Structural topology and dimensional reduction in uranyl oxysalts: eight novel phases in the methylamine-(UO2)(NO3)2-H2SeO4-H2O system

Single crystals of eight novel uranyl selenates, (CH3NH3)(2)[(UO2)(SeO4)(2)(H2O)](H2O) (I) and (CH3NH3)(2)[(UO2)(SeO4)(2)(H2O)] (II), (CH3NH3)(2)[(UO2)(2)(SeO4)(3)] (III) and (CH3NH3)(H3O)[(UO2)(2)(SeO4)(3)(H2O)](H2O) (IV), (CH3NH3)(4)[(UO2)(3)(SeO4)(5)](H2O)(4) (V) and (CH3NH3)(H5O2)(H3O)(2)[(UO2)(3)(SeO4)(5)](H2O)(4) (VI), (CH3NH3)(4)(H3O)(2)[(UO2)(5)(SeO4)(8)(H2O)](H2O)(4) (VII), and (CH3NH3)(1.5)(H5O2)(1.5)(H3O)(3)[(UO2)(5)(SeO4)(8)(H2O)](H2SeO4)(2.6)(H2O)(3) (VIII), have been prepared by isothermal evaporation from aqueous solutions and structurally characterized. The observed structural topologies of uranyl selenate units have been investigated using graph theory. The principle of dimensional reduction has been used for analysis of the uranyl oxysalts with general chemical formula A (n) (UO2) (p) (TO4) (q) (H2O) (r) (A = monovalent cation, and T = S, Se, Cr, Mo), which allowed to construct three-component composition-structure diagram with separate dimensionality fields for different chemical compositions.