Unexpected Structural Complexity in Cesium Thorium Molybdates

Three cesium thorium molybdates [Cs2Th­(MoO4)3, Cs2Th3(MoO4)7, and Cs4Th­(MoO4)4] were synthesized via the high-temperature solid-state method. Cs2Th­(MoO4)3 crystallizes in orthorhombic space group Pnnm, containing [Th­(MoO4)3]2– chains extending along the [100] direction. Cs2Th3(MoO4)7 is based on an open framework with channels occupied by Cs+ ions and running parallel through the [100] direction. It is the first case in which thorium atoms coordinate simultaneously in three distinct environments, namely, 7-coordinated pentagonal bipyramid, 8-coordinated square antiprism, and 9-coordinated tricapped trigonal prism. Cs4Th­(MoO4)4 is monoclinic, built from [Th­(MoO4)4]4– sheets formed by vertex sharing of MoO4 tetrahedra and ThO8 antiprisms. The Raman and infrared spectra were recorded, and the vibrations related to internal and external Mo–O bonds in the MoO42– coordination geometry were discussed.