In this work, ab initio calculations are performed to study chalcogen-chalcogen interactions in binary furan-YHX and thiophene-YHX (X=F, Cl, Br; Y=S, Se) complexes. Interaction energies of these complexes vary between -13.65 and -23.96 kJ/mol at MP2/aug-cc-pVTZ level. For a given X, complexes of SeHX have shorter chalcogen-chalcogen distances than SHX counterparts. The strength of the furan-YHX and thiophene-YHX complexes for a given Y decreases as follows: X = F > Cl > Br. Even though chalcogen-chalcogen interactions are mainly dominated by electrostatic effects, interaction energy decomposition analysis shows that polarization and dispersion effects also make important contributions to the stability of these complexes. In addition, charge-transfer from the O (S) lone pair to the orbital leads to stabilization of these complexes. To further characterize the nature of chalcogen-chalcogen interactions, molecular electrostatic potential and quantum theory of atoms in molecules analyses are performed. Cooperative effects are observed when hydrogen bond and chalcogen-chalcogen interactions coexist in furan-YHF-HCN and thiophene-YHF-HCN.
