A spectroscopic and computational study of Al(III) complexes in sodium cryolite melts: Ionic composition in a wide range of cryolite ratios

A spectroscopic and computational study of Al(III) complexes in cryolite melts: Effect of cation nature

“…2. The same conformations were found previously for an ${\text{AlF}}_4^{-}·{\text{Na}}^{+}$ pair [18]. The free energy of (i) $\iff$ (ii) process corrected for medium effects ($\mathrm{\Delta }{G}_{(i)/(\mathit{ii})}$) was calculated to be −7.9, −5 [18], −2.1 kcal mol−1 for Li, Na, K, respectively.…”

“…1. Deconvolution of the spectra for potassium and especially lithium melts is ambiguous, thus in contrast to sodium melts [18], any quantitative analysis of equilibrium constants is impossible. We can maintain, however, the most important qualitative trends: (1) a slight shift of v max towards lower values takes place in a sequence Li…Na…K, i.e.…”

“…One should mention that even approximate fitting is enough to determine the frequencies for the maxima of the principle bands with high accuracy. For assignment of these three bands (Table 2) we used the same approach as applied earlier for sodium melts [18].…”

“…Our calculations are related to neutral ensembles, with the charge excess of anionic Al(III) complexes compensated by the cations. We thus assume that the formed ion pairs (small clusters) address the short – range effects of the ionic environment (a similar model was used in [18]). For the description of Al, F, Li and K atoms the standard triple-zeta 6-311G valence basis set augmented by polarization (d) functions was employed.…”

“…Raman spectroscopy forms a natural link between molecular modelling and the prediction of microscopic properties of melts, as calculated spectra can be employed to verify model results. In our previous communication [18] we have reported some results on a combined experimental and computational study of sodium cryolite in 1–3 CR intervals, in order to demonstrate the possibilities of such an approach. In what follows we present experimental Raman spectra for lithium and potassium cryolites melts in the same range and discuss the reasons of cation-dependent spectral behaviour on the basis of molecular-level treatment of assumed equilibria.…”