Correlation between ¹⁹F Environment and Isotropic Chemical Shift in Barium and Calcium Fluoroaluminates

Abstract

High-speed MAS (19)F NMR spectra are recorded and reconstructed for 10 compounds from BaF(2)-AlF(3) and CaF(2)-AlF(3) binary systems which leads to the determination of 77 isotropic (19)F chemical shifts in various environments. A first attribution of NMR lines is performed for 8 compounds using a superposition model as initially proposed by B. Bureau et al. The phenomenological parameters of this model are then refined to improve the NMR line assignment. A satisfactory reliability is reached with a root-mean-square (RMS) deviation between calculated and measured values equal to 6 ppm. The refined parameters are then successfully tested on alpha-BaCaAlF(7) whose structure was recently determined. Finally, the isotropic chemical shift ranges are defined for shared, unshared, and "free" fluorine atoms encountered in the investigated binary systems. So, the fluorine surroundings can be deduced from the NMR line positions in compounds whose structure is unknown. Such an approach can also be applied to fluoride glasses.

Fluorinated Cu/Zn/Al/Zr hydrotalcites derived nanocatalysts for CO2 hydrogenation to methanol

“…2. Therefore, the main peak at À173.8 ppm was attributed to the AlF 6 octahedra [31]. The NMR peaks of HT-F0.9 and HT-F2.1 were much broader than that of Na 3 AlF 6 , which reveals that other types of fluorine coordination were present.…”

The Relationship Between 27Al Quadrupolar Parameters and AlF63– Octahedron Connectivity in Crystalline and Glassy Fluoroaluminates

“…The crystalline compounds were synthesized as powders by solid-state reaction of mixtures containing the fluorides AlF 3 , CaF 2 and/or BaF 2 ; the synthesis conditions are detailed in ref. [33] The purity and crystallinity of the phases were monitored by powder Xray diffraction analysis. The glassy phases were obtained by heating BaF 2 /CaF 2 /AlF 3 mixtures at 1000°C over a period of 1 h, followed by quenching in cold water.…”

“…[18,19] The crystalline compounds belonging to these systems that are not included in this study are as follows: Ba 5 AlF 13 and Ba 5 Al 3 F 19 , the crystal structures of which are unknown, [31] δ-BaAlF 5 [32] which, to the best of our knowledge, cannot be obtained by a solid-state reaction, and Ba 3 AlF 9 -Ia, which we were unable to synthesize. [33] SATRAS experiments were carried out for all the studied samples. For multi-site crystalline phases and glasses, MQ-MAS spectra were also recorded.…”

Assessment of DFT functionals with NMR chemical shifts

“…In the case of organic molecules and H or C nuclei a set of empirical rules are already established and routinely applied. 2 However, for other (heavier) nuclei, or larger molecules and in particular for solids such rules are more difficult to build [3][4][5][6][7][8] and the interpretation of the experimental data is more complicated task. [9][10][11] The interpretation procedure can be aided by ab-initio calculations provided that the computed spectra can properly reproduce the experimental results.…”