Acta Crystallographica Section C

Crystal Structure Communications

Volume 69, Part 12 (December 2013)

inorganic compounds

Acta Cryst. (2013). C69, 1457-1461    [ doi:10.1107/S0108270113030011 ]

On the possibility for Rb- and Eu-cation ordering in type-I clathrates: synthesis and homogeneity range of the novel compounds Rb8-xEux(In,Ge)46 (0.6 [less-than or equal to] x [less-than or equal to] 1.8)

M. C. Schäfer and S. Bobev

Abstract: Studies in the Rb-Eu-In-Ge system confirm the existence of the phase Rb8-xEux(In,Ge)46 (0.6 [less-than or equal to] x [less-than or equal to] 1.8), crystallizing with the cubic clathrate type-I structure. The In and Ge content can be varied, concomitant with changes in the Rb-Eu ratio. Two of the three framework sites are occupied by statistical mixtures of Ge and In atoms, while the site with the lowest multiplicity is taken by the In atoms only. Based on the three refined formulae [hepta­rubidium europium nona­indium hepta­triaconta­germanide, Rb7.39(3)Eu0.61(3)In8.88(5)Ge37.12(5), and two forms of hexa­rubidium dieuropium deca­indium hexa­triaconta­germanide, Rb6.30(3)Eu1.70(3)In9.76(4)Ge36.24(4) and Rb6.24(2)Eu1.76(2)In10.16(5)Ge35.84(5)] and the explored different synthetic routes, it can be suggested that the known ternary phase Rb8In8Ge38 and the hypothetical quaternary phase Rb6Eu2In10Ge36 represent the boundaries of the homogeneity range. In the former limiting composition, both the (Ge,In)20 and the (Ge,In)24 cages are fully occupied by Rb atoms only, whereas Rb6Eu2In10Ge36 has Rb atoms encapsulated in the larger tetra­kaideca­hedra, with Eu atoms filling the smaller penta­gonal dodeca­hedra. For the solid solutions Rb8-xEux(In,Ge)46, Rb and Eu are statistically disordered in the dodeca­hedral cage, and the tetra­kaideca­hedral cage is only occupied by Rb atoms.

CCDC references: 969913, 969914 and 969915

Formula: Rb7.39Eu0.61In8.88Ge37.12 and two analogues

Keywords: crystal structure; type-I clathrates; quaternary Rb-Eu-In-Ge system; cage compounds.

hkldisplay filedownload file

Structure factor file (CIF format) (17.4 kbytes)
[ doi:10.1107/S0108270113030011/fn3157Isup2.hkl ]
Contains datablock I

hkldisplay filedownload file

Structure factor file (CIF format) (17.4 kbytes)
[ doi:10.1107/S0108270113030011/fn3157IIsup3.hkl ]
Contains datablock II

hkldisplay filedownload file

Structure factor file (CIF format) (17.4 kbytes)
[ doi:10.1107/S0108270113030011/fn3157IIIsup4.hkl ]
Contains datablock III


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