Optimizing Lithium Ion Conduction through Crown Ether-Based Cylindrical Channels in [Ni(dmit)₂]⁻ Salts

The synthesis of artificial ion channels is one of the core areas of biomimetics and is aimed at achieving control over channel functionality by careful design and selection of the constituent components. However, the optimization of ionic conductivity in the channel in the crystalline state is challenging because of crystal strain, polymorphism, and potentially limited stability. In this study, the pore size of cylindrical channels was controlled with the aim of optimizing ionic conductivity. We prepared two isomorphic salts, Li2([18]­crown-6)3[Ni­(dmit)2]2(H2O)4 (1) and Li2([15]­crown-5)3[Ni­(dmit)2]2(H2O)2 (2), both of which possess ion channels formed by a one-dimensional array of crown ethers, Li+ ions, and crystalline water molecules. Meanwhile, [Ni­(dmit)2]− (S = 1/2) molecules formed a ladder configuration with Jrung/kB = −631(5) K, Jleg/kB = −185(5) K for 1, and Jrung/kB = −517(4) K, Jleg/kB = −109(5) K for 2. For 1, the Li+ ionic conductivity at 293 K in the crystalline state was enhanced from 1.89(18) × 10–8 S·cm–1 to 2.46(6) × 10–7 S·cm–1 via dehydration. Furthermore, analysis of Li+ ionic conductivities of 2, which incorporated a crown ether with a smaller cavity (the cavity diameters of [18]­crown-6 and [15]­crown-5 are 2.60–3.20 Å and 1.70–2.20 Å, respectively) at the same temperature both before and after dehydration revealed conductivities of 1.93(31) × 10–8 S·cm–1 and 7.01(21) × 10–7 S·cm–1, respectively. This molecular design approach can contribute to increasing the ionic conductivity as well as the development of all-solid-state lithium ion batteries and other electronic device fabrications.人工离子通道的合成是仿生学（biomimetics）的核心研究领域之一，旨在通过对组成组分的精准设计与筛选，实现对通道功能的调控。然而，受晶体应变、多晶型现象以及潜在稳定性不足的限制，优化晶态通道内的离子电导率极具挑战。本研究通过调控圆柱形通道的孔径以优化离子电导率，制备了两种同构盐：Li₂([18]冠醚-6)₃[Ni(dmit)₂]₂(H₂O)₄（记为化合物1）与Li₂([15]冠醚-5)₃[Ni(dmit)₂]₂(H₂O)₂（记为化合物2），二者均拥有由冠醚（crown ether）、锂离子（Li+）与结晶水分子构成的一维阵列型离子通道。与此同时，[Ni(dmit)₂]⁻（自旋S=1/2）分子形成了梯形构型：对于化合物1，其梯间耦合项与玻尔兹曼常数（kB）的比值Jrung/kB为−631(5) K，梯链耦合项与玻尔兹曼常数的比值Jleg/kB为−185(5) K；对于化合物2，Jrung/kB为−517(4) K，Jleg/kB为−109(5) K。针对化合物1，经脱水处理后，其晶态下293 K时的锂离子电导率从1.89(18)×10⁻⁸ S·cm⁻¹提升至2.46(6)×10⁻⁷ S·cm⁻¹。此外，对化合物2的分析显示，该化合物采用了孔径更小的冠醚（[18]冠醚-6与[15]冠醚-5的孔径范围分别为2.60–3.20 Å与1.70–2.20 Å），在脱水前后的相同温度下，其锂离子电导率分别为1.93(31)×10⁻⁸ S·cm⁻¹与7.01(21)×10⁻⁷ S·cm⁻¹。该分子设计策略不仅有助于提升离子电导率，还可为全固态锂离子电池（all-solid-state lithium ion batteries）及其他电子器件的开发与制备提供支撑。