Hydrothermal Synthesis and Single Crystal Structures of New Thorium Fluorides: A3Ba2Th3F19 (A = Na, K, Rb)

Abstract

A new family of mixed alkali–alkaline earth metal thorium fluorides based on the formulation A3Ba2Th3F19 (A = Na, K, Rb) has been synthesized and structurally characterized. The compounds crystallize in the cubic space group Im-3m with a = 12.1222 (14) and 12.3052 (14) A for the K and Rb end members, respectively. This is only the second thorium fluoride reported as a single crystal structure to incorporate alkali and alkaline earth metals into the same structure. Crystals were obtained from the equimolar reaction of Ba(OH)2·H2O, ThF4 and ABF4 in a 2 M AF solution under hydrothermal conditions (545 °C and 1 kbar). Barium atoms substitute at the alkali metal sites and preferential site substitution is supported by the crystallographic analysis. Additional substitution at the alkali metal site has also been shown for K2.2Na0.8Ba2Th3F19 and K1.85Rb1.15Ba2Th3F19 using dissimilar alkali tetrafluoroborate and fluoride mineralizers in the reaction. A new family of mixed alkali–alkaline earth metal thorium fluorides has been synthesized and structurally characterized by single crystal X-ray diffraction, greatly adding to the limited crystal chemistry reported about such compounds.