For obtaining a transformation function σ iso → δ iso for titanium (oxy)fluorides, a reasonable reference system is TiF 4 . TiF 4 is formed from corner-sharing TiF 6 octahedra (Fig. ) and contains twelve inequivalent fluorine sites that can be classified into two groups: bridging fluorine atoms, that are bonded to two titanium centres, and terminal fluorine atoms, that are bonded to only one titanium centre . High-resolution 19 F NMR data for TiF 4 have previously been reported by Murakami et al. , who derived a linear σ iso → δ iso transformation function by fitting this model function to DFT-calculated σ iso and experimental δ iso data [99]. While the DFT and FIG. . 19 F σiso and σcsa values for TiF4 from DFT calculations (VASP, PBE + DFT-D3), plotted against the corresponding experimental δiso and δcsa values, respectively . Panels (b) and (e) show all data, and corresponding linear-least-squares fits (dashed lines). Panels (a) and (c), and (d) and (f), show the same data, selecting values for terminal F and bridging F only, respectively; each panel shows the original linear model obtained from fitting to the full dataset (dashed lines) and a revised linear model obtained by fitting to the corresponding data subset only (solid lines). The resulting best-fit linear models are δiso = -0.830σiso + 44.1 and δcsa = -0.671σcsa for bridging F, and δiso = -1.116σiso + 67.2 and δcsa = -0.918σcsa for terminal F.