KxP2W2O16: A bronze with a tunnel structure built up from PO4 tetrahedra and WO6 octahedra

The structure of a $\text{K}{}_{\mathrm{x}}\text{P}{}_2\text{W}{}_4\text{O}{}_{16}\text{(x ? 0.4)}$ crystal was established by X-ray analysis. The solution in the cell of symmetry $\text{P2}{}_1\text{m}$, with a = 6.6702(5), b = 5.3228(8), c = 8.9091(8) Å, β = 100.546(7)°, Z = 1, has led to R = 0.033 and R_w = 0.036 for 2155 reflections with $\text{σ(I)}\text{I}\text{≤ 0.333}$. This structure can be described as two octahedra-wide ReO₃-type slabs connected through “planes” of PO₄ tetrahedra. A new structural family K_xP₂W_2nO_6n+4 can be foreseen which is closely related to the orthorhombic P₄W₈O₃₂ and the monoclinic Rb_xP₈W_8nO_24n+16 series.