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

Abstract

Ab initio calculations were carried out to investigate the interaction between para-substituted pyridines (X-C5H4N, X=NH2, CH3, H, CN, NO2) and OCS. Three stable structures of pyridine.OCS complexes were detected at the MP2=full/aug-cc-pVDZ level. The A structure is characterized by N…S chalcogen bonds and has binding energies between −9.58 and −12.24 kJ/mol. The B structure is bonded by N…C tetrel bond and has binding energies between −10.78 and −11.81 kJ/mol. The C structure is characterized by π-interaction and has binding energies between −10.76 and −13.33 kJ/mol. The properties of the systems were analyzed by AIM, NBO, and SAPT calculations. The role of the electrostatic potential of the pyridines on the properties of the systems is outlined. The frequency shift of relevant vibrational modes is analyzed.

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.…”

“…A recent study reveals that the interaction between substituted pyridines and the CS 2 molecule results in four different types of complexes: two types (A and C) of complexes were found to be stabilized by N…S interaction; whereas B complexes were formed via tetrel bond and D complexes through a combination of N…S and other weak interactions [39] . The chalcogen bonded (Type A ) complexes were characterized with binding energies ranging between −11.57 and −9.34 kJ/mol.…”

“…The chalcogen bonded (Type A ) complexes were characterized with binding energies ranging between −11.57 and −9.34 kJ/mol. In another work dealing with OCS molecule, the X‐pyr.OCS chalcogen bonded complexes were characterized with binding energy varying between −12.24 and −9.58 kJ/mol [43] . The σ‐hole on the S‐atom of OCS is stronger by almost 17 kJ/mol in comparison to CS 2 molecule, but there is very little effect on the binding energy.…”

Versatility of the Cyano Group in Intermolecular Interactions

“…Nor is there a limitation to planar geometries, as π-holes are also common in linear molecules, such as the area above the C atom of CO 2 [ 42 , 43 , 44 , 45 , 46 , 47 , 48 ], OCS [ 49 , 50 , 51 ], N 2 O, and CS 2 [ 52 , 53 , 54 ]. Just as their σ-hole analogs facilitate attractions toward a nucleophile, the same is true of these π-holes.…”