Anion topology

Figure 4. Chains of polygons used to generate sheet anion-topologies.

The autunite anion-topology is a simple array of squares located such that their comers correspond (Fig. 5). Two uranyl oxide hydrates, y-[(U02)(0H)2] [33] and P-[(U02)(0H)2] [34], contain sheets with this anion topology. The topologically identical sheets in these two stmctures contain only uranyl square bipyramids that are located in half of the squares of the underlying anion topology. Each square bipyramid shares all four of its equatorial vertices with four different uranyl square bipyramids, thus each is four-connected and all of the connections within the sheet involve only the sharing of vertices. The sheets in these stmctures are electroneutral, there are no interlayer constituents, and the sheets are linked directly by H bonds. 

Figure 5. The autunite sheet anion-topology (a) and corresponding sheet of vertex-sharing uranyl square bipyramids from the structures of p and y [(U02)(0H)2] (b).

Figure 6. The protasite sheet anion-topology generated by stacking chains (a), and the sheet of uranyl pentagonal bipyramids that occurs in 10 structures (b).

Sheets in the structure of the rare Pb uranyl oxide hydrate mineral sayrite [48] are based upon the anion topology shown in Figure 11. The topology contains the P, R, U and D chains with the sequence RUPURDPDRUPU... The... 

The structure of a-[(U02)(0H)2] [54] contains sheets of uranyl hexagonal bipyramids (Fig. 17), and the sheet anion topology consists only of hexagons. This is the only uranyl oxide hydrate that contains hexagonal bipyramids, although this coordination type is common in uranyl carbonates, uranyl nitrates, and uranyl phosphates of the phosphuranylite group. 

Figure 19. The uranophane anion-topology (a) and uranyl silicate sheets based upon this anion topology (b-d) which differ only in the orientations of the sihcate tetrahedra.

The sheet in the structure of wyartite contains square and pentagonal bipyramids that are occupied by pentagonal bipyramids that contain and carbonate triangles (Fig. 25). The sheets are closely related to those with the P-UsOs sheet anion-topology found in the structures of spriggite and... 

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