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

A series of orthoborate-based ionic materials of bis(glycolato)borate ([BGB]) and bis(ethylene-1,2-dioxy)borate anions ([BEDB]) coupled with tetrabutylphosphonium ([P-4444]) and tetrabutylammonium ([N-4444]) 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 [P-4444][BGB], [P-4444][BEDB], and [N-4444][BEDB] salts feature significantly wider plastic phase I temperature ranges than their analogues. FTIR spectroscopy, multinuclear (N-15, P-31, C-13, and B-11) 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 [P-4444][BGB] among the ionic materials.