The Crystal Structure of Kx(MgxIn1–x)F3 (x = 0.38): a New Magnéli‐Bronze Type Fluoride

K_x(Mg_xIn_1–x)F₃ (x = 0.38) is monoclinic, pseudo tetragonal: a = 12.781(2) Å, b = 12.787(2) Å, c = 7.930(1) Å, β = 90,00(1)°, Z = 20. The crystal structure was solved in the space group P2₁/a (No. 14), subgroup of the tetragonal space group P4/mbm (No. 127), from X‐ray single crystal data using 4302 unique reflections (1770 with F_o/σ(F_o) > 4). The final observed R factor is 0.053. K_x(Mg_xIn_1–x)F₃ has the Magnéli‐bronze structural type, which consists in a tridimensional framework of mixed (Mg_xIn_1–x)F₆] octahedra linked together by corners. The potassium ions are mainly located in large almost fully occupied 15‐coordinated sites and in practically empty 12‐coordinated cavities.