Structures based on other plane 3-connected nets

Structures based on other plane 3-connected nets 

A few examples are known of crystal structures based on more complex nets. Borocarbides MB2C2 are formed by scandium and the rare-earth metals, and they consist of layers of composition B2C2 interleaved with metal atoms. In the compounds of the 4f metals the layer is the 4 8 layer, the pattern of atoms being similar to that of Fig. 3.27(b), the open and shaded circles now representing B and C atoms. The scandium compound is of special interest as the only example at present known of the layer consisting of equal numbers of 5-gons and 7-gons. 

We mentioned earlier the structure of red phosphorus as a second example of interwoven layers. In this structure each individual layer is itself a multiple layer with a complex structure which is described on p. 675. 

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