Structural investigations of β-CaAlF5 by coupling powder XRD, NMR, EPR and spectroscopic parameter calculations

β-CaAlF5 was synthesized by solid-state reaction. The precise structure was refined from X-ray powder diffraction data in the monoclinic space group P21/c   with lattice constants a=5.3361Å, b=9.8298Å, c=7.3271Å, and β=109.91°β=109.91° (Z=4Z=4). The structure exhibits isolated chains of AlF63- octahedra sharing opposite corners.19F and 27Al solid state NMR spectra were recorded using MAS and SATRAS techniques. An EPR spectrum was recorded for β-CaAlF5:Cr3+. The experimental spectra were simulated in order to extract the NMR and EPR parameter values. Five fluorine sites and one low symmetry aluminium site were found in agreement with the refined structure.These parameters were calculated using empirical and ab-initio methods. The agreement obtained between the calculated 19F chemical shift values, 27Al quadrupolar parameters, Cr3+ EPR fine structure parameters and the experimental results demonstrates the complementarity of XRD, magnetic resonance experiments and theoretical methodologies.

Graphical abstractView of β-CaAlF5, exhibiting isolated chains of AlF63- octahedra sharing opposite corners.Figure optionsDownload full-size imageDownload as PowerPoint slide