Compounds of Metals with Boron, Carbon, and Nitrogen

Cementite, FeaC, has an interesting structure, involving both octahedral and trigonal-prismatic arrangements of six iron atoms about a carbon atom (Slrukiurbericht, II, 33). The iron boride FeB (Struktur-bericht, III, p. 12) contains trigonal prisms of iron atoms about the boron atoms, the Fe—B distance being about 2.15 A, which is approxi- 

The process of forming boron-boron bonds is carried on further in aluminum boride, AIB, which has a very simple hexagonal structure, consisting of hexagonal layers of boron a,toms, like the layers of carbon atoms in graphite, with aluminum atoms in the spaces between the layers (Pig. 11-15). The B—B bond length is 1.73 A, corresponding to n = 0.66 that is, two valence electrons per boron atom are used in the B—B bonds, which are two-thirds bonds. 

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