CUTM2[B2O5](2) - THE FIRST METABORATE WIT H A (2)(INFINITY)[B2O5](4-)-ANION

Single crystals of the compound CuTm2[B2O5](2) were obtained by a B2O3 flux technique. The compound contains a hitherto unknown metaborate a nion with the formula (2)(infinity)[B2O5](4-). It crystallizes in the monoclinic space group C-2h(5)-P2(1)/c with a = 452.18(7); b = 720.0(2 ); c = 929.2(5) pm; beta = 90.16(5)degrees; Z = 2. The metaborate laye rs consists of four and eight membered rings of edge-sharing BO4-tetra hedra resembling the complex anion in the isotypic gadolinite structur e of FeY2[BeSiO5](2). The layers are connected via copper-centered elo ngated oxygen octahedra and slightly distorted thulium-centered tetrag onal oxygen antiprisms.