Two salt-inclusion uranyl silicates, [K3Cs4F][(UO2)(3)(Si2O7)(2)] (compound 1) and [NaRb6F][(UO2)(3)(Si2O7)(2)] (compound 2), have been synthesized at high temperature using mixtures of alkali metal fluorides as fluxes and structurally characterized by single-crystal X-ray diffraction. Both compounds contain UO6 tetragonal bipyramids linked by disilicate groups to form three-dimensional framework structures with identical framework composition but different framework structures and salt inclusions. Both structures contain elliptical 12-ring channels where the K2Cs4F and Rb6F units are located. They are the first examples of salt-inclusion uranium silicates. The frameworks of 1 and 2 are thermally stable up to 850 and 750 degrees C, as indicated from powder X-ray diffraction. The F-19 and Si-29 MAS NMR spectra and the second-harmonic-generation response of 1 are consistent with the crystal structure analysis results. Crystal data: [K3Cs4F][(UO2)(3)(Si2O7)(2)], Cmc2(1), a = 7.8095(3) angstrom, b = 22.2819(7) angstrom, c = 14.0861(4) angstrom, and Z = 4; [NaRb6F][(UO2)(3)(Si2O7)(2)], Pnnm, a = 11.1429(2) angstrom, b = 13.5151(3) angstrom, c = 7.8868(1) angstrom, and Z = 2.
