La-4[(C-2)(1-x)Ge-x](3), lanthanum(III) dicarbide(4-) germanide(4-) mixed crystals: A continuous transition between the cubic structure types cl40 (Rb4O6/Pu2C3) and cl28 (Th3P4)

La-4(C-2)(2)Ge was obtained as a minor component from the reaction of the e lements in corundum crucibles enclosed in stainless steel ampoules at 1360 K, The compound is gray with metallic luster. The crystal structure (space group I (4) over bar 3d (No, 220); a = 8.995(1) Angstrom; Z = 4; R(F) = 0.0 33, R-w(F-2) = 0.061 for 106 reflections tall data) with 2 theta(max) = 50 degrees measured on four-circle diffractometer) may be described as a 3D fr amework of condensed Las dodecahedra (bisdisphenoids) centered by Ge atoms and C-2 dumbbells (d(C-C) 1.22 Angstrom). La-4(C-2)(2)Ge and the previous r eported cubic compounds La2C3 corresponds to La-4(C-2)(3), "La5C1.5Ge3" cor responds to La-4(C-2)(0.60)Ge-2.40, and La4Ge3 demonstrate the existence of a large range of homogeneity La-4[(C-2)(1-x)Ge-x](3) between the yellow tr ansparent ethenide (4-) La2C3 and La4Ge3. In the series, the C-2 dumbbells are replaced by Ge atoms, corresponding with the formal charges C-2(4-), Ge 4-, and La3+, These mixed crystals (Pearson symbol cI28 double left right a rrow 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. (C) 1999 Academic Press.