Structure determination of β-Pb2ZnF6 by coupling multinuclear solid state NMR, powder XRD and ab initio calculations

Abstract

The results from one-dimensional multinuclear (¹⁹F, ²⁰⁷Pb and ⁶⁷Zn) magic-angle spinning nuclear magnetic resonance experiments combined with the use of the ISODISPLACE program allow for the space group determination of β-Pb₂ZnF₆ (no. 138 P4₂/ncm). The structure was refined from X-ray powder diffraction data (a = 5.633 (1) Å and c = 16.247 (1) Å, Z = 4). β-Pb₂ZnF₆ has one six-fold coordinated Zn, one eleven-fold coordinated Pb and five F non-equivalent crystallographic sites and is built from alternated layers parallel to the (a, b) plane; tilted ZnF₄²⁻ layers of corner sharing ZnF₆⁴⁻ octahedra and FPb⁺ layers of edge sharing FPb₄⁷⁺ tetrahedra. The structure of β-Pb₂ZnF₆ was then optimized using the ab initio code WIEN2k and the calculated ⁶⁷Zn EFG is in agreement with the NMR results. ¹⁹F–¹⁹F proximities and ¹⁹F–²⁰⁷Pb connectivities were evidenced using through-space and through-bond NMR correlation experiments, respectively, and support the proposed structure. ¹⁹F–²⁰⁷PbJ-coupling was also used to select fluorine resonances depending on the number of neighbouring lead ions, leading to an unambiguous assignment of the different ¹⁹F resonances.