Theoretical study of the nature of σ-hole regium bond between CuX/AgX/AuX and pyridine

Context

The σ-hole regium bond complexes between coinage metal monohalide molecule CuX/AgX/AuX (X = F, Cl, and Br) and pyridine (C₅H₅N), which have linear orientation and perpendicular orientation, have been systematically probed at the MP2/aug-cc-pVTZ level. By comparing the calculated interaction energy, we can see that the linear orientation interactions are a little stronger than the corresponding perpendicular orientation interactions in C₅H₅N-CuX/AgX/AuX complexes. The binding energies for linear orientation regium bond complexes range from − 34 to − 60 kcal/mol, while those perpendicular orientation regium bond complexes are from − 24 to − 50 kcal/mol. Both types of interactions energies all tend to follow the Au > Cu > Ag order and reduced with the decrease in electronegativity F > Cl > Br in C₅H₅N-CuX/AgX/AuX complexes. The electrostatic energy is the major source of the attraction for the linear orientation regium bond interactions, while for the perpendicular orientation regium bond interactions are mainly due to electrostatic and induction energy.

Methods

All the complexes and respective monomers were optimized at the MP2/aug-cc-pVTZ level. Relativistic effects were considered for Cu, Ag, Au, and Br by using the aug-cc-pVTZ-PP basis set. The NBO population analysis and AIM and IRI analysis were carried out. The interaction energies of the σ-hole regium bonds complexes were decomposed by using the symmetric adaptive perturbation theory (SAPT).