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La4[(C2)1−xGex]3, Lanthanum(III) Dicarbide(4-) Germanide(4-) Mixed Crystals: A Continuous Transition between the Cubic Structure Types cI40 (Rb4O6/Pu2C3) and cI28 (Th3P4)

IN MEMORIAM PROFESSOR JEAN ROUXEL
https://doi.org/10.1006/jssc.1999.8374Get rights and content

Abstract

La4(C2)2Ge was obtained as a minor component from the reaction of the elements in corundum crucibles enclosed in stainless steel ampoules at 1360 K. The compound is gray with metallic luster. The crystal structure (space group I43d (No. 220); a=8.995(1) Å; Z=4; R(F)=0.033, Rw(F2)=0.061 for 106 reflections (all data) with 2θmax=50° measured on four-circle diffractometer) may be described as a 3D framework of condensed La8 dodecahedra (bisdisphenoids) centered by Ge atoms and C2 dumbbells (d(C–C)=1.22 Å). La4(C2)2Ge and the previous reported cubic compounds La2C3≙La4(C2)3, “La5C1.5Ge3” ≙La4(C2)0.60Ge2.40, and La4Ge3 demonstrate the existence of a large range of homogeneity La4[(C2)1−xGex]3 between the yellow transparent ethenide (4-) La2C3 and La4Ge3. In the series, the C2 dumbbells are replaced by Ge atoms, corresponding with the formal charges C4−2, Ge4−, and La3+. These mixed crystals (Pearson symbol cI28⇔40) represent a continuous transition between the structure types cI40 (Rb4O6/Pu2C3) and cI28 (Th3P4). The results are discussed together with the general trends in the members of both structures types.

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  • 1

    Present address: Max-Planck-Institut für Chemische Physik fester Stoffe, Bayreuther Straße 40, Haus 16, D-01187 Dresden, Germany.

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    To whom correspondence should be addressed.

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