Crystal structures of the La3AgSnSe7 and R3Ag1−δSnS7 (R=La, Ce; δ=0.18−0.19) compounds

The crystal structures of new quaternary compounds La3AgSnSe7 (space group P63, Pearson symbol hP24, a=1.0805(4) nm, c=0.6245(1) nm, R1=0.0315), La3Ag0.82SnS7 (space group P63, Pearson symbol hP23.64, a=1.0399(1) nm, c=0.6016(1) nm, R1=0.0149) and Ce3Ag0.81SnS7 (space group P63, Pearson symbol hP23.62, a=1.0300(1) nm, c=0.6002(1) nm, R1=0.0151) were determined by means of X-ray single crystal diffraction. Structural investigations of the R3Ag1−δSnS7 (R=La, Ce; δ=0.18-0.19(1)) compounds at 450 and 530 K were performed. Low temperature data (12 K) for Ce3Ag0.81SnS7 were also collected. The nearest neighbours of the La(Ce), Ag and Sn atoms are exclusively Se(S) atoms. The latter form distorted trigonal prisms around the La(Ce) atoms, and distorted tetrahedrons around the Sn atoms. The Ag (Ag1) atoms have triangular surroundings: they are located very close to the planes built of three Se(S) atoms. The Ag2 atoms in the structures of the La3Ag0.82SnS7, Ce3Ag0.81SnS7 compounds are located practically in the centres of trigonal antiprisms. The pseudo-potentials determined through the Ag atoms show relatively low barrier between two nearest positions which decreases when temperature rises.