Structure chemical aspects of silver(I) chalcogenide halides and preparation of the x = 1 member of the solid solution Ag₅Te ₂Cl_1-xBr_x

The maximum grade of substitution to be reached in solid solutions Ag ₅Te₂Cl_1-xBr_x by solid state melting reactions starting from the elements, is x = 0.65. Using solvothermal synthesis in aqueous ammonia solution, the area of stability can be extended to pure bromide (x = 1). X-Ray diffraction experiments have substantiated the isostructural features of Ag₅Te₂Br compared with the chlorine analog. At r. t. Ag₅Te₂Br crystallizes monoclinically, in the β-Ag₅Te₂Cl structure type, with lattice parameters of a = 14.000(5), b = 7.702(3), c = 13.856(6) Å, β = 90.61(4)°, space group P2₁/n. A topological approach, first introduced for the characterization of complex structures of silver(I) (poly)chalcogenide halides, has been transferred to the Ag₅Q ₂X system. Based on this formalism the anion substructures can be described by simple nets or strands created by the connection of positions at distances close to or even larger than the sum of the van der Waals radii. In case of the present system, only honeycomb-like telluride nets and halide strands are necessary to explain the complex anion substructure. A deeper understanding of the physical properties, like the anisotropic silver mobility, can be achieved by this topological approach which was not possible with other structure description models.