Acta Crystallographica Section B

Volume 65, Part 2 (April 2009)

research papers

 

Ln₃M_1 - TX₇ - quasi-isostructural compounds: stereochemistry and silver-ion motion in the Ln₃Ag_1 - GeS₇ (Ln = La-Nd, Sm, Gd-Er and Y; = 0.11-0.50) compounds

M. Daszkiewicz, L. D. Gulay and O. S. Lychmanyuk

Abstract: The crystal structures of the Ln₃Ag_1 - GeS₇ (Ln = La-Nd, Sm, Gd-Er, Y; = 0.11-0.50, space group P6₃) compounds were determined by means of X-ray single-crystal diffraction and the similarities among the crystal structures of all Ln₃M_1 - TX₇ (space group P6₃; Ln - lanthanide element, M - monovalent element; T - tetravalent element and X - S, Se) compounds deposited in the Inorganic Crystal Structure Database (ICSD) are discussed. Substitutions of each element in Ln₃M_1 - TX₇ result in a different structural effect. On the basis of the data deposited in the ICSD the large family of the Ln₃M_1 - TX₇ compounds was divided into three groups depending on the position of the monovalent element in the lattice. This position determines what kind of stereoisomer is present in the structure, either the ++ enantiomer or the +- diastereoisomer. Since the silver ions can occupy a different position and the energy barriers between positions are low the ions can move through the channel. It was shown that this movement is not a stochastic process but a correlated one.

Keywords: chalcogenides; rare-earth compounds; ionic diffusion; stereochemistry.

	Structure factor file (CIF format) (37.1 kbytes) [ doi:10.1107/S010876810900144X/bp5017lasup2.hkl ] Contains datablock la
	Structure factor file (CIF format) (36.2 kbytes) [ doi:10.1107/S010876810900144X/bp5017cesup3.hkl ] Contains datablock ce
	Structure factor file (CIF format) (29.4 kbytes) [ doi:10.1107/S010876810900144X/bp5017prsup4.hkl ] Contains datablock pr
	Structure factor file (CIF format) (35.6 kbytes) [ doi:10.1107/S010876810900144X/bp5017ndsup5.hkl ] Contains datablock nd
	Structure factor file (CIF format) (30.3 kbytes) [ doi:10.1107/S010876810900144X/bp5017smsup6.hkl ] Contains datablock sm
	Structure factor file (CIF format) (32.4 kbytes) [ doi:10.1107/S010876810900144X/bp5017gdsup7.hkl ] Contains datablock gd
	Structure factor file (CIF format) (30.2 kbytes) [ doi:10.1107/S010876810900144X/bp5017tbsup8.hkl ] Contains datablock tb
	Structure factor file (CIF format) (32.8 kbytes) [ doi:10.1107/S010876810900144X/bp5017dysup9.hkl ] Contains datablock dy
	Structure factor file (CIF format) (32.5 kbytes) [ doi:10.1107/S010876810900144X/bp5017hosup10.hkl ] Contains datablock ho
	Structure factor file (CIF format) (31.7 kbytes) [ doi:10.1107/S010876810900144X/bp5017ersup11.hkl ] Contains datablock er
	Structure factor file (CIF format) (32.9 kbytes) [ doi:10.1107/S010876810900144X/bp5017ysup12.hkl ] Contains datablock y

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