Theoretical study of the interaction between pyridine derivatives and atomic chlorine. Substituent effect and nature of the bonding

Abstract

The interaction of pyridine derivatives (H, ) with atomic chlorine is investigated theoretically by the density functional theory (DFT)-based LC-BLYP/aug-cc-pVDZ method. Pyridines and Cl • are held together by a (2c-3e) bond and the intermolecular distances range from 2.313 to 2.343Å. The existence of a N. . .Cl bond is confirmed by the atom-in-molecule analysis of the systems. The binding energies of the adducts, ranging from −42.08 to −53.96 kJ mol −1 , are linearly correlated to the proton affinity of the pyridines. The charge transfer from pyridine to Cl • varies between 0.222 and 0.277 e. The spin density analysis shows that the strongest complex has the highest (2c-3e) character. The CH bonds are contracted and the ν(CH) vibrations are blueshifted owing to the decrease in σ * (CH) occupation. This decrease results not only from the classical anomeric effect but also from the σ (CC) and σ (CN) → σ * (CH) delocalisation in the heteroaromatic ring.

Nature and Strength of the π‐Hole Chalcogen Bonded Complexes between Substituted Pyridines and SO3 Molecule

“…Table 1 lists the values of PA, IE and the values of the minimum electrostatic potential, V s,min , of the substituted pyridines calculated at the MP2=full/aug‐cc‐pVTZ level. As discussed in our previous works, [38,39] the PA and V s,min of the pyridines increases with the inclusion of electron donating substituents at the para position whereas it decreases for the electron withdrawing substituents. The electrostatic potential diagram of SO 3 molecule is given in Supporting Information as Figure SI.2.…”

“…As shown in Table 2, the binding energies of the π‐hole chalcogen bonded X‐pyr.SO 3 complexes range between −109.78 and −81.56 kJ/mol, indicating a wide modulation of the binding strength with the substitution. As observed for the complexes of substituted pyridines with CS 2 , OCS and Cl, [38,39,43] the binding strength of the X‐pyr ⋅ SO 3 complexes increase with the inclusion of EDG, whereas it decreases for the EWG. The deformation energy (DFE) indicates the extent of deformation in the monomer structures owing to the formation of a/the complex, and this value varies from 35 to 47 kJ/mol for the pyr ⋅ SO 3 complexes.…”

“…studied the halogen bonded pyridine‐XY complexes (X, Y=F, Cl, Br) and predicted a binding strength of −11.69, −27.06, −40.32, −48.66, −63.59 and −81.12 kJ/mol for Pyr‐F 2 , Pyr‐Cl 2 , Pyr‐Br 2 , Pyr‐BrCl, Pyr‐ClF and Pyr‐BrF, respectively [44] . Moreover, in a previous work, we have predicted a binding energy ranging from −58.53 to −42.08 kJ/mol for the X‐pyr.Cl complexes (X=NH 2 , CH 3 , H, CN, NO 2 ) calculated at LC‐BLYP/aug‐cc‐pVDZ level [38] . All these results suggest that the present pyr ⋅ SO 3 complexes are much stronger than the aforementioned complexes.…”

Nature of the Interaction of Pyridines with OCS. A Theoretical Investigation

“…The interaction of OCS with N derivatives [34,47] has also been discussed recently. The interaction of guest molecules with pyridines is interesting to investigate because the substitution allows one to modulate their basic strength, as for example in their interaction with atomic chlorine [48].…”

Comparison between Chlorine-Shared and π–Halogen Bonds Involving Substituted Phosphabenzene and ClF Molecules

“… 48 Moreover, interaction of pyridine with the Cl 0 atom results in a shortening of the ortho CH bond by 0.8 and 1.6 mÅ, and consequently, a blue shift in ν(CH) stretching vibration ranging between 19 and 27 cm –1 has been predicted. 50 Therefore, it seemed interesting to investigate the changes of CH bond lengths in the present complexes as well. For T1-X-PPBZ·ClF complexes, the contraction of the C1H 0 bonds ranges between 1.4 and 1.9 mÅ.…”