THE CRYSTAL STRUCTURE 0F SODIUM AND EUROPIUM BORATE. A.M. Agayev, G K. Abdullayev, The Azerbaiian Academy of oil, Prospekt Azadlik, 20, Baku, Azerbaijan.

Sodium and Europium borate NaEuBO₂(OH)₂OH (I) was obtained under hydrothermal conditions in Na₂O-Eu₂O₃-B₂O₃-H₂O system at 400 C. It is isomorphous with compounds NaHoBO₂(OH)₂OH, crystals are yellow-white and has shortly prismatic habitus. The crystal structure was determined by single-crystal x-ray analysis (diffractometer, Mo radiation, 970 reflections, least square refinement with anisotropic approximation, R=0.053). The cell dimensions are; a=5,213, b=6,526, c=6,235Å, ß=114,8, z=2, d=4,929²/cm³, space group p2₁/m.

The crystal structure of I consists oi isolated BO₂(OH)₂ 3-tetrahedra (B-O=1,486-1, 532Å) and coordination polyhedra of metallic cations. The sodium cations are inside the distorted becaped trigonal prisms formed by two O atoms and 6 OH groups (Na-0=2,2l3-2,654Å). The Europium cations are also inside the distorted eight coordinated polyhedra formed by four oxygens atoms and four OH groups (Eu-O=2,362-2,735Å). Each Na and Eu-Polyhedra form zig-zag chains along the axis b being conneccted through the general rib with the nearest symmetrically equvalent polyhedra. Such chains being associated by general summits and ribs of B-tetrahedra and hydrogen bonds between them, form the framework structure.