КРИСТАЛЛИЧЕСКАЯ СТРУКТУРА И ФАЗОВЫЕ ПРЕВРАЩЕНИЯ CA[(UО2)6(MOО4)7(H2О)2](H2О)N (N ~ 7.6)

Abstract

The new calcium uranyl molybdate, Ca[(UO2)6(MoO4)7(H2O)2](H2O)n (n ~ 7.6), was synthesized by hyd-rothermal method. The compound is orthorhombic, space group C2221, a= 11.3691(9), b= 20.0311(15), c = 23.8333(18) Å3, V= 5427.7(7) Å 3. Crystal structure has been determined by direct methods and refined to R, = 0.05 on the base of 3473 independent reflections. Structure is based upon framework of corner-sharing UO7 pen-tagonal bipyramids and MoO4 tetrahedra. The Ca2+ ions and H2O groups reside within the framework cavities. Phase transformations of Ca[(UO2)6(MoO4)7(H2O)2](H2O)n (n ~ 7.6) were studied by the high-temperature X-ray powder diffraction method. The compound is stable until 450 ± 25 °C, at that temperature it decomposes into UO2MoO4 and CaO.