Structural and theoretical study on the 1:2 addition complex of 1,2,4,5-bis{8′,11′-dithia[4.3.3]propella(3′,4′)}benzene with I2

The crystal structure of the title compound, C22H26S4·2I2, contains two centrosymmetric molecules of 1,2,4,5-bis{8′,11′-dithia[4.3.3]propella(3′,4′)}benzene, and four I2 molecules in the unit cell of space group P21/c. The cyclohexene rings adopt boat conformation, whereas tetrahydrothiophene rings have envelope conformation. The iodine molecules are linked to one type of the sulphur atoms of the propellane molecule by a charge-transfer bond, with S⋯I distance of 2.7844(12) and I–I = 2.8153(5) Å. The second type of symmetrically independent sulphur atoms are engaged in a weak interaction of C–H⋯S type with the H⋯S distance of 3.09(1) Å. The geometry optimisation of the crystal structure at the B3LYP level with MIDI! basis set gave good agreement with the experimental data (S⋯I distance of 2.754 and I–I = 2.923 Å). NBO analysis for the complex showed that the S⋯I interaction is due to charge transfer from the lone pair on the sulphur to the vacant σ* orbital of the I2 acceptor.

► Propellane: tricyclic compound with elongated conjoining bond common for three rings.
► One sulphur atom of tetrahydrothiophene rings interacts with I2 molecule by CT bond.
► Charge transfer from the lone pair of the sulphur to the vacant σ* orbital of the I2.
► Second sulphur atom of tetrahydrothiophene rings is an acceptor in C–H⋯S interaction.