Unit carbon nitrides

Two novel donor-acceptor phenylazomethine dendrimers with a 5-triazine core and butoxybenzene units have been synthesized <05TL8861>. Three novel nitrogen-rich nanolayered, nanoclustered and nanodendritic carbon nitrides have been prepared from 4,4, 6,6 -tetra(azido)azo-l,3,5-triazine (TAAT) <05AG(E)737>. 

FIGURE 11.8 Crystal structure of a graphitic carbon nitride sheet constructed from melem units and electronic structure of the Kohn-Sham orbitals for the VB and CB of polymeric melon. Reprinted with permission from Ref. [37]. Nature Publishing Group. 

Diamond. Diamond [7782 0-3] is the hardest substance known (see Carbon, diamond, natural). It has a Knoop hardness of 78—80 kN/m (8000—8200 kgf/m ). The next hardest substance is cubic boron nitride with a Knoop value of 46 kN/m, and its inventor, Wentorf, beheves that no manufactured material will ever exceed diamond s hardness (17). In 1987 the world production of natural industrial diamonds (4) was about 110 t (1 g = 5 carats). It should be noted that whereas the United States was the leading consumer of industrial diamonds in 1987 (140 t) only 260 kg of natural industrial diamonds were consumed this is the lowest figure in 48 years (4), illustrating the impact that synthetic diamonds have made on the natural diamond abrasive market. 

More complex (ternary and quaternary) nitride ceramics can also be formed from polymeric precursors. Thermal decomposition of [CH3Si(N = C = N)i.5]n has been shown by N NMR to form NSi3 units when the protons are lost from the system during heating at 600-800°C (Gabriel et al. 1999). The product is an amorphous mixture of Si3N4 and carbon which reacts to form an amorphous Si-C-N ceramic phase. Similar studies have been carried out on the formation of Si-B-N ceramics from single phase... 

In metallic or ionic lattices there exist nets of linked boron and phosphorus atoms, their oxides, and silicon oxide units. Why are there no nets of carbon and nitrogen atoms in metallic carbides and nitrides as there are in borides ... 

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