Theoretical comparative study on interactions of the pseudo-π type (CH 2 ) 3  … MX with (CH 2 ) 3  … HX/XY (M = Cu, Ag, Au; X, Y = F, Cl, Br)

Theoretical calculation at the X3LYP/aug-cc-pVTZ level was performed to research the interactions in the pseudo-π type complexes of (CH₂)₃ … MX (M = Cu, Ag, Au; X = F, Cl, Br) and compared with the isomorphous (CH₂)₃ … HX and (CH₂)₃ … XY (X, Y = F, Cl, Br) complexes. Equilibrium geometries, molecular electrostatic potentials, the energy decomposition analysis, relevant natural bond orbital characteristics and the atoms in molecules topological analysis were conducted to investigate the interaction energies of the dimer complexes. The results demonstrated that all complexes have C_2v symmetry with all heavy atoms coplanar. In (CH₂)₃ … MX, the interaction energy reduced with the decrease of electronegativity in F, Cl and Br, respectively, and a better linear relationship between the interaction energy and electron charge density is observed. The energy decomposition analysis reveals that the dominant driving force for the pseudo-π interaction in (CH₂)₃ … MX (M = Cu, Ag) is the electrostatic energy, while in (CH₂)₃-AuX, the polarisation energy is important. Hydrogen- and halogen-bond complexes were formed in (CH₂)₃ … HX and (CH₂)₃ … XY complexes and shown non-covalent interactions, and the interaction energies are lower than that of (CH₂)₃ … MX complexes.