Supramolecular Insulating Networks Sheathing Conducting Nanowires Based on Organic Radical Cations

Six materials, (EDT-TTF)4BrI2(TIE)5 (1, where EDT-TTF = ethylenedithiotetrathiafulvalene and TIE = tetraiodoethylene), (EDST)4I3(TIE)5 (2, where EDST = ethylenedithiodiselenadithiafulvalene), (MDT-TTF)4BrI2(TIE)5 (3, where MDT-TTF = methylenedithiotetrathiafulvalene), (HMTSF)2Cl2(TIE)3 (4, where HMTSF = hexamethylenetetraselenafulvalene), (PT)2Cl(DFBIB)2 (5, where PT = bis(propylenedithio)tetrathiafulvalene and DFBIB = 1,4-difluoro-2,5-bis(iodoethynyl)benzene), and (TSF)Cl(HFTIEB) (6, where TSF = tetraselenafulvalene and HFTIEB = 1,1′,3,3′,5,5′-hexafluoro-2,2′,4,4′-tris(iodoethynyl)-biphenyl), consisting of conducting nanowires were obtained by galvanostatic oxidation of the donor molecules in the presence of the corresponding halide anions and iodine-containing neutral molecules. We report their characterizations using single-crystal crystallography, electrical resistance measurements, and electron spin resonance. The structures are built on stacks of planar cations of the donors that are isolated electrically by an insulating network consisting of supramolecular assemblies of the halide anions and neutral molecules held together by a halogen bond. The size and shape as well as the orientation (tilt) of the donors are matched by the self-organization of the insulating sheaths in all cases, providing a pea-in-a-pod example in the field of supramolecular chemistry. The observed resistivities, resistivity anisotropies, and electron spin resonance behaviors of these salts are analyzed by tight-binding band calculations and resistance-array modeling. Crystal 6 with insulating layer of 1 nm thickness exhibits 8 orders of magnitude anisotropy in its resistivity, indicating high potential of the supramolecular network as sheathing material. The observation of such networks leads us to propose a roadmap for future development toward multidimensional memory devices.