Solution-synthesized stable triaza[4]triangulene triradical with a quartet ground state.

Bai, Xudong; Zhang, Di; Zhang, Yushuang; Wang, Yihan; Cheng, Yanning; Xie, Yi; Zhu, Ziqi; Jiang, Shang-Da et al. · Nat Commun · 2026

basic_science · Level V

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Abstract

As a renowned class of open-shell molecules characterized by triangular nanographenic structures and novel magnetic properties with high-spin ground states, triangulenes are attractive targets to both synthetic chemists and molecular magnet researchers. Here, a highly stable aza-derivative of [4]triangulene triradical (1) is achieved, with a quartet ground state (S = 3/2). By virtue of the stability under ambient conditions (τ<sub>1/2</sub> ~ 9 days in the solid state and 28 h in an air-saturated solution), thorough structural and magnetic characterizations are performed. Crystallographic analysis confirms that 1 has a planar triangular polycyclic aromatic skeleton embedded with delocalized spins. Concurrently, continuous-wave and pulsed EPR spectroscopies provide unambiguous evidence supporting its high-spin ground state. SQUID measurements reveal impressively large doublet-quartet energy gap (ΔE<sub>D-Q</sub> = 3.18 kcal/mol), indicating very strong intramolecular ferromagnetic spin-spin exchanges (J/k<sub>B</sub> = +534 K) rendered by the triangulene structure.