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

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˙+) and (1˙--K-crown), 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˙+) 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.