Acta Crystallographica Section C

Crystal Structure Communications

Volume 62, Part 7 (July 2006)

inorganic compounds

Acta Cryst. (2006). C62, i53-i56 [ doi:10.1107/S0108270106014880 ]

Rubidium dimolybdate, Rb₂Mo₂O₇, and caesium dimolybdate, Cs₂Mo₂O₇

Z. A. Solodovnikova and S. F. Solodovnikov

Abstract: The crystal structures of dirubidium heptaoxodimolybdate, Rb₂Mo₂O₇, and dicaesium heptaoxodimolybdate, Cs₂Mo₂O₇, in the space groups Ama2 and P2₁/c, respectively, have been determined for the first time by single-crystal X-ray diffraction. The structures represent two novel structure types of monovalent ion dimolybdates, A₂Mo₂O₇ (A = alkaline elements, NH₄, Ag or Tl). In the structure of Rb₂Mo₂O₇, Mo atoms are on a twofold axis, on a mirror plane and in a general position. One of the Rb atoms lies on a twofold axis, while three others are on mirror planes. Two O atoms attached to the Mo atom on a mirror plane are located on the same plane. Rubidium dimolybdate contains a new kind of infinite Mo-O chain formed from linked MoO₄ tetrahedra and MoO₆ octahedra alternating along the a axis, with two terminal MoO₄ tetrahedra sharing corners with each octahedron. The chains stack in the [001] direction to form channels of an approximately square section filled by ten-coordinate Rb ions. Seven- and eight-coordinate Rb atoms are located between chains connected by a c translation. In the structure of Cs₂Mo₂O₇, all atoms are in general positions. The MoO₆ octahedra share opposite corners to form separate infinite chains running along the c axis and strengthened by bridging MoO₄ tetrahedra. The same Mo-O polyhedral chain occurs in the structure of Na₂Mo₂O₇. Eight- to eleven-coordinate Cs atoms fill the space between the chains. The atomic arrangement of caesium dimolybdate has an orthorhombic pseudosymmetry that suggests a possible phase transition P2₁/c [rightwards arrow] Pbca at elevated temperatures.

Formula: Rb₂Mo₂O₇ and Cs₂Mo₂O₇


	Structure factor file (CIF format) (71.8 kbytes) [ doi:10.1107/S0108270106014880/iz3004Isup2.hkl ] Contains datablock I

	Structure factor file (CIF format) (399.5 kbytes) [ doi:10.1107/S0108270106014880/iz3004IIsup3.hkl ] Contains datablock csmo

Notes:

To open or display or play some files, you may need to set your browser up to use the appropriate software. See the full list of file types for an explanation of the different file types and their related mime types and, where available links to sites from where the appropriate software may be obtained.

The download button will force most browsers to prompt for a file name to store the data on your hard disk.

Where possible, images are represented by thumbnails.