Inorganic Chemistry, Vol.54, No.11, 5504-5511, 2015
Flux Synthesis, Structure, Properties, and Theoretical Magnetic Study of Uranium(IV)-Containing A(2)USi(6)O(15) (A = K, Rb) with an Intriguing Green-to-Purple, Crystal-to-Crystal Structural Transition in the K Analogue
The flux growth of uranium(IV) oxides presents several challenges, and to the best of our knowledge, only one example has ever been reported. We succeeded in growing two new reduced uranium silicates A(2)USi(6)O(15) (A = K,. Rh) under flux growth conditions in sealed copper tubes. The compounds crystallize hi a new structure type with space group C2/c and lattice parameters a = 24.2554(8) angstrom, b = 7.0916(2) angstrom, c = 17.0688(6) angstrom, beta = 97.0860(6)degrees (K) and a = 24.3902(8) angstrom, b = 7.1650(2) angstrom, c = 17.2715(6) angstrom, beta = 96.8600(6)degrees (Rb). A(2)USi(6)O(13) (A = K, Rb) are isocompositional to a previously reported Cs2USi6O15, and the two structures are compared K2USi6O15 undergoes an interesting crystal-to-crystal structural phase transition at T approximate to 225 K to a triclinic structure, which is accompanied by an intense color change. The magnetic properties of A(2)USi(6)O(15) (A = K, Rh, Cs) ate reported and differ from the magnetism observed in other U4+ compounds. Calculations are performed on the (UO6)(-8) clusters of K2USi6O15 to study the cause of these unique magnetic properties.