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 π‐dimer. Upon three‐electron reduction, bilayer nanographene fragment molecule (C96H24Ar6)2 (Ar=2,6‐dimethylphenyl) (12) was transformed to a triply negatively charged species 123.−, 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). 123.− 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 π‐fused rings with 96 conjugated sp2 carbon atoms. Spin frustration is observed with the frustration parameter f>31.8 at low temperatures in 123.−, which indicates graphene upon reduction doping may behave as a quantum spin liquid. A triply negatively charged radical species based on a bilayer of a C96 nanographene was synthesized and characterized. It is stabilized as an open‐shell doublet ground state with an excited quartet state. It is the largest well‐defined open‐shell graphenic bilayer and also the first example of a triply negatively charged radical π‐dimer. Spin frustration is observed in this species.