Nitridoborate Ions

In this younger field of chemistry, some examples of anions may be still missing. One possible candidate is the [BN4] ion with a tetrahedral coordination of boron as in cubic BN, others may be adopted from oxoborates. Another interesting feature is the existence of structures with condensed nitridoborate anions derived from portions of BN structures. Until now the only example with a condensed anion structure is U(BN), containing kinked B-B bonded chains of (BN)x with B-B distances near 188 pm, slightly longer than in [B2N4] .  

Nitridoborate anions are surrounded by metal atoms in a typical pattern that allows the prediction of new structures, to some degree. In any case, this typical pattern helps one to understand the construction scheme of structures and to memorize the particular structures. 

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Reactions suggest that Ca3(BN2)N can be viewed as an intermediate in the reaction (4). The substitutional effect of nitride by nitridoborate ions reflects that the linear [N=B=N] ion (with a typical B-N distance around 135 pm) can be viewed as a pseudo-nitride. 

For the generation of more nitrogen-rich compounds, a nitride is included in the reaction. This synthesis allows the formation of different nitridoborate (8) ions as well as nitridoborate nitrides (9) [26] ... 

Structures of the lanthanide nitridoborates appear as layered structures with approximate hexagonal arrangements of metal atoms, and typical coordination preferences of anions. As in many metal nitrides, the nitride ion prefers an octahedral environment such as in lanthanum nitride (LaN). As a terminal constituent of a BNx anion, the nitrogen atom prefers a six-fold environment, such as B-N Lns, where Ln atoms form a square pyramid around N. Boron is typically surrounded by a trigonal prismatic arrangement of lanthanide atoms, as in many metal borides (Fig. 8.10). All known structures of lanthanide nitridoborates compromise these coordination patterns. 

Lanthanide nitridoborates can be divided into three classes salt-like compounds, semiconductors, and conductors or superconductors, as already shown in Fig. 8.7. Salt-like structures are usually transparent materials, marked by the typical color of the lanthanide ion. Here we discuss only nitridoborate compounds of lanthanum. The compounds La3(B3N, ) [27], La5(B3N, )(BN3) [28], Lag(B3N6)(BN3)N [29], and La3(BN3)N all count as salt-like materials, with La, ... 

B3N6] A [BN3] and N (Fig. 8.11). Band-structure calculations performed for La3(B3N5) revealed a band gap in the order of 4 eV. The corresponding nitridoborate oxide La5(BN3)Og [30] is also salt-Hke, owing the typical nitridoborate structure pattern regarding the environment of the [BN3] ion with lanthanum... 

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