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.