Silicon diagonal relationship with boron

FIGURE 1.59 Boron (top) and silicon (bottom) have a diagonal relationship. Both are brittle solids with high melting points. They also show a number of chemical similarities. 

Silicon dioxide is quite different from carbon dioxide. Instead, in accordance with the diagonal relationship, it resembles boron oxide. Only one kind of direct bond is known for each natural compound of these two elements, namely B—O and Si—O. The linkage of the oxygen free electron pair with the free d-orbital of silicon or the free p-orbital of boron increases the strength of the bond, which then takes the form... 

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