Triply-Reduced Hexa-peri-hexabenzocoronenes: Solid-State Structures and Magnetic Properties

Abstract

Discotic polycyclic aromatics have attracted great interest in both fundamental chemistry and material science due to their degenerate frontier orbitals, high molecular symmetry, unique solid-state packing, and ability to bear a certain number of unpaired electrons that can be applied in molecular spintronics and quantum computing. In this work, chemical reduction of hexa-peri-hexabenzocoronenes, HBC (1) and tBu-HBC (2), as “superbenzenes”, has been investigated with K metal in THF solution. These reactions readily afforded the triply reduced HBC-based products which have been isolated as single-crystalline materials. The X-ray diffraction study confirmed the formation of π-complexes [K+(18-crown-6)(THF)2][{K+(18-crown-6)}2(13–)] (3) and [K+(18-crown-6)(THF)2][{K+(18-crown-6)}2(23–)] (4). In 3 and 4, two potassium ions were found to bind the central six-membered rings of 13– and 23– with one potassium counterion remaining solvent-separated from the complexes. A notable geometry distortion of the HBC core upon three-electron acquisition and metal binding was revealed in both complexes. The presence of bulky substituents in 2 affected the coordination and crystal packing of otherwise similar building units in 4 vs 3. The magnetic properties of 4 supported the existence of a well-isolated S = 3/2 ground state of the 23– triradical in the solid state.