S = 1/2 tetracene monoradical cation/anion: ion-based one-dimensional antiferromagnetic chains

Abstract

The monoradical cation 1˙⁺ and anion 1˙⁻ based on tetracene were generated by one-electron oxidation and one-electron reduction of the bulky tetracene (1), respectively, which contain the largest π-fused skeletons reported to date. For monoradical species, 1˙⁺ and 1˙⁻, EPR spectra and DFT calculation results indicate the spin density delocalized over the whole molecules. Notably, in the solid state, 1˙⁺ and 1˙⁻, respectively, pack into (1˙⁺)_n and (1˙⁻-K-crown)_n, characterized by single-crystal X-ray diffraction studies. The intermolecular interactions of 1˙⁺ and 1˙⁻ are, respectively, through van der Waals forces and exchange couplings supported by metal ions. The monoradical cation polymer (1˙⁺)_n was the first example based on PAHs. The EPR spectra at 90 K of 1˙⁺ and 1˙⁻ all show forbidden transitions (Δm_s = ±2), indicating the existence of electronic coupling between the neighboring radicals, with respective 2J = −6.54 K and 2J = −0.22 K characterized by SQUID measurements.