Nitridoborates of the lanthanides: synthesis, structure principles, and properties of a new class of compounds.

ABSTRACT

Investigations of the nitridoborates of lanthanides (Ln) have progressed significantly during the last few years. New compounds have been synthesized and characterized and are presented here together with some of their properties. Currently two distinct methods serve for the preparation of nitridoborate compounds; either hexagonal boron nitride undergoes a fragmentation through the reaction with LnN, or dinitridoborate ions are converted into other nitridoborate ions. Lanthanide nitridoborates contain molecular anions such as [BN]n-, [BN2]3-, [B2N4]8-, [B3N6]9-, and [BN3]6- which may occur in combinations with other nitridoborates or with additional nitride ions. In crystal structures of lanthanide nitridoborates these anions are arranged in layers and are surrounded by metal atoms in a characteristic fashion. Terminal N atoms are capped by metal atoms forming a square-pyramid, and B atoms prefer a trigonal-prismatic environment of metal atoms. Nitridoborates form saltlike as well as metal-rich compounds and have the potential to show a lot of what are considered to be important solid-state properties, thus they have a good chance to establish their position within the group of relevant materials.