Cd3B7O13(OH) : a new synthetic hydroxy boracite

A new member of the boracite-family of compounds M 3 B 7 O 13 X was synthesized under hydrothermal conditions. This cadmium hydroxy boracite, Cd 3 B 7 O 13 (OH), crystallizes in the trigonal crystal system (space group R3c, No. 161; a = 8.8109(1) A, c = 21.4572(4) A) and is isotypic to the iron-rich boracite congolite, (Fe,Mg) 3 B 7 O 13 Cl. The crystal structure has been refined by Rietveld analysis of X-ray powder diffraction data. The boracite structure consists of a three-dimensional framework of vertex-linked BO 4 -tetrahedra and BO 3 -triangles, the large interstices of which contain the five-coordinated cation M and the anion X.