Crystal structures of new silver ion conductors Ag7Fe3(X2O7)4(X = P, As)Electronic supplementary information (ESI) available: CIF files and tables of full details of the refinement, atomic parameters, bond valence sums, second and third order displacement parameters for Ag1 in β-Ag7Fe3(P2O7)4and β-Ag7Fe3(As2O7)4(298 K), distances between neighbor silver sites and size of the oxygen windows for Ag7Fe3(P2O7)4and Ag7Fe3(P2O7)4at 100 and 298 K. CCDC reference numbers 707710–707713. For crystallographic data in CIF or other electronic format see DOI: 10.1039/b819846b

The crystal structures of new Ag7Fe3(X2O7)4(X = P, As) compounds, prepared through ion exchange from their sodium analogs, are reported. They adopt the monoclinic crystal system and exhibit an Ag ordering on cooling evidenced by a lowering of the symmetry from C-centered to primitive Bravais lattices. Crystal structures were determined from single-crystal X-ray diffraction at 100 K and 298 K for each composition. The structure consists of FeO6octahedra sharing their corners with P2O7dimers to form a three-dimensional framework [Fe3(P2O7)4]7−into which the silver ions are located. The differences between the four structures lie on the distribution of the silver ions within this framework, at the origin of a strong anisotropy in conductivity. Temperature displacement factors on Ag sites are generally higher in the arsenate than in the phosphate, in good correlation with conductivity data. [ABSTRACT FROM AUTHOR]