Transition metal nitrides bonding

This paper consists of three parts. The first part describes the high pressure synthesis of bimetallic compounds of NbN and MN where M is a Group 13 metal such as Al, Ga, or In. The second part discusses crystal structure investigations of a series of alkaline earth and transition metal nitrides, carried out to understand the bonding surrounding the transition metals. The third part describes the preparation of new metastable transition metal nitride and their solid solutions by rf-sputter deposition. 

The bonding of 4d transition metal nitrides and carbides can be treated in a very similar way the nomnetal contribution to the electron density is about the same, whereby the contribution from 4d electrons causes a more spatial extension... 

It has been found that the bond overlap population of metal-metal bond plays an important role on the thermal stability of transition metal nitride. 

It has been found for examining empirically the thermal properties of the metal nitrides that the number of valence electrons is more advantageous than the average number of valence electrons per atom. DV-Xa molecular orbital calculations for several metal nitrides reveal that the thermal stability of transition metal nitride is intensely dominated by the bond overlap population of the metal-metal bond. 

A review has described transition metal nitrides.53 The majority of Ti nitrido compounds have been stabilized by somewhat sterically encumbering organometallic ligands.54"5 However, (Ti((Pr1NCH2CH2)3N))2(/r3-N)Na(THF) (4) was unexpectedly synthesized by the reaction of ClTi(Pr1NCH2CH2)3N)3 and Na[NH2] in THF. Structural evidence supports Ti—N 7r bonding.57... 

The complex nature of the bonding structure in transition metal nitrides incorporates a mixture of covalent, metallic and ionic components [126]. The nature on this bonding leads to high hardness, chemical inertness and, good electrical conductivity of these mixed nitride thin films. In what follows, we describe the surface chemical alteration of both a control and oxidized Ti—Al—N films (i.e., two different types of deposition room temperature (A) and liquid N2 temperature (B)), by measuring the chemical shifts in the Ti (2p), Al (2p), O (Is) and N (Is) XPS spectra. 

A mixture of metallic, covalent and ionic components prevails in the bonding of transition metal carbides, nitrides, and carbonitrides. The metallic character is shown by the high electrical conductivities of these compounds. The bonding mechanism has been described extensively by a variety of approaches for calculating the density of states (DOS) and hence the electron density in f.c.c. transition metal carbides, nitrides, and oxides [11]. In the DOS of these compounds there is a minimum at a valence electron concentration (VEC) of 8, which corresponds to the stoichiometric composition of the group ivb carbides TiC, ZrC, and HfC. Transition metal carbides have a lower DOS at the Fermi level than the corresponding transition metal nitrides, hence the electrical properties such as electrical and thermal conductivity and the superconducting transition temperature, T, are lower than those of the nitrides. 

Guillermet AF, Frisk K (1994) Thermochemical assessment and systematics of bonding strengths in solid and liquid MeN 3d transition-metal nitrides. J Alloys Comp 203 77-89 Shamsuddin M, Nasar A (1988/1989) Thermodynamic properties of cadmium telluride. High Temp Sci 28 245-254... 

Unlike the transition-metal nitrides and unlike boron carbide and silicon carbide, the covalent nitrides are excellent electrical insulators. Their electrons are strtmgly and covalently bonded to the nucleus and are not available for metallic bonding (see Sec. 3.1 of Ch. 4). 

Although none of these metals form bulk nitrides, the transition metal-nitrogen bond energies are still significant. For ruthenium the surface bond strength (566 kJ mol" ) is not markedly lower than on iron (585 kJ mol" ) (Table 9.2) and even the inactive metals such as palladium have bond strengths of around... 

---