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

Neutron Diffraction Study of Significant sp3 and sp2 C-H Bond Shortening in a Fluorinated Pyridinium Saccharinate

We have experimentally shown by neutron diffraction significant shortening of both sp³- and sp²-hybridized C-H bonds to 1.092(2) and 1.081(1) Å in a hydrogen-bonded crystal of a difluorinated compound, 4-((2,2-difluoroethoxy)methyl)pyridinium saccharinate. Both MP2 and DFT calculations affirmed the C-H bond shrinkages. Sanderson's electronegativity equalization principle provides insight into the shortening of the C-H covalent bond lengths for both sp³- and sp²-hybridized carbon atoms. To the best of our knowledge, this neutron diffraction study has revealed the largest extents of sp³ and sp² C-H bond shrinkages with a 3-sigma rule being satisfied.

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

Ab initio MP2/aug-cc-pVTZ calculations have been carried out in order to study the nature of P···Cl halogen bonding interaction between a phosphorus atom in an aromatic ring in para-substituted phosphabenzene (PPBZ) and ClF molecule. The interaction of PPBZ with ClF results in two different types of complexes: (i) complex formation through the chlorine-shared halogen bond (T1-X-PPBZ·ClF) and (ii) complex formation via halogen-π interaction (T2-X-PPBZ·ClF). T1-X-PPBZ·ClF complexes are found to be more stable than the T2-X-PPBZ·ClF complexes. This work also presents a general criterion to distinguish a chlorine-shared halogen bond from a traditional halogen bond and sheds light on the formation of the chlorine-shared halogen bond. The binding energy of T1-X-PPBZ·ClF complexes correlates well with the negative electrostatic potential of the P atom and PA value of the substituted PPBZ. The properties of both T1-X-PPBZ·ClF and T2-X-PPBZ·ClF complexes are analyzed using atom-in-molecule, natural bond orbital, and symmetry-adapted perturbation theory calculations. The variation of the Cl-F bond distances and the redshifts of the ν(ClF) vibration resulting from the interaction with PPBZs are discussed.

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

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.

Unusual Fluorine Substitution Effect on S···Cl Bonding between Sulfides and Atomic Chlorine

A theoretical investigation on the interaction of various sulfides and their fluorinated counterparts (H₂S, HSF, F₂S, CH₃SH, CH₃SF, CH₂FSH, CH₂FSF, NH₂SH, NH₂SF) with atomic chlorine has been carried out using density functional theory (DFT) based LC-BLYP/aug-cc-pVTZ and sophisticated ab initio CCSD(T)/aug-cc-pVQZ methods. The present study is intended to discuss the influence of the substituents implanted at the sulfur atom on the bonding parameters. The optimized geometries reveal that intermolecular S···Cl distances are short and range between 2.423 and 2.561 Å. A strong contraction of the S-F bond is also predicted. Two-center-three-electron S···Cl bonds are formed; the interaction energies are large and range from -33.9 to -70.1 kJ mol^-1. Very surprisingly, the interaction energies are greater and the intermolecular distances are shorter for F-substituted sulfides than for unsubstituted ones. This is in complete contrast with the lower proton affinities and less negative electrostatic potentials of fluorinated sulfides. AIM analysis, the charge transfer from the sulfur atom to the Cl atom, and the spin densities on the Cl and S atoms are considered to explain this unusual behavior. The hyperconjugation energies from the LP(F) to the σ*(S-Cl) antibonding orbital can be considered as one of the stabilizing factors for the greater stability of the fluorinated complexes over the nonfluorinated ones.