CaAl2(BO3)2O: Crystal Structure

The structure of the aluminum borate CaAl2(BO3)2O has been established by single-crystal X-ray diffraction methods. It crystallizes in the trigonal space group R3c(h) (Z = 6) with unit-cell parameters a = 4.810(6) Å, c = 46.633(5) Å, and V = 934(1) Å3. The structure was determined from 274 unique reflections and refined to the final residuals R = 0.024 and wR = 0.032. It is characterized by an association of BO3 triangles, CaO6 octahedra, AlO4 tetrahedra, and unique, two-coordinate O atoms. Structural comparisons are made to Na+ β-alumina.