NaCl in a 1:1 stoichiometry is the only known stable form of the Na–Cl crystal under ambient conditions, and non-1:1 Na–Cl species can only form under extreme conditions, such as high pressures. Here we report the direct observation, under ambient conditions, of Na₂Cl and Na₃Cl as two-dimensional (2D) Na–Cl crystals, together with regular NaCl, on reduced graphene oxide membranes and on the surfaces of natural graphite powders from salt solutions far below the saturated concentration. Molecular dynamics and density functional theory calculations suggest that this unconventional crystallization process originates from the cation–π interaction between the ions and the π-conjugated system in the graphitic surface, which promotes the ion–surface adsorption. The strong Na⁺–π interaction and charge transfer lead to stoichiometries with an excess of Na⁺. With unique electron and spin distributions and bonding, the resulting 2D crystals may have unusual electronic, magnetic, optical and mechanical properties.

化学计量比为1：1的NaCl是Na–Cl晶体在环境条件下唯一已知的稳定形式，非1：1 Na–Cl物种只能在极端条件下（例如高压）形成。在这里，我们报告在环境条件下，在还原的氧化石墨烯膜和天然石墨粉末表面上，以二维（2D）Na–Cl晶体以及规则的NaCl形式直接观察到Na ₂ Cl和Na ₃ Cl的情况。盐溶液远低于饱和浓度。分子动力学和密度泛函理论计算表明，这种非常规的结晶过程起源于离子与π之间的阳离子-π相互作用石墨表面的共轭体系，可促进离子表面吸附。强的Na ⁺ - π相互作用和电荷转移导致的化学计量与过量的Na ⁺。具有独特的电子和自旋分布以及键合，所得的2D晶体可能具有异常的电子，磁性，光学和机械特性。