Magnitude and Origin of the Attraction and Directionality of the Halogen Bonds of the Complexes of C₆F₅X and C₆H₅X (X=I, Br, Cl and F) with Pyridine

Abstract

The geometries and interaction energies of complexes of pyridine with C6F5X, C6H5X (X=I, Br, Cl, F and H) and RFI (RF=CF3, C2F5 and C3F7) have been studied by ab initio molecular orbital calculations. The CCSD(T) interaction energies (Eint) for the C6F5X–pyridine (X=I, Br, Cl, F and H) complexes at the basis set limit were estimated to be −5.59, −4.06, −2.78, −0.19 and −4.37 kcal mol−1, respectively, whereas the Eint values for the C6H5X–pyridine (X=I, Br, Cl and H) complexes were estimated to be −3.27, −2.17, −1.23 and −1.78 kcal mol−1, respectively. Electrostatic interactions are the cause of the halogen dependence of the interaction energies and the enhancement of the attraction by the fluorine atoms in C6F5X. The values of Eint estimated for the RFI–pyridine (RF=CF3, C2F5 and C3F7) complexes (−5.14, −5.38 and −5.44 kcal mol−1, respectively) are close to that for the C6F5I–pyridine complex. Electrostatic interactions are the major source of the attraction in the strong halogen bond although induction and dispersion interactions also contribute to the attraction. Short‐range (charge‐transfer) interactions do not contribute significantly to the attraction. The magnitude of the directionality of the halogen bond correlates with the magnitude of the attraction. Electrostatic interactions are mainly responsible for the directionality of the halogen bond. The directionality of halogen bonds involving iodine and bromine is high, whereas that of chlorine is low and that of fluorine is negligible. The directionality of the halogen bonds in the C6F5I– and C2F5I–pyridine complexes is higher than that in the hydrogen bonds in the water dimer and water–formaldehyde complex. The calculations suggest that the CI and CBr halogen bonds play an important role in controlling the structures of molecular assemblies, that the CCl bonds play a less important role and that CF bonds have a negligible impact.

Double Hole–Lump Interaction between Halogen Atoms

“…In all the cases, the most important stabilization term 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 8 corresponds to the dispersion followed by the electrostatic term, in agreement with previous report 41,42 save in the strongest complex FI···IF, where the electrostatic term is slightly more important than the charge transfer and the dispersion ones. The analysis of the polarization shows that the charge transfer term is the dominant one being always larger than the rest of the term.…”

Photo-Induced Atom-Transfer Radical Reactions Using Charge–Transfer Complex between Iodine and Tertiary Amine

“…Charge-Transfer Complex between Amine and Iodine on halogen bonding interactions have been a subject of current interest. 30,31) To understand the above results, we calculated the optimized structures of iodine complexes. The calculation shows that the noncovalent interaction between trimethylamine and I 2 is strong to form the stable CT complex, while pyridine weakly interacts with I 2 .…”

Halogen Bonding in Crystal Engineering

“…Probably the most commonly used halogen bonding acceptors are covalently bonded halogens and nitrogen atoms. [8,11,[20][21][22][23][24] Metal halides, oxygen, sulfur, selenium and even silicon have, however, been reported to have the capacity to act as halogen bond acceptors with suitable donors. [25][26][27][28][29][30][31] …”

“…[24,[55][56][57]66] On the basis of both the existing experimental and theoretical studies, it can be stated that electron withdrawing substituents increase the strength of the halogen bond donor, while the electron-donating groups reduce it. [24,55,66] Figure 21. Halogen bonding of the iodine atoms for (C12H13F3 I + )(CF3O3S -) (a); (C11H12Cl2I + )(CF3O3 S -) (b) and 2(C13H12F6I + ) 2(CF3O3S -) CH2Cl2 (c) [67] In Fig.…”