or crystals. These have routinely been characterized as type‐I and type‐II halogen bonding . These bonding modes are applicable to intermolecular interactions formed by other main group elements of the periodic table …”

“…This is the case for a great majority of crystal structures, but the lower and upper limits of this range can be 60 and 170°, respectively, provided the intermolecular motif follows a type‐I cis topology (ii and iii of Scheme a). In this case, one does not need to have the requirement of a positive site on the halogen to interact with the negative site . Although some have suggested this interaction to occur when two halogen atoms minimize repulsion by interfacing the neutral regions of their electrostatic potential surfaces, this is incorrect as such a bonding topology develops when the dispersed electron densities on the two halogen atoms overlap locally.…”