Elektrochemische Synthesen, XIV [1] Radikalkation-Salze des Naphthalins / Electrochemical Syntheses, XIV [1]. Radical Cation Salts of Naphthalene

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.