Structures of Lanthanum Nitridoborates

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,  

Lanthanide compounds with [BN] ions can be considered as metal-like. In spite of our speculations regarding a hypothetical Ca(BN), the [BN] ions are known only from ternary compounds until now. Prominent examples are CaNi(BN) 

Calculated band structures of aU these compounds feature the fermi level above a density-of-state peak that is consistent with the 3d bands for nickel. The [BN] anion in CaNi(BN) compromises an electronic situation with a filled 3(7 (HOMO) level that is B-N anti-bonding (Fig. 8.13). Any additional electron will 

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