CUHO2[B2O5](2) - AN UNEXPECTED STRUCTURE TYPE IN THE SERIES OF COPPERLANTHANOID BORATES

Single crystals of the new compound CuHo2[B2O5](2) were obtained by us ing a B2O3 flux technique with CuO and Ho2O3 at 1050 degrees C. X-ray investigations on single crystals led to the space group P2(1)/c (Nr. 14) with lattice parameters a = 454.3(2); b = 726.0(4); c = 936.0(5) p m; beta = 90.77(1)degrees; Z = 2. The compound is isotypic to CuTb2[B2 O5](2) as well as to the gadolinite structure (FeY2[BeSiO5](2)). The s tructure exhibits layer-like infinity[B2O5](4-), a two-dimensional ani on consisting of edge sharing BO4-tetrahedra, which form four and eigh t-membered rings. The layers are connected by elongated CuO6-octahedra and slightly distorted tetragonal LnO(8)-antiprisms.