Seltenerdethenidhalogenide Ln2n+6(C2)n+4X2n+2: Darstellung, Struktur, Verwachsung und Verzwilligung
Résumé
The compounds Ln10(C2)6X6 are formed by heating mixtures of LnX3, Ln und C in tantalum capsules under Ar atmosphere with the ratio LnX3:Ln:C = 2:4:6 for La10(C2)6Br6 at 1040 ºC, 30 d (yield ca. 20 %), Ce10(C2)6Br6 at 1200 ºC, 12 d, (80 %), Pr10(C2)6Br6 at 1140 ºC, 5 d, (20 %) and 2:8:12 for Gd10(C2)6Cl6 at 1170 ºC, 39 d, (100 %). They crystallize isotypical in a new structure type in C2/m with a = 22.809(5) Å, b = 3.9855(8) Å, c = 16.599(3) Å, β = 123.32(3)° (La10(C2)6Br6), a = 22.483(5) Å, b = 3.9253(8) Å, c = 16.375(3) Å, β = 123.15(3)° (Ce10(C2)6Br6), a = 22.360(10) Å, b = 3.895(2) Å, c = 16.269(8) Å, β = 123.44(3)° (Pr10(C2)6Br6) and a = 21.507(4) Å, b = 3.7193(7) Å, c = 15.331(3) Å, β = 123.34(3)° (Gd10(C2)6Cl6). The structure of Ln10(C2)6X6 is composed of Ln octahedra centered by (C2) groups, which are connected via common edges to form sheets which are further connected perpendicularly by chains of Ln triple octahedra to form tunnels, which contain the X atoms coordinating the triangular faces of the Ln octahedra. The compounds are semicoductors according to ionic formulations (Ln3+)10(C24–)6(X–)6 suggested by the C-C double bond assignment.
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