Insight into the Metal-Involving Chalcogen Bond in the PdII/PtII-Based Complexes: Comparison with the Conventional Chalcogen Bond

The metal-involving Ch<middle dot><middle dot><middle dot>M chalcogen bond and the conventional Ch<middle dot><middle dot><middle dot>O chalcogen bond between ChX(2) (Ch = Se, Te; X = CCH, CN) acting as a Lewis acid and M(acac)(2) (M = Pd, Pt; Hacac = acetylacetone) acting as a Lewis base were studied by density functional theory calculations. It has been observed that the nucleophilicity of the Pt-II complexes is higher than that of the corresponding Pd-II complexes. As a result, the Pt-II complexes tend to exhibit a more negative interaction energy and larger orbital interaction. The strength of the chalcogen bond increases with the increase of the chalcogen atom and the electronegativity of the substituent on the Lewis acid and vice versa. The metal-involving chalcogen bond shows a typical weak closed-shell noncovalent interaction in the (HCC)(2)Ch<middle dot><middle dot><middle dot>M(acac)(2) complexes, while it exhibits a partially covalent nature in the (NC)(2)Ch<middle dot><middle dot><middle dot>M(acac)2 complexes. The conventional Ch<middle dot><middle dot><middle dot>O chalcogen bond displays the character of a weak noncovalent interaction, and its strength is generally weaker than that of metal-involving Ch<middle dot><middle dot><middle dot>M interactions. It could be argued that the metal-involving chalcogen bond is primarily determined by the correlation term, whereas the conventional chalcogen bond is mainly governed by the electrostatic interaction.