Edge trigonal prisms

Figure 6. The structures of (a) Li2Mn03and (b) layered Mn02 derived from (a), showing the sheets of edge-sharing MnOfj (shaded) and Li06 octahedra (unshaded) in (a), and alternate layers of MnOfi octahedra and trigonal prisms in (b) (after Ref-16]). The trigonal prisms are believed to be partially occupied by residual lithium ions.

Molybdenum disulfide has a layered structure. Each layer is a sandwich consisting of between two layers of ions (Fig. 9.5). The sulfur ions form trigonal prisms and half of the prisms contain a molybdenum ion in the middle. The chemical reactivity of M0S2 is associated with the edges of the sandwich, whereas the basal planes are much less reactive. The edges form the sites where gases adsorb and where the catalytic activity resides. 

Layer of edge-sharing trigonal prisms in MoS2... 

Omnicapped trigonal prism Edge-coalesced icosahedron... 

The ratio of the height to the mean edge length of the base of the trigonal prisms is also not untypical of the unfilled structure type, being 1.47 cf. 1.45 in C37(Co3Si), 1.18 in C23(PbClj)... 

The silicon positions in the face-sharing pairs of trigonal prisms (in the CrB, twinned c.c.p. 1 lamellae) are only half-occupied. They are at the centres of a pair of edge-sharing... 

Fig. 2.57 Structure of trigonal prisms formed by twinning of HCP. (a) Dimension of trigonal prism. The edge of the trigonal prism across the twin plane is shorter than the other edges, (b),...

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