Nitrides of transition metals

Some of these compounds have already been mentioned. They are extremely numerous, more than one nitride being formed by many transition metals. For example, five distinct phases (apart from the solid solution in the metal) have been recognized in the Nb-N system up to the composition NbN. Of the great variety of structures adopted by these compounds we shall mention only some of the simpler ones. 

In the so-called interstitial nitrides the metal atoms are approximately, or in some cases exactly, close-packed (as in ScN, YN, TiN, ZrN, VN, and the rare-earth nitrides with the NaCl structure), but the arrangement of metal atoms in these compounds is generally nor the same as in the pure metal (see Table 29.13, p. 1054), Since these interstitial nitrides have much in common with carbides, and to a smaller extent with borides, both as regards physical properties and structure, it is convenient to deal with all these compounds in Chapter 29. 

The nitrides of Mn, Fe, Co, and Ni form a group of less stable compounds of greater complexity than those of the earlier Periodic Groups—compare the formulae of the nitrides of the metals of the first transition series  

Interstitial structures are not possible for the larger P and As atoms, and apart from a few cases such as LaP, PrP, and GeP with the NaCl structure there is usually little similarity between nitrides and phosphides (or arsenides). Compare, for example, the formulae of the nitrides and phosphides of Mo and W M02N, W2N, MoN, and WN, but M03P, W3P, MoP, WP, M0P2, and 

A short section on the structures of metal phosphides is included in Chapter 19. 

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There have been significant advances during the last decade in the synthesis of high specific surface area (Sg) carbides and nitrides of transition metals.1 2 This has naturally prompted interest in the application of these materials as catalysts. Carbides of molybdenum and tungsten received the most attention because they catalyze many reactions that typically occur on noble metals. In several reactions, molybdenum carbides show catalytic activity similar to that of ruthenium and surface reactivity of tungsten carbides resembles that of platinum.3-7... 

Carbides and nitrides of transition metals are usually hard and some of them are used as hard materials. Tungsten carbide, which was briefly described above, is a major component of cutting tools and wear-resistant materials. Titanium carbide. Tie, and nitride, TiN, are two other major hard materials that are widely used in tools. They also find application as hard coatings (in particular, TiN [177]) and components of ceramic matrix composites [178]. Both TiC and TiN show a very... 

However, on the other hand, despite lack of limitations when using ammonium chloride in systems SHS-Az for obtaining nitrides of transitive metals, there is an opportunity to make halides more effective ... 

Use the Miedema parameters to derive the existence of borides, carbides, and nitrides of transition metals. 

Hoi] Holleck, H., Binary and Ternary Carbides and Nitrides of Transition Metals and Their Phase Relationships (in German), Report KfK 3087B, Kemforschungszentrum, Karlsruhe, 181-183 (1981) (Phase Diagram, Review, 41)... 

Nitrogenation used Fe-free and Mo-free metallic system. The system comprised main metallic compounds where the reductant can adsorb nitrogen irreversibly and then hydrolyze the nitride of transition metals to ammonia. The experiment carried out at University of Stanford is an example. 

Toth, L. (1971). Carbides and Nitrides of Transition Metals. New York cddctnic Press... 

The conversion of coordinated NSCI into a nitrido ligand provides a useful synthesis of transition-metal nitrides. For example, treatment of ReCl4(NSCl)(POCl3) with triphenylphosphine generates the nitrido complex ReNClaCPPhsla. "... 

Leclercq, L., Almazouari, A., Dufour, M., and Leclercq, G. 1996. Carbide-oxide interactions in bulk and supported tungsten carbide catalysts for alcohol synthesis. In Chemistry of transition metal carbides and nitrides, ed. S. T. Oyama, 345-61. Glasgow Blackie. 

Main-group elements X such as monovalent F, divalent O, and trivalent N are expected to form families of transition-metal compounds MX (M—F fluorides, M=0 oxides, M=N nitrides) that are analogous to the corresponding p-block compounds. In this section we wish to compare the geometries and NBO descriptors of transition-metal halides, oxides, and nitrides briefly with the isovalent hydrocarbon species (that is, we compare fluorides with hydrides or alkyls, oxides with alkylidenes, and nitrides with alkylidynes). However, these substitutions also bring in other important electronic variations whose effects will now be considered. 

Figure 4.31 Optimized structures of transition-metal nitrides and imides (4.65).

Considering other families of similar compounds, the contributions given by Guillermet and Frisk (1992), Guillermet and Grimvall (1991) (cohesive and thermodynamic properties, atomic average volumes, etc. of nitrides, borides, etc. of transition metals) are other examples of systematic descriptions of selected groups of phases and of the use of special interpolation and extrapolation procedures to predict specific properties. 

There are three anions that may loosely claim to be nitrides. Pentazolides (salts of cyclic N ) will all be explosive. Some azides (salts of N3) fall just short of being explosive but all are violently unstable. The true nitrides, nominal derivatives of N3-, are more various. In addition to some ionic structures, there are polymeric covalent examples, and some monomeric covalent ones, while most of those of transition metals are best considered as alloys. Several are endothermic and explosive, almost all are thermodynamically very unstable in air with respect to the oxide. Many are therefore pyrophoric if finely divided and also may react violently with water and, more particularly, acids, especially oxidising acids. A few are of considerable kinetic stability in these circumstances. There is no very clear classification of probable safety by position in the periodic table but polymeric and alloy structures are in general the more stable. Individual nitrides having entries ... 

The chemistry of transition metal carbides and nitrides", S.T.Oyama (ed.), Blackie Academic and Professional, Glasgow, 1996. 

R. Marchand, X. Gouin, F. Tessier and Y. Laurent, in "The chemistry of transition metal carbides and nitrides , S.T. Oyama (ed.), Blackie Academic and Professional, Glasgow, 1996, Chapter 13, p. 252. 

Source Refs. 31 and 32. Reprinted from J Cryst Growth. 66. S Iwama el al.. Growth of ultrafine particles of transition metal nitrides, pp 189-194. Copyright 1984, with permission from Elsevier Science. 

A less explored area of transition metal catalysis involves bond formation between Group 14 elements and nitrogen. In direct analogy to previously discussed areas of research, silicon-nitrogen bonds can be formed by dehydrocoupling, hydrosilylation, and dehydrogenative silylation. The compounds produced are valuable for use in organic synthesis or as polymer precursors to silicon nitride ceramics. 

The field of transition metal carbides and nitrides is growing rapidly, as additional uses for these interesting materials emerge. Interest in the subject is evidenced by a recent workshop proceedings, a monograph on theory, and several reviews and encyclopedia articles. However, there has been no comprehensive coverage of the topic since the 1970s. 

This volume, which is unique in its coverage, provides a general introduction to the properties and nature of transition metal carbides and nitrides, and covers their latest applications in a wide variety of fields. It is directed at both experts and nonexperts in the fields of materials science, solid-state chemistry, physics, ceramics engineering and catalysis. The first chapter provides an overview, with other chapters covering theory of bonding, structure and composition, catalytic properties, physical properties, new methods of preparation, and spectroscopy and microscopy. 

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