Decacyclene Radical Anions Showing Strong Low-energy Intramolecular Absorption and Magnetic Coupling of Spins in a Hexagonal Network.

Two salts of the aromatic hydrocarbon decacyclene, {cryptand[2.2.2](Cs+ )} (decacyclene.- ) (1) and {Bu3 MeP+ }(decacyclene.- ) (2), were obtained. In both salts, decacyclene.- radical anions formed channels occupied by cations. However, corrugated hexagonal decacyclene.- layers could be outlined in the crystal structure of 1 with several side-by-side C⋅⋅⋅C approaches. The decacyclene.- radical anions showed strong distortion in both salts, deviating from the C3 symmetry owing to the repulsion of closely arranged hydrogen atoms and the Jahn-Teller effect. Radical anions showed intense unusually low energy absorption in the IR-range, with maxima at 4800 and 6000 cm-1 . According to the carculations, these bands can originate from the SOMO-LUMO+1 and SOMO-LUMO+2 transitions, respectively. Radical anions exhibited a S=1/2 spin state, with an effective magnetic moment of 1.72 μB at 300 K. The decacyclene.- spin antiferromagnetically coupled with a Weiss temperature of -11 K. Spin ordering was not observed down to 1.9 K owing to spin frustration in the hexagonal decacyclene.- layers.