Neutron Powder Diffraction, Multinuclear, and Multidimensional NMR Structural Investigation of Pb5Ga3F19

The room temperature structure of Pb5Ga3F19 is investigated by combining neutron diffraction and multinuclear F-19, Ga-71, and Pb-207 one-dimensional and two-dimensional solid-state nuclear magnetic resonance (NMR) experiments. Two models built in space group 14cm are reported for the description of the crystalline structure of Pb5Ga3F19. The structure is built from a network of both opposite corner-sharing Ga2F(6)(3-) octahedra forming infinite chains along the c-axis and isolated GalF(6)(3-) octahedra. The two models present two slightly different views of the strong static disorder of the fluorine ions belonging to the Ga2F(6)(3-) octahedra. Ga-71 NMR results show that the local environment of all Ga2 ions is identical, which indicates a tilt of the Ga2F(6)(3-) octahedra within the chains. Pb-207 NMR experiments confirm that the environment of only one of the two lead sites, Pb1, is strongly affected by the disorder, which gives rise to three broad distinct Pb-207 NMR lines for this site. All F-19 NMR lines are assigned using the F-19 DQ-SQ MAS experiment. F-19-Pb-207 through-bond and through-space heteronuclear correlation experiments are carried out for the first time, supporting assignment of both the F-19 and Pb-207 NMR spectra. These correlation experiments also show that both models correctly describe the medium-range order of the structure of Pb5Ga3F19.