FTIR and multinuclear magnetic resonance studies of tris(oxaalkyl) borates and their complexes with Li+ and Na+ cations

Abstract

FTIR and NMR of ¹H, ¹³C, ¹¹B, ⁷Li and ²³Na nuclei were used for the study of the complexation of Li⁺ and Na⁺ cations by three tris(oxaalkyl) borates. The NMR techniques proved the formation of complexes and the fluctuation of Li⁺ and Na⁺ cations in the respective channels formed by three oxaalkyl chains. In the FTIR spectra of Li⁺ complexes with three tris(oxaalkyl) borates, continuous absorption in the far-infrared region indicates the fast fluctuations of Li⁺ ion between O atoms of the channels. The dependence of the continua shape on the length of the channels, i.e., the number of minima in the multiminima potentials, demonstrates that the fluctuation of Li⁺ ion occurs along the channel. Owing to the larger mass and diameter of the Na⁺ cation in the Na⁺–tris(oxaalkyl) borate complexes, only systems with longer channels show a large Na⁺ polarizability due to the fast fluctuation of Na⁺ cations in a multiminima potential.