Structural design of ionic conduction paths in molecular crystals for selective and enhanced lithium ion conduction

Abstract

The molecular crystals [Li{N(SO2CF3)2}{C6H4(OCH3)2}2] and [Li{N(SO2CF3)2}{C6F2H2(OCH3)2}2] with solid-state lithium ion conductivity have been synthesized by the addition of two equivalents of 1,2-dimethoxybenzene or 1,2-difluoro-4,5-dimethoxybenzene to Li{N(SO2CF3)2}, respectively. Single-crystal X-ray diffraction analysis revealed the formation of ionic conduction paths with an ordered arrangement of lithium ions in these crystal structures, afforded by the self- assembled stacking of molecular-based channels consisting of N(SO2CF3)2 anion and 1,2-dimethoxybenzene frameworks as a result of intermolecular aromatic and hydrogen interactions. These compounds show selective lithium ion conductivity as the anions behave as a component unit of the conduction paths. The relationship between the crystal structure and ionic conductivity of the molecular crystals provides a clue to the development of novel solid electrolytes based on molecular crystals showing fast and selective lithium ion conduction.

Keywords: conducting materials; crystal engineering; ion channels; lithium; self-assembly; supramolecular chemistry.