Coordination Abilities of 4,5-Dicyano-2-(trifluoromethyl)imidazolate Anion toward Sodium Cation: Structural and Spectroscopic Studies of Solid and Liquid Glyme-Solvated Electrolyte Systems

Comprehensive structural analysis of sodium 4,5-dicyano-2-(trifluoromethyl)­imidazolate (NaTDI) solvates with glymes (1–4), tetrahydrofuran, and crown ethers has been performed. Several structural motifs obtained from single-crystal X-ray analysis of complementary series of crystalline adducts with varying O:Na ratios were correlated with spectroscopic and thermal data to provide new information about the coordination ability of heterocyclic anions toward sodium cations. Presented results provide a basis for developing models of poly­(ethylene oxide) electrolytes and liquid systems for sodium ion battery electrolytes. We have found a wide variety of anion–cation coordination types which allow us to compare them with analogous lithium solvates in terms of Brown’s valence-matching principle and Lewis acid strength (Sa) parameters. Noticed aggregation modes of sodium salts confirm the occurrence of a solvate disproportionation conductivity mechanism at high salt concentrations which can be used for developing new heterocyclic salt systems for sodium batteries.

本研究针对4,5-二氰基-2-(三氟甲基)咪唑酸钠（NaTDI）与乙二醇二甲醚类（1~4）、四氢呋喃及冠醚形成的溶剂化物完成了全面的结构解析。通过对氧钠比例各异的一系列互补晶体加合物开展单晶X射线衍射分析，并将所得的多种结构基元与光谱学及热分析数据相结合，为阐明杂环阴离子与钠离子的配位能力提供了全新的研究认知。本研究成果可为聚环氧乙烷电解质及钠离子电池电解液用液态体系的模型构建提供理论依据。研究发现了多种阴离子-阳离子配位模式，可基于布朗价匹配原理与路易斯酸强度（Sa）参数，将其与同类锂溶剂化物进行对比分析。观察到的钠盐聚集模式证实，高盐浓度下存在溶剂化物歧化导电机制，该机制可用于开发适用于钠离子电池的新型杂环盐体系。