Group 2 metal nitrides

The crystals of M[Be2N2] (M = Mg, Ca, Sr) are composed of complex anion layers with covalent bonds between Be and N atoms. For example, Mg[Be2N2] contains puckered six-membered rings in the chair conformation. These rings are condensed into single nets and are further connected to form double layers, 

Crystal structures of (a) Mg[Be2N2] and (b) Ca[Be2N2]. Small circles represent Be, large circles N, while circles between layers are either Mg or Ca. 

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Wallace C H 1998 The rapid solid-state synthesis of group III and transition metal nitrides at ambient and high pressures PhD Dissertation University of California, Los Angeles... 

Although there are several hundred biaary nitrides, only a relative few ternary bimetallic metal nitrides are known (6). A group of ternaries of the composition where M is an alkah, alkaline-earth, or a rare-earth metal and M is a transition or post-transition metal, have been synthesized (6). 

The most extensive group of nitrides are the metallic nitrides of general formulae MN, M2N, and M4N in which N atoms occupy some or all of the interstices in cubic or hep metal lattices (examples are in Table 11.1, p. 413). These compounds are usually opaque, very hard, chemically inert, refractory materials with metallic lustre and conductivity and sometimes having variable composition. Similarities with borides (p. 145) and carbides (p. 297) are notable. Typical mps (°C) are ... 

As a result of their reactivity, particular attention must be given to preparation and purification of the metals, the conditions under which the metals, alloys and compounds are handled and the choice of material for the containment vessel. Ultrapure group-IIB metals may be used without further purification, but it is advisable to purify the group-IIA metals by a multidistillation process, the final distillation preferably being carried out in situ. The reactants and products are best handled in an atmosphere of a purified inert gas, usually He or Ar (N2 cannot be used because of the ready formation of group-IIA metal nitrides) alternatively, they can be handled under vacuum or, in rare cases, under halide fluxes. The containment vessel is normally fabricated from a refractory. 

For quenching experiments, which were necessary to freeze-in the equilibrium states between the phase bands, the samples were reheated in a vacuum furnace under 500 mbar N2 to the original annealing temperature and dropped onto a copper plate kept below 470 K (200°C). With this treatment the Group 5 transition metal nitrides underwent a slight change in surface composition because it was impossible to adjust the appropriate nitrogen pressures. This, however, did not influence the compositions at the interface boundaries inside the diffusion couples. 

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. 

Local and Long-Range Effects on NMR Shieldings in Main-Group Metal Oxides and Nitrides... 

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