Triphenylide-Based Molecular SolidA New Candidate for a Quantum Spin-Liquid Compound

The
reduction of polycyclic aromatic hydrocarbons with alkali metals
results in solids having intriguing magnetic properties the understanding
of which has been hitherto severely hampered by the lack of single-phase
samples. Here, we report on the successful reduction of triphenylene
with stoichiometric amount of potassium in 1,2-dimethoxyethane (DME)
solution. Comprehensive diffraction measurements of the obtained K2(C18H12)2(DME) solid demonstrate
the importance of cation-π interactions as responsible for the
characteristic stacking of the triphenylide molecular ions. Electron
paramagnetic resonance and magnetization measurements reveal K2(C18H12)2(DME) is a Mott
insulator with strikingly strong nearest neighbor antiferromagnetic
interactions between S = 1/2 spins of (C18H12)•– radical anions. Low dimensionality
hinders long-range magnetic ordering and establishes a spin state
that resembles gapped quantum spin liquid state.

碱金属还原多环芳烃可得到具有独特磁学特性的固体产物，但此前由于缺乏单相样品，学界对这类材料磁学性质的理解一直受到严重制约。本研究通过在1,2-二甲氧基乙烷（1,2-dimethoxyethane, DME）溶液中，以化学计量比的金属钾还原三亚苯，成功获得目标产物。对所得K₂(C₁₈H₁₂)₂(DME)固体开展的全面衍射表征结果表明，阳离子-π相互作用是驱动三亚苯阴离子自由基分子离子形成特征堆叠结构的关键因素。电子顺磁共振与磁化强度测试结果显示，K₂(C₁₈H₁₂)₂(DME)属于莫特绝缘体（Mott insulator），其(C₁₈H₁₂)•⁻自由基阴离子的S=1/2自旋之间存在极强的近邻反铁磁相互作用。低维结构抑制了长程磁有序的形成，使其自旋态近似于有隙量子自旋液体态。