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A novel rigid uranyl tungstate sheet in the structures of Na2[(UO2)W2O8] and α- and β-Ag2[(UO2)W2O8]. / Krivovichev, Sergey V.; Burns, Peter C.
In: Solid State Sciences, Vol. 5, No. 2, 01.02.2003, p. 373-381.Research output: Contribution to journal › Article › peer-review
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TY - JOUR
T1 - A novel rigid uranyl tungstate sheet in the structures of Na2[(UO2)W2O8] and α- and β-Ag2[(UO2)W2O8]
AU - Krivovichev, Sergey V.
AU - Burns, Peter C.
N1 - Funding Information: This research was supported by the Environmental Management Science Program of the Office of Science, U.S. Department of Energy, grant DE-FG07-97ER14820 and by the Russian Foundation for Basic Research for S.V.K. (grant 01-05-64883). We thank an anonymous reviewer for the valuable comments.
PY - 2003/2/1
Y1 - 2003/2/1
N2 - Crystals of Na2[(UO2)W2O8] and α- and β-modifications of Ag2[(UO2)W2O8] were synthesized by high-temperature solid-state reactions and their structures have been determined. The structure of Na2[(UO2)W2O8] (triclinic, P1, a = 6.6484(6), b = 7.5308(7), c = 8.4869(7) Å, α = 89.952(2), β = 86.190(2), γ = 73.299(2)°, V = 406.02(6) Å3, Z = 2) was solved by direct methods and refined to R1 = 0.043 (wR2 = 0.084). The structure of α-Ag2[(UO2)W2O8] (monoclinic, P21/c, a = 8.4263(7), b = 7.4897(7), c = 12.927(1) Å, β = 95.443(2)24°, V = 812.2(1) Å3, Z = 4) was solved by direct methods and refined to R1 = 0.049 (wR2 = 0.104). The structure of β-Ag2[(UO2)W2O8] (orthorhombic, Pnma, a = 8.6415(6), b = 7.5610(6), c = 12.4513(9) Å, V = 813.6(1) Å3, Z = 4) was solved by direct methods and refined to R1 = 0.059 (wR2 = 0.154). The crystal structures of the compounds are based upon sheets of UrO5 pentagonal bipyramids (Ur = UO22+, uranyl ion) and WO6 octahedra with the composition [(UO2)W2O8]. The UrO5 pentagonal bipyramids share equatorial edges, resulting in chains one polyhedron wide that extend along [010] in all three structures. The WO6 octahedra share corners to form chains of composition [WO5] parallel to [010]. Two adjacent [WO5] chains are linked into double [W2O8] chains by the sharing of edges between WO6 octahedra. The chains of UrO5 bipyramids and the [W2O8] chains are linked into sheets by the sharing of edges between UrO5 bipyramids and WO6 octahedra. The sheets are parallel to (100) in Na2[(UO2)W2O8] and to (001) in α- and β-Ag2[(UO2)W2O8]. Na and Ag are located in the interlayers, and provide linkage of the sheets. Geometrical parameters of the [(UO2)W2O8] sheets in the structures of Na2[(UO2)W2O8] and α- and β-Ag2[(UO2)W2O8] are identical within ∼ 3%, which indicates a relatively rigid sheet. Thus, the role of the interlayer cations is to compensate the charge of the sheet and to link adjacent sheets. The α- and β- modifications of Ag2[(UO2)W2O8] differ only in stacking sequences of uranyl tungstate sheets and can be considered as Ag2[(UO2)W2O8]-2M and Ag2[(UO2)W2O8]-2O polytypes, respectively.
AB - Crystals of Na2[(UO2)W2O8] and α- and β-modifications of Ag2[(UO2)W2O8] were synthesized by high-temperature solid-state reactions and their structures have been determined. The structure of Na2[(UO2)W2O8] (triclinic, P1, a = 6.6484(6), b = 7.5308(7), c = 8.4869(7) Å, α = 89.952(2), β = 86.190(2), γ = 73.299(2)°, V = 406.02(6) Å3, Z = 2) was solved by direct methods and refined to R1 = 0.043 (wR2 = 0.084). The structure of α-Ag2[(UO2)W2O8] (monoclinic, P21/c, a = 8.4263(7), b = 7.4897(7), c = 12.927(1) Å, β = 95.443(2)24°, V = 812.2(1) Å3, Z = 4) was solved by direct methods and refined to R1 = 0.049 (wR2 = 0.104). The structure of β-Ag2[(UO2)W2O8] (orthorhombic, Pnma, a = 8.6415(6), b = 7.5610(6), c = 12.4513(9) Å, V = 813.6(1) Å3, Z = 4) was solved by direct methods and refined to R1 = 0.059 (wR2 = 0.154). The crystal structures of the compounds are based upon sheets of UrO5 pentagonal bipyramids (Ur = UO22+, uranyl ion) and WO6 octahedra with the composition [(UO2)W2O8]. The UrO5 pentagonal bipyramids share equatorial edges, resulting in chains one polyhedron wide that extend along [010] in all three structures. The WO6 octahedra share corners to form chains of composition [WO5] parallel to [010]. Two adjacent [WO5] chains are linked into double [W2O8] chains by the sharing of edges between WO6 octahedra. The chains of UrO5 bipyramids and the [W2O8] chains are linked into sheets by the sharing of edges between UrO5 bipyramids and WO6 octahedra. The sheets are parallel to (100) in Na2[(UO2)W2O8] and to (001) in α- and β-Ag2[(UO2)W2O8]. Na and Ag are located in the interlayers, and provide linkage of the sheets. Geometrical parameters of the [(UO2)W2O8] sheets in the structures of Na2[(UO2)W2O8] and α- and β-Ag2[(UO2)W2O8] are identical within ∼ 3%, which indicates a relatively rigid sheet. Thus, the role of the interlayer cations is to compensate the charge of the sheet and to link adjacent sheets. The α- and β- modifications of Ag2[(UO2)W2O8] differ only in stacking sequences of uranyl tungstate sheets and can be considered as Ag2[(UO2)W2O8]-2M and Ag2[(UO2)W2O8]-2O polytypes, respectively.
KW - Anion topology
KW - Crystal structure
KW - Polytypism
KW - Uranyl tungstate
UR - http://www.scopus.com/inward/record.url?scp=0037319759&partnerID=8YFLogxK
U2 - 10.1016/S1293-2558(03)00009-8
DO - 10.1016/S1293-2558(03)00009-8
M3 - Article
AN - SCOPUS:0037319759
VL - 5
SP - 373
EP - 381
JO - Solid State Sciences
JF - Solid State Sciences
SN - 1293-2558
IS - 2
ER -
ID: 88648848