Uranyl sulfate structure

As can be derived from the schemes (26) and (27), the reactions of complex formation will take place in the direction XVIII XVII XVI I V—>XIX—>XX. In the end, they must lead to the formation of the [1102(804)2(1120)] complex, which is the most stable and the most abundant complex in uranyl sulfates. It is of interest that it was a uranyl disulfate K2[U02(S04)2(H20)].H20, a complex of the XX t5 e, which was used by Becquerel in his discovery of radioactivity. In the structures of the XX complexes, the U atoms have CN = 7. We note that, according to the scheme (27), the most stable complexes should the electroneutral complexes XIX for which ANe = 0.25 and CNu = 7. Indeed, there are some data in the literature that provide some evidence concerning the existence of such complexes in crystals. 

Fig. 70 shows 2D sheets and their topological description for other uranyl sulfates with F anions. In the structures of USFO-4 and USFO-5, uranyl pentagonal bipyramids again share comers to form chains that are further interlinked by sulfate tetrahedra. In USFO-4 (Fig. 70a), the sulfate tetrahedra are tridentate and the 2D graph (Fig. 70d) corresponds to structural topologies observed in some phosphate minerals [172]. 

Radioactivity is emitted from atomic nuclei that are unstable and spontaneously change their structure. In 1896, Henri Becquerel first discovered radioactivity when he placed a piece of zinc uranyl sulfate wrapped in paper on a photographic plate. Two years later, Marie and Pierre Curie discovered two highly radioactive elements, polonium and radium, in pitchblende. a particles, the nuclei of helium atoms, were among the radiations emitted by these substances which were spontaneously transmuting. Indeed, since the earth had billions of years ago lost its original complement of light, inert helium, all helium in our... 

Sulfates and sulfites. Mono- and bis-sulfate complexes of actinyl ions, An02S04 and An02(S04)2 , are generally prepared from acidic solutions. The geometry about the actinide metal center is pentagonal biypyramidal from actinyl, sulfato, and aquo oxygen atoms. A tris(sulfato) complex has been reported, but it is very weak if it does exist. Ternary hydroxo, sulfato complexes have been reported for uranyl, but they have not been structurally characterized. 

However, it should be noted that, for U02 S04 1, the most eharacteristie eoordination of sulfate ions relative to the uranyl ions is not bidentate bridging (B, Fig. 10) but tridentate bridging (T, Fig. 10). Due to the inelusion of third O atom into the coordination, electron-donor ability of sulfate ions increases significantly they have El= 3Ei = 6.3e. For this reason, the most stable electroneutral complexes have the composition [U02(S04)(H20)2], since for them Ne = 7.8 + 6.3 + 2-1.9 = 17.9 e and ANe = 0.1 e i.e. less than for the complexes XIX. This explains why the [U02(S04)(H20)2] complexes occur in crystal structures more frequently than the [U02(S04)(H20)3] complexes. 

Analysis shows that, if all sulfate ions are coordinated by uranyl ions in a bidentate cyclic fashion, the most stable among the complexes XVI-XX given in (26) and (27) must be the complex [U02(S04)s]" (XVIII). This complex has Ne = 18.3 e, whereas others have ANe > 0.6 e. This is confirmed by the recent data on the structure of (C5Hi4N2)2[U02(S04)3] IPUKOT, which is the only known example of uranyl trisulfate with CNu = 8 (Fig. 1 la). In this regard, it is worthy to note that, in other known uranyl trisulfates [K4[U02(S04)3] 14062, (C4Hi4N2)2[U02(S04)3].2H20 IKUDAT and... 

Fig. 30. Sheet of uranyl coordination polyhedra (cross-hatched) in the structure of (K,Na)Na3 [(1102)506(804)] (a) and its anion topology (b). Projection of the structure along the b axis (c sulfate tetrahedra are lined) and local coordination of the [U(2)02] uranyl cation.

Fig. 69. The uranyl fluoride sulfate sheet in the structure of Rb[U02(S04)F] (a). Its idealized graph (h) can be obtained from 3.12.12 basic graph (c) by deleting some of its comers and edges. The presence of tridentate tetrahedra results in appearance of geometrical isomers (d, e see text for details).

In USFO-5 (Fig. 70b), sulfate tetrahedra are bidentate. The 2D sheet in the structure of USFO-6 (Fig. 70c) is remarkable in that it contains tetramers of comer-sharing uranyl bipyramids linked by tridentate sulfate tetrahedra. Note that the graphs shown in Figs. 70d, e and f are derivatives of the basic 3.12.12 graph (Fig. 69c). 

Niinisto L. Toivonen J. and Valkanen J. Structures of complex uranyl VI sulfates. In Fourth European crystallographic meeting, Oxford, 7977Prout C. K. convenor (Oxford, 1977), 572. 

Among the uranyl complexes listed in Table 20.1 there are about a dozen containing the sulfate ion. In each of these the central configuration is a pentagonal bipyramid in which those SO ions involved are always mono-dentate. Frequently, however, these tetrahedral ions link two or three bipyramids together, forming layers or chains. An unusual feature of the -UO SO structure is that one of the apical uranyl O atoms is also an equatorial ligand in an adjacent bipyramid. 

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