Strong Iodine···Oxygen Interactions in Molecular Conductors Incorporating Sulfonate Anions

Strong I···O halogen bonds are identified in a series of cation radical salts of the donor molecule 3,4-diiodo-3′,4′-ethylenedithiotetrathiafulvalene (EDT-TTFI2, 1) with ClO4– and various organic sulfonates, such as racemic camphor sulfonate, 1,5- and 2,6-naphtalene bis(sulfonate), and 2,6-anthracene bis(sulfonate). In all compounds, oxygen atoms of sulfonate moieties appear thus as powerful halogen bonding acceptors with I···O distance much shorter than the van der Waals contacts (down to 77%). A full charge transfer (ρ = 1) is found in (1)ClO4 and (1)2[2,6-Napth(SO3)2], with a dimerization of the stacks of 1•+ cation radicals and a diamagnetic behavior. The mixed-valence (ρ = 1/2) salts (1)2[(rac)-camph(SO3)]·Solv, (1)5[2,6-Anthr(SO3)2], and (1)4[1,5-Napht(SO3)2] form conducting stacks with semiconducting behavior. Band structure calculations and magnetic measurements performed on (1)4[1,5-Napht(SO3)2] show a strongly one-dimensional electronic structure, at the origin of the semiconducting behavior.