CU2TH4(MOO4)(9) - A NEW STRUCTURAL SKELET ON

The compound Cu2Th4(MoO4)(9) is cubic, space group <I(4)over bar>3d wi th a = 14.477(7) Angstrom and Z = 4. Its crystal structure has been de termined from single crystal data by X-ray diffraction: Th(MoO4)(9) un its are constituted by a ThO9 polyhedron sharing corners with MoO4 tet rahedra. The 3D framework delimits 12 cages per unit cell, two-thirds of which are occupied by Cu-I isolated atoms, in agreement with EXAFS results, A crystal chemistry study has been performed: isomorphous cat ionic substitutions involving small, monovalent cations (Li+, Cu+) are possible, leading to isotypic compounds with empty or partially occup ied cages. Structural refinement of the isotypic compound La-4(MoO4)(3 )(ReO4)(6) by the Rietveld method confirms the existence of empty cage s and thus the relative stability of this new structural skeleton. (C) 1998 Academic Press.