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 center dot 2I(2), contains two centrosymmetric molecules of 1,2,4,5-bis{8',11'-dithia[4.3.3]propella(3',4)}benzene, and four I-2 molecules in the unit cell of space group P2(1)/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 center dot center dot center dot I distance of 2.7844(12) and I-I = 2.8153(5) angstrom. The second type of symmetrically independent sulphur atoms are engaged in a weak interaction of C-H center dot center dot center dot S type with the H center dot center dot center dot S distance of 3.09(1) angstrom. The geometry optimisation of the crystal structure at the B3LYP level with MIDI! basis set gave good agreement with the experimental data (S center dot center dot center dot I distance of 2.754 and I-I = 2.923 angstrom). NBO analysis for the complex showed that the S center dot center dot center dot I interaction is due to charge transfer from the lone pair on the sulphur to the vacant sigma* orbital of the I-2 acceptor. (C) 2012 Elsevier B.V. All rights reserved.