Tubular Chains, Single Layers, and Multiple Chains in Uranyl Silicates: A₂[(UO₂)Si₄O₁₀] (A = Na, K, Rb, Cs)

Abstract

Four new uranyl silicates with the same framework composition but different crystal structures, Na2[(UO2)­Si4O10]­·0.5H2O (1), K2[(UO2)­Si4O10] (2), Rb2[(UO2)­Si4O10] (3), and Cs2[(UO2)­Si4O10] (4), have been synthesized under supercritical hydrothermal conditions at 590 °C and 1620 bar and characterized by single-crystal X-ray diffraction and infrared and photoluminescence spectroscopy. Crystal data for compound 1: tetragonal, I4/mcm (No. 140), a = 18.0332(7) Å, c = 7.7752(5) Å, V = 2528.5(2) Å3, Z = 8, R 1 = 0.0447; compound 2: monoclinic, P21/n (No. 14), a = 8.2970(17) Å, b = 7.7403(15) Å, c = 8.7906(18) Å, β = 104.83(3)°, V = 545.74(19) Å3, Z = 2, R 1 = 0.0140; compound 3: monoclinic, P21/c (No. 14), a = 10.3483(3) Å, b = 23.7297(6) Å, c = 7.6278(2) Å, β = 110.482(1)°, V = 1754.68(8) Å3, Z = 6, R 1 = 0.0194; compound 4: orthorhombic, Cmca (No. 64), a = 7.7157(3) Å, b = 19.8719(8) Å, c = 24.0160(10) Å, V = 3682.3(3) Å3, Z = 12, R 1 = 0.0277. The silicate anions in the structures of these compounds form tubular chains, single layers, and multiple chains which are linked by UO6 tetragonal bipyramids to form three-dimensional frameworks. The tubular chains and single layers are of the new type with respect to the sequence of vertex orientations. The multiple chain is observed for the first time and contains Q 2, Q 3, and Q 4 Si. The structures of these silicate anions can be correlated with the sizes of alkali metal cations.

Hydrothermal Synthesis and Structural Investigation of a Crystalline Uranyl Borosilicate

“…Among the many compound classes that have been studied for waste form applications, uranyl silicates and borates have received considerable attention. The variable arrangement of SiO 4 tetrahedra in uranyl silicate compounds has resulted in a multitude of different structure types, many of which are three-dimensional [9][10][11][12][13][14][15][16][17]. Likewise, the ability of BO 3 and BO 4 units to polymerize to form polyborate units has given rise to a rich structural chemistry in uranyl borates [3,[18][19][20][21][22][23][24].…”

Structural and Spectroscopic Investigation of Novel 2D and 3D Uranium Oxo-Silicates/Germanates and Some Statistical Aspects of Uranyl Coordination in Oxo-Salts

“…Three different types of silicate layers have been found up to now in the uranium silicates family. The silicate layer of α-K 2 (UO 2 )­Si 4 O 10 can be denoted as a loop-branched dreier (three) single layer with 4- and 8-membered silicate rings . The nuclear glass alteration product KNa 3 (UO 2 ) 2 (Si 4 O 10 ) 2 ·4H 2 O as described above and the synthetic compound Na 2 (UO 2 )­Si 4 O 10 ·2.1H 2 O synthesized via mild hydrothermal conditions both contained an unbranched vierer (four) single layer with 4- and 8-membered silicate rings.…”

“…The silicate layer of α-K 2 (UO 2 )-Si 4 O 10 can be denoted as a loop-branched dreier (three) single layer with 4-and 8-membered silicate rings. 11 The nuclear glass alteration product KNa 3 (UO 2 ) 2 (Si 4 O 10 ) 2 •4H 2 O 9 as described above and the synthetic compound Na 2 (UO 2 )-Si 4 O 10 •2.1H 2 O 12 synthesized via mild hydrothermal conditions both contained an unbranched vierer (four) single layer with 4and 8-membered silicate rings. The tetravalent uranium silicates A 2 USi 6 O 15 (A = K, Rb) 2 dreier (three) layer which has been found in thorium silicate Cs 2 ThSi 6 O 15 .…”

Unusual Heterometallic Cation‐Cation Interactions in Uranyl Zinc Germanates

“…The family of uranyl silicates represents one of the most stable and abundant uranium minerals owing to their insoluble nature and the widespread distribution of silicon dioxide in the earth crust, respectively. [2f], A variety types of natural uranyl silicates, including coffinite, gummite, uranophane, and sklodowskite, and numerous man‐made salts have been discovered or synthesized with their detailed structures thoroughly characterized . As the group neighbor of silicon, germanium imitates silicon in terms of coordination behavior, which typically coordinates with metal ions in the form of GeO 4 4– oxoanion with a tetrahedral geometry.…”

“…It is noteworthy that silicate, phosphate, and arsenate anions exclusively adopt a tetrahedral coordination geometry in all uranium bearing phases. [13d], The assembly of uranyl [(UO 2 ) 2+ ] ∞ chains and [GeO 5 6– ] ∞ chains results in a 3D uranyl germanate framework with 12‐membered channels (Figure b). Zn 2+ cations reside in the channels via the CCIs with three neighboring UO 2 2+ cations [U(1) × 1 and U(3) × 2] and they are further coordinate with three water molecules [O(w1) × 2 and O(w2) × 1] (Figure c).…”