Subnitride

Alkali and Alkaline Earth Metal Suboxides and Subnitrides... 

The alkali metal suboxides are well understood in terms of formation, structure, and properties, yet we still face some unsolved problems that will also be addressed in the following. In contrast, the first suboxide of barium came to light only recently [24], and one has to see whether this compound is the tip of another iceberg, as turned out to be the case with the subnitrides of alkaline earth metals. 

Table 3.1-1 summarizes the crystallographically characterized group 1 metal suboxides, and group 2 metal subnitrides, the latter containing additional alkali or other metals [25]. 

Tab. 3.1-1. Structurally characterized suboxides and subnitrides of alkali and alkaline earth metals, respectively, Z refers to the structural formula.

The structural principle of combining salt-like bonded units with stoichiometric amounts of alkali metal in the structure of Ba2ONa is equivalent to that which characterizes the alkali metal suboxides as well as the subnitrides of alkaline earth metals, such that a variation at least according to a general formula [Ba20 Na% can be expected. Indeed, there are indications of the existence of further suboxides in... 

The structural principle of alkali metal suboxides has been unique for many years. Early attempts to synthesize cluster-type subnitrides of Ba resulted in the only compound, Ba2N, that is isotypic with Ca2N. Beyond these, the Sr analogue Sr2N, and most recently Sr4N3 [34], have been characterized. 

When reacting Ba dissolved in liquid Na with nitrogen at temperatures not too far from the melting point of the solvent, there was evidence for the formation of Ba-rich nitride clusters prior to the deposition of solid Ba2N [8]. Using both Na as well as a K-Na alloy as solvents, an extensive class of new subnitrides can be prepared. They contain [M6N] octahedra, either discrete or condensed into finite clusters and infinite arrays, respectively. 

All suboxides and subnitrides described in the preceding sections are metallic. In the case of the alkali metal suboxides this property has been demonstrated by measurements of the electrical conductivity [58], CS7O, for example, exhibits a free electron like behavior in the temperature dependence of its resistivity rather similar to the element Cs itself. The characteristic colors of the alkali metal suboxides have been mentioned before, and spectroscopic investigations to be discussed in the following provide a more quantitative access to the metallic properties and the underlying chemical bonding. 

CsnO3]Cs10. Unfortunately, no well defined cut-off from secondary electrons can be measured with the subnitrides whose work function values therefore remain unknown. 

Experimental HP-HT synthesis of solid solutions in the B6O-B4C system and the first conclusive synthesis of a new boron subnitride BeNi- are reported by Hubert et al. [548, 549]. AU the experiments have been performed... 

Vanadium Subnitride, VgN, is described as a black powder which is not attacked by hydrochloric acid or caustic potash solution. It is soluble in concentrated nitric and sulphuric acids, and evolves ammonia on being heated with solid caustic potash. 

---