Structure and solid-state NMR spectroscopy of the ternary pnictides Li 3LaX 2 (X = P, As, Sb, Bi)

Winter F., Dupke S., Eckert H., Pöttgen R.

Abstract

The ternary pnictides Li3LaX 2 (X = P, As, Sb, Bi) were synthesized by the reaction of the elements in sealed niobium ampoules in a resistance furnace. The new phase Li3LaAs2 was obtained for the first time and completes this pnictide series. The structure of Li 3LaAs2 was investigated by X-ray diffraction on a single crystal: Li3LaSb2 type, P 3 ̄ m1, a = 435.68(6) pm, c = 710.8(1) pm, wR2 = 0.1033, 162 F 2 values, and ten variables. The structure is a filled derivative of the CaAl2Si2 type. The Li2 atoms have tetrahedral arsenic coordination. These Li2As4 tetrahedra are condensed via common edges forming layers in the ab plane which are separated by lanthanum atoms. The "filling" Li1 atoms are placed within the Li2-As polyanionic network. The chemical shift values of the 7Li solid-state MAS NMR spectra show that the lithium atoms are fully ionized and the compound can be described by the Zintl-Klemm concept as (3Li+)(La3+)(2As3-). The static 7Li solid-state NMR spectra show no lithium mobility. Graphical abstract: [Figure not available: see fulltext.] © 2014 Springer-Verlag Wien.