Synthesis and structure of a potassium nitridoditungstenate (K6W2N4O3), a potassium digermanate (K6Ge2O7) and a rubidium digermanate (Rb6Ge2O7)

Light yellow single crystals of potassium nitridoditungstate (K₆W₂N₄O₃) and pale single crystals of potassium digermanate (K₆Ge₂O₇) were obtained by the reaction of the metal oxides WO₃ (molar ratio, 1 : 15.7) or GeO₂ (molar ratio, 1 : 2) in alkali metal amide melts in an autoclave at 530–600 °C for 6–8 days. Colourless single crystals of rubidium digermanate (Rb₆Ge₂O₇) were prepared by the reaction of GeO₂ with rubidium amide (molar ratio, 1 : 2) in ammonia at 350 °C in a high-pressure autoclave (H. Jacobs and D. Schmidt, in E. Kaldis (ed.), High-pressure Ammonolysis in Solid State Chemistry, Current Topics in Materials Science, Vol. 8, North Holland, Amsterdam, 1981, p. 379) (p(NH₃) = 5.5 kbar) for 10 days. In all three cases other nitrogen-containing products were present.

The structures of the title compounds were determined on the basis of single-crystal data. They are isotypic or structurally closely related to each other: K₆W₂N₄O₃: P2₁/n, a = 6.720(2) Å, b = 9.473(1) Å, c = 9.581(2) Å, β = 91.99(2)°, Z = 2, R/R_w = 0.040/0.048, N(I) > 3σ(I) 2057, N(Var.) = 71. K₆Ge₂O₇: Pn, a = 6.529(2) Å, b = 9.079(4) Å, c = 9.162(6)Å, β = 91.85(4)°, Z = 2, R/R_w = 0.022/0.024, N(I) 3σ(I) = 1486, N(Var.) = 135. Rb₆Ge₂O₇: P2₁/n, a = 6.839(4) Å, b = 9.437(6) Å, c = 9.460(6) Å, β = 91.53(5)°, Z = 2, R/R_w = 0.061/0.074, N(I) 3σ(I) = 1055, N(Var.) = 71.