Synthesis, crystal structure and Hirshfeld analysis of a new crystalline modification of the radical ion salt octa­methyl­ene­tetra­thia­fulvalenium triiodide (OMTTF)I3

The reaction between 4,5,6,7-tetra­hydro-2-(4,5,6,7-tetra­hydro-1,3-benzodi­thiol-2-yl­idene)-1,3-benzodi­thiole (common name: 4,4′,5,5′,6,6′,7,7′-octa­hydro­dibenzo­tetra­thia­fulvalene, OMTTF) and an excess of iodine in tetra­hydro­furan (THF) yielded the respective radical organic polyiodide salt, C14H16S4+·I3−. The asymmetric unit contains one and a half formula unit of both the cation and the anion, with the half-ions completed through inversion symmetry. The (OMTTF^\bullet+) positive charge can be assigned by the bond distances and the planar structure of the C2S2C=CS2C2 central fragment. In the crystal, trimers of triiodide anions are connected through secondary inter­molecular I⋯I inter­actions into almost linear I93− polyanions. The non-centrosymmetric OMTTF radical cations are linked by S⋯S inter­actions into centrosymmetric dimers, while the centrosymmetric OMTTF cations remain as discrete units. The (OMTTF^\bullet+) radical cations and the triiodide anions are linked by weak C—H⋯I and C—H⋯S inter­actions into a three-dimensional network. This work reports the fourth crystalline modification of the C14H16S4^\bullet+·I3− salt. The three previous modifications were obtained from a mixture of aceto­nitrile and toluene [Konarev et al. (2005). Synth. Met. 151, 231–238].