Three new uranyl tungstates,
A
8(UO
2)
4(WO
4)
4(WO
5)
2 (
A=Rb (
1), Cs (
2)), and Rb
6(UO
2)
2O(WO
4)
4 (
3), were prepared by high-temperature solid-state reactions and their structures were ...solved by direct methods on twinned crystals, refined to
R
1
=
0.050
, 0.042, and 0.052 for
1,
2, and
3, respectively. Compounds
1 and
2 are isostructural, monoclinic
P2
1/
n, (
1):
a
=
11.100
(
7
)
,
b
=
13.161
(
9
)
,
c
=
25.018
(
17
)
Å
,
β
=
90.033
(
13
)
°
,
V
=
3654
(
4
)
Å
3
,
Z
=
8
and (
2):
a
=
11.252
(
2
)
Å
,
b
=
13.815
(
3
)
Å
,
c
=
25.736
(
6
)
Å
,
β
=
89.988
(
2
)
°
,
V
=
4000.2
(
16
)
Å
3
,
Z
=
8
. There are four symmetrically independent U
6+ sites that form linear uranyl O=U=O
2+ cations with rather distorted coordination in their equatorial planes. There are six W positions: W(1) and W(2) have square-pyramidal coordination (WO
5), whereas W(3), W(4), W(5), and W(6) are tetrahedrally coordinated. The structures are based upon a novel type of one-dimensional (1D) (UO
2)
4(WO
4)
4(WO
5)
2
4− chains, consisting of WU
4O
25 pentamers linked by WO
4 tetrahedra and WO
5 square pyramids. The chains run parallel to the
a-axis and are arranged in modulated pseudo-2D-layers parallel to (0
1
0). The A
+ cations are in the interlayer space between adjacent pseudo-layers and provide a 3D integrity of the structures. Compounds
1 and
2 are the first uranyl tungstates with 2/3 of W atoms in tetrahedral coordination. Such a high concentration of low-coordinated W
6+ cations is probably responsible for the 1D character of the uranyl tungstate units. The compound
3 is triclinic,
P1¯
a
=
10.188
(
2
)
,
b
=
13.110
(
2
)
,
c
=
18.822
(
3
)
Å
,
α
=
97.853
(
3
)
,
β
=
96.573
(
3
)
,
γ
=
103.894
(
3
)
°
,
V
=
2388.7
(
6
)
Å
3
,
Z
=
4
. There are four U positions in the structure with a typical coordination of a pentagonal bipyramid that contain uranyl ions, UO
2
2+, as apical axes. Among eight W sites, the W(1), W(2), W(3), W(4), W(5), and W(6) atoms are tetrahedrally coordinated, whereas the W(7) and W(8) cations have distorted fivefold coordination. The structure contains chains of composition (UO
2)
2O(WO
4)
4
6− composed of UO
7 pentagonal bipyramids and W polyhedra. The chains involve dimers of UO
7 pentagonal bipyramids that share common O atoms. The dimers are linked into chains by sharing corners with WO
4 tetrahedra. The chains are parallel to −101 and are arranged in layers that are parallel to (1
1
1). The Rb
+ cations provide linkage of the chains into a 3D structure. The compound
1 has many structural and chemical similarities to its molybdate analog, Rb
6(UO
2)
2O(MoO
4)
4. However, the compounds are not isostructural. Due to the tendency of the W
6+ cations to have higher-than-fourfold coordination, part of the W sites adopt distorted fivefold coordination, whereas all Mo atoms in the Mo compound are tetrahedrally coordinated. Distribution of the WO
5 configurations along the chain extension does not conform to its ‘typical’ periodicity. As a result, both the chain identity period and the unit-cell volume are doubled in comparison to the Mo analog, which leads to a new structure type.
One-dimensional chains in the structure of Cs
8(UO
2)
4(WO
4)
4(WO
5)
2.
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Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Three new uranyl tungstates, A{sub 8}(UO{sub 2}){sub 4}(WO{sub 4}){sub 4}(WO{sub 5}){sub 2} (A=Rb (1), Cs (2)), and Rb{sub 6}(UO{sub 2}){sub 2}O(WO{sub 4}){sub 4} (3), were prepared by ...high-temperature solid-state reactions and their structures were solved by direct methods on twinned crystals, refined to R{sub 1}=0.050, 0.042, and 0.052 for 1, 2, and 3, respectively. Compounds 1 and 2 are isostructural, monoclinic P2{sub 1}/n (1): a=11.100(7), b=13.161(9), c=25.018(17)A, {beta}=90.033(13){sup o}, V=3654(4)A{sup 3}, Z=8 and (2): a=11.252(2)A, b=13.815(3)A, c=25.736(6)A, {beta}=89.988(2){sup o}, V=4000.2(16)A{sup 3}, Z=8. There are four symmetrically independent U{sup 6+} sites that form linear uranyl O=U=O{sup 2+} cations with rather distorted coordination in their equatorial planes. There are six W positions: W(1) and W(2) have square-pyramidal coordination (WO{sub 5}), whereas W(3), W(4), W(5), and W(6) are tetrahedrally coordinated. The structures are based upon a novel type of one-dimensional (1D) (UO{sub 2}){sub 4}(WO{sub 4}){sub 4}(WO{sub 5}){sub 2}{sup 4-} chains, consisting of WU{sub 4}O{sub 25} pentamers linked by WO{sub 4} tetrahedra and WO{sub 5} square pyramids. The chains run parallel to the a-axis and are arranged in modulated pseudo-2D-layers parallel to (010). The A{sup +} cations are in the interlayer space between adjacent pseudo-layers and provide a 3D integrity of the structures. Compounds 1 and 2 are the first uranyl tungstates with 2/3 of W atoms in tetrahedral coordination. Such a high concentration of low-coordinated W{sup 6+} cations is probably responsible for the 1D character of the uranyl tungstate units. The compound 3 is triclinic, P1-bar a=10.188(2), b=13.110(2), c=18.822(3)A, {alpha}=97.853(3), {beta}=96.573(3), {gamma}=103.894(3){sup o}, V=2388.7(6)A{sup 3}, Z=4. There are four U positions in the structure with a typical coordination of a pentagonal bipyramid that contain uranyl ions, UO{sub 2}{sup 2+}, as apical axes. Among eight W sites, the W(1), W(2), W(3), W(4), W(5), and W(6) atoms are tetrahedrally coordinated, whereas the W(7) and W(8) cations have distorted fivefold coordination. The structure contains chains of composition (UO{sub 2}){sub 2}O(WO{sub 4}){sub 4}{sup 6-} composed of UO{sub 7} pentagonal bipyramids and W polyhedra. The chains involve dimers of UO{sub 7} pentagonal bipyramids that share common O atoms. The dimers are linked into chains by sharing corners with WO{sub 4} tetrahedra. The chains are parallel to -101 and are arranged in layers that are parallel to (111). The Rb{sup +} cations provide linkage of the chains into a 3D structure. The compound 1 has many structural and chemical similarities to its molybdate analog, Rb{sub 6}(UO{sub 2}){sub 2}O(MoO{sub 4}){sub 4}. However, the compounds are not isostructural. Due to the tendency of the W{sup 6+} cations to have higher-than-fourfold coordination, part of the W sites adopt distorted fivefold coordination, whereas all Mo atoms in the Mo compound are tetrahedrally coordinated. Distribution of the WO{sub 5} configurations along the chain extension does not conform to its 'typical' periodicity. As a result, both the chain identity period and the unit-cell volume are doubled in comparison to the Mo analog, which leads to a new structure type.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
