Anion Coordination
Interactions in Solvates with the Lithium Salts LiDCTA and LiTDI
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Abstract
Lithium 4,5-dicyano-1,2,3-triazolate
(LiDCTA) and lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI)
are two salts proposed for lithium battery electrolyte applications,
but little is known about the manner in which the DCTA<sup>–</sup> and TDI<sup>–</sup> anions coordinate Li<sup>+</sup> cations.
To explore this in depth, crystal structures are reported here for
two solvates with LiDCTA(G2)<sub>1</sub>:LiDCTA and (G1)<sub>1</sub>:LiDCTAwith diglyme and monoglyme, respectively; and
seven solvates with LiTDI(G1)<sub>2</sub>:LiTDI, (G2)<sub>2</sub>:LiTDI, (G3)<sub>1</sub>:LiTDI, (THF)<sub>1</sub>:LiTDI, (EC)<sub>1</sub>:LiTDI, (PC)<sub>1</sub>:LiTDI, and (DMC)<sub>1/2</sub>:LiTDIwith
monoglyme, diglyme, triglyme, tetrahydrofuran, ethylene carbonate,
propylene carbonate, and dimethyl carbonate, respectively. These latter
solvate structures are compared with the previously reported acetonitrile
(AN)<sub>2</sub>:LiTDI structure. The solvates indicate that the LiTDI
salt is much less associated than the LiDCTA salt and that the ions
in LiTDI, when aggregated in solvates, have a very similar TDI<sup>–</sup>···Li<sup>+</sup> cation mode of coordination
through both the anion ring and cyano nitrogen atoms. Such coordination
facilitates the formation of polymeric ion aggregates, instead of
dimers. Insight into such ion speciation is instrumental for understanding
the electrolyte properties of aprotic solvent mixtures with these
salts