Hexagonal supramolecular organic conductors based on diiodo(pyrazino)tetraselenafulvalene: high yield recovery of the neutral π-donor by a simple chemical reaction

Abstract

Conducting cation radical salts based on a pyrazine-fused iodine-bonded π-donor diiodo(pyrazino)tetraselenafulvalene (DIPSe) and octahedral anions AF6 (A = P, As, Sb) have been prepared by electrochemical oxidation. X-Ray structure analysis revealed that these three salts are isostructural and crystallize in the hexagonal P63/mcm space group. There is a strong and directional I⋯N iodine bond among the donor molecules, which is 18–19% shorter than the sum of the van der Waals radii. The hexagonal lattice is filled with the equilateral triangles of the donor molecules tailored by the I⋯N iodine bond and there are also two types of supramolecular channels including the counter anion and the crystalline solvent. The room temperature resistivities of these three salts are in the order of 10−2 Ω cm with metallic behaviour and they show a gentle upturn at around 250 K. In addition to the high-symmetrical crystal structure and the metallic conductivity, high yield recovery of the neutral π-donor from the cation radical salts has been accomplished by a simple chemical reaction. In situ1H-NMR monitoring of the reaction process indicates that the DIPSe cation radical was reduced by water and the characteristic supramolecular channels, which allow water molecules to access the cation radicals deep in the crystal, are essential for smooth progress of the recovery process.