Inorganic Solid-State Chemistry with Main Group Element Carbodiimides

Organosilicon carbodiimides have been successfully applied as single-source precursor compounds for the synthesis of novel ternary Si-, C-, and N-containing solid phases. Their thermally induced decomposition gives either amorphous silicon carbonitrides or polycrystalline silicon nitride and silicon carbide mixtures, materials that are presently of technological interest for their exceptional hardness, strength, toughness, and high temperature resistance even in corrosive environments. This review is concerned with the synthesis, characterization, and thermal stability of element carbodiimides. The main part of this paper is focused on polymeric silicon-based carbodiimides obtained by the reaction of chloro(organo)silanes with bis(trimethylsilyl)carbodiimide. In the case of RSiCl3, novel poly(silylcarbodiimide) gels are formed. Starting from silicon tetrachloride, new crystalline SiCN phases (namely, SiC2N4 and Si2CN4), have been isolated. Their crystal structures as well as their thermal behavior in the range between room temperature and 1600 °C are discussed. Moreover, preliminary results on the synthesis of germanium- and boron-containing carbodiimides are reported. It is also shown that carbon-based carbodiimides can be obtained by the reaction of cyanuric halides with bis(trimethylsilyl)carbodiimide. These materials are investigated as precursors for the synthesis of new carbon nitrides with high hardness.