INORGANIC SOLID-STATE CHEMISTRY WITH MAIN-GROUP ELEMENT CARBODIIMIDES

Organosilicon carbodiimides have been successfully applied as single-s ource precursor compounds for the synthesis of novel ternary Si-, C-, and N-containing solid phases. Their thermally induced decomposition g ives either amorphous silicon carbonitrides or polycrystalline silicon nitride and silicon carbide mixtures, materials that are presently of technological interest for their exceptional hardness, strength, toug hness, and high temperature resistance even in corrosive environments. This review is concerned with the synthesis, characterization, and th ermal stability of element carbodiimides. The main part of this paper is focused on polymeric silicon-based carbodiimides obtained by the re action 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 (nam ely, SiC2N4 and Si2CN4), have been isolated. Their crystal structures as well as their thermal behavior in the range between room temperatur e and 1600 degrees C are discussed. Moreover, preliminary results on t he synthesis of germanium- and boron-containing carbodiimides are repo rted. It is also shown that carbon-based carbodiimides can be obtained by the reaction of cyanuric halides with bis(trimethylsilyl)carbodiim ide. These materials are investigated as precursors for the synthesis of new carbon nitrides with high hardness.