pi-Pimer, pi-Dimer, pi-Trimer, and 1D pi-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated pi Interactions and Physical Properties in Crystalline State

We herein present the efficient syntheses, crystal structures, and physical properties of a series of novel benzene triimide (BTI) radical anions, emphasizing the relationship between molecular structure with spin-spin intermolecular interactions and physical properties in the crystalline state. BTI radical crystals were preparedby reducing various substituted BTIs (1) with cobaltocene (CoCp2), followed by sequential crystallization processes. Two isolable radical species, that is, neutral molecule-radical anion pair (2) and monoradical species (3), were obtained from BTIs bearing small substituents (ethyl and propyl), while for those bearing larger substituents (butyl, hexyl, and benzyl) sole monoradicals (3) were produced. The radical species showed diverse intermolecular stackings in the crystalline state referred to as pi-pimer, pi-dimer, alternating pi-trimer, and one-dimensional (1D) slipped pi-stacks depending on the length and size of the substituents. Different spin-spin interactions arising from the substituent-tuned radical packings were demonstrated by electron spin resonance (ESR) spectra. The structure-property relationship was studied in terms of magnetism and conductivity. The radical pi-pimers and pi-stacks with effective charge transport exhibited paramagnetic property and conductivity feasibly at room temperature, while pi-dimers and pi-trimers featuring thermally populated spin-triplet states were antiferromagnetic and nonconductive due to their strong radical-radical pairing effect. [GRAPHICS] .