U(VI) Coordination Modes in Complex Uranium Silicates: Cs[(UO₆)₂(UO₂)₉(Si₂O₇)F] and Rb₂[(PtO₄)(UO₂)₅(Si₂O₇)]

Abstract

Crystals of two new inorganic uranyl silicates, Cs[(UO6)2(UO2)9(Si2O7)F] (1) and Rb2[(PtO4)(UO2)5(Si2O7)] (2), were produced from melts in evacuated silica tubes. Their structures have been solved by direct methods: 1 is trigonal, P-31c, a = 10.2040(3), c = 17.1278(5) Å, V = 1544.45(10) Å3, R1 = 0.042; 2 is tetragonal, P4/mbm, a = 16.0400(24), c = 3.9231(6) Å, V = 1009.34(10) Å3, R1 = 0.045. 1 is the first example of cation–cation interactions between the uranyl polyhedra in uranyl silicates. Therein, UVI adopts three coordination modes, UO6 octahedra, UO6F, and UO7 pentagonal bipyramids, with the latter sharing common edges to form U2O12 dimers. Three dimers associate into six-membered rings via cation–cation interactions. The structure of 1 can be described as a complex uranyl fluoride silicate framework with channels filled by the U1 atoms and disordered Cs+ cations. 2 represents a new type of topology never observed before among the structures of uranyl compounds; it is also a first complex uranium platinum oxide. Therein, the UO6 tetragonal bipyramids share edges to form chains. Five such chains are stitched into a complex ribbon via the silicon polyhedra. The ribbons are connected into a framework by the PtO4 squares; rubidium atoms are located in the channels of the framework.

Keywords

• uranium
• silicates
• platinates
• cation–cation interactions
• framework structures