Self-assembled core–shell clusters in deep eutectic solvents based on tetra-n-alkylammonium cations for high dissolution of strongly hydrogen-bonded small molecules

Strongly hydrogen-bonded compounds such as 1,3,5-triamino-2,4,6‑trinitrobenzene (TATB, an important insensitive high explosive) have excellent stability, but poor solubilities to limit their recrystallization, purification and recycling. In this study, core–shell clusters based on symmetrical tetra-n-alkylammonium [TTA]⁺ are designed to provide an inner cavity to incorporate TATB, and thus the clusters can separate TATB from original hydrogen-bonded networks to increase largely the solubility. Based on this design, deep eutectic solvents (DESs) based on [TTA]⁺ cations are first developed to yield self-assembled core–shell clusters for solubilizing TATB. Ninety-nine DESs based on [TTA]⁺ were prepared by combining with halide ions and hydrogen bond donors, and TATB's solubility increases with the formation of core–shell clusters. Tetrabutyl ammonium ([TBA]⁺ )-based DES (CS-1) displays excellent dissolution toward TATB. Room-temperature solubility of TATB in CS-1 with 32.88 mg/mL is about 10 times higher than recently reported ionic liquids and approximately 470 times higher than DMSO. Compared to traditional solvents, CS-1 shows economical and high dissolution ability toward TATB. The dissolution mechanism is demonstrated by experimental characterizations and theoretical calculations. After forming Zundel-type complexes between TATB and F^-, the complexes as the core are surrounded by [TBA]⁺ as the shell to yield core–shell clusters through self-assembly of electrostatic interaction.