Lack of Cooperativity in the Triangular X₃Halogen-Bonded Synthon?

Abstract

We have investigated 44 crystal structures, found in the Cambridge Structural Database, containing the X 3 synthon (where X = Cl, Br, I) in order to verify whether three type II halogen−halogen contacts forming the synthon exhibit cooperativity. A hypothesis that this triangular halogen−bonded motif is stabilized by cooperative effects is postulated on the basis of structural data. However, theoretical investigations of simplified model systems in which the X 3 motif is present demonstrate that weak synergy occurs only in the case of the I 3 motif. In the present paper we computationally investigate crystal structures in which the X 3 synthon is present, including halomesitylene structures, that are usually described as being additionally stabilized by a synergic interaction. Our computations find no cooperativity for halomesitylene trimers containing the X 3 motif. Only in the case of two other structures containing the I 3 synthon a very weak or weak synergy, i.e. the cooperative effect being stronger than −0.40 kcal mol −1 , is found. The crystal structure of iodoform has the most pronounced cooperativity of all investigated systems, amounting to about 10% of the total interaction energy.

The Pnictogen Bond: The Covalently Bound Arsenic Atom in Molecular Entities in Crystals as a Pnictogen Bond Donor

“…We note that the X 3 bonding topology is very similar to that found in crystalline PI 4 [ 67 ] and in crystal materials containing halogens [ 135 ]; these interactions have been referred to as synergic interactions and are recognized to be the result of cooperative interactions between halogen–halogen-bonded X 3 or X 4 (X = F, Cl, Br, I) synthons [ 136 , 137 , 138 , 139 , 140 , 141 ]. This hypothesis needs to be tested in a future study on simplified model clusters of AsCl 3 , inter alia , as has been done elsewhere [ 135 ]. In that study, the authors examined 44 crystals deposited into the CSD featuring the X 3 synthon (X = Cl, Br, I) to verify whether the Type-IIa halogen–halogen contacts forming the synthon display any cooperativity.…”

Triangular Interchalcogen Interactions: A Joint Crystallographic Data Analysis and Theoretical Study

“…Similar to windmill X 3 interactions, the Ch 3 interactions tend to be strengthened as the atomic size of chalcogens increases and also show no or only weak cooperativity. However, HBs and π–π stacking contribute significantly to the synergy for the complexes consisting of the Ch 3 motifs, while the cooperativity occurring in the X 3 patterns depends largely on the X···X interaction strength. ,, …”

“…15,16 Of particular attention is the fact that the unique triangular X 3 synthons containing three type II X•••X contacts have been observed in a variety of halogenated molecular crystals. 17,18 Furthermore, such triangular windmill structures were also detected in the self-assemblies of fully halogenated aromatic molecules on metal surfaces. 19−21 Density functional theory (DFT) calculations on model systems unraveled that windmill X 3 interactions follow the strength trend of conventional halogen bonds (Cl < Br < I) and display no or weak cooperativity.…”

“…Intermolecular X···X interactions have been extensively studied from both experimental and theoretical points of view. − It is well known that there are two main types of X···X interactions: dispersion interaction is the dominant factor in type I, while type II stems primarily from electrostatics. , Of particular attention is the fact that the unique triangular X 3 synthons containing three type II X···X contacts have been observed in a variety of halogenated molecular crystals. , Furthermore, such triangular windmill structures were also detected in the self-assemblies of fully halogenated aromatic molecules on metal surfaces. − Density functional theory (DFT) calculations on model systems unraveled that windmill X 3 interactions follow the strength trend of conventional halogen bonds (Cl < Br < I) and display no or weak cooperativity. ,− However, to the best of our knowledge, analogous triangular Ch 3 motifs, which consist of three Ch···Ch contacts, remain completely unexplored to date. Undoubtedly, the Ch 3 motifs should exhibit quite different features with respect to the well-studied X 3 patterns, as a result of the divalent nature of chalcogen atoms.…”

Interplay of Hydrogen and Halogen Bonding in the Crystal Structures of 2,6‐Dihalogenated Phenols

“…[25] Halogen bonds have been studied for a long time and are still a research topic of highest interest. [26][27][28][29] The number of contributions in this field during the past few years is significant and covers a wide area, from understanding the nature of this kind of noncovalent interactions [30][31][32][33][34][35][36][37][38] to the targeted design of halogene-based supramolecular entities [39][40][41][42][43][44] and applications in organocatalysis. [45,46] Studies on halogenated molecules interacting with biomolecular systems have opened up entirely new approaches in drug development.…”