On the assignment of F-19 MAS NMR spectra of fluoroaluminates using through-space spectral edition of F-19-(27) Al and F-19-F-19 connectivities

Advantages and limitations of F-19-Al-27 and F-19-F-19 dipolar-based 2D NMR experiments for F-19 MAS spectra assignments of fluoroaluminates are presented. In beta-BaAlF5, combination of 2D MAS F-19-Al-27 CP-HETCOR and F-19-F-19 DQ-SQ NMR correlation experiments allows complete unambiguous assignment of the ten poorly resolved resonances of same relative intensities of the F-19 MAS NMR spectrum. The gain in resolution of the F-19 MAS 2D spectrum compared to a 1D spectrum is evidenced, allowing distinction of the two shared-fluorine resonances of Ba3Al2F12. Limitations of the F-19 MAS DQ-SQ NMR experiment are shown for Ba3Al2F12 and for alpha-CaAlF5. For beta-BaAlF5 and Ba3Al2F12, final line assignments question those previously established from F-19 isotropic chemical shift calculations, which demonstrate that such experiments are essential for correct line assignments and assessment of calculation results.