A Triply Negatively Charged Nanographene Bilayer with Spin Frustration

We report on the largest open-shell graphenic bilayer and also the first example of triply negatively charged radical pi-dimer. Upon three-electron reduction, bilayer nanographene fragment molecule (C96H24Ar6)(2) (Ar=2,6-dimethylphenyl) (1(2)) was transformed to a triply negatively charged species 1(2)(3).(-), which has been characterized by single-crystal X-ray diffraction, electron paramagnetic resonance (EPR) spectroscopy and magnetic properties on a superconducting quantum interference device (SQUID). 1(2)(3).(-) features a 96-center-3-electron (96c/3e) pancake bond with a doublet ground state, which can be thermally excited to a quartet state. It consists of 34 pi-fused rings with 96 conjugated sp(2) carbon atoms. Spin frustration is observed with the frustration parameter f > 31.8 at low temperatures in 1(2)(3).(-), which indicates graphene upon reduction doping may behave as a quantum spin liquid.

Automated summary

This study reports on the largest open-shell graphenic bilayer and the first example of a triply negatively charged radical pi-dimer. The transformation of a bilayer nanographene fragment molecule to a triply negatively charged species was characterized using various techniques. The resulting compound exhibits spin frustration and suggests that reduced graphene may behave as a quantum spin liquid.