Abstract By anodic oxidation of naphthalene in H2CCl2/O.O2m Bu4NPF6 at -45 °C dark red-violet crystals of (C10H8)2PF6 can be obtained by electrocrystallisation. They are stable at low temperatures, however, decompose on warming. In solution and in the polycrystalline state these radical cation salts show only narrow e.p.r. signals without h.f.s. The specific conductivity of a polycrystalline pellet at room temperature was determined to be 0.12 ±0.046 Ohm-1 cm-1 . The structure determination of (C10H8)2PF6 yielded the tetragonal space group P42/n, Z = 2, a = b = 1156(2), c = 640(1) pm. Patterson synthesis and difference Fourier analyses showed the compound to have a columnar stacking of C10H8 units the long molecular axes of which are twisted alternately by 90° around a screw axis in c-direction, and the molecular planes of which are 320 pm apart. The PF6-ions have four nearest C10H8 neighbours lying in pairs in parallel planes 63 pm above and below that plane of PF6- perpendicular to the c-axis and containing a PF4 group. This is the first established case for a columnar structure of a pure hydrocarbon radical cation. (C10H8)2AsF6 is isomorphous.
Pure hydrocarbon cycles in TMC-1: Discovery of ethynyl cyclopropenylidene, cyclopentadiene, and indene