The crystal structure of the cesium bronze Cs(Mo0.95W0.05)7O21

The crystal structure of Cs(Mo0.95W0.05)7O21 has been determined from a single-crystal X-ray diffraction experiment. The crystal is orthorhombic (space group Pnma), with a = 17.638(5), b = 5.448(1), c = 17.945(7)Å, and Z = 4, for a formula unit Cs(Mo0.95W0.05)7O21. The intensities (I) of 1431 reflections, for which I > 3σ(I), were considered observed. The structure was solved by direct and Fourier methods and refined by least squares to a value of 0.019 for the conventional R factor. It is based on the corner sharing of molybdenum coordination polyhedra, forming chains of five very distorted "octahedra" and two terminal tetrahedra. These chains, similar to those found in the structures of γ- and η-Mo4O11, pack to form a three-dimensional network, thus generating voids in which the Cs atoms are located with a coordination number of 12