Tetrahedron complex Layer

As example one may consider the observed anionic tetrahedron complexes of the four normal valence compounds with the same classification code °8/3, shown in Figure 13. The first three tetrahedron complexes are constructed alone of < 8/3 base tetrahedra. In Na2Ge2Se5 and Na2Ge2S5 the base tetrahedra are only comer linked, however in Rb4ln2Sg comer and edge linked. Even if there are only comer linked base tetrahedra the anionic tetrahedron complex may have the shape of a two-dimensional layer or a cyclic molecule. Rnally, the anionic tetrahedron complex in Cs4Ge Se5, a multicyclic molecule, is constructed, instead of 8/3 base tetrahedra, of °8/2 and 8/4 base tetrahedra in equal proportions. 

The structures of silicates and related compounds contain anionic tetrahedron complexes of different configuration (single tetrahedra, pyrogroups, rings, chains, layers, frameworks etc.). Their comparative analysis considerably contributes to the sdentiiic ideas on the structures of crystalline materials in general. The interest in... 

If one takes into account the most specific features of a Si,0 tetrahedron complex, such as the number of tetrahedra in the chain period, or the types of rings which can be recognized in different layers, it is possible to estimate the total number of anionic tetrahedron complexes in the silicates as one hundred. 

Problem 1 Compare the anionic tetrahedron complexes of the two layer sbuctures shown in Figure 16a and 16b. Describe their common and distinctive structural features. Determine the chemical formulae and the cheuges of the two tetrahedron complexes. 

An interesting and possibly significant aspect of this structure is that each of the four spherons of the inner core has ligancy 9 (its neighbors are the three other inner-core spherons, three of the outer tetrahedron, and another three of the outer layer). Each of these four inner-core spherons with its nine neighbors can be described as forming a KM complex, and the LN core can be described as four interpenetrating KM complexes. 

There are numerous complex fluorides of alkali metals and metals of Groups The structures of RbBe2Fs and CsBe2Fs were mentioned in Chapter 3 as examples of the plane 6-gon net and the cubic (10,3) net. Each BeF4 tetrahedron shares 3 vertices to form respectively a layer or a 3D framework of composition Be2Fj. 

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