Charge-transfer complexes of iodoform with 1,4-dioxane, -dithiane, and -diselenane: Theoretical electron density and energy decomposition analysis

Charge-transfer complexes of iodoform paired with 1,4-dioxane ( C 4 H 8 O 2 ), 1,4-dithiane ( C 4 H 8 S 2 ), and 1,4-diselenane ( C 4 H 8 Se 2 ) were investigated based on MP2 and DFT calculations. These complexes show highly directional interaction structurally in which the closest contact is along the extension of the covalent bond CI in iodoform pointing to the lone pair of chalcogen atom in 1,4-dioxane, -dithiane, and -diselenane. The electron-density topological analysis indicates the charge-transfer interactions in the I ⋯ O (S, Se) contacts belong to the nature of noncovalent weak interaction. Natural bond orbital (NBO) calculations reveal that the electron densities are transferred from the lone pairs of O (S, Se) to the σ ∗ antibonding orbital of CI bond. The interaction energies and second-order perturbation stabilization energies increase in the order of O < S < Se. The decomposition of the interaction energy suggests that the induction energy makes the dominant contribution in these charge-transfer complexes.