LiLa4N2I7 as the first lithium-containing nitride halide of the lanthanides: Synthesis, crystal structure and spectroscopic characterization

摘要

Initially, the quaternary nitride iodide LiLa4N2I7 was synthesized at 600 degrees C by a partial metathesis reaction of lithium nitride (Li3N) and lanthanum triiodide (LaI3) within 7 days. Single-phase samples were obtained through annealing of the corresponding binary compounds (LiI, LaN and LaI3) for 20 days overall (4 days at 600 degrees C prior to 16 days at 500 degrees C). The title compound crystallizes in the orthorhombic space group Pnma with four formula units per unit cell (a = 1374.17(9), b = 1213.45(8), c = 1079.91(7) pm at 100 K). The dominating structural features are trans-edge shared [NLa 4 ] 9+ tetrahedra building up (l)(infinity){[NLa4/2e](3+)} chains running along [010]. The linkage of these chains via iodide anions leads to a three-dimensional framework, which embeds isolated trigonal bipyramids [LiI4+1](4-) with one long besides four short contacts. Infrared spectra of crystalline samples show four main bands between 300 and 600 cm(-1), which can probably be assigned as vibrational modes of the condensed [NLa4](9+) tetrahedra. Li-7-MAS NMR spectroscopy reveals a different coordination sphere of Li+ in rocksalt-type LiI than in LiLa4N2I7, but no significant lithium-cation mobility.