Structure and Phase Transitions of Aromatic Radical Cation Salts — a New Class of Organic Metals

Stable radical cation salts of a variety of simple arenes can be prepared by anodic oxidation. These highly conducting crystals of the composition (Ar2‐y)+X− (0 < y < 1, X = BF−4, ClO−4, PF−6, AsF−6, SbF−6) are deposited on the anode during the electrocrystallization. They can be considered as new family of organic conductors built up from simple, easily obtainable building blocks. — The packing found between the aromatic rings can be regarded as a model for the interchain interactions in conducting polymers, e.g. doped poly‐p‐phenylene. — The crystal structures of most radical cation salts can be characterized as columnar structures. The molecular overlap plays an important role in the electrical and magnetic properties. The geometry of this overlap is changed in metal‐insulator transitions which occur near 200 K. The phase transition in FA2PF6 has been investigated in detail and recent results are discussed. — In contrast to most radical cation salts which owing to their columnar structures are one‐dimensional conductors the salt of 2,6‐dimethylnaphthalene can be characterized as two‐ or three‐dimensional organic metal. The crystal structure of DMN3(SbF6)2(CH2Cl2) has been solved and is discussed in this paper.