Exploring influence of fluorine substitution on the strength and nature of halogen bond between iodobenzene and hydrogen cyanide

Abstract

In the present study, the intermolecular I … N halogen bond (XB) interaction between iodobenzene (IBZ) and its fluorinated derivatives (as Lewis acids LA 1 through LA 20) with HCN (as Lewis base LB) is theoretically explored to shed light on the electronic nature and strength of the mentioned non-covalent interaction (NCI). The hydrogen atoms of phenyl ring in IBZ were substituted by fluorine atom to probe different impacts of this atom. Such a substitution is paid attention from the number as well as the position of fluorine atoms points of view. Our analyses reveal that this XB interaction whose interaction energy spans a narrow range between 1.0 and 3.0 kcalÁmol −1 should be classified as a weak NCI. The symmetry-adapted perturbation theory (SAPT) analysis evidences that the I … N XB in the investigated binary complexes (BCs) is mainly dominated by electrostatic and dispersion interactions, and, in the meantime, induction interactions can safely be ignored. Among the many I … N XB descriptors, V s,max , which corresponds to the most positive value of electrostatic potential computed for the iodine atom in LAs, plays a key role. Indeed, such an easily and rapidly computable quantity (V s,max ) allows a sufficiently accurate prediction of interaction energy together with SAPT-derived components analysis to become feasible by a simple inclusion of V s,max value within the numerous explored estimators. Although the strength of I … N XB interaction in the studied BCs is increased by an increase in the number of fluorine substituent, the position of fluorine atom cannot significantly alter the strength of the mentioned interaction.

Proximity Effects of Substituents on Halogen Bond Strength

“…This group also confirmed our finding that m-substitution increases the interaction more than does the placement of the substituent in the p-position. Consistent with the data presented above for NH 3 as the base, the effects of different positions of an F substituent relative to I on a phenyl ring diminish in the o > m > p order for NCH as the nucleophile, 76 and the bond strengthening increases as more such F groups are added to the ring, which is a conclusion which was recently echoed by Naghani et al 77 A similar pattern was noted 78 for SF 5 substituents when halogen bonded to pyridine. Concomitant with the experimental determination of relevant crystal structures, the theoretical analysis 79 of carboxyl-substituted iodobenzenes verified the ability of this EWS to deepen the σ-hole on I, more so for a larger number of such groups.…”

A comprehensive theoretical analysis on the intermolecular hydrogen bond interactions with the Lewis bases having multiple hydrogen bonding abilities

“…:750 Å thereby show a mutual penetration [57] as a signature of HB interactions. On the other hand, the positive values of Δd HalÀH (sixth column in Table 2) portray an elongation in the Hal-H distance as a consequence of filled-empty electron density delocalization (or CT)…”

“…As the experimentally observable quantity, ρ BCP plays a crucial role among QTAIM topological descriptors by which not only the strength of a given NCI could be explored but, mostly, it also correlates very well with the values of IE and SAPTderived energy components. [27,57] Lefebvre et al [58] have recently proposed a so useful electron density-based descriptor, namely, independent gradient model (IGM) which is capable of separately portraying both noncovalent and covalent interactions in a quite evident and an effortless fashion. A much more rigorous and powerful version of IGM has been introduced by Tian Lu, namely, "IGM based on Hirshfeld partition of molecular density", IGMH, in which the gradients of atomic densities involved in the analysis are evaluated using Hirshfeld partitioning scheme of actual electron density.…”

“…Consequently, it is quite reasonable to expect that values of CP-IE are well linearly correlated with those of SAPTderived electrostatics contribution, E els . [27,57] It should also be noted that such correlation, CP - vice versa, does not have any practical usage since two computationally very expensive quantities are correlated to each other. On the other hand, we found that CP-IE values are very well linearly correlated with values of ρ at the BCP of HBs (Figure 4).…”

Elucidating the Role of Electron-Donating Groups in Halogen Bonding

“…While many studies focus on augmenting the σ-hole or halogen bond strength through stronger electron-withdrawing substituents bonded to the R-group, − the polarizability of the halogen atom, or the hybridization of the R-group, ,, very few have examined other means to enhance halogen bonds. With the emergence of the hydrogen bond-enhanced halogen bonds (HBeXB), − there has been a new surge of research and development into the field of halogen bonding.…”