Resonance structures phosphazenes

Fig. 16.23 Structure of tnmcnc phosphazene. PjNjCU (a) contributing resonance structures (b) molecular structure as determined by X-ray diffraction. [From Builen. C. J J. Chem. Svc. (A) 1971. 1450. Reproduced with permission.]...

Major covalent nitrides include those of boron, sulfur, and phosphorus. Some indication of the nature of the phosphorus nitrides (the phosphazenes) was given in the last section. Boron nitrides have rather similar formulas but involve >77 77 B=N bonds instead of dir—pir P=N bonds. Figure 16.7 shows borazine, sometimes known as inorganic benzene. Note that two resonance structures are necessary to describe this molecule using valence-bond concepts. Experimentally, we find that all the B—N bonds have the same bond length, intermediate between that characteristic of single and double bonds. (Sulfur nitrides will be discussed in Chapter 17.)... 

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