SYNTHESIS AND X-RAY-ANALYSIS OF KCUGD2MO4 O16 AND KCUTB2MO4O16

Single crystals of the so far unknown compounds KCuGd2Mo4O16 (I) and K CuTb2Mo4O16 (II) have been prepared by flux technique. The compounds c rystallize with monoclinic symmetry. space group C-2h(6)-C2/c with (I) : a = 5.278(2), b = 12.666(5), c = 19.604(14) Angstrom; beta = 92.76(6 )degrees; (II): a = 5.259(13), b = 12.616(3), c = 19.556(9) Angstrom, beta = 92.93(4)degrees, Z = 4. Molybdenum exhibits tetrahedral coordin ation. The surroundings of copper can be described by distorted tetrah edra, capped by two more distant oxygen atoms, and the rare earth ions show a square antiprism. Potassium is inside an irregular polyhedron. The relationship of the structures of (I) and (II) is discussed with respect to the KLnMo(2)O(8) type compounds. Coulomb term calculations of the lattice energy indicate an oxidation state of copper higher tha n Cu-I.