Synthesis, crystal structure and Hirshfeld analysis of a new crystalline modification of the radical ion salt octa-methyl-ene-tetra-thia-fulvalenium triiodide (OMTTF)I 3 .

The reaction between 4,5,6,7-tetra-hydro-2-(4,5,6,7-tetra-hydro-1,3-benzodi-thiol-2-yl-idene)-1,3-benzodi-thiole (common name: 4,4',5,5',6,6',7,7'-octa-hydro-dibenzo-tetra-thia-fulvalene, OMTTF) and an excess of iodine in tetra-hydro-furan (THF) yielded the respective radical organic polyiodide salt, C14 H16 S4 + ·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 + ) positive charge can be assigned by the bond distances and the planar structure of the C2 S2 C=CS2 C2 central fragment. In the crystal, trimers of triiodide anions are connected through secondary inter-molecular I⋯I inter-actions into almost linear I9 3- polyanions. The non-centrosymmetric OMTTF radical cations are linked by S⋯S inter-actions into centrosymmetric dimers, while the centrosymmetric OMTTF cations remain as discrete units. The (OMTTF + ) radical cations and the triiodide anions are linked by weak C-H⋯I and C-H⋯S inter-actions into a three-dimensional network. This work reports the fourth crystalline modification of the C14 H16 S4 + ·I3 - salt. The three previous modifications were obtained from a mixture of aceto-nitrile and toluene [Konarev et al. (2005 ▸). Synth. Met. 151 , 231-238].