THE CRYSTAL-STRUCTURE OF LA3MO4.33AL0.67O14 AND THE ELECTRONIC-STRUCTURE OF LA3MO4XO14(X = SI - MO1/3AL2/3 - AL1/2V1/2)

Black needles of La//3Mo//4//. //3//3Al//0//. //6//7O//1//4 were prepared by electrolytic reduction at 1100 degree C of a melt containing Na//2MoO//4, MoO//3, and La//2O//3 held in an alumina crucible. The compound is isomorphous with La//3Mo//4SiO//1//4, crystallizing in space group Pnma with a equals 17. 750(3) Angstrom, b equals 5. 6600(9) A, c equals 11. 070(2) A, V equals 1112. 1(6) A**3, and Z equals 4. The structure was refined by a full-matrix least squares to R//F equals 3. 43%, R//W//F equals 4. 45%, with 1912 independent reflections. As in La//3Mo//4SiO//1//4, the structure contains Mo//3O//1//3 clusters and chains of edge-sharing MoO//6 octahedra with alternately short (2. 535 A) and long (3. 167 A) Mo-Mo distances, but unlike La//3Mo//4SiO//1//4, the tetrahedral silicon is replaced by a random distribution of 1/3 Mo and 2/3 Al.