Transition metal-nitrogen systems

Chemical diffusion in transition metal-carbon and transition metal-nitrogen systems... 

W. Lengauer. Multiphase reaction diffusion in transition metal-carbon and transition metal-nitrogen systems // J.Alloys Compounds - 1995 - V.229 - P.80-92. 

Several of the transition metal-nitrogen systems are not yet fully established. This is especially the case for some of the metals in groups 6-9, probably because of the lower technical relevance of the nitrides and the high nitrogen pressures needed for equilibrium investigations. 

Figure 6 Phase diagrams of group 4 transition metal-nitrogen systems, (a) Zr-N. (Ref. 11. Reproduced by permission of Materials Information Society/ASM International), (b) Hf-N. (Reprinted from Ref 28. 1991, with permission from Elsevier)...

Ternary phases with structures different from those of the phases of the binary boundary systems are more the exception than the rule. Such phases have been reported in the systems Nb-Mo-N, Ta-Mo-N, Nb-Ta-N, Zr-V-N, Nb-Cr-N, and Ta-Cr-N. Information about ternary transition metal-nitrogen systems is often available for specific temperatmes only. This is even more the case for quaternary nitride systems, which play a role in the production of carbonitride cermets where quaternary compounds of the types (Ti,Mo)(C,N) and (Ti,W)(C,N) are of interest (see Carbides Transition Metal Solid-state Chemistry), as well as in layer technology where titanium nitride-based coatings of the type Ti(C,B,N) are prepared by magnetron sputtering. Layers consisting of ternary compounds of the type (Ti,Al)N and (Ti,V)N also have favorable properties with respect to abrasion resistance. 

Transition Metal-Nitrogen Systems and Structure of Phases... 

Several of the transition metal-nitrogen systems were established only recently and there is still some lack of knowledge for systems for the investigation of which a high nitrogen partial pressure is necessary. As for the carbides systems only recent results will be presented here (see also [10]). 

The main trends of phase formation in transition metal-carbon or transition metal-nitrogen systems are well known (see Goldschmidt (1967)). For example, ina-va subgroup metals form stable carbides, which are characterised by good thermomechanical properties, but on going to... 

Carbon does not stabilize the hep low-temperature modifications of these metals (in contrast to nitrogen) and the solnbility of C in the a-phases is much smaller as compared to the group 4 transition metal nitride systems. 

Moreover, they also developed a transition-metal-ftee system for amides synthesis from styrenes using ammonia as nitrogen source [24] (Scheme 3.6). The amount of 10.8 equivalents of TBHP was necessary for this transformation. Various primary aryl amides were obtained in moderate to good yields (25-81 %). Benzaldehydes should be the key intermediates which are generated from styrenes via C-C double bond cleavage under oxidation conditions. Finally, the intermediates reacted with ammonia to give the desired amides. 

Monomeric thiazyl halides can be stabilized by coordination to transition metals and a large number of such complexes are known (Section 7.5). In addition, NSX monomers undergo several types of reactions that can be classified as follows (a) reactions involving the n-system of the N=S bond (b) reactions at the nitrogen centre (c) nucleophilic substitution reactions (d) halide abstraction, and (e) halide addition. Examples of each type of behaviour are illustrated below. 

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