Ionic Interaction Effects on the Structure and Dynamics of Orthoborate Ionic Materials

Abstract

A series of orthoborate-based ionic materials of bis(glycolato)borate ([BGB]) and bis(ethylene-1,2-dioxy)borate anions ([BEDB]) coupled with tetrabutylphosphonium ([P₄₄₄₄]) and tetrabutylammonium ([N₄₄₄₄]) cations have been synthesized, and their physicochemical properties are characterized. The ionic materials based on the most popular orthoborate anion, bis(oxalato)borate anion ([BOB]), which contains four carbonyl groups, are all liquid at ambient temperature, while the bis(glycolato)borate ([BGB]) anion, with two carbonyl groups, and the bis(ethylene-1,2-dioxy)borate ([BEDB]) anion, without carbonyl groups, render solids at ambient temperature. The ionic materials based on the [BGB] anion display the highest decomposition temperatures, and those based on the BEDB anion are the lowest. The [P₄₄₄₄][BGB], [P₄₄₄₄][BEDB], and [N₄₄₄₄][BEDB] salts feature significantly wider plastic phase I temperature ranges than their analogues. FTIR spectroscopy, multinuclear (¹⁵N, ³¹P, ¹³C, and ¹¹B) solid-state NMR spectroscopy, and single-crystal X-ray diffraction were all used to unveil the ionic interactions and structural features, which display weaker ionic interactions for [BEDB] compared to [BGB] when bearing the same cation and present relatively higher crystallinity of [P₄₄₄₄][BGB] among the ionic materials.

A series of orthoborate-based organic ionic materials have been synthesized, rendering ionic liquids, plastic crystals and solids, and their ionic interactions and structural features together with physicochemical properties are unveiled by employing multinuclear solid-state NMR spectroscopy, FTIR, and single-crystal X-ray diffraction.