Octaammine Eu^II and Yb^II azides and their thermal decompositions to the nitrides

The common preparation for many nitrides is the synthesis from the corresponding metals and nitrogen at quite high temperatures and/or high pressures. Here we present a route to metal nitrides by the use of ammine metal azides under relatively mild conditions. Europium(II) and ytterbium(II) azides are prepared in liquid ammonia at -36 C in form of their temperature-sensitive octaammine complexes. These were investigated by single-crystal X-ray diffraction at low temperatures, and their structures seem to be the first evidence for the existence of homoleptic ammine Eu^II and Yb^II complexes, as well as that the coordination number of these divalent cations can go beyond six with NH₃ ligands. In one of the cases presented here the observed coordination polyhedron is better described as a bicapped trigonal prism (C_2v), in one case better as square-antiprismatic (D_4d). Warming of these compounds to room temperature leads to the lanthanoid metal azides still containing approximately 1 equiv. of ammonia. The behaviour of these azides towards further heating was investigated: By very careful and slow decomposition, the nitrides of europium(III) and ytterbium(III) are obtained at only 230 C at ambient pressure. This method may be suitable to obtain other metal nitrides at remarkably low temperatures and pressures. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)