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

Abstract

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⁺&sdot;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^&bull;+) 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&sdot;&sdot;&sdot;I interactions into almost linear I₉³⁻ polyanions. The non-centrosymmetric OMTTF radical cations are linked by S&sdot;&sdot;&sdot;S interactions into centrosymmetric dimers, while the centrosymmetric OMTTF cations remain as discrete units. The (OMTTF^&bull;+) radical cations and the triiodide anions are linked by weak C—H&sdot;&sdot;&sdot;I and C—H&sdot;&sdot;&sdot;S interactions into a three-dimensional network. This work reports the fourth crystalline modification of the C₁₄H₁₆S₄^&bull;+&sdot;I₃⁻ salt. The three previous modifications were obtained from a mixture of acetonitrile and toluene [Konarev <em>et al.</em> (2005). <em>Synth. Met.</em> 151, 231–238].